Birds don’t mind the lights – if it’s dim enough

Have you have ever been on an airplane at night and looked down on the illuminated earth? Our various light sources can be seen from miles away and the brightening of the night sky above cities even has a name – urban sky glow. Obviously, light sources at night are needed in modern civilisations, but diminishing darkness can cause severe problems, such as altering wake–sleep rhythms and affecting health. Although we have found ways to live with light pollution, other animals cannot always avoid it.

Zeynep Ulgezen, from Wageningen University in The Netherlands, and an international team of colleagues wanted to know the consequences for birds of sleeping under night illumination. For their study, the researchers caught great tits (Parus major) from an urban and a forested area and tested whether they preferred to sleep under constant darkness or under weak green or white LED light (1.5 lx). Next, they exposed the birds to constant darkness or nightly white or green illumination for 14 days, and monitored the birds’ sleep, activity and how much energy they spent per night. The researchers also took blood samples from the birds before and after the treatment to determine the animals’ oxalic acid levels, a biomarker for sleep disruption, and compared the memory and learning skills of the great tits exposed to the different light conditions, by training them to differentiate between colours and select a certain colour in return for a reward.

To their surprise, Ulgezen and her colleagues found that all of the birds preferred to sleep under light instead of in constant darkness, and – when given the choice – the birds preferred green over white light sources. When the researchers looked into the consequences of sleeping under light, they found no effect of nightly illumination on the birds’ memory and learning, and their blood levels did not show any indication of sleep disruption. However, both light sources caused the birds to be more active at night. The great tits that slept under white light became active almost 3 h earlier than those sleeping in constant darkness and half an hour earlier than those that slept under green light. Consequently, the birds facing nightly light pollution spent more energy than the birds that slept in complete darkness. But the effect of light also depended on the origin of the birds. The animals that were captured in a forest were most active under nocturnal white light, while urban birds showed the same amount of activity under green and white light.

This study suggests not only that urban birds can get used to the lights of the city, but also that birds actually prefer to have – at least a little – light at night. While the researchers have used light intensities that mimic realistic light pollution, the illumination was still relatively weak, and birds nesting under street lamps would experience light that was up to 13-fold more intense. But why do birds prefer light over darkness? Ulgezen and her colleagues suggest that the birds chose the illuminated areas for a simple reason: more light allows them more time to forage and enchant members of the opposite sex.



Songbirds have a thing for patterns

You might think that young children would first learn to recognize sounds and then learn how those categories of sounds fit together into words. But that isn’t how it works. Rather, kids learn sounds and words at the same time. In fact, the higher-level patterns—those words—are key in learning to recognize and place speech sounds into meaningful categories. That’s why children who grow up in Japanese-speaking homes don’t recognize the difference between ‘r’ and ‘l’ sounds. In Japanese, that distinction doesn’t matter. Now, researchers reporting in the Cell Press journal Current Biology on June 25 present evidence from European starlings showing that songbirds learn their songs in much the same way.

“It wasn’t clear whether this kind of learning—where knowledge of a pattern informs understanding about the categories that make up the patterns—was unique to humans and language, or is a more general process shared with other animals,” says Timothy Gentner of the University of California, San Diego. “We showed that this kind of learning is shared with, at least, songbirds. When birds learn to recognize patterns of song elements, they get a big boost in their ability to categorize those elements.”

Starlings’ songs consist of short, stereotyped patterns of simple notes grouped into ‘motifs’ and longer, well-defined sequences of motifs organized into bouts. Those motifs fall into one of four categories: whistles, warbles, rattles, or high frequencies. Gentner and his colleagues wanted to find out how patterns influence starlings in their ability to categorize those sounds.

Jordan Comins, a graduate student in Gentner’s lab and lead author of the study, trained four starlings to differentiate complex auditory patterns following the form AABB and BBAA from those that followed the form ABAB and BABA, where A and B denote natural motif categories of warbles and rattles. The researchers trained a second group in the same way, except that they shuffled the patterns.

