Removing introduced predators might not provide greater protection of nesting birds in Australia’s temperate forests and woodlands, according to a new University of Queensland study.
UQ School of Biological Sciences researcher Graham Fulton’s review of 300 scientific papers on nest predation has found that getting rid of medium-sized predators might actually increase attacks from smaller predators.
“In Australia, the introduction of foxes and cats, along with the reduction in dingo numbers is thought to have adversely impacted a range of smaller animals,” he said.
Mr Fulton said areas where foxes were baited showed increased nesting success, but controlling fox numbers could increase the number of cats, which also target birds.
In turn, controlling cat numbers could empower smaller predators such as black rats or mice.
“But it’s not only predators which are to blame, humans are too,” he said.
“Birds such as currawongs, grey butcherbirds, Australian magpies and crows have increased their range and numbers as a result of the clearing of forest and woodlands.
“These same birds are known predators of nestlings and eggs.”
He said more research was needed to improve the understanding of interactions between birds, their predators, and their habitats.
The study is published in Pacific Conservation Biology
(Physorg; University of Exeter; 10 May; Photo: Alex Thornton)
Jackdaws recognise each other’s voices and respond in greater numbers to warnings from familiar birds than strangers, new research shows.
The birds produce a harsh “scolding call” when they spot a predator, calling fellow jackdaws to mob the intruder and drive it away.
University of Exeter researchers have discovered that each bird has a unique call, and the size of the mob depends on which bird calls the warning.
The scientists played recordings of individual calls and found that the largest mobs assembled when birds heard the cry of a member of their own colony.
“Joining a mobbing event can be dangerous, as it involves approaching a predator, so it makes sense for individuals to be selective in whom they join. Our results show that jackdaws use the ability to discriminate between each other’s voices when deciding whether to join in potentially risky collective activities,” said Dr Alex Thornton, of the Centre for Ecology and Conservation on the University of Exeter’s Penryn Campus in Cornwall.
“We also found a positive feedback loop – if birds joining a mob made alarm calls of their own, this in turn caused more birds to join in, magnifying the size of the mob.”
The researchers studied wild jackdaws, a highly social member of the crow family, as part of the Cornish Jackdaw Project, a long-term study of jackdaw behaviour and cognition in sites across Cornwall.
In playbacks at nest-box colonies during the breeding season, they broadcast the warning calls of a resident from each nest-box, another member of the same colony, a member of a different colony, and a rook (a species that often associates with jackdaws).
Jackdaws were most likely to respond to a warning from a bird from the resident nest-box owner, followed in turn by other colony members, non-colony members and rooks.
Responses were also influenced by caller sex, with jackdaws less likely to echo a warning if the caller was a female stranger from a different colony.
The paper, published in the journal Scientific Reports, is entitled: “Caller characteristics influence recruitment to collective anti-predator events in jackdaws.”
(Samantha Knight And Ryan Norris, The Conversation; 9 May 2018; Photo: Julia Baak)
With the arrival of spring, we look forward to the return of hundreds of species of migratory songbirds from their wintering grounds.
Sparrows, swallows, warblers and thrushes, among other songbirds, will be returning from their wintering sites anywhere between the southern United States and distant South America.
Some of these birds will return with a small “backpack” that has recorded their entire migration from their North American breeding grounds to their wintering grounds and back.
Birds provide important ecosystem services, such as preying on insects, dispersing seeds, scavenging carcasses and pollinating plants. Unfortunately, there have been dramatic declines in many migratory songbirds over the past few decades, with some of these populations dropping by more than 80 per cent.
If we are to find ways to slow or reverse these declines, we must first figure out what’s causing them. Climate change, habitat loss and predation by cats are among the leading causes of bird declines.
But with the vast distances these birds move over the course of the year, it can be difficult to pinpoint the main cause for a given species —and where it’s occurring.
Migratory connections
To answer this question, we need to know where individual birds spend their time throughout the year.
We have a good idea of the range —or the total area —the birds occupy during the breeding and wintering periods. But ranges are composed of many populations, and we still have a very poor understanding of how individuals within each of these populations are connected between seasons.
Individuals from different breeding populations may remain segregated during the winter. For example, some ovenbirds winter in the Caribbean whereas others spend their winters in Mexico and Central America.
