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