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La paradoja del ingeniero intervencionista

22 de Julio del 2012 - Rolando Rodríguez Muñoz (Gijón)

Lo que determina si un espacio o paisaje es natural o no es la existencia de intervención humana. Por definición, los paisajes naturales son aquellos que no están manejados por el hombre. Cuando este actúa se produce una degradación en mayor o menor medida, que da lugar a un paisaje artificial. Por tanto, en lo que respecta al mantenimiento o conservación de ambos tipos de paisajes, la diferencia estriba en que los naturales no requieren manejo alguno, mientras que los artificiales necesitan de un manejo continuado. De hecho, cuando un paisaje natural es intervenido pierde su condición de natural. Del mismo modo, cuando un paisaje artificial deja de ser manejado, éste tiende a regenerarse por sí solo hasta que el abandono hace que recupere un estado más o menos similar al que tenía cuando era natural. En pocas palabras, el abandono convierte un paisaje en natural y el manejo en artificial.
Estas diferencias pueden parecer obvias, pero no siempre es así. En una entrevista publicada el pasado 9 de julio en este mismo diario el ingeniero agrónomo Asier Arrese les da la vuelta y afirma que los espacios naturales son espacios degradados y que los espacios degradados son naturales. De manera paradójica, describe la intervención del hombre como vital para la conservación y desarrollo de los espacios naturales, y afirma que sin esa intervención estos se degradan por sí solos. Por otra parte, resulta preocupante que un experto en gestión de áreas naturales, como así es presentado en la entrevista, considere los montes no intervenidos como espacios desaprovechados. O también que utilice el ejemplo del País Vasco como modelo de gestión de la naturaleza, argumentando que allí la presión sobre el terreno es mucho mayor. Sin duda la presión en los espacios naturales asturianos es menor que la ejercida en la mayor parte del País Vasco, de ahí que Asturias aún conserve osos, urogallos y lobos, que ya sólo coexisten en los bosques donde la acción del hombre es inexistente desde hace décadas. Estas tres especies desaparecieron del País Vasco hace mucho tiempo, y tan sólo el lobo ha comenzado a recolonizar las zonas colindantes con Cantabria y Burgos, donde aún existen áreas en un razonable estado de conservación natural.
Necesitamos terrenos en los que cultivar los productos que utilizamos para vivir, pero si queremos conservar nuestro patrimonio natural tenemos que dedicar una parte del territorio a esa finalidad, y eso se traduce en mantener esa parte libre de intervención. Si fuese necesario ponerle una etiqueta al tipo de aprovechamiento a que están destinados esos terrenos, podemos utilizar un término bien conocido y acuñado ya hace mucho tiempo, reserva natural.

Hummingbirds shake off downpours

Iturria: ABC Science

Wednesday, 18 July 2012 Rachel Sullivan
ABC

Their small size and high metabolic rate means they need to forage constantly, even during heavy rain (Source: Victor M Ortega /University of California, Berkeley)

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Hummingbirds can shake off the effects of heavy rain and hover in a heavy downpour thanks to shock-absorbing feathers, a new US study has found.

Going out in heavy rain is particularly challenging for small flying animals because of the relatively larger impact of raindrops and the weight of the water they carry around.
Raindrops can increase drag, affect control and manoeuvrability, and potentially cause structural damage to the wing itself.
Despite this, waiting it out isn't an option for some birds, bats and insects particularly those from humid environments.
Hummingbirds, which are among the smallest flying vertebrates, are found in neotropical cloud forest regions and lowland rainforest where heavy rains are common.
Their small size and high metabolic rate means they need to forage constantly, and they have evolved an insect-like ability to hover as they drink nectar from downwards facing flowers.
Dr Victor Ortega and Robert Dudley from the Animal Flight Lab at University of California Berkeley looked at how different rainfall intensities affect the hovering performance of Anna's hummingbird Calypte anna.
Male hummingbirds were filmed hover-feeding in the lab under a range of simulated rainfall levels. They then studied the film in slow motion to identify any kinematic (postural and movement) changes made by the birds in response to the increasing rainfall.
Their findings appear in the latest edition of the Proceedings of the Royal Society B.

Adjusting motion

"In our experiment, drops of light-to-moderate and heavy precipitation were only 0.002 per cent and 0.04 per cent of the hummingbird's body mass respectively," says Ortega. "However, these tiny drops can produce huge peak forces during the impact: 16 per cent and 38 per cent of body weight for light-to-moderate and heavy precipitation, respectively.
"Despite these enormous forces, we demonstrated that hummingbirds can deal very well in light-to-moderate precipitation, practically without cost," he says.
But when the rain intensity increased, the birds adjusted their motion to compensate for the impact of the raindrops and their wet plumage.
"During heavy rain, a hummingbird orients its body and tail horizontally, increases wing beat frequency and reduces wing beat amplitude," says Ortega.
"Surprisingly, these tiny birds can maintain flight control in heavy rain conditions with increased metabolic costs of only 9 per cent."
"Wing feathers particularly help to reduce drop impact forces because they are flexible, and due to this, part of the kinetic energy of the drop is transferred into bending."

Mosquitoes and crane flies

As yet, it is unknown whether other small animals exhibit a similar strategy for dealing with downpours.
A recent study showed that mosquitoes can survive drop impacts because their low body mass allows them to glance off the much heavier drops.
"However nobody knows how kinematics are affected during drop impacts," says Ortega, who has been recently exploring the takeoff performance of crane flies (Tipulidae) during rainfall.
"Crane flies are ten times bigger than mosquitoes and two orders of magnitude smaller than hummingbirds.
"I am sure that future research will solve these questions."

Birds' Perceptual and Maneuvering Abilities Inspire Small Unmanned Aerial Vehicles

Iturria: Science Daily

ScienceDaily (July 25, 2012) — The Office of Naval Research (ONR) is looking at birds' perceptual and maneuvering abilities as inspiration for small unmanned aerial vehicle (UAV) autonomy.