The researchers found that the birds presented with clear patterns of sounds were at a big advantage over the other group in their ability to correctly categorize the motifs they’d heard. The findings show that rely on patterns in much the same way that people do.
“We ‘hear’ words, not sequences of ,” Gentner says. “While it is tempting to think that this is a uniquely human way of perceiving the world, it is not.”

Birds may not have language, but they still can teach us much about the biological and psychological mechanisms that make language and possible, the researchers say. Having identified this basic form of shared top-down learning, Gentner’s team will now explore more subtle details of the perceptual categories and in the birds to see how precisely they match human speech acquisition. They will also examine the extent to which pattern knowledge shapes the representation of complex vocal signals in the songbird brain.

Birds have fundamental rights, can’t be kept in cages: Delhi High Court

Birds have the fundamental right to “live with dignity” and fly in the sky without being kept in cages or subjected to cruelty, Delhi High Court has said while holding that running their trade was a “violation of their rights”.

Justice Manmohan Singh expressed anguish that instead of being allowed to fly free, they were “exported illegally to foreign countries without availability of proper food, water or medical aid”.

“I am clear in mind that all the birds have fundamental rights to fly in the sky and all human beings have no right to keep them in small cages for the purposes of their business or otherwise,” the judge said.

The high court issued notice to Delhi Police as well as the bird owner, Md Mohazzim, and sought their responses by May 28.

The high court made the observations and issued the orders while staying the direction of a trial court which had allowed some birds to be released to the same person from whom they were rescued on his plea.

The trial court order was stayed on a plea by NGO People for Animals, which had challenged the release of birds into custody of owners without hearing the NGO which had freed the birds.

The NGO, in its plea filed through advocate SD Windlesh, has alleged that the trial court released the birds into Mohazzim’s custody despite arriving at a finding that he was not the owner of the birds.

Granting relief to the NGO, the high court said, “This court is of the view that running the trade of birds is in violation of the rights of the birds. They deserve sympathy. Nobody is caring as to whether they have been inflicted cruelty or not despite a settled law that birds have a fundamental right to fly and cannot be caged and will have to be set free in the sky.”

“Birds have fundamental rights including the right to live with dignity and they cannot be subjected to cruelty by anyone including claim made by the respondent.


Massive southern invasions by northern birds linked to climate shifts

With puzzling variability, vast numbers of birds from Canada’s boreal forests migrate hundreds or thousands of miles south from their usual winter range. These so-called irruptions were first noticed by birdwatchers decades ago, but the driving factors have never been fully explained. Now scientists have pinpointed the climate pattern that likely sets the stage for irruptions – a discovery that could make it possible to predict the events more than a year in advance.

The researchers found that persistent shifts in rainfall and temperature drive boom-and-bust cycles in forest seed production, which in turn drive the mass migrations of pine siskins, the most widespread and visible of the irruptive migrants. “It’s a chain reaction from to seeds to birds,” says atmospheric scientist Court Strong, an assistant professor at the University of Utah and lead author of the study.

Many seed-eating boreal species are subject to irruptions, including Bohemian and cedar waxwings, boreal chickadees, red and white-winged crossbills, purple finches, pine and evening grosbeaks, red-breasted nuthatches, and common and hoary redpolls. The authors focused on the pine siskin, a species featured prominently in earlier work on irruptive migrations.

Previous studies have found evidence that irruptions are triggered by food shortages caused by the large-scale collapse of seed production in northern pine, spruce and fir forests.

“We’ve known for a long time that weather was probably important, but prior analyses by ecologists have been unable to identify exactly what role weather was playing in this phenomenon,” says ecologist Walt Koenig, a senior scientist at the Cornell Lab of Ornithology and co-author of the new study incorporating climate science. “It’s a good example of the value of interdisciplinary work,” Koenig says.

To resolve the question, the scientists turned to a remarkable trove of data gathered by backyard birders as part of Project FeederWatch, a citizen science initiative run by the Cornell Lab of Ornithology. FeederWatcher volunteers systematically record bird sightings from November through early April and they gave the scientists more than two million observations of pine siskins since 1989. The crowd-sourced data makes it possible to track the movement of bird populations at a continent-wide scale.