Or a bird may mix with individuals that originate from other breeding populations, such as bobolinks that mix in South America during the winter.
These patterns of migratory connectivity have critical implications for predicting how migratory songbirds will respond to environmental change.
Habitat loss —deforestation, for example —in one place can have different effects. If habitat loss occurs in a wintering area where breeding populations mix, it may have wide-ranging, yet diffuse, effects on the breeding populations. But if the habitat loss occurs in a wintering area that is occupied by a single breeding population, the effect may be more focused.
For example, habitat loss in South America will likely have range-wide effects on bobolinks, while habitat loss in the Caribbean may only influence a portion of the breeding populations of ovenbirds.
Backpacks for birds
We know that the breeding and wintering populations of most species mix to some extent, but…
Common cuckoos and oriental cuckoos in eastern Russia appear to be expanding their breeding range into western Alaska, where songbirds are naive to the cuckoos’ wily ways, researchers report. A new study suggests the North American birds could suffer significant losses if cuckoos become established in Alaska.
Like brown-headed cowbirds, cuckoos are “brood parasites,” laying their eggs in the nests of other species, said University of Illinois animal biology professor Mark Hauber, who led the new research with Vladimir Dinets of the University of Tennessee, Knoxville. Cuckoos time their egg-laying so that their chicks will hatch first. The chicks then kick the other eggs out of the nest, “thereby eliminating the entire reproductive success of their hosts,” Hauber said.
“Brood parasitism is a rare strategy among birds. Only about 1 percent of birds engage in it,” he said. “Obligate brood parasites do it always. They never build a nest, they never incubate the eggs, they never feed their chicks. Instead, they sneak their eggs into somebody else’s nest, forcing the foster parent to take care of the young.”
Birdwatchers and ornithologists occasionally report seeing oriental cuckoos and common cuckoos in Alaska, and Alaskan natural history museums already contain a handful of cuckoo specimens collected locally, Hauber said. These birds are likely traveling from sites in Beringia, in eastern Russia.
“We don’t have evidence of them breeding in Alaska, but it’s likely already occurring,” Hauber said. “We wanted to know whether the potential Alaskan hosts are ready for this cuckoo invasion.”
In the new study, researchers tested whether more than a dozen Alaskan bird species had evolved defenses to counter the cuckoos’ parasitic ways. Such defenses are common among bird species that frequently encounter brood parasites elsewhere.
(Mariëtte Le Roux; Nature Ecology & Evolution; 7 May 2018)
Why have some birds opted for a taxing life of constant migration—seeking out temperate climes to feed as winter arrives, only to return months later to breed?
Seemingly paradoxically, the behaviour is driven by a quest for energy efficiency, a study said Monday.
Migrating birds, researchers found, gain more energy from whatever is on the destination menu than they expend getting there and back, or could find without making the trek.
Why don’t they just stay in the warm place? Because there is too much competition for food with other species, said the study published in the journal Nature Ecology & Evolution.
Instead, they return to their cold, northern hemisphere home where they don’t have to fight others for the food there is.
The work “provides strong support for the hypothesis that birds distribute themselves in an optimal way in terms of energy,” study co-author Marius Somveille of the University of Oxford’s zoology department told AFP.
While it was known that birds migrate in search of food, it has remained a puzzle why they have adopted this exacting lifestyle.
The new study explains the behaviour of not only migratory birds, but also that of sedentary or “resident” ones, its authors said.
These too weighed the available food against greener pastures, and came to a different conclusion.
Most resident birds are found in the tropics, where food is easier to get by.
Fly or die
The study used a theoretical model to examine why birds migrate—about 15 percent of the total—while others do not.
It started with a model world with similar climatic differences between regions than our real one.
The researchers then added virtual birds, and the estimated amount of “energy”, or food, available in different regions.
Given these inputs, the model birds dispersed very similarly to what happened in real life.
The birds started off in the food-rich tropics, but growing competition forced some to start moving further afield.
“In our increasingly crowded virtual world, species progressively started exploiting more extreme pockets of seasonally available energy supply, often migrating longer distances,” the team wrote.
The model adds to our understanding of how Earth’s plants and animals came to be distributed as they are, the researchers added.
