(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.”
(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.
A team of researchers want to see if these birds are populating land cleared along the route of a powerline—as well as areas that have been recently logged—in New Hampshire and Maine.
In other parts of the country, the shrubby habitat of these younger forests have been found to offer much-needed protection for the birds from predators, as well as a steady diet of insects and fruit.
One of the researchers says these habitats are “incredibly important” for the songbirds in those parts of northern New England.
“Our goal is to get a better understanding for how these habitats function in our landscape,” said Matt Tarr, a wildlife specialist at the University of New Hampshire Cooperative Extension.
Tarr and his colleagues will catch the songbirds in mist nests starting later this month, band them and then track them over the next two years. They will be focused on 24 transmission line rights of way and 12 areas that been logged in southeastern New Hampshire and southern Maine.
Tarr said there are as many as 40 species of songbirds that nest in young forests and another group that nest in mature forests.
“However, there is growing evidence suggesting that after their birds finish their nesting and the young leave the nest, they leave mature forests and come into the young forest to complete their development.”
The nearly $250,000 study is being funded by the federal Natural Resources Conservation Service as well as the National Fish and Wildlife Foundation’s New England Forests and Rivers Fund. A contributor to the New England fund is the utility Eversource, which has proposed the Northern Pass energy transmission project that has sparked criticism from property owners, tourism officials and others.
Northern Pass entails building a 192-mile electricity transmission line from Pittsburg to Deerfield, New Hampshire, carrying enough Hydro-Quebec energy to southern New England markets to power about a 1.1 million homes.
Tarr said the study isn’t about finding an upside to transmission lines but rather trying to determine how birds use the forests that emerge after a project is built.
“It helps us understand how transmission lines function in providing that habitat on the landscape,” he said.
The information they get could be critical to policymakers as they work to create more young forests for birds as well as other species like cottontail rabbits in New England.
“Do they have positive effects or do they have negative effects?” he said. “We might find these rights of way aren’t used as we think they are for mature forest birds. That would be important for us to know.”
“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.
(Meghan Bartels 5 May 2017;Photo: Josh Henderson)
Animal Services was able to rescue just three birds after a massive number of spring migrants hit a glass-sided tower in Galveston.
The numbers are horrifying: 90 Nashville Warblers, 60 Blackburnian Warblers, 42 Chestnut-sided Warblers, 41 Ovenbirds—and that’s just four of the 25 dead species collected from the 23-story American National Insurance building in Galveston, Texas, on Thursday morning. In total, 395 small feathered bodies were found, and they were all victims of building collisions.
Josh Henderson, the head of Animal Services for the Galveston Police Department, was called to the scene at 7:20 a.m. He was able to rescue three of the stunned birds, which were then taken to a wildlife triage center. But the sheer number of casualties shocked him. “This is the largest event like this I have ever been a part of in over 10 years,” Henderson said in a press release.
After sorting and IDing the bodies, Henderson’s final list also included: 29 Yellow Warblers, 26 Black-and-white Warblers, 24 Magnolia Warblers, 21 American Redstarts, 15 Indigo Buntings, 8 Black-throated Green Warblers, 5 Kentucky Warblers, 4 Eastern Wood-Peewees, 3 Golden-winged Warblers, 2 Painted Buntings, 2 Orchard Orioles, plus a Hooded Warbler, Gray Catbird, Blue Grosbeak, Rose-breasted Grosbeak, Orange-crowned Warbler, Summer Tanager, Worm-eating Warbler, Red-eyed Vireo, and Cerulean Warbler.
Window and building strikes are a common problem for songbirds, particularly in cities located in popular migration flyways. The island of Galveston lies in the Gulf of Mexico, which is a common crossover point for flocks coming up from the Yucatan and Latin America. With spring migration in full swing, hundreds of thousands of birds are currently racing through the region to reach their northern breeding grounds. To make matters worse, Galveston got almost a quarter inch of rain on Wednesday, which might have encouraged the long-distance travelers to look for shelter.
When birds encounter glass, they see the image it reflects rather than a hard surface; so when a building’s internal or external lights are left on over night—the latter being the case for the American National Insurance building—birds can easily get disoriented. Some might think it’s a place to rest, especially if they spy office plants inside, while others might just see a clear passage. Both can cause them to crash into windows or even the side of the building—often to a fatal end. After surviving a trek that takes them over hundreds of miles of land and open water, it’s an unjust end for the intrepid migrants.
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.”