“Avid birders across the U.S. and Canada have contributed sustained observations of birds at the same broad geographic scale in which weather and climate have also been observed and understood,” says co-author Julio Betancourt, a senior scientist with the U.S. Geological Survey in Reston, Virginia.

Pine siskins breed during summer in Canadian boreal forests, where they rely heavily on tree seeds for food. When seeds are abundant, pine siskins in eastern North America largely stay put in the northern coniferous forests of Canada through the winter. But when seed production is poor, pine siskins and other boreal birds move elsewhere to find overwintering habitat with adequate food. During these irruptive years, the eastern populations of pine siskins forage as far south as the Appalachian Mountains. Western populations show less variability in irruptive movements.

Amateur birdwatchers have recorded dramatic shifts in siskin migrations over the years. The winter ending in 1990, for example, featured a massive “superflight” south of the boreal forest, while during the winter ending in 2004 there was a near absence of boreal pine siskins in the U.S. The winter ending in 2009 saw another big irruption south of the boreal forest, followed by greatly reduced counts the following winter.

In the new study, researchers combined FeederWatch observations with climate data in a statistical analysis. This allowed them to link bird population movements with established patterns of climate variability across North America. As expected, they found that extremely cold winters tend to drive birds south during the irruption year.

More surprisingly, the researchers found a teeter-tottering pattern between the north and south that influences bird migrations two to three years later. When the prevailing weather is wet and cold and unfavorable to seed production in one region, it tends to be warmer and drier and favorable to seed production in the other region.

This climate “dipole” tends to push and pull bird migrations across the continent. The heaviness of in a given year depends on how favorable the climate was during the two or three previous years required to set and ripen seeds. That means that, in principle, it might be possible to predict irruptions up to two years in advance.

The finding also raises a question about the impact of : could the perturbation by massive carbon dioxide emissions disrupt the coupling between north and south such that unfavorable conditions unfold simultaneously, leaving birds with poor seed supplies everywhere in some years?

The answer is unknown. “The is the world’s largest terrestrial biome and is home to more than half of North America’s bird species,” says co-author Benjamin Zuckerberg, an assistant professor of wildlife ecology at the University of Wisconsin-Madison. “It is likely that these irruptions, driven by climate, are a critical indicator of how climate change will affect northern forests and their dependent species.”

The study, funded by the National Science Foundation, was published today in the online version of the Proceedings of the National Academy of Sciences.
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Birds colour-match their interior designs

Birds colour-match their interior designs

Researchers at the University of St Andrews have produced the first experimental evidence that birds actively select nest-building materials that camouflage their nests: published today in influential ornithological journal The Auk.

Scientists from the University’s School of Biology wallpapered male zebra finches’ (Taeniopygia guttata) cages in different colours before filming them choose which colour of material with which to build their nests.

Given the choice of paper strips in two different colours, zebra finches largely chose strips that were a colour-match to the paper covering the walls of their cage.

These findings confirm that birds choose to their nests by matching the colour of material they use to the nests background, rather than happening to build camouflaged nests as a simple consequence of the that are available.

Being able to match the nest material to the nest site in this way may help the birds to conceal their nests from predators. Predation is a major cause of nest loss for birds. While there is good evidence that birds will move their nest in order to reduce predation risk, this is the first data to show that birds will camouflage their nests in order to reduce predation.

What’s more, many of the chose a small proportion of that were not the same colour as the cage walls, suggesting that birds may also employ a second method of disguise to conceal their nests known as disruptive camouflage. By using a small proportion of non-camouflage material in the nest the bird may break up the outline of its nest so that it look less like a nest and is, therefore, less attractive to predators.

The findings build on previous research carried out by the University of St Andrews, which showed that is not just an innate skill but is an experience-dependent process during which birds learn what works best.

Report author, Dr Ida Bailey said:

“We know from previous work that birds will learn to choose nest material of a colour they associate with a successful nesting attempt but this is the first evidence that they choose material so as to camouflage their nests. Camouflage is, then, another feature of nest building that we now know birds consider when they choose the materials with which to build their nests.

