Migratory schedule of swallows uncovered

Date:  January 22, 2019

Source:  University of Guelph

Each year, migratory birds journey from their breeding grounds to their wintering grounds, making pit stops along the way.

Now a first-ever University of Guelph study has uncovered precisely when and where tree swallows -- a common migratory bird -- stop during flights that can span more than 3,500 kilometres across North America. The findings tell us more about migration and help us understand threats faced by the birds throughout the journey, said Prof. Ryan Norris, Department of Integrative Biology.

"Migratory birds are really just visitors up here," said Norris, who worked on the study with post-doc researcher Elizabeth Gow, which was conducted in Norris Lab. "They breed for a couple of months and then spend the rest of the year in migration and at their tropical wintering grounds. If we are to make any progress towards understanding what is causing their declines, we need to know how these stages of the annual cycle are linked."

Published recently in the journal Proceedings of the Royal Society B, the study is the first to track the timing of 12 geographically distinct North American breeding populations of tree swallows across the continent. Previous studies have followed just one population at a single latitude.

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Tree swallow study: Stressful events have long-term health impacts

Date:  August 28, 2018

Source:  Cornell University

Little is known about how brief yet acute stressors -- such as war, natural disasters and terror attacks -- affect those exposed to them, though human experience suggests they have long-term impacts.

Two recent studies of tree swallows uncover long-term consequences of such passing but major stressful events. Both studies provide information on how major stressful events have lasting effects and why some individuals are more susceptible to those impacts than others.

"We aren't looking at humans in either of these studies, but this research certainly could have implications for how humans respond to stress," said Maren Vitousek, assistant professor in the Department of Ecology and Evolutionary Biology. "The basic way that most vertebrates respond to stress is quite similar. We often see similar things predicting stress resilience in humans and in other animals."

The first study was published in Proceedings of the Royal Society B. Vitousek is the paper's first author.

The researchers developed a new method for manipulating hormone levels in free-living birds: They dissolved a stress hormone (glucocorticoid) in a gel and put it on eggs in tree swallow nests. The females, the only ones who incubate, absorbed the hormone through their skin. They were given five separate doses for an hour each early in their reproductive periods.

After absorbing the hormone, females fed their offspring at lower rates once they hatched, which led to much smaller offspring compared to two types of controls (one type with gel but no hormone on an egg and the other undisturbed). The smaller offspring in turn had lower survival rates.

"The take-home message here is that the hormones that birds would be exposed to if they had a short-term stressor do have these long-term effects," Vitousek said.

The researchers also found that birds exposed to higher doses of glucocorticoid were more likely to endure lingering impacts, she said. This result suggests that individuals who naturally mount a stronger hormonal response to brief challenges may be at greater risk of suffering from lingering effects of stress, Vitousek said.

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Report: Nonstick Chemicals May Be Affecting Birds Along Mississippi River

A new U.S. Geological Study report suggests that chemicals found in nonstick cookware and water repellents could be affecting tree swallows living along the upper Mississippi River.

It's been known that the Mississippi River around and south of the Twin Cities is contaminated with perfluoroalkoxy (PFA), a chemical found in many household products. The report says wastewater discharges and contaminated groundwater from manufacturer 3M's facilities have created hotspots for PFAs, even though it's been more than a decade since the company stopped producing them.

USGS researchers studying tree swallows in Wisconsin and Minnesota found that birds with high concentrations of PFAs are less likely to hatch. USGS Wildlife Biologist Chris Custer says the probability of problems increases with contamination: “I like to use George Burns [as an example]: he smoked cigars and cigarettes until he was 100 and never got lung cancer. Another person smoking the same amount might die in their thirties. It's the same thing with bird eggs. You can have the same amount of contamination and in some, it will cause a poor hatching and another with a different genetic makeup might hatch fine.”

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Birds studied to understand trade-offs between reproduction, immunity

University of Delaware post-doctoral researcher Ian Stewart is conducting research to answer this question a bit more scientifically. His subjects – tree swallows – make human parents look like slouches. Both the mother and father tree swallow feed their hatchlings every five minutes, 12 hours a day.  (It should be noted, though, that their parenting gig is much shorter than ours—after 17 or 18 days the young leave the nest.) Stewart is studying these small, migratory birds to better understand the trade-offs they make between reproduction and immunity. His research could potentially help scientists who study human biology better understand our own immune system and its stressors. Stewart is part of a young but growing interdisciplinary field called ecoimmunology, which combines aspects of immunology with ecology, biology, physiology and evolution. He chose to focus his research on tree swallows and bluebirds because both are fairly tolerant of human interaction. "Some birds don't like being observed but tree swallows and bluebirds don't get stressed from being watched or handled," notes Stewart.  There's another very important benefit to working with these birds—since they nest in boxes, not up in the trees, they're a heck of lot easier to catch.  Throughout the breeding season, Stewart catches the parent birds, injects them with a harmless antigen and releases them. Then, he re-catches the same birds a few days later to take blood samples and assess each bird's immune response to the antigens.  "Some of the tree swallows work harder at parenting," notes Stewart. "It may be because the bird has four hatchlings to feed instead of just three. Other times, the bird is simply more energetic at taking care of its hatchlings, regardless of brood size." 

Read more at:

 http://phys.org/news/2012-11-birds-trade-offs-reproduction-immunity.html#jCp