It could also be useful in predicting the future movements of other animals—to determine how they might migrate in response to global warming, for example.
(National Geography, Arnaud Da Silva, Mihai Valcu, and Bart Kempenaers, Max Planck Institute for Ornitholog; 2018)
In spring songbirds greet the rising and setting sun with a cacophony
of chirps meant to entice mates and claim territory. But artificial light
has made the night sky brighter and disrupted the seasonal rhythms
of birds that use day length as a cue to sing. Of six songbird species
that scientists studied in Germany, four started singing earlier in the year
because of night lighting. The long-term effects of light pollution on
birds’ ecosystems, and their survival, remain unclear.
(Field Museum, ScienceDaily 2 February 2018; Photo:Arlene Koziol)
With woodpeckers, the answer’s in the question—true to their name, they peck wood. And when they do, they peck hard—with each peck, the bird undergoes a force of 1,200 to 1,400 g’s. By comparison, a measly force of 60-100 g’s can give a human a concussion. The fact that a woodpecker can undergo fourteen times that without getting hurt has led helmet makers to model their designs around these birds’ skulls. However, a new study in PLOS ONE complicates this story by showing that woodpecker brains contain build-ups of a protein associated with brain damage in humans.
“There have been all kinds of safety and technological advances in sports equipment based on the anatomic adaptations and biophysics of the woodpecker assuming they king. The weird thing is, nobody’s ever looked at a woodpecker brain to see if there is any damage,” says Peter Cummings of the Boston University School of Medicine, one of the new study’s authors.
To find the answer to this question, researchers used bird brains from the collections of The Field Museum and the Harvard Museum of Natural History and examined them for accumulation of a specific protein, called tau.
“The basic cells of the brain are neurons, which are the cell bodies, and axons, which are like telephone lines that communicate between the neurons. The tau protein wraps around the telephone lines—it gives them protection and stability while still letting them remain flexible,” explains lead author George Farah, who worked on the study as a graduate student at the Boston University School of Medicine.
In moderation, tau proteins can be helpful in stabilizing brain cells, but too much tau build-up can disrupt communication from one neuron to another. “When the brain is damaged, tau collects and disrupts nerve function—cognitive, emotional, and motor function can be compromised,” says Cummings.
Since excessive tau can be a sign of brain damage in humans, Farah and his team decided to examine woodpecker brains for tau build-up. The Field Museum and Harvard loaned the researchers bird specimens pickled in alcohol—Downy Woodpeckers for the experimental data and non-head-injury-prone Red-winged Blackbirds as a control. The researchers then removed the birds’ brains—“The brains themselves were well-preserved, they had a texture almost like modeling clay,” says Farah—and took incredibly thin slices, less than a fifth the thickness of a sheet of paper. The slices of brain tissue were then stained with silver ions to highlight the tau proteins present.
The verdict: the woodpeckers’ brains had far more tau protein accumulation than the blackbirds’ brains. However, while excessive tau buildup can be a sign of brain damage in humans, the researchers note that this might not be the case for woodpeckers. “We can’t say that these woodpeckers definitely sustained brain injuries, but there is extra tau present in the woodpecker brains, which previous research has discovered is indicative of brain injury,” says Farah.
“The earliest woodpeckers date back 25 million years—these birds have been around for a long time,” says Cummings. “If pecking was going to cause brain injury, why would you still see this behavior? Why would evolutionary adaptations stop at the brain? There’s possibility that the tau in woodpeckers is a protective adaptation and maybe not pathological at all.”
So, woodpeckers show signs of what looks like brain damage in humans, but it might not be a bad thing. Either way, the researchers believe that the study’s results could help us humans. For example, the knowledge about woodpecker brains that could help make football equipment safer for kds, says Cummings. On the other hand, he notes, “If the tau accumulation is a protective adaptation, is there something we can pick out to help humans with neurodegenerative diseases? The door’s wide open to find out what’s going on and how we can apply this to humans.”
Farah notes that the study relied heavily upon the museum collections that the bird brains came from. “Museums are gateways to the past and a source of new innovation,” he says. “The role of museums in this project was immense—we couldn’t have done our study with just one woodpecker.”