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The Office of Naval Research (ONR) is looking at birds' perceptual and maneuvering abilities as inspiration for small unmanned aerial vehicle (UAV) autonomy. (Credit: Image courtesy of Office of Naval Research)

An ONR-funded, five-year Multidisciplinary University Research Initiative (MURI) program is examining the control and behavioral processes of birds and other small animals when flying at high speeds through complex environments, such as forests or urban settings. Researchers are trying to understand why birds make particular flight path choices and how they can do so quickly at higher speeds than would be safe for current engineered air systems in these environments.
The goal is to develop and successfully demonstrate a small aircraft that can navigate obstacles in very complex and unstructured surroundings, while maintaining speeds as fast as 5 meters per second. The theoretical results being developed may also be applicable to larger UAVs for particular tasks, such as landing at difficult, unprepared sites.
"Autonomous systems technology can be a great way to deliver increased capability to the Navy and Marine Corps at an affordable price," said Marc Steinberg, a research program officer in ONR's Science of Autonomy Program. "We can provide warfighters with a lot more flexibility and enable new mission performance, from flight under a forest canopy and in urban canyons to damage control applications onboard ships. Flying animals provide evidence it is possible to build compact platforms with limited sensing that can safely move through challenging environments."
In the lab, researchers set up an artificial forest with tall pipes serving as trees at Harvard University's Concord Field Station. Birds and a Massachusetts Institute of Technology (MIT)-built UAV are wired with small digital video cameras and motion-capture technology similar to that used in Hollywood. Both are studied in parallel to compare and learn from performance as the research progresses. A goal is to move to flight in a real forest by the program's end.
The idea is not to copy the birds but to incorporate lessons about how they navigate and use dynamic obstacle avoidance methods into a system that can make real-time decisions that take into account its surroundings. For example, researchers already have discovered a theoretical speed at which the probability of a collision is high in forests with an average distribution of trees; if a UAV stays below that threshold, the probability of an accident lowers dramatically. The program also has begun to reveal the types of flight strategies used by birds in these environments.
"We want to build small-scale UAVs that can fly quickly through indoor and/or cluttered environments, but controlling these UAVs is very different than controlling a fighter jet flying up above the clouds," said Dr. Russ Tedrake, X Consortium associate professor of electrical engineering and computer science and aeronautics and astronautics at MIT and the MURI lead. "To be successful, we have to solve a number of incredibly hard problems in computer vision and nonlinear control. This long-term project lets us focus on the basic research questions that will lead to fundamental results and, ultimately, dramatic new capabilities for UAVs."
In addition to providing warfighters greater flexibility, small UAVs are more agile and easily transportable, and they're less expensive. A program goal is to be able to do this type of flight with cheap, lightweight digital video cameras as the main sensors. This would eliminate the need for other sensors typically used, such as laser-based ones that add cost and weight, and the MURI is testing feasibility.
The MURI involves researchers and engineers from MIT, Harvard University, Carnegie Mellon University, New York University and Stanford University.
To see a video of the small UAVs in flight, go to: http://www.youtube.com/watch?v=voN9CCmzxYk.

Songbirds Migrate On Strict Schedule

Iturria: Science Daily

ScienceDaily (July 25, 2012) — A new study by York University researchers finds that songbirds follow a strict annual schedule when migrating to their breeding grounds -- with some birds departing on precisely the same date each year.

This is a wood thrush in Belize. (Credit: Kevin Fraser)

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The study, published in the journal PLoS ONE, is the first to track the migration routes and timing of individual songbirds over multiple years. Researchers outfitted wood thrushes with tiny geolocator "backpacks," recording data on their movements.
Spring departure dates of birds heading from the tropics to North American breeding grounds were surprisingly consistent, with a mean difference of only three days from year to year, the study reports. Fall migration, however, was far less predictable. Males on average flew faster than females, and first-timers lagged behind those with more than one journey under their wings.
The geolocators, which are smaller than a dime, are mounted on birds' backs with thin straps looped around their legs. The devices measure light, allowing researchers to estimate latitude and longitude by recording sunrise and sunset times.
"It's quite surprising that the schedules of these birds are so consistent across the entire route, with some of them departing the tropics and arriving at breeding sites in North America on the same day in different years," says study author Kevin Fraser, a postdoctoral Fellow in York's Department of Biology, Faculty of Science & Engineering. "Much like airplanes, there are many factors that can influence birds' flight schedules, such as weather at departure and expected conditions at the other end of the journey. Amazingly, these small songbirds are highly consistent in their timing between years."
Interestingly, while their departure times are precise, songbirds' migratory routes can vary widely. "Migratory routes sometimes differed by several hundred kilometres between years, which may reflect a fine-tuning of migration in response to wind and weather conditions en route, such as during large open-water crossings like the Gulf of Mexico," he says.
As for arrival times, birds need to be early to lay their claim to prime breeding grounds -- but not too early.
"There is intense pressure for birds to get back to breeding grounds early to secure good territories, nest sites and, of course, mating opportunities. The early birds tend to do better and raise more young. However, cool weather in early spring can reduce food availability and even survival of early birds," Fraser says. He cautions that songbirds' consistent timing may come at a cost.
"The concern is that birds may not be able to flexibly adjust their schedules to meet new conditions with climate change," says Fraser. "This is a topic we're pursuing in current research."
The birds Fraser tracked were tagged in Pennsylvania and Costa Rica, at field research sites of his supervisor, York University Professor Bridget Stutchbury, who has studied the behavioural ecology of birds for decades. Her 2007 book, Silence of the Songbirds, details the threat to the species posed by climate change and habitat destruction.
"Numbers [of wood thrush] have plummeted in Canada by over fifty percent since the 1960s. When we lose the wood thrush, and other songbirds, we lose an integral part of the forest itself," Stutchbury says.

Helping Family Is Key for Social Birds

Iturria: Science Daily

ScienceDaily (July 11, 2012) — Social birds that forgo breeding to help to raise the offspring of other group members are far more likely to care for their own close relatives than for more distant kin, a new study has found.

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Babbler by a nest. (Credit: Photo by Lucy Browning)

The study, which looked at a highly social species from outback Australia, the chestnut-crowned babbler, also found that these birds work much harder to care for their brothers and sisters than the young of less-related group members.
The findings, published in the journal Proceedings of the Royal Society B, provide new insights into understanding why some individuals cooperate with each other for a common good rather than pursuing their own selfish reproductive agenda.
"Cooperation is a major evolutionary puzzle," says Dr Lucy Browning from the University of New South Wales and the University of Cambridge, who led the study and is a post-doctoral researcher at the UNSW Arid Zone Research Station, at Fowlers Gap, in far-western NSW.
"One idea is that by helping relatives with whom they share DNA, they can pass on their genes indirectly, but testing this idea in birds and mammals has proved surprisingly difficult.
"An alternative theory is that such cooperation is actually selfish because in group-living species like babblers, individuals can increase their own welfare by helping to make their group larger, irrespective of how closely related they are.
"The fact that babblers preferentially help family members makes it seem likely that promoting the success of kin is the reason they cooperate."
Babblers live in groups in which most members help to take care of young chicks in the nest, despite not being the parents themselves. But like any team activity, some individuals do the lion's share of all the work, while others do nothing at all.
"We wanted to get to the bottom of why some 'helpers' were so industrious while others were apparently so lazy," says Dr Browning. "We found that when helpers are caring for their brothers and sisters, they feed them three times more often than when they are unrelated. In other words, they are much more 'helpful' when looking after family."
The study took place between 2006 and 2008, with birds being fitted with tiny radio transponders that were detected each time an individual visited the nest in order to feed the chicks.

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Herbicidas en el parque de Ulia

Iturria: Ugatza Ornitologia Elkartea

Los compañeros de Ugatza denuncian, con toda la razón, la inexplicable aplicación de esta práctica en una zona que se pretende conservar precisamente por sus valores naturales. reproducimos íntegra su entrada.

