Tag Archives: study

Cowbird moms choosy when selecting foster parents for their young

(University of Illinois at Urbana-Champaign 23 May; Photo: Loren Merrill, Scott Chiavacci)

Brown-headed cowbirds are unconventional mothers. Rather than building nests and nurturing their chicks, they lay their eggs in the nests of other species, leaving their young ones to compete for resources with the foster parents’ own hatchlings. Despite their reputation as uncaring, absentee moms, cowbird mothers are capable of making sophisticated choices among potential nests in order to give their offspring a better chance of thriving, a new study shows.

Brown-headed cowbirds are known to lay their eggs in the nests of more than 200 other bird species of varying sizes, and typically do so after the host bird has laid her own eggs. The new study, led by a team at the University of Illinois, found that when cowbird mothers chose the nest of a larger host bird, they preferred those that held smaller-than-average eggs for that species. Smaller host eggs give the cowbird eggs a better chance of being successfully incubated; smaller host hatchlings mean the cowbird chicks face less competition for food and nest space.

“It implies a level of resolution in cowbird decision-making that people hadn’t seen before,” said Loren Merrill, a postdoctoral researcher at the Illinois Natural History Survey who conducted the study with INHS scientists Scott Chiavacci and Thomas Benson and Illinois State University researcher Ryan Paitz.

“Scientists originally saw cowbirds as egg dumpers that would put their eggs in any nest they found,” Merrill said. “And while that may be the case in some areas, or for some birds, it doesn’t tell the whole story. In fact, the more people have looked at cowbird behavior, the more our understanding has evolved of exactly how discriminating cowbirds can be.”

From April through August for five seasons ending in 2015, the researchers hunted through 16 shrubland sites across Illinois, looking for cowbirds and nests in which cowbirds might place their eggs.

“Nest searching is really fun fieldwork, except when you’re trekking through poison ivy- and hawthorn-infested lands,” Merrill said. “You either get really lucky and see nesting material in a bird’s mouth, and you watch until they lead you to a nest, or you listen and watch for the vocalizations and behaviors the adults use when you are close to a nest.”

Cowbirds use similar tactics to scout for host nests.

“They do a lot of skulking around the underbrush,” Merrill said. “They’ll also perch in an inconspicuous place and just watch. They are cuing in on the behavior of hosts that are building their nests or taking food back to nests.”

Read more

‘Bare Parts’ are an Important but Underappreciated Avian Signal

AUK-16-136

(Erik Iverson 24 May 2017; Photo K Tarvin)

Birds are well-known for being among the most colorful of all animals, with many species displaying striking, brightly-colored feathers. Scientists have long wondered why color is so important to fitness, and hundreds of studies have been published on the relationships between plumage and traits such as age, physiological condition, reproductive success, and attractiveness to mates. However, there is a growing awareness that plumage is not the only important site of coloration among birds; there is also considerable variation within and between species in the color of bills and in bare skin such as legs, feet, ceres, or wattles. Yet compared to plumage, these ‘bare part’ ornaments have received relatively little attention; a 2006 review of carotenoid coloration in birds, for instance, identified only 14 studies of bare parts versus 130 studies of plumage.

Unlike plumage, bare part color has the potential to be highly flexible. For example, carotenoid-based bare parts can lose their color within days of food deprivation or within hours of stress. Amidst growing suggestions that changes in bare part color could have important implications for signaling, one of the authors, Jordan Karubian, was studying Red-Backed Fairywrens (Malurus melanocephalus) in Australia. In this species, males either acquire a territory and display black breeding plumage and bills, or stay dull and serve as helpers at the nest. Jordan noticed that when a breeding male died and a dull male took over its vacancy, the dull male’s bill would darken within several weeks. Experiments confirmed this effect and showed that dull males with newly black bills also had testosterone levels comparable to birds with black plumage. I joined Jordan’s lab as an undergraduate and studied fairywrens as well, and when I was looking for a topic for an honors thesis Jordan suggested that bare parts were an expanding area in need of a review. That thesis grew and grew, eventually becoming my master’s work and encompassing 321 published studies of bare-part coloration and signaling.

Our review shows that despite the research focus on plumage, bare part signals might be more common than plumage-based ones and are an important visual signal in many species that lack bright plumage altogether. Carotenoids, melanin, and structural colors are all flexible in bare parts, and rapid blood flushing through skin can change color even more rapidly. Bare part color provides up-to-date information about a signaler, allowing competitors, mates, and offspring to adjust their strategies and maximize their fitness. Carotenoid-signaling with bare parts may also be less costly than with plumage, allowing signaling by females and non-breeding males. In species where both plumage and bare parts of the same color exist, the two are likely to be ‘multiple messages,’ conveying different aspects of condition or targeting different audiences. We believe that more careful and extensive characterization of bare part coloration will contribute greatly to our understanding of this underappreciated dynamic signal, and help inform a more inclusive theory of animal communication.

 

Wild geese in China are ‘prisoners’ in their own wetlands

(Physorg 22 May 2017)
In many places in the world, goose populations are booming as the birds have moved out of their wetland habitats to exploit an abundance of food on farmland. But, new evidence reported in Current Biology on May 22 confirms, that’s not working so well for migratory waterbirds that overwinter in China.
The findings help to explain why China’s waterbirds are in decline, researchers say.