Ben Marks, The Field Museum’s Collections Manager of Birds, said of the researchers’ request to use the Museum’s bird brains, “With one of the world’s best bird collections, we’re always trying to let people know what we have, why we have it, and what it can be used for. We get over a hundred requests for specimen loans every year—this one stood out because it was a novel approach that had real world applications. Some of the specimens used in this study were collected in the 1960s. Our staff cared for them for over 50 years before until they were requested for this study and used in a way the original collector couldn’t even envision.”
Scott Judd trained his camera lens on the white dot in the distance. As he moved up the Lake Michigan shoreline, the speck on a breakwater came into view and took his breath away: it was a snowy owl, thousands of miles from its Arctic home.
“It was an amazing sight,” said Judd, a Chicago IT consultant. “It’s almost like they’re from another world. They captivate people in a way that other birds don’t.”
The large white raptors have descended on the Great Lakes region and northeastern U.S. in huge numbers in recent weeks, hanging out at airports, in farm fields, on light poles and along beaches, to the delight of bird lovers.
But for researchers, this winter’s mass migration of the owls from their breeding grounds above the Arctic Circle is serious business.
It’s a chance to trap and fit some of the visitors with tiny transmitters to help track them around the globe and study a long-misunderstood species whose numbers likely are far fewer than previously thought, researchers say.
“There is still a lot that we don’t know about them … but we aim to answer the questions in the next few years,” said Canadian biologist Jean-Francois Therrien, a senior researcher at Hawk Mountain Sanctuary in Pennsylvania.
The solar-powered transmitters can last for years, collecting information such as latitude, longitude, flight speed and air temperature that is downloaded to a server when the birds fly into range of a cell tower.
The use of transmitters, which intensified during the last North American mass migration in winter 2013-14, already has yielded big surprises.
Instead of 300,000 snowy owls worldwide, as long believed, researchers say the population likely is closer to 30,000 or fewer. The previous estimate was based on how many might be able to breed in a given area.
That calculation was made assuming snowy owls acted like other birds, favoring fixed nesting and wintering sites. But researchers discovered the owls are nomads, often nesting or wintering thousands of miles from previous locations.
The miscalculation doesn’t necessarily mean snowy owls, which can grow to about 2 feet long with 5-foot wingspans, are in decline. Scientists simply don’t know because they never had an accurate starting point.
This month, snowy owls were listed as vulnerable—one step away from endangered—by the International Union for Conservation of Nature. They’re protected in the U.S. under the Migratory Bird Act.
This year’s mass migration is a bit of good news. Researchers once thought these so-called “irruptions” signaled a lack of prey in the Arctic, but now believe the opposite: Breeding owls feed on lemmings, a rodent that lives under Arctic snowpack and whose population surges about every three or four years. More lemmings means the owl population explodes— and that more birds than usual will winter in places people can see them.
But researchers worry that climate change will affect the owl population because lemmings are exceptionally sensitive to even small temperature changes.
Lemmings “depend on deep, fluffy, thick layers of insulating snow” to breed successfully, said Scott Weidensaul, director at Project SNOWstorm, an owl-tracking group whose volunteers have put transmitters on more than 50 snowy owls in the past four years .
The snowy owl population collapsed in Norway and Sweden in the mid-1990s, all but vanishing there for almost two decades before reappearing at lower numbers, experts said. In Greenland, where the population collapsed in the late 1990s, researchers found a few nests in 2011 and 2012 after six years with no recorded nests, but owls didn’t come back in 2016 or 2017, when lemmings should have been peaking.
The National Oceanic and Atmospheric Administration reported this month that the far northern Arctic is warming twice as fast as the rest of the globe.
But it’s tough to assess lemming population trends in remote areas. Although researchers hope to enlist native villagers to help, it’s mostly up to owls with transmitters for now.
Snowy owls somehow seem to find lemmings even if they are thousands of miles from where their population last peaked, Therrien said.
“They look around the Arctic,” he said. “The movement is amazing to watch on a map: There are no straight lines. They’re zigzagging.”
Norman Smith, a snowy owl expert with Mass Audubon in Massachusetts, said he’s heartened that many independent researchers worldwide joined forces to share information on snowy owls.