“Like us they don’t choose just any coloured material to build their homes, they avoid colours that would clash with their surroundings. Knowing this gives us a better idea of how may actively reduce the chances of predators finding their nests. It also opens up the possibility that this is yet another aspect of nest building that inexperienced builders may get wrong and need to learn about during their lives.”

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What drives the evolution of bird nest structures?

How to protect your chicks from predators? Build a dome over them! There is tremendous diversity among the nests of birds, in nest location, structure, materials, and more, but we know very little about the forces that shaped the evolution of this incredible variety. In a new paper published this week in The Auk: Ornithological Advances, Zachary Hall, Sally Street, Sam Auty, and Susan Healy of the University of St. Andrews in Scotland test the hypothesis that domed-shaped nests arose as a result of some species transitioning to nesting on the ground, where the risk from predators is greater.

Hall was completing his Ph.D. work on the neurobiology of nest-building behavior when he noticed that very little work had been done on trying to understand why different bird species build such drastically different nest structures. “I thought this was strange,” he explains, “because the shape of a nest seems to be the most striking and diverse feature across .” The hypothesis that dome-shaped nests resulted from the increased predation risk when competition for nest sites led some birds to begin nesting on the ground was first proposed almost twenty years ago, but techniques at the time did not provide a way to test it. Applying statistical techniques he had previously used in his neurobiology study, Hall and his colleagues collected previously published descriptions of the nests of 155 species of babbler and mapped nest height and structure to the birds’ family tree.

Their analysis confirmed that babblers’ ancestors likely built above-ground, cup-shaped nests, and that the addition of a dome to cover the nest corresponded with switching to nesting at ground level. “This new study by Hall, Street, Auty, and Healy looks at the evolution of two key aspects of animals as architects: how they shape their homes and where they put them. It shows very nicely how we can take advantage of recent progress in avian phylogenetics to test ideas about the evolutionary history behind the modern-day co-occurrence of particular pairs of traits,” according to Don Dearborn, an expert in the evolution of reproductive strategies in birds. “I am very happy how well nest structure integrated into our analyses, but this study is only the tip of the iceberg, and we hope future work can use a similar approach to identify other factors that may have influenced the evolution of structure,” adds Hall.

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Climate Change and its impact on migatory birds

At the Salim Ali Centre for Ornithology and Natural History’s International Conference on Indian Ornithology, I met scientists who picked up and discussed climate change and its impact on migratory birds.

Migratory behaviour of birds
Birds have long been used as indicators of environmental change. A global status report entitled “Bird Species and Climate Change” indicated that birds are “the quintessential ‘canaries in the coal mine’ when it comes to climate change.” The report assembles scientific evidence, which
demonstrates a “trend towards major bird extinction from global warming.”
Most species (84%) listed on the appendices of the Conservation of Migratory Species of Wild Animals (CMS) have the potential to be affected by climate change in some way.
About 53% from changes to water regime (droughts, lowered water tables, and so on),
24% from mismatches with food supplies, 18% from sea-level rise, 17% from habitat
shifts, 17% from changes in prey range, and 7% from increased storm frequency. These
are estimates based on expert opinion. The total proportion thought to be threatened
by climate change impacts is greater than that threatened from all other human-induced
When we study the migratory birds, the most important issue that emerges is the habitat quality. The birds need a coherent network of sites to facilitate their migratory journeys. Habitat quality is especially important on staging or stop-over sites, as during these times the birds need to consume large amounts of resources rapidly to continue their onward journey.
Such high quality sites may be crucial to allow migrants to cross large ecological barriers, such as oceans or deserts. The impacts of climate change can have disastrous effects on migratory species.
In the International Conference on Indian Ornithology (ICIO) 2011 held at the Salim Ali Centre for Ornithology and Natural History (SACON), Coimbatore, scientists discussed their preliminary studies on the migratory pattern of birds and how climate change was affecting India. Scientists, in their presentations, discussed how changes in temperature led to changes in reproduction patterns.
Beyond that, there was a range of expansion of birds towards the poles. This raises a gamut of issues for the migratory birds. They might not be able to find food. Even if they find food, they might not be able to find food at the right time.
There is a migratory restlessness in the birds and a great deal of mistiming in terms of food. As the birds travel from one place to another they need to protect themselves from the predators, need to
find the “right” kind of food during the journey because they need it to fly for long hours and survive through this migration journey.
One of the biggest threats to a significant number of migratory birds is the impact of warming on the polar regions. There is already evidence that a decrease in the melting of snow cover is leading to lack of land. This implies that the area available for the large populations of migratory birds that breed in these regions may shrink significantly and would eventually affect their numbers.
Says Dr Prakash Rao, Assistant Professor, Symbiosis International Institute of International Business, who has been doing research on climate change and its impact on migratory birds, “There were not many changes in the migratory pattern of birds till the 1900s. As a result of climate change, significant loss of key species has occurred. If the current rates of emissions continue, 15%–37% of the species could go extinct by 2050.”
In May 2008, an International Union for the Conservation of Nature (IUCN) assessment concluded that “climate change and even some attempts to tackle it are pushing one in eight species of birds
towards extinction.”