 

A pocos días de la inauguración del Centro de Interpretación de la Naturaleza de Ulia, que pretende promocionar el conocimiento y la defensa del medio ambiente, la flora, la fauna, etc., nos encontramos con que a menos de 150 m del lugar, en pleno parque, una zona de aproximadamente 6.000 m2 ha sido tratada con herbicida. En pleno verano.

Se ha “sugerido” a los dueños de perros que no entren en la zona. Los caminos han sido cortados con vallas y el perímetro, más o menos señalizado con cinta roja y blanca. Parece que la prohibición de entrar en el área será de tres o cuatro semanas…

 

Los herbicidas pueden ser especialmente dañinos para los pájaros, reptiles y otros animales que viven en la zona, como la Ardilla roja que vuelve a ser observada en Ulia después de muchos años.

 

Desde Ugatza proponemos que si es imprescindible eliminar determinada vegetación, raíces, tocones.., se haga de forma manual o mecánica, y no utilizando productos potencialmente peligrosos.

Pedimos al departamento correspondiente del Ayuntamiento de Donostia, que explique a la ciudadanía qué objetivo tienen esas labores que se están desarrollando en Ulia, qué tipo de herbicida se ha utilizado, y su toxicidad, cuánto tiempo van a permanecer cerrados los caminos, y si al finalizar los trabajos se va a efectuar un informe sobre la situación de la fauna y flora del lugar, que se debería repetir pasado un tiempo desde la utilización del producto.

 

Además solicitamos al Ayuntamiento que se vigile estrechamente la hora de cierre y el acceso y aparcamiento de vehículos próximos a los bares y restaurantes del monte.

Ithurria: Saiak

Harrera » Komunikabideak » Aztorearen balentriak

Aztorearen balentriak

Komunikabideak | 2012-05-05

BBC ingles telebista kateak naturari buruzko dokumentala ederrak ekoiztu ohi ditu. Aldi honetan aztorearen hegal egiteko moldeaz (accipiter gentilis) egin duen bideo ikusgarri bat eman nahi genuke agerian. Ongi adierazten baitu Euskal Herrian ere atxeman daitekeen harrapari honek basoetan gaindi ihizin ibiltzeko daukan aparteko trebezia.

http://www.youtube.com/embed/2CFckjfP-1E?rel=0

Xehetasunak

BBC: “Testing to th

Not Just for the Birds: Human-Made Noise Has Ripple Effects On Plants, Too

Iturria: Science Daily

ScienceDaily (Mar. 20, 2012) — A growing body of research shows that birds and other animals change their behavior in response to humanmade noise, such as the din of traffic or the hum of machinery. But human clamor doesn't just affect animals. Because many animals also pollinate plants or eat or disperse their seeds, human noise can have ripple effects on plants too, finds a new study.

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To find out if noise affected the number of piñon pine seeds that animals ate, the researchers scattered piñon pine seeds underneath piñon pine trees in noisy and quiet sites, using a motion-triggered camera to figure out what animals took the seeds. (Credit: Photo courtesy of Clinton Francis.)

In cases where noise has ripple effects on long-lived plants like trees, the consequences could last for decades, even after the source of the noise goes away, says lead author Clinton Francis of the National Evolutionary Synthesis Center in Durham, North Carolina.
The study appears in the March 21 issue of Proceedings of the Royal Society B.
In previous studies, Francis and colleagues found that some animals increase in numbers near noisy sites, while others decline. But could animals' different responses to humanmade noise have indirect effects on plants, too?
Because they can't move, many plants rely on birds and other animals to deliver pollen from one flower to the next, or to disperse their seeds.
To find out what animal responses to noise might mean for plants, the researchers conducted a series of experiments from 2007 to 2010 in the Bureau of Land Management's Rattlesnake Canyon Wildlife Area in northwestern New Mexico.
The region is home to thousands of natural gas wells, many of which are coupled with noisy compressors for extracting the gas and transporting it through pipelines. The compressors roar and rumble day and night, every day of the year.
The advantage of working in natural gas sites is they allow scientists to study noise and its effects on wildlife without many of the confounding factors often associated with noisy areas like roadways or cities, such as pollution from artificial light and chemicals or collisions with cars.
To find out what animal responses to humanmade noise might mean for plants, first the researchers did an experiment using patches of artificial plants designed to mimic a common red wildflower in the area called scarlet gilia.
Each patch consisted of five artificial plants with three "flowers" each -- microcentrifuge tubes wrapped in red electrical tape -- which were filled with a fixed amount of sugar water for nectar. To help in estimating pollen transfer within and between the patches, the researchers also dusted the flowers of one plant per patch with artificial pollen, using a different color for each patch.
Din levels at noisy patches were similar to a highway heard from 500 meters away, Francis explained. When the researchers compared the number of pollinator visits at noisy and quiet sites, they found that one bird species in particular -- the black-chinned hummingbird (Archilochus alexandri) -- made five times more visits to noisy sites than quiet ones.
"Black-chinned hummingbirds may prefer noisy sites because another bird species that preys on their nestlings, the western scrub jay, tends to avoid those areas," Francis said.
Pollen transfer was also more common in the noisy sites. If more hummingbird visits and greater pollen transfer translate to higher seed production for the plants, the results suggest that "hummingbird-pollinated plants such as scarlet gilia may indirectly benefit from noise," Francis explained.
Another set of experiments revealed that noise may indirectly benefit some plants, but is bad news for others.
In a second series of experiments at the same study site, the researchers set out to find out what noise might mean for tree seeds and seedlings, using one of the dominant trees in the area -- the piñon pine (Pinus edulis).
Piñon pine seeds that aren't plucked from their cones fall to the ground and are eaten by birds and other animals. To find out if noise affected the number of piñon pine seeds that animals ate, the researchers scattered piñon pine seeds underneath 120 piñon pine trees in noisy and quiet sites, using a motion-triggered camera to figure out what animals took the seeds.
After three days, a number of animals were spotted feeding on the seeds, including mice, chipmunks, squirrels, birds and rabbits. But two animals in particular differed between quiet and noisy sites -- mice, which preferred noisy sites, and western scrub jays, which avoided them altogether.
Piñon pine seeds that are eaten by mice don't survive the passage through the animal's gut, Francis explained, so the boost in mouse populations near noisy sites could be bad news for pine seedlings in those areas.
In contrast, a single western scrub jay may take hundreds to thousands of seeds, only to hide them in the soil to eat later in the year. The seeds they fail to relocate will eventually germinate, so the preference of western scrub jays for quiet areas means that piñon pines in those areas are likely to benefit.
In keeping with their seed results, the researchers counted the number of piñon pine seedlings and found that they were four times as abundant in quiet sites compared with noisy ones.
It may take decades for a piñon pine to grow from a seedling into a full-grown tree, Francis said. This means the consequences of noise may last longer than we thought. "Fewer seedlings in noisy areas might eventually mean fewer mature trees, but because piñon pines are so slow-growing the shift could have gone undetected for years, he explained.
"Fewer piñon pine trees would mean less critical habitat for the hundreds of species that depend on them for survival," he added.
Other authors of the study include Catherine Ortega, most recently of Fort Lewis College, and Alexander Cruz and Nathan Kleist of the University of Colorado, Boulder.