“We can now show what we suspected all along, namely that geese do not sneak off the wetlands to feed on farmland at night, but rather remain within the wetlands close to where they feed and roost both by day and night,” says Lei Cao of the Chinese Academy of Sciences. “Whilst this saves them energy and the risk of death from the hunters and poachers they encounter on dry land, it does constrain them to the wetlands and the quality of the food that they can find there.”

The waterbirds that spend their winters in China’s Yangtze River wetlands travel a long way to get there, migrating from Russia, Mongolia, and other parts of China to avoid the icy northern winters.

“These birds have nowhere else to go; farther north everything is frozen, and to the south there are no vast river systems or freshwater wetlands,” Cao says.

Cao and her colleagues have been concerned about geese and other waterbirds in China since surveys they conducted in the early 2000s showed that the birds were in decline. In the new study, they wanted to learn more about where the birds spend their time.

The researchers attached GPS tracking devices to 67 wintering wild geese representing five different species at three important wetlands in China’s Yangtze River Floodplain and followed the animals throughout the winter.

The tracking data showed that 50 of the birds representing species known to be in decline never left degraded natural wetlands where they’ve spent their winters for generations. Another 17 individuals from two species that show more stable population trends used wetlands the vast majority of the time. However, they did occasionally venture into neighboring rice paddies.

“This is a vital piece of evidence to support our hypothesis that, because Chinese geese are clearly ‘prisoners’ of their wetland habitats, their recent declines relate to reductions in the quality and extent of these wintering habitats upon which they rely,” Cao says.

The results help to confirm earlier studies linking declines among Chinese wintering geese to habitat loss and a degraded food supply. But what keeps geese in China from taking advantage of neighboring rice paddies and other agricultural lands in the way geese do in other places?

Cao and colleagues speculate that it’s because of greater human activity in cereal and rice fields in China. Chinese farmers also raise domestic ducks and geese in the stubble fields, leaving little food behind for their wild counterparts. Wintering geese are also a popular target of hunters who use shotguns, nets, traps, and poison to kill thousands upon thousands of birds every year. As a result, they conclude, the geese are effectively imprisoned in increasingly degraded wetland habitats.

The researchers say they’ll continue to explore the unique threats faced by these birds in China. They’re also building international collaborations and partnerships throughout East Asia to study and identify trouble spots for the birds all along their long-distance migratory routes.

New Zealand’s mainland yellow-eyed penguins face extinction unless urgent action taken

University of Otago 16 May 2017; Photo Thomas Mattern)

Iconic Yellow-eyed penguins could disappear from New Zealand’s Otago Peninsula by 2060, latest research warns. Researchers call for coordinated conservation action.

In a newly published study in the international journal PeerJ, scientists have modelled factors driving mainland Yellow-eyed penguin population decline and are calling for action to reduce regional threats.

According to the researchers’ prediction models, breeding success of the penguins will continue to decline to extinction by 2060 largely due to rising ocean temperatures. But these predictions also point to where our conservation efforts could be most effective in building penguins’ resilience against climate change.

The Yellow-eyed penguin, classified as endangered by the International Union for Conservation of Nature (IUCN), is a key attraction for New Zealand tourism. Yet, the chances of seeing the penguins in the wild are quietly slipping away, the new research suggests.

Lead study author Dr Thomas Mattern of the University of Otago says his team’s predictions are conservative estimates and do not include additional adult die-off events such as the one seen in 2013 in which more than 60 penguins died.

“Any further losses of Yellow-eyed penguins will bring forward the date of their local extinction,” Dr Mattern says.

If the recent poor breeding years — 2013 onwards — are included in the simulation of the future penguin population, things get progressively worse.

“When including adult survival rates from 2015 into the models the mean projection predicts Yellow-eyed penguins to be locally extinct in the next 25 years,” adds Dr Stefan Meyer, another of the co-authors.

The researchers note that Yellow-eyed penguins are iconic within New Zealand. Dr Mattern says these birds greet visitors to the country on billboards in all major airports, are featured on the NZ $5 note, and are widely used for branding and advertising.

“Yet despite being celebrated in this way, the species has been slowly slipping towards local extinction,” he says.

“It is sobering to see the previously busy penguin-breeding areas now overgrown and silent, with only the odd lonely pair hanging on,” says Dr Ursula Ellenberg, who has researched Yellow-eyed penguins for the past 14 years.

Increasing sea surface temperatures in part explain the negative trend in penguin numbers.

“The problem is that we lack data to examine the extent of human impacts, ranging from fisheries interactions, introduced predators to human disturbance, all of which contribute to the penguins’ demise,” says Dr Mattern.

“However, considering that climate change explains only around a third of the variation in penguin numbers, clearly those other factors play a significant role. Unlike climate change, these factors could be managed on a regional scale,” he says.

Professor Phil Seddon, Director of Wildlife Management at the University of Otago, says besides shining an alarming light on the state of the Yellow-eyed penguin on the New Zealand mainland, the study also underlines the importance of long-term data sets.