“There are direct and indirect losses due to climate change. Coastal birds like crane, storks, and birds of prey are at risk. The impact of climate change can be first noticed in the coastal
regions,” says Dr Rao. He further adds, “The impact in India is dependent on monsoon variability, crop production, melting of snow caps feeding the Ganges, erosion of coastal areas, sea level rise, agricultural ecosystems, erratic rainfall, and so on. Birds using these agricultural landscapes will be affected. Also, the long distance palaectic (includes the terrestrial eco-regions of
Europe, Asia north of the Himalayan foothills, northern Africa, and the northern and central parts of the Arabian Peninsula) migratory birds will see more danger.”
The Bird Species and Climate Change report brought out by WWF warns that extinction rates “could be as high as 38% in Europe, and 72% in north-eastern Australia, if global warming exceeds 2 ºC above pre-industrial levels (currently it is 0.8 ºC above pre-industrial levels).” Unfortunately, the current approach to bird conservation, which focuses on protecting specific
and limited areas containing high bird diversity will inevitably fail, simply because climate change will force birds to shift into unprotected zones as they desperately try to cope with an ever-warming planet and shifting habitats. In the US, bird populations have also shrunk, and nearly a third of the bird species living in the eastern Midwest and the Great Lakes areas could be lost.
In other parts of the world, the situation is just as precarious, if not worse. In North America, spring migration is occurring earlier and fall migration later in many species. For example, 25 migratory
bird species are arriving in Manitoba, Canada, earlier than they did 63 years ago.
As changes between seasons continue to become less clear, many birds are mistiming their migratory pattern. These shifts make them vulnerable to heat waves, droughts or cold snaps.
Of particular concern is the fact that some bird populations are abandoning their migrations altogether. For instance, cranes are starting to spend the winter in Germany rather than fly south to Spain or Portugal. Birds exhibiting this behaviour risk remaining in regions that can potentially be too cold for them to survive.
In such cases, a single severe winter event could decimate entire populations.
“Erratic rainfall could affect rain dependent birds like floricans and bustards in India,” explains Dr Rao.
Certain steps have been taken to track migratory birds and study their patterns.
One of them is the popular ringing method. Here, a metal band is affixed to the leg of the bird. Rings used are of negligible weight as compared to the bird’s body weight and the ring size varies according to the size of bird. Coloured plastic leg and neck bands are also used in large birds, such as geese. The leg on which the ring/ band is fitted also varies according to the year. The band is usually put on the left leg, if ringing is done during odd years (e.g. 2011, 2013, and so on), and on the right, if done during even years (2012, 2014, and so on). The ring recovery data is then obtained when the birds are re-sighted, recaptured, hunted, or found dead.
Colour marking is another tool, which uses bright colour marks that enables observation of the bird from a distance through a telescope or binoculars without the need to capture/shoot the birds. The unique combination of colours and marks allows for identification of individuals or marking locations. Also, temporary plumage dyes are often used on large waders to aid short-distance movement studies. Satellite tracking, transmitters, and radars are now increasingly being used to track the movement of migratory birds.
According to Dr Rao, “An assessment needs to be done in selected ornithological habitats. With strong empirical evidence and climate modelling data, we need to improve the data collection for these birds.”
Migrant Watch, an initiative by Dr Suhel Qader of the National Centre for Biological Sciences (NCBS) is a participatory approach to track the arrival of migratory birds in India. There are registered members of Migrant Watch who provide updated information on the sighting of migratory birds. The website lists the migratory birds that are being tracked. The members can upload the time and place of the sighting of the bird. They even have the option of uploading a picture of the bird. On the basis of the data generated from users, the arrival time of the bird is tracked. In this citizen-science initiative, people help scientists to generate a pool of data from
which the bird arrival can be tracked.
According to the Millennium Ecosystem Assessment, climate change is likely to become one of the most significant drivers of biodiversity loss by the end of the century. Biodiversity conservation can go a long way in offsetting the carbon emissions and reducing the negative effects of climate change. The conserved or restored habitats can remove carbon dioxide from the atmosphere, thus, helping to address the climate change issue by storing carbon. Moreover, conserving intact ecosystems like mangroves can help reduce the disastrous impacts of climate change, such as flooding and storm surges.
It becomes imperative that measures are taken to save the wildlife habitat, which in turn, would help in reducing carbon emissions, retaining the forest cover, and protecting many species from extinction.