Black-browed Albatross shows population increase

Iturria: BirdLife International

Black-browed Albatross shows population increase

Tue, Jul 24, 2012

Americas, Europe, News, Top Stories

Falkland populations of Black-browed Albatross appear to be on the increase (Save the Albatross)

A new report indicates a healthy increase in the numbers of Black-browed Albatrosses breeding in the Falkland Islands (Las Malvinas). The report, submitted to the Environment Committee of the Falkland Islands Government, indicated that recent and historical survey results show an increase in this threatened species.

Black-browed Albatross is currently classified as Endangered by BirdLife on behalf of  the IUCN Red List. Over two-thirds of the global population breed in the Falkland Islands, so the status of the Falklands population has significant bearing on the global conservation status of the species.

Within the Falkland Islands (Las Malvinas) different methods have been used independently to census the Black-browed Albatross population. Ian, and more recently, Georgina Strange have conducted aerial photographic surveys of colonies in the Falkland Islands since 1964, with archipelago-wide surveys in 1986, 2005 and 2010. Members of Falklands Conservation have carried out ground and boat-based surveys of the Falklands population in 2000, 2005 and 2010. Up until and including the 2005 census results, these initiatives reported contrasting population trends. The aerial based surveys indicated an increase in the population between the mid 1980s and 2005 and the ground based surveys a decline between 1995 and 2005.

However, the aerial and ground based surveys conducted in 2010 both reveal an increase in the population between 2005 and 2010 of at least 4% per annum. The positive trends from both of these surveys is further supported by favourable survival and breeding data from an ongoing study carried out by scientists at New Island (one of the twelve breeding sites in the Falkland Islands (Las Malvinas)), and an additional aerial photographic survey carried out later in the 2010 breeding season. The breeding population estimate obtained from the 2010 ground-based survey was larger than the estimate for 2000. Furthermore, the 2010 ground-based estimates for the two largest colonies in the Falklands (at Steeple Jason and Beauchêne islands) were similar to those derived from surveys carried out in the 1980s.

Dr Cleo Small from RSPB/BirdLife’s Global Seabird Programme said: “When 17 out of the world’s 22 species of albatross are listed as threatened with extinction, it is hugely encouraging that Black-browed Albatross colonies in the Falkland Islands are now known to be increasing. There is still some way to go – with the UK Overseas Territories other major population on South Georgia continuing to decline. But this result gives us great hope for turning around the fortunes of other albatrosses. Bycatch in fisheries is their main threat, and efforts are underway in many longline and trawl fleets worldwide to reduce the numbers killed. If we can keep this up, there is real hope that the black-browed albatross will set a trend for the future.”

Dr Anton Wolfaardt, ACAP (Agreement on the Conservation of Albatrosses and Petrels) officer for the UK South Atlantic Overseas Territories and author of the report said: “The exact reasons for the increase are not entirely clear, but efforts to reduce seabird bycatch, and beneficial feeding conditions, are likely to have contributed.” On the basis of the reported results, and the fact that the Falklands population comprises approximately 70% of the global total, the report recommends that consideration should be given to downlisting the species from Endangered. The report has been submitted to BirdLife International for use in the Red List assessment process. The report also recommends that efforts to further improve seabird bycatch mitigation should continue, both to buffer the local population against possible future changes, and to improve the conservation status of other populations and species.

Iturria: Science Daily

Bigger Birds in Central California, Courtesy of Global Climate Change, Study Suggests

ScienceDaily (Nov. 1, 2011) — Birds are getting bigger in central California, and that was a big surprise for Rae Goodman and her colleagues. Goodman uncovered the trend while working as a graduate student for Associate Professor of Biology Gretchen LeBuhn, analyzing data from thousands of birds caught and released each year at two sites near San Francisco Bay and Point Reyes National Seashore.

The SF State scientists found that birds' wings have grown longer and birds are increasing in mass over the last 27 to 40 years.
What's making the birds bigger? The researchers think that the trend is due to climate change, but their findings put a twist in the usual thinking about climate change and body size. A well-known ecological rule, called Bergmann's Rule, states that animals tend to be larger at higher latitudes. One reason for this rule might be that larger animals conserve body heat better, allowing them to thrive in the generally colder climate of higher latitudes.
Under this reasoning, some scientists have predicted that animals would get smaller as Earth has warmed up over the past 100 years. But the study, published in the journal Global Change Biology, suggests that the connection may not be so simple.
Climate change may affect body size in a variety of ways, they note in their paper. For instance, birds might get bigger as they store more fat to ride out severe weather events, which are expected to be more common under global climate change. Climate change could also alter a region's plant growth, which may eventually lead to changes in a bird's diet that affect its size.
LeBuhn said she was "completely surprised" to find that the central California birds were growing larger over time. "It's one of those moments where you ask, 'what's happening here?'" The results were so unexpected, she said, that the findings made them take a step back and look more closely at how climate change could influence body size.
The bird data come from two long-term "banding stations" in central California, where a wide variety of birds are captured, banded about the leg with an identification tag, and weighed and measured before being released. Many of the same birds were captured each year, allowing the researchers at the sites to build up a unique database that could be used to track changes among the birds over several decades.
The researchers used data from 14,735 individual birds collected from 1971 to 2010 at the Palomarin Field Station, near the southern end of the Point Reyes National Seashore, by researchers from PRBO Conservation Science. Their study also included data on 18,052 birds collected between 1983 and 2009, from the Coyote Creek Field Station at the southern end of the San Francisco Bay by the San Francisco Bay Bird Observatory.
"At the time I started my research, a few studies had looked at body size changes in a few species in Europe and the Middle East, but no one had examined bird body size changes in North America," said Goodman, who graduated from SF State in 2010 and now teaches biology and environmental science at San Francisco's Jewish Community High School of the Bay.
"We had the good fortune to find an unexpected result -- a gem in research science," she added. "But we were then left with the puzzle of figuring out what was going on."
After testing and discarding a number of other explanations, Goodman and her colleagues were confident that climate change was behind the longer wings and bigger bodies in most of the birds. The birds may be responding to climate-related changes in plant growth or increased climate variability in central California, the researchers suggest in the paper.
The findings offer a glimpse at the potent effects of climate change across a wide range of species, LeBuhn said. "Even over a pretty short period of time, we've documented changes in important traits like body size, where we don't expect to see much flexibility."
"But in some ways," she added, "it gave me a little more hope that these birds are able to respond -- hopefully in time -- to changes in climate."