“It’s amazing what we’ve learned, but we need a bigger database of birds,” said Smith, who has been trapping owls at Boston’s Logan International Airport for more than 35 years and fits them with a leg band or transmitter before letting them go. He put a satellite tracker on an owl for the first time in 2000, proving that they could make it back to the Arctic.
Last week, Smith released a young female on a barrier beach along the Atlantic Ocean. It flew south, then circled back and flew overhead. As he drove over a bridge to the mainland, the owl was sitting on a post, surveying its new winter home.
New UC San Francisco research finds that although young male songbirds are genetically predisposed to sound like their fathers, enriched early experience with a foster-father can overcome this genetic destiny. This finding has striking implications for our thinking about how experience influences the genetics of complex human traits like learning ability or even psychiatric disease, the authors say.
Neuroscientists like UCSF’s Michael Brainard, Ph.D., have long studied songbirds like the Bengalese finch (Lonchura striata domestica) as a model of how complex behaviors like human language are shaped by early experience. Like human language, a male finch’s unique mating song is learned early in life by listening to and mimicking adult “tutors.” In nature, this is usually the bird’s father, but young birds raised by unrelated adults in the lab will learn to sing their foster-father’s song instead.
Now Brainard’s lab has shown that not all early experiences are equal in their influence over impressionable young birds: exposed only to a computerized “synthetic tutor,” young birds will revert to singing like a biological father they’ve never known or heard. The research—published the week of December 25, 2017 in PNAS—suggests that finch song has a stronger genetic component than had previously been realized, but also that this genetic drive can be suppressed by the right kind of early life experience.
“What we saw is that the genetic contribution to a bird’s song depends on the specifics of that bird’s experience. This is a striking demonstration that heritability for complex behaviors like birdsong is not fixed, as is often assumed, but instead can vary dramatically depending on the experience of an individual,” said Brainard, a professor of physiology and of psychiatry at UCSF, Howard Hughes Medical Institute investigator, and member of the UCSF Weill Institute for Neurosciences.
As noted, researchers have long considered the structure of adult birdsong to be dominated by the influence of whatever song a bird hears as a chick. However, David Mets, Ph.D., a postdoctoral scholar in the Brainard lab and the new paper’s first author, noticed a surprising amount of variation between the songs of individual Bengalese finches in the lab, even when all birds were exposed to the same experimentally controlled tutor song early in life.
To determine whether these differences might be caused by a previously overlooked genetic contribution to the birds’ song, Mets developed a careful set of experiments to control the contribution of genetics and experience. He removed eggs from their nests shortly after they were laid to ensure chicks never heard their fathers’ song, even in the egg. He then exposed the hatchlings only to carefully controlled computer-generated songs, which he varied in tempo in an attempt to influence the tempo of the song the young birds would learn.
To the researchers’ surprise, they found that these birds largely ignored the tempo of the synthetic songs, and developed adult songs with tempos much closer to their fathers’ songs—which they had never heard. The researchers quantified this observation, showing that 55 percent of variability in the experimental birds’ songs could be explained by differences in their fathers’ songs, but only 21 percent was driven by differences in the synthetic song they heard as chicks.
In a second set of experiments, Mets got rid of the synthetic tutor and instead exposed finch chicks—which also had never heard their fathers’ songs—to unrelated live adult males. The researchers were again surprised to discover a complete reversal of the results seen with synthetic tutoring: the live tutor’s song contributed 53 percent to the tempo of the young birds’ adult songs, with differences in their fathers’ songs contributing only 16 percent.
“This was really exciting because it showed that the experience provided by a live tutor can actually reduce the contribution of genetics to complex behavior like birdsong,” Mets said. “We knew before that live tutors helped birds learn better and faster, but we were surprised to find that this experience can actually override the bird’s genetics.”
“We’ve gotten used to the idea that complex traits and behaviors can have a big genetic component,” Brainard added, citing human studies of identical twins separated at birth who nonetheless share surprising similarities in things like their sense of humor, fashion sense, and so on. “But those stories tend to assume that the genetic component is fixed—academic achievement is either 20 percent genetic or 80 percent genetic. We’re showing here that the contribution of genetics is anything but fixed—in the case of academic achievement, the school you go to may well overcome any contribution of genetics.”
The findings raise the possibility that human genetic studies that fail to account for differences in individuals’ experience could be producing misleading conclusions about the genetic contributions to complex behaviors, Brainard said.