“In the current era of fast science, long-term projects have become a rarity. Without more than 35 years’ worth of penguin monitoring data we would probably be still at a loss as to what is happening to a national icon, the Yellow-eyed penguin,” Professor Seddon says.

Despite this urgency, Yellow-eyed penguins continue to drown as unintentional bycatch in nets set in penguin foraging areas, suffer from degradation of their marine habitat because of human activities, and die from unidentified toxins.

The authors conclude that “now we all know that Yellow-eyed penguins are quietly slipping away we need to make a choice. Without immediate, bold and effective conservation measures we will lose these penguins from our coasts within our lifetime.”

Wind and rain change breeding patterns for swallows

(Dana Kobilinsky 15 May 2017; Photo: Dan Doak)

Fewer storms that bring wind and rain may be causing North American tree swallows (Tachycineta bicolor) to lay their eggs earlier in the spring, according to new research.

The impacts of this early egg laying isn’t known, but the trend points to what researchers say is an overlooked effect of climate change. Many studies look at the effects of warming temperatures on wildlife, but these researchers took into account the effects that less wind and rain in central Alaska have on the birds.

“In spring when the birds are doing their business, their habitat is not warmer at all,” said Daniel Doak, a professor at the University of Colorado Boulder and the senior author on the recent study that his undergraduate student led. “It’s a weak trend. But the storminess trend is very strong.”

As part of their study published in Proceedings of the Royal Society B, the researchers looked at data collected on swallows in two study sites in central Alaska over the past 15 years.  The swallows are an extremely resilient species, Doak said, which makes them easy to study. “They’re a model species for effects on many different species,” he said. “They’re easy to study because they are less perturbed by human disturbances.”

The researchers recorded phenology information such as when the individual birds were laying eggs, hatching and fledging. Then, they reviewed weather station data from NOAA and the National Park Service and took note of climate data including temperatures, windiness and precipitation.

They found that frequent, small spring windstorms, which tend to slow down the breeding process, have become rarer over the past three decades. As the springs have gotten less windy, the birds are laying eggs earlier.

“Birds fine tune what they’re doing when there’s climate variation year to year,” Doak said. He and the other authors hope to study nest success, fledging and rearing of the species at these sites to determine what effects an earlier breeding time has, but he also hopes the study shows the importance of studying climate change impacts other than temperature.

“Climate change really has multiple dimensions,” he said. “We’ve been simplifying it down to the fact that things are getting warmer.”

Even non-migratory birds use a magnetic compass

(Lund University 18 May 2017)

Not only migratory birds use a built-in magnetic compass to navigate correctly. A new study from Lund University in Sweden shows that non-migratory birds also are able to use a built-in compass to orient themselves using the Earth’s magnetic field.

The researchers behind the current study have received help from a group of zebra finches to study the magnetic compass of what are known as resident birds, that is, species that do not migrate according to the season. Zebra finches are popular pet birds in many homes. Originally, they come from Indonesia and Australia where they search for food in a nomadic way.

“We wanted to know how a magnetic compass works in non-migratory birds like these”, says Atticus Pinzón-Rodríguez, doctoral student in biology at the Faculty of Science at Lund University.

In the current study, researchers have looked closer at the zebra finches’ ability to utilise the Earth’s magnetic field and the different properties of this built-in compass. The results show that the zebra finches use a magnetic compass with very similar functions to that of migratory birds, i.e. one with a very specific light dependency and thus sensitivity to different colours and light intensities.

“Our results show that the magnetic compass is more of a general mechanism found in both migratory birds and resident birds. It seems that although zebra finches do not undertake extensive migration, they still might be able to use the magnetic compass for local navigation”, says Atticus Pinzón-Rodríguez.

Although the magnetic compass of birds has been studied by the research community for a long time, the understanding of how it works is still very incomplete, according to Atticus Pinzón-Rodríguez.

Male Birds Adjust Courtship Behavior Based on Social Context

AUK-16-214 1 J Welklin

(AOS 17 May 2017; Photo: J. Welklin)

Male birds that have already paired up with a female aren’t above looking for a little action on the side. A new study from The Auk: Ornithological Advances explores how male juncos adjust their courtship behavior to their social landscape, finding that while both paired and unpaired males will try to get the attention of a new female on their turf, they go about it in different ways.

A male bird’s courtship behavior can be affected by factors like his size and hormone levels, but ornithologists are increasingly realizing that social context—whether or not the male already has a mate, and what other birds are around to witness his exploits—also plays a role. Dustin Reichard of Ohio Wesleyan University (formerly Indiana University) and his colleagues set out to tease apart the roles these different issues play in the courtship of Dark-eyed Juncos, comparing how unpaired males, paired males whose mates were present, and paired males whose mates were elsewhere behaved when presented with a new female.

They found that paired males approached females more rapidly, spent more time close to the females, were more active, and spent more time with their body feathers erect than unpaired males. Paired males also sang fewer long-range songs than their single counterparts, perhaps not wanting other birds to overhear, although the actual presence or absence of their mates didn’t affect their behavior.

Read more