Iturria: Science Daily

Small Sea Birds Hold Heat Rather Than Cranking Up the Furnace

ScienceDaily (May 5, 2011) — A new study offers some clues about how small aquatic birds survive in extremely cold climates.

Staying warm is hard work for aquatic birds. Heat loss is around twenty times greater in water than in air, so aquatic birds have to increase their resting metabolism to generate heat on the water. Heat loss is an even greater issue for small birds, so it was assumed that small birds would have to increase their metabolism in water even more than large birds do.

But according to a study by researchers at the University of Wyoming, that's not always the case. The researchers studied the metabolism of Cassin's auklets, a small sea bird found throughout the Northern Pacific Ocean. They found that auklets do increase their metabolism on the water, but not as much proportionately as some larger birds do.
In fact, ducks, auks, cormorants, and small penguins responded quite differently to air and water temperatures, perhaps reflecting very different demands during evolutionary history.
The research is published in the May/June 2011 issue of the journal Physiological and Biochemical Zoology.

Iturria: The Guardian

Bird-friendly California vineyards may have fewer pests

Insectivorous cavity-nesting birds can be encouraged to occupy vineyards by giving them nest boxes. New research documents that these birds reciprocate by providing significant eco-friendly pest control services to winegrape growers

Adult male western bluebird, Sialia mexicana, photographed at Bald Hill Park, Corvallis, Oregon (USA).
Image: Walter Siegmund (Creative Commons Attribution-Share Alike 3.0 Unported license).


I was in graduate school when I first read Rachel Carson's classic book, Silent Spring [Amazon UK; Amazon US]. In her book, Dr Carson presented evidence showing that rampant pesticide abuse was killing birds and destroying the environment -- and was also killing humans. This poignant commentary on chemical pesticide abuse stunned the public and launched the environmental movement. It led people to ask: Is it possible to grow sufficient food crops without constantly resorting to pesticides and other heavy-duty poisons?

Ironically, not applying pesticides to crops whilst simultaneously providing a bird-friendly environment may control insect pest populations. A team of researchers, led by Julie Jedlicka, a NSF Postdoctoral Fellow at University of California Berkeley, designed several experiments to test this.
"Insectivorous birds are often overlooked as sources of pest predation, however, they are likely providing pest control services in many agricultural fields, we just need to look for it", says Dr Jedlicka. She has studied bird-friendly coffee farms in Chiapas, Mexico.
"Much of what we know about biodiversity in agriculture is from the tropics", she explains. But can we take what we've learned in the tropics and apply it to agriculture in North America?

"I decided for my PhD I wanted to see whether we could create bird-friendly agricultural systems in the temperate zone", writes Dr Jedlicka in email. "Having moved recently to California, vineyards were a logical choice. I was inspired by grassroots efforts of some winegrape growers who had established songbird nest boxes in their vineyards."
Realizing that there was great research potential by systematically following up the winegrape growers' efforts, Dr Jedlicka expanded upon their methods to study the effects of insectivorous birds on winegrape agriculture. In this study, she focused on western bluebirds.
Western bluebirds, Sialia mexicana, are generalist insectivorous thrushes that are found in open coniferous and deciduous forests, wooded riparian areas, semi-open country -- and in agricultural areas -- throughout the western United States and Mexico.
Western bluebirds nest in cavities. Previous research in California showed that when provided nest boxes, they have higher reproductive success than when relying on natural cavities: the birds start laying eggs earlier, they have lower predation rates, their nestlings have fewer parasites, and more of their chicks fledge (doi:10.1046/j.1526-100X.2002.00129.x).
But because natural nest cavities are a limited resource, competition between bluebirds and other bird species to possess these cavities can be fierce. Additionally, western bluebirds do not tolerate the presence of another pair of bluebirds if their nest is too close: they must be separated by at least 15-30 metres (50-100 feet). Thus, by keeping these bluebird habits in mind, it is easy to control their density by providing nest boxes in suitable agricultural areas.
Bluebird nest box in a California vineyard.
Image: Julie Jedlicka (with permission).
After placing the nest boxes in the vineyard, the team documented where the bluebirds spent most of their time in relation to these boxes. Predictably, they found that the bluebirds were concentrated near their nest boxes early in the season, which is when pairs establish ownership over their chosen nest cavity, construct the nest, lay their eggs and incubate them. As the season progressed, bluebirds were observed at greater distances away from their nests with increasing frequency when bluebird adults were often seen foraging with young birds in small flocks consisting of three to five individuals (figure 1; larger view):

But what impact were all these birds having on insect populations? To answer this question, the team set up sentinel prey studies.
"Sentinel prey studies, which monitor removal rates of immobilized, tethered, or frozen prey in the field are common in the entomology literature for comparing relative predation pressure under different conditions", the authors explain in their paper.
Dr Jedlicka pinned larvae from a variety of insect species to pieces of cardboard and placed them 5 metres apart between the rows of grapes. All cardboard pieces were in place before 7:00 am. Dr Jedlicka returned approximately six hours later to collect the cardboard pieces and scored the pinned larvae as either present or missing -- and likely consumed by predators (figure 2):