The researchers now hope to use the Bengalese finch as a model to explore how genetics and experience interact in the brain to influence complex behaviors like birdsong. “Where in the brain are the father’s genes and early life experience competing for control over song tempo?” Mets asked. “That’s the next really exciting question.”
The results also suggest a broader opportunity to understand the specific features of enriched early experiences that allows them to override genetic predispositions, Brainard said: “This is far into the future, of course, but it highlights the potential of early behavioral intervention to help mitigate negative genetic traits, such as a predisposition to psychiatric disease.”
Many animals have evolved to stand out. Bright colours are easy to spot, but they warn predators off by signalling toxicity or foul taste.
Yet if every individual predator has to eat colourful prey to learn this unappetising lesson, it’s a puzzle how conspicuous colours had the chance to evolve as a defensive strategy.
Now, a new study using the great tit species as a “model predator” has shown that if one bird observes another being repulsed by a new type of prey, then both birds learn the lesson to stay away.
By filming a great tit having a terrible dining experience with conspicuous prey, then showing it on a television to other tits before tracking their meal selection, researchers found that birds acquired a better idea of which prey to avoid: those that stand out.
The team behind the study, published in the journal Nature Ecology & Evolution, say the ability of great tits to learn bad food choices through observing others is an example of “social transmission.”
The scientists scaled up data from their experiments through mathematical modelling to reveal a tipping point: where social transmission has occurred sufficiently in a predator species for its potential prey to stand a better chance with bright colours over camouflage.
“Our study demonstrates that the social behaviour of predators needs to be considered to understand the evolution of their prey,” said lead author Dr Rose Thorogood, from the University of Cambridge’s Department of Zoology.
“Without social transmission taking place in predator species such as great tits, it becomes extremely difficult for conspicuously coloured prey to outlast and outcompete alternative prey, even if they are distasteful or toxic.
“There is mounting evidence that learning by observing others occurs throughout the animal kingdom. Species ranging from fruit flies to trout can learn about food using social transmission.
“We suspect our findings apply over a wide range of predators and prey. Social information may have evolutionary consequences right across ecological communities.”
Thorogood (also based at the Helsinki Institute of Life Science) and colleagues from the University of Jyväskylä and University of Zurich captured wild great tits in the Finnish winter. At Konnevesi Research Station, they trained the birds to open white paper packages with pieces of almond inside as artificial prey.
The birds were given access to aviaries covered in white paper dotted with small black crosses. These crosses were also marked on some of the paper packages: the camouflaged prey.
One bird was filmed unwrapping a package stamped with a square instead of a cross: the conspicuous prey. As such, its contents were unpalatable — an almond soaked with bitter-tasting fluid.
The bird’s reaction was played on a TV in front of some great tits but not others (a control group). When foraging in the cross-covered aviaries containing both cross and square packages, the birds exposed to the video were quicker to select their first item, and 32% less likely to choose the ‘conspicuous’ square prey.
“Just as we might learn to avoid certain foods by seeing a facial expression of disgust, observing another individual headshake and wipe its beak encouraged the great tits to avoid that type of prey,” said Thorogood.
“By modelling the social spread of information from our experimental data, we worked out that predator avoidance of more vividly conspicuous species would become enough for them to survive, spread, and evolve.”
Great tits — a close relation of North America’s chickadee — make a good study species as they are “generalist insectivores” that forage in flocks, and are known to spread other forms of information through observation.
Famously, species of tit learned how to pierce milk bottle lids and siphon the cream during the middle of last century — a phenomenon that spread rapidly through flocks across the UK.
Something great tits don’t eat, however, is a seven-spotted ladybird. “One of the most common ladybird species is bright red, and goes untouched by great tits. Other insects that are camouflaged, such as the brown larch ladybird or green winter moth caterpillar, are fed on by great tits and their young,” said Thorogood.
“The seven-spotted ladybird is so easy to see that if every predator had to eat one before they discovered its foul taste, it would have struggled to survive and reproduce.
“We think it may be the social information of their unpalatable nature spreading through predator species such as great tits that makes the paradox of conspicuous insects such as seven-spotted ladybirds possible.”
BirdLife 20 