Tag Archives: nesting

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

Study on blue tits: Smell first, and then beg

(Universitaet Bielefeld 12 May 2017)

Nestling blue tits can discriminate between the smell of other nestlings and adapt their begging behaviour accordingly. This is the outcome of the latest study by Dr. Barbara Caspers and Dr. Peter Korsten from Bielefeld University to be published today on the 12th of May in the journal Functional Ecology.

In this subproject, Dr. Barbara Caspers and Dr. Peter Korsten from Bielefeld University and Marta Rossi from the University of Sussex in Brighton (Great Britain) examined the begging behaviour of seven-day-old blue tit nestlings from a population near the Dutch city of Groningen. ‘Blue tit nestlings beg to obtain food from their parents and may have to compete with as many as ten peers in the nest that are not all necessarily full siblings,’ explains Dr. Peter Korsten. In earlier studies of other songbirds, it was already found that this competition intensifies when nestlings are competing with non-kin. Then nestlings beg even more intensively for food.

In the present study, the research team presented nestlings of blue tits with two different smells: an familiar smell of siblings from their own nest and an unfamiliar smell of unrelated nestlings from another nest. In both experimental situations, the biologists then measured how much the nestlings begged. Results showed that blue tit nestlings beg longer and more intensely after being exposed to the smell of the unfamiliar nestlings compared to the familiar smell of their own nest mates. ‘Up to now, we did not know how songbird nestlings were able to discriminate between the smell of close kin and less related individuals when competing for food from their parents. Our study shows that they may well smell this difference,’ says Caspers.

Science had long assumed that birds cannot smell at all. Behavioural researchers together with Dr. Barbara Caspers at Bielefeld University have already been able to disprove this in earlier studies on zebra finches.

England’s first ‘Swift City’ takes flight

Swifts flying at low level over rooftops

(RSPB 6 May 2017; Photo Nigel Blake)

• Known for their aerobatic displays over our gardens, swifts fly over 6000 miles from central and southern Africa every year to the UK to nest and raise their young. Although numbers of the migratory bird have almost halved in the past twenty years.
• Ahead of UN World Migratory Bird Day on 10 May, the RSPB has teamed up with nine partners to launch England’s first ‘Swift City’ in Oxford.
• The ambitious two-year project will see current nesting sites protected and more than 300 new sites created throughout the historic city to allow the charismatic bird to thrive.
To help reverse the decline in swift numbers and nesting sites Europe’s biggest conservation charity has teamed up with nine partners to launch England’s first ‘Swift City’ in Oxford.
Every year the enigmatic swift announces the arrival of the British summer as they complete a 6,000 mile migration from central and southern Africa to nest and raise their young in the UK. These iconic species are truly Olympian birds; landing only to breed, they fly up to 500 miles per day often eating, sleeping and even mating in the air. However with falling population numbers there are now less than 87,000 breeding pairs arriving in the UK, down from almost 150,000 (-47%) pairs just two decades ago.
Part of this decline is being linked to a reduction in potential nesting sites – as old buildings are renovated and new ones are built they often don’t include nesting space. The two-year project will see the Oxford Swift City team take a closer look at the city’s swift populations, their nesting sites and important foraging areas, as well as helping local communities take action to help swifts where they live.
To help swift thrive in the historic city, the team will also work with local builders and planners to help protect the areas, buildings and neighbourhoods that we know they travel across the world to make their home, as well as creating a further 300 suitable nesting sites throughout Oxford.

Look at These Sweet Bald Eagles Protecting Their Eggs From the Snow

(Meaghan Lee Callaghan; 14 March 2017)

At the U.S. National Arboretum, both eagle parents settled on their nest to warm their eggs, and each other, through the cold, icy night.

Overnight Monday and all day Tuesday, Winter Storm Stella pelted the East Coast with snow, sleet, and hail. The wintry weather shut down much of the human world, with an estimated 18 million Americans snowed in under a blizzard warning.

Nesting birds, however, don’t get snow days, and so they must endure unfavorable conditions to shelter their young. Two years ago, we witnessed via webcam two Bald Eagles persist as falling snow buried their nest, and today, Winter Storm Stella gave another pair of Bald Eagles in Washington D.C. a chance to show off their own parental dedication.

Unlike that first pair, though, during this storm, both parents were filmed incubating the nest at the same time. Stacked on top of each other, the two eagles huddled close together, providing extra warmth and snow protection for their two eggs—and each other.

After hunkering down Monday evening with the snow starting to fall, the mother eagle didn’t leave the nest almost all night. Her one brief respite came early Tuesday morning, during which her mate tried to take over incubating duties. But a few minutes later, she returned, as if to say, “Thanks, but I’ve got this,” according to the American Eagle Foundation, which operates the webcam in partnership with the U.S. Department of Agriculture.

The Bald Eagle duo is the pride and joy of the U.S. National Arboretum in Washington, D.C., where they’ve been nesting since 2014 in a tulip poplar tree. Aptly named “Mr. President” and “the First Lady,” they laid two eggs in the middle of February, and many onlookers have closely followed their nurturing instincts over a webcam. With super parents like these, staff expect the eggs to hatch at the end of March.