As you can see, sentinel insects near active bluebird nest boxes were 3.5 times more likely to disappear than those located randomly throughout the vineyard (controls), indicating a high level of predation by resident bluebirds (figure 2, larger view). Since a previous study found that each pair of bluebirds raising five nestlings requires 124 grams of "bugs" (arthropods) daily (doi:10.1890/1051-0761(2006)016[0696:AEOVPO]2.0.CO;2), this level of efficiency is hardly surprising.
A western bluebird nest containing six eggs.
Image: Julie Jedlicka (with permission).
A bluebird pair produces at least one and often two broods per year in California, and each clutch averages between four and six eggs. Young birds from the first clutch typically remain at the nest to help the parents rear the second brood. So using a little mathematics, we can see that one pair of western bluebirds will quickly becomes a group of 12 hungry birds that consumes 248 grams of insects -- a very large number. These would include crop pests although the birds are probably also consuming neutral insects as well as arthropod predators of crop pests.
In this study, not only were the sites with nest boxes better protected from potential pest infestations, but even more important, there was no evidence that other bird species that may eat grapes were attracted to the nest boxes. Most birds that are considered "grape predators" don't nest in cavities (nor in nest boxes).
"I think it is important for the public to know that agricultural systems can provide habitat for wildlife", explains Dr Jedlicka in email. "There are ways to design and structure [agricultural areas] so they are highly productive and beneficial for wildlife."
Providing nest boxes to bluebirds is a low-maintenance, low-cost and ecologically-friendly way to benefit from the significant "ecosystem services" that these birds provide by simply being alive. Further, these methods are regionally adaptable.
"Great tits (Parus major) are cavity nesting species that respond well to nest boxes in agricultural lands" in Europe, explains Dr Jedlicka in email. "They were found to reduce caterpillar damage in apple orchards in the Netherlands (Mols and Visser 2002; doi:10.1046/j.1365-2664.2002.00761.x)." Mols and Visser later expanded their first study to commercial orchards and found similar effects [doi:10.1371/journal.pone.0000202].
The question now remains whether vineyards themselves are providing enough food for bluebird populations. Perhaps the bluebirds are relying on uncultivated natural patches in the vineyards to find food instead of only preying on insects in the grapes?
"I am trying to systematically analyze what role bluebirds are playing as predators in vineyards", replies Dr Jedlicka. "My future work is analyzing what adult and nestling bluebirds have been eating by analyzing prey [DNA] from [the birds'] fecal matter."
Knowing precisely which arthropods are being consumed by generalist insectivores, and in what quantities, is still not known.
"It has been a black hole in the community ecology literature for a long time because prey items are so small and birds are so highly mobile. We are just beginning to gain the tools we need to answer these questions."
Sources:
Julie A. Jedlicka, Russell Greenberg, & Deborah K. Letourneau (2011). Avian Conservation Practices Strengthen Ecosystem Services in California Vineyards. PLoS ONE, 6(11):e27347 doi:10.1371/journal.pone.002734
Julie Jedlicka [emails; 8 & 9 November 2011]
Other studies cited:
Mols, C., & Visser, M. (2002). Great tits can reduce caterpillar damage in apple orchards. Journal of Applied Ecology, 39 (6), 888-899 doi:10.1046/j.1365-2664.2002.00761.x
Mols, C., & Visser, M. (2007). Great Tits (Parus major) Reduce Caterpillar Damage in Commercial Apple Orchards. PLoS ONE, 2 (2) doi:10.1371/journal.pone.0000202
Germaine, Heather L. and Stephen S. Germaine (2002). Forest Restoration Treatment Effects on the Nesting Success of Western Bluebirds (Sialia mexicana). Restoration Ecology, 10 (2), 362-367 doi:10.1046/j.1526-100X.2002.00129.x

Iturria: BBC News

19 July 2012 Last updated at 03:02

Storm petrel seabirds can smell their relatives

By Victoria Gill BBC Nature

The birds use their sense of smell to choose a genetically compatible mate

Seabirds are able to pick out their relatives from smell alone, according to scientists.

In a "recognition test", European storm petrels chose to avoid the scent of a relative in favour of approaching the smell of an unrelated bird.
The researchers think this behaviour prevents the birds from "accidentally inbreeding".
The study is the first evidence that birds are able to sniff out a suitable mate.
It is published in the journal Animal Behaviour.

Seabird secrets

• See the secret bird surveys carried out from the air
• Find out how the world's largest falcon spends much of its life hunting at sea
• See how an iron-age structure provides the perfect petrel roosting site

Lead researcher Francesco Bonadonna, from the Centre of Functional and Evolutionary Ecology in Montpellier, France, told BBC Nature that the birds used smell to recognise and communicate their "genetic compatibility".

Sniffing out a genetically suitable mate is a well-known phenomenon in mammals. But until recently, scientists thought that birds relied on vision and sound when choosing a partner.
According to Dr Bonadonna, the fact that they use odours explains how these birds manage to return to their family colony to breed and avoid mating with a relative.
European storm petrels remain in the colony they are born in throughout their life, so this site is also home to several of their family members.
"These birds are [also] theoretically faithful to one mate for life," the researcher explained to BBC Nature.
"So a bad choice may have catastrophic consequences."
He said that smell or "chemical communication" was "the most ancient and simplest form of communication" in the animal kingdom, adding, "it makes sense that the birds would use it".

Birds that smell

Tim Birkhead Behavioural ecologist, University of Sheffield

Storm Petrels are small nocturnal seabirds that breed in dark burrows or crevices.
One of the most striking features of these birds is that they smell - a warm, musky smell.
It is known that they find their food out on the ocean by means of a sophisticated olfactory ability (or sense of smell), so it isn't too surprising that they use this sense of smell in their social lives.
Many species of birds and other animals have ways of making sure they avoid mating with a relative: storm petrels do it by smell.
Tim Birkhead is the author of the book Bird Sense

Scent swabs

To find out how much information the seabirds could gather from the scent of another individual, Dr Bonadonna and his colleagues collected bird scents by "taking swabs" from a selection of birds in their study colony.

The diminutive birds nest on a tiny island off the coast of Spain called Isla de Benidorm. Thanks to almost two decades of survey work on this particular colony, the scientists had a record of exactly which bird was related to which.
Once they had their scent swabs, the scientists set a group of petrels a test, placing one cotton swab with the scent of a relative on one arm of a Y-shaped maze and a swab containing the scent of an unrelated bird on the other.
Almost all of the birds that performed the test chose to walk along the arm containing the scent of the unrelated bird.
"This also ties in with the fact that, in 18 years of studying these birds, we have never found a related pair nesting together," Dr Bonadonna said.
Prof Rus Hoelzel from the University of Durham stressed how important kin recognition was for animals.

"Scent swabs" allowed the researchers to study how one bird responded to the smell of another

"There are various ways individuals may recognise kin, and [smell] has recently been found to be quite a common mechanism in mammals, but there had been little evidence for this in birds," he told BBC Nature.
"This study now provides some careful experimentation and good evidence [for it]."
Dr Bonadonna added that studying animal behaviour in detail was crucial in order to understand the consequences that human activity might have on them.
He added: "Our manipulation and pollution of the environment [and] even our 'blind' attempts to restore or preserve human-changed environments may have catastrophic consequences just because we do not have any idea of how animals may react." 

Iturria: Science Daily

What It Takes to Be the Perfect Invading Parasite

ScienceDaily (July 17, 2012) — Scientists from the Zoological Society of London (ZSL) are the first to document the characteristics of invading parasites, using malaria in New Zealand bird species.

Blood sampling New Zealand endemic hihi, Notiomystis cincta, to screen for avian malaria. (Credit: ZSL/A. Harris)

The study, published July 18 in Ecology Letters, identifies the factors influencing the success of parasites unintentionally introduced to new environments.

Avian malaria is a disease caused by species of parasites, of the genus Plasmodium, which infects birds. Just like human malaria, it is spread by mosquitoes, and the parasites spend part of their lives in red blood cells of birds. Avian malaria is common in continental areas, but is often absent from isolated islands where mosquitoes are less prevalent.
More than 800 exotic and native host birds were studied in a range of areas across Northern New Zealand. They detected parasite infection by extracting DNA from blood and analyzing it to look at specific segments of genes. They then looked in more detail at the characteristics of the parasites they found to see if they had features that made them more likely to be present in bird hosts in New Zealand.
ZSL's Dr John Ewen, who is from New Zealand himself, says: "We have found a surprisingly high diversity of malaria parasites in New Zealand, including two found nowhere else in the world. However, most parasites we found are recent arrivals, probably from infected birds released by humans. They tend to be widespread and common strains, which can infect a broad range of bird hosts. These findings will help us understand the what, when and how of exotic parasite introductions globally."
The global movement of parasites beyond their native country is an increasing problem, especially in the conservation of species. Many introduced parasites flourish in new environments and some can even be invasive. Little is known about the traits which enable parasites to survive and thrive.
ZSL's Professor Tim Blackburn added: "While we know a lot about the traits of successful vertebrate species invasions, our knowledge of the parasites they may carry is largely a blank page. This is alarming given that these co-introduced parasites can have catastrophic consequences for the natives they encounter, an example illustrated by smallpox introduced to the New World by the early European colonists."
This is the first study looking at the specific features of the exotic parasites within an isolated island bird community. New Zealand has a highly threatened bird community, sensitive to many human caused changes with exotic species being a major threat. ZSL scientists and colleagues are continuing to work on developing appropriate risk assessments for New Zealand's iconic native biodiversity and in understanding why some environments are more likely to be invaded by parasites than others.