Oldest albatross Wisdom lost her egg

n December, 2014, EarthSky reported that a Laysan albatross named Wisdom – said to be the world’s oldest known, banded, wild bird at an estimated age of 63 – had been photographed incubating her newest egg. Wisdom returns to Midway Atoll National Wildlife Refuge and Battle of Midway National Memorial each year to nest and raise her chicks. She lays only one egg a year. This month, though (February 2015), the Papah?naumoku?kea Marine National Monument reported on its Facebook page:

To Wisdom Lovers Far and Wide:

There comes a time when nature reminds us when there is life, there is death. In January, 2015 Deputy Refuge Manager Bret Wolfe observed Wisdom, the world’s oldest known albatross, sitting on her nest without an egg, (she and her mate were both sharing incubation duties for most of December 2014).

So what’s up with the missing egg? Of the over 694,000 albatross nests counted on Midway Atoll National Wildlife Refuge during December 2014 a percentage of those nests with eggs have not hatched and some eggs have disappeared. The island’s natural egg predators such the ruddy turnstones or bristle-thighed curlews can actually take eggs that are not closely attended. Cockroaches and other scavengers such as mice can quickly move in to clean house and devour shell remnants of damaged eggs. When this happens the albatross pair abandons their nest and tries again next year. Additionally, Laysan albatross occasionally skip a year or even two as they use their precious energy resources to complete a full molt while at sea or simply take a breather to replenish their energy after accomplishing an exhaustive seven-month incubation and chick rearing effort. Wisdom and her mate have been sighted and they appear to be fine. Don’t forget that Wisdom has maintained a record-breaking track record for rearing chicks beyond an age that humans understood was possible. We are therefore hopeful Wisdom and her mate will return next year to start nature’s cycle of rearing chick number 30 something!

For more information and photos visit:

Bottom line: People around the world cheered in late 2014, when an albatross named Wisdom – world’s oldest known, banded, wild bird at an estimated age of 63 – laid a new egg. Now nature reminds us that life and death go hand in hand.

Manmade noises impacts birds decline..

How noise can affect interactions between human and natural systems is the topic of a National Science Foundation grant awarded to researchers at Penn State and Boise State University.
The researchers are analyzing how traffic sounds influence interactions between humans and in proximity.

The four-year, $600,000 project is intended to determine whether manmade generated in wildlife areas with already declining bird diversity weakens people’s perceived value of wildlife. If it weakens people’s perceptions, does it also diminish the amount of support people offer for , further contributing to the decline of bird diversity?

The researchers also want to know if a greater awareness of the sounds of wildlife increases the value placed on environmental diversity and the overall human perception of nature.