Iturria: Nature

Hummingbirds don’t mind the rain

17 Jul 2012 | 23:01 BST | Posted by Daniel Cressey | Category: Biology & Biotechnology

Despite the raindrops falling on its head, this hummingbird remains stable.

Hummingbirds manage to maintain complete control over their aerial position, even when their tiny bodies are being hammered by raindrops.
These minute birds – which use their amazing hovering skills to harvest nectar – have to feed almost daily or they will perish. Given tat they inhabit regions that are not exactly arid, they are almost certain to be forced to fly in the rain at some point.
Armed with five Anna’s Hummingbirds (Calypte anna), a garden water-gun and a laboratory, Victor Ortega-Jimenez and Robert Dudley of the University of California, Berkeley aimed to work out just how much it cost them to do so.
They placed the birds in Perspex cubes and watched them feed under light, moderate and heavy simulated rain. Light and moderate rain had little effect on the birds, but heavy rain made them adopt a more horizontal posture and substantially increased the frequency of their wing beats (as shown in the slightly John Woo-esque video below), the researchers report in Proceedings of the Royal Society B.
“We demonstrated that hummingbirds can deal very well in light-to-moderate precipitation, practically without costs,” says Ortega-Jimenez. “But, even in heavy rain, despite the evident postural and wing kinematic changes produced by drop impacts and plumage wettability, these tiny birds can maintain flight control.”

See also: Mosquitoes don’t let the rain get them down – High-speed video reveals how flying pests remain airborne when raindrops strike.
Image and video: © Victor M. Ortega

Iturria: NY Times

Observatory

For These Flashy Males, No Modest Mate Will Do

By NICHOLAS BAKALAR

Published: July 9, 2012

Everyone knows that male birds are usually the ones with pretty colors, and that dull-looking females look for flashy mates. But male blue tits, apparently, judge females by their looks. And new research suggests that the males are more attentive fathers to their babies if the mother is pretty.

Enlarge This Image

Chris Gash

Birds of the species, both male and female, have shiny blue feathers on their heads that reflect ultraviolet light. For the study, published online in the journal Frontiers in Zoology, scientists captured females while they were taking care of chicks and assigned them to either an experimental group or a control group, smearing the crests of the first group with UV-blocking chemicals to make the feathers look dull. Then they restored the birds to their nests.

The male birds made significantly fewer feeding excursions for the nestlings of females with the UV-blocking chemicals on their feathers. The reason, the authors say, is that males judged females with poor coloration less likely to produce healthy offspring, and therefore less worthy of energy expended taking care them — what the researchers call the differential allocation hypothesis.

Providing food is costly, and males do not waste their effort on babies unlikely to reproduce their genes.

“Everyone has focused on male ornaments,” said an author of the study, Matteo Griggio, a postdoctoral researcher at the University of Veterinary Medicine in Vienna. “But in this case, we focused on the females, and found that the males, the fathers, change their behavior according to the females’ appearance. This is one of the first studies to do that.”

Bird moult allometry

Iturria: Birds and Science

Saturday, 18 July 2009

Bird moult allometry

Take a cable from your computer and measure the perimeter of your fist. This is, more or less, the length of your foot (check it now!). This is useful to buy socks without compromising the hygiene of the country, but it also enhances our understanding of bird moult. The ratio fist perimeter/foot length is constant among people; that is, it follows an isometric law: if you plot for different people fist perimeter on the x-axis and foot length in the y-axis, both in log-scale, you will find a linear relationship with slope = 1. If this slope was different from one, it would be an allometric relationship. That is, one measure relates as a predictable power of the other, but in a non-proportional way. Studying the allometry of bird moult, Rohwer et al. have done a big step on the understanding of bird evolution (see open-access full paper here).

Any bird lover knows that small birds can moult all their feathers at least once a year. However, larger species may need three years to renew all of them. Why? Rohwer et al. show this is an allometric problem: the relationship between the weight of a species and its daily growth rate of primaries follows an allometric law (also known as power law or scaling law) with a slope = 0.171 (lower line in the figure). That is, the larger the bird species the faster the growth of feathers. For instance, feathers of a 10g bird grow around 0.5 mm a day, and a 10Kg bird grows feathers at a 1 mm/day rate. The problem is that species size scale with the total length of all primaries with a slope of 0.316 (upper line); a slope almost two times larger! In other words, larger bird species have comparatively larger feathers than feather growth rates. What does it mean? It means that a tiny 10g bird moulting one feather at a time needs four months to finish a complete moult, but a huge 10Kg bird needs almost a whole year! This is why small songbirds can do even two complete moults a year while vultures may waste three years to renew a set of feathers.

Why larger birds do not compensate their larger feathers with a higher speed of moult? that is, why are the two lines in the plot not parallel? the answer seems straightforward: there are nutritional or energetically constraints that do not allow a faster moult. This is as evident as false: these authors show that species moulting all the flight feathers simultaneously (such as ducks) have the same speed of feather growth than similarly-weighted species moulting one feather at a time! Thus, they say, energetic or nutritional constraints can not explain why big birds need more time to moult. These authors advance a potential explanation, but further research will be needed to explain this fundamental issue in bird moult.

My point of view: This is an amazing piece of work. Often, big patterns are so familiar to us that we take them for granted, not realising that explaining them is the big challenge we should face. It is true that without a long history of bird moult research it would have been difficult that somebody could answer the question addressed in this paper. However, it is also true that this major pattern was known from long ago, and it has needed a clever-minded research group to face it and solve it in a so-interesting study.

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L’al.lometria de la muda de les aus

Agafa un cable de l’ordenador i mesura el contorn del teu puny. Aquesta és, més o menys, la longitud del teu peu (comprova-ho). Com ho sé? Perquè es tracta d’una llei isomètrica: en diferents persones el quocient entre la longitud del peu i el perímetre del puny és constant. Si grafiquem la longitud del contorn del puny en l’eix de les abscisses i la del peu en les ordenades i posem els eixos en escala logarítmica obtenim una recta amb pendent 1. Si la pendent fos diferent d’1 tindríem una llei al•lomètrica, és a dir, una mesura es relaciona de manera potencial i predictible, però no proporcional, respecte l’altre. Saber tot això serveix per comprar mitjons sense comprometre la higiene del país, però també per entendre molt millor la muda de les aus, com han fet Rohwe et al. en el seu últim estudi (veure l'article de lliure accés aquí).

Qualsevol amant de les aus sap que els ocells petits solen mudar tot el plomatge com a mínim una vegada a l’any. En canvi, espècies més grans com els rapinyaires poden trigar 2-3 anys en renovar completament el plomatge. Perquè? Per una qüestió purament al•lomètrica: la relació entre el pes de les espècies d’au i els mil•límetres que creix una ploma primària cada dia segueix una llei al•lomètrica (també anomenada llei de potencia o llei d’escala) amb pendent 0.171 (línea inferior de la gràfica). És a dir, com més gran és una espècie d’au més mil•límetres creixen cada dia les seves plomes. Per exemple, en una espècie d’uns 10g les plomes creixen 0.5 mm al dia, mentre que en una espècie de 10Kg creixen a un ritme d’1 mm/dia. El problema, és que la relació entre el pes de l’espècie i la suma de la longitud de totes les plomes primàries d’un individu escala amb un pendent de 0.316 (línea superior); casi el doble! Dit d’una altra manera, les aus grans muden, comparativament, molt a poc a poc per la longitud de plumes que tenen. Què vol dir això? Doncs que per mudar, ploma a ploma, totes les primàries, una au de 10 g triga uns quatre mesos i una de 10Kg triga casi un any! Aquesta és l’explicació del perquè els ocells petits poden fer inclús dues mudes complertes a l’any mentre que un voltor pot trigar tres anys en acabar de renovar tot el plomatge.

Per què les espècies més grans no compensen millor la longitud de les plomes amb un major creixement? És a dir, per què no son paral·leles les dues línies de la gràfica? La resposta sembla senzilla: hi ha una limitació energètica o nutricional que impedeix créixer més ràpid les plomes... sembla evident però és fals: les espècies com els ànecs que muden totes les plomes de vol simultàniament (deixant de poder volar durant setmanes) tenen un ritme de creixement de cada una de les plomes igual que les plomes de les espècies que les muden una a una. Per tant, diuen Rohwer et al., les limitacions energètiques o de nutrients no poden explicar el perquè els ocells grans triguen més a mudar. Els autors avancen una possible explicació però caldran nous estudis per continuar entenent aquestes coses tant fonamentals sobre la muda de les aus.

El meu punt de vista: No puc fer altra cosa que aplaudir amb totes les meves forces aquests investigadors. Sovint, els grans patrons ens son tant familiars que no els percevem com a quelcom que cal explicar, quan, en realitat, són els que haurien de preocupar-nos més. És cert que sense la llarga història de recerca sobre muda ningú es podria haver plantejat un estudi com aquest. Però també és cert que ja fa molts anys que sabíem el suficient sobre muda per poder haver donat aquest pas tant interessant.

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La alometría de la muda de las aves

Coge un cable del ordenador y mide el contorno de tu puño. Esta es, más o menos, la longitud de tu pie (compruébalo). Cómo lo sé? Porque se trata de una ley isométrica: en diferentes personas el cociente entre la longitud del pie y el contorno del puño es constante. Por lo tanto, si graficamos la longitud del contorno del puño en el eje de las abscisas y la del pie en las ordenadas y ponemos los ejes en escala logarítmica obtenemos una recta con pendiente 1. Si la pendiente fuese diferente de 1 tendríamos una ley alométrica, es decir, una medida se relaciona de manera predecible, pero no proporcional, respecto a la otra. Saber todo esto sirve para comprar calcetines sin comprometer la higiene del país, pero también para entender mucho mejor la muda de las aves, como han hecho Rohwer et al. en su último estudio (ver artículo de libre acceso aquí).

Cualquier amante de las aves sabe que los pájaros pequeños suelen mudar todo el plumaje al menos una vez al año. En cambio, especies más grandes como las rapaces pueden tardar 2-3 años en renovar completamente el plumaje. Porqué? Por una cuestión puramente alométrica: la relación entre el peso de las especies de ave y los milímetros que crece una pluma primaria cada día sigue una ley alométrica (también llamada ley de potencia o ley de escala) con pendiente 0.171 (línea inferior de la gráfica). Es decir, cuanto mayor es una especie de ave más milímetros crecen cada día sus plumas. Por ejemplo, en una especie de unos 10g las plumas crecen 0.5 mm al día, mientras que en una especie de 10kg crecen a un ritmo de 1 mm/día. El problema es que la relación entre el peso de la especie y la suma de la longitud de las plumas primarias escala con una pendiente de 0.316 (línea superior); casi el doble! Dicho de otra manera, las aves más grandes tienen, comparativamente, una muda muy lenta por lo largas que tienen las plumas. ¿Qué quiere decir esto? Pues que para mudar, pluma a pluma, todas las primarias una pequeña ave de 10 g tarda unos cuatro meses y una de 10Kg tarda casi un año! Esta es la explicación del porqué los pájaros pequeños pueden hacer incluso dos mudas completas al año mientras que un buitre puede tardar tres años en terminar de renovar todo el plumaje.

¿Por qué las especies más grandes no compensan mejor la longitud de las plumas con un mayor crecimiento? Es decir, ¿por qué no son paralelas las dos líneas de la gráfica? La respuesta parece senzilla: hay una limitación energética o nutricional que impide crecer más rápido las plumas ... esto es tan evidente como falso: las especies como los patos que mudan todas las plumas de vuelo simultáneamente (dejando de poder volar durante semanas) tienen un ritmo de crecimiento de cada una de las plumas igual que las plumas de las especies que las mudan una a una. Por tanto, dicen Rohwer et al. las limitaciones energéticas o de nutrientes no puede explicar el porqué los pájaros grandes tardan más en mudar. Los autores avanzan una posible explicación pero serán necesarios nuevos estudios para continuar entendiendo estos aspectos tan fundamentales sobre la muda de las aves.

Mi punto de vista: No puedo hacer otra cosa que aplaudir con todas mis fuerzas estos investigadores. Frecuentemente, los grandes patrones nos son tan familiares que no los percibimos como algo que hay que explicar, cuando, en realidad, son los que deberían preocuparnos más. Es cierto que sin la larga historia de investigación sobre muda nadie se podría haber planteado un estudio como éste. Pero también es cierto que hace ya muchos años que sabíamos lo suficiente sobre muda para poder haber dado este paso tan interesante.

> Photo by Julian Robinson (Flickr; Creative Commons).

Rohwer, S., Ricklefs, R., Rohwer, V., & Copple, M. (2009). Allometry of the Duration of Flight Feather Molt in Birds PLoS Biology, 7 (6) DOI: 10.1371/journal.pbio.1000132