“We are very excited about this study,” said co-investigator Peter Newman, professor and head of the Department of Recreation, Park, and Tourism Management, Penn State. “We talk a lot about working across disciplines but actually doing it is another story. This study allows social scientists to work together with biologists to clearly define coupled human-natural relationships and how they work systemically. To me, these types of studies truly shed light on complex environmental challenges and help to train our grad students to tackle them in the future.”

“Our hypothesis is that as manmade noise fills the soundscape and drives birds and other animals away, groups and individuals come to value wildlife less,” said principal investigator and Boise State biologist Jesse Barber. “That decline then leads to a reduction in support for nature conservation, which spirals into a further decline in wildlife diversity.”

The researchers are focusing on traffic sounds, but believe their data will apply to other human-caused noise as well. Because birds are much easier to observe and count in the wild than other animals, they will be at the heart of the study.

Birds will be counted along wilderness roadways with cars traveling at maximum speed, and again at reduced speed or during road closures. The researchers will survey people to determine if they believe slowdowns and the resulting decrease in are worth the transportation trade-offs if both people and wildlife benefit.

Bad reputation of crows demystified

In literature, crows and ravens are a bad omen and are associated with witches. Most people believe they steal, eat other birds’ eggs and reduce the populations of other birds. But a new study, which has brought together over 326 interactions between corvids (the bird group that includes crows, ravens and magpies) and their prey, demonstrates that their notoriety is not entirely merited.

Corvids are the subject of several population control schemes, in both game and conservation environments. These controls are based on the belief that destroying them is good for other birds. They are also considered to be effective predators capable of reducing the populations of their prey.

However, a study published recently in the journal ‘Ibis‘ analysed the impact of six species of corvid on a total of 67 species of bird susceptible to being their prey, among which are game birds and passerine birds.

The project, which compiled the information of 42 scientific studies and analysed a total of 326 interactions between corvids and their prey, shows that they have a much smaller effect on other bird species than was previously thought.

As Beatriz Arroyo – author of the study and a researcher at the Institute of Research in Game Resources (IREC), a joint centre of the University of Castilla-La Mancha, the Castilla-La Mancha Community Council and the CSIC (Spanish National Research Council) in Spain – tells SINC: “In 81% of cases studied, corvids did not present a discernible impact on their potential prey. Furthermore, in 6% of cases, some apparently beneficial relationships were even observed.”

Greater impact on reproduction

To find out what impact corvids have on their prey, the researchers – in conjunction with the University of Cape Town (South Africa) – conducted several experiments in which they isolated crows, ravens and magpies, among other predators, to observe how they affected the reproduction and abundance of other birds.

According to the works analysed, when crows were taken away from their habitat, the survival rates of chickens and the number of eggs of other species were higher in most cases. Nevertheless, with respect to abundance, without corvids an increased size of the populations of other birds was observed only in a small number of cases.

According to the study, when crows were removed from the environment, in 46% of cases their prey had greater reproductive success, while their abundance fell in less than 10% of cases.

Additionally, these experimental studies carried out in nine different countries (Canada, France, Norway, Poland, Slovakia, Spain, Sweden, the UK and the USA) revealed that, if corvids are eliminated but other predators are not, the impact on the productivity of their prey would be positive in only 16% of cases; whilst without corvids and other predators, including carnivores, the productivity of other birds improves in 60% of cases.

This suggests that crows, ravens and magpies, amongst others, have a lower impact on prey than other threats. “Compensatory predation can also occur,” the researcher explains.

In the study they also compared the effects between different groups of corvids. In these results it is striking that “magpies had much less impact on prey than other species,” Arroyo claims.

Comparing crows and magpies, the scientists showed that in 62% of cases crows impacted negatively on the reproduction of their prey, whilst magpies had a negative effect in 12% of cases. “But no differences related to the abundance of prey were noted,” the scientist affirms.

For the authors of this piece of research, given the results it is necessary to “be cautious” when drawing conclusions on the impact of magpies or crows on the populations of their prey. “This method of managing populations is frequently ineffective and unnecessary,” Arroyo finishes.

Source: EurekaAlert