Birds play the waiting game in tough environmental conditions

Date:  May 23, 2018

Source:  American Ornithological Society Publications Office

Every animal's ultimate goal in life is to generate offspring to pass on its genetic material to the next generation. But sometimes, resources are scarce and the task of reproduction is too difficult or risky. If resources are limited and tough to find, reproductive efforts may fail anyway. In these situations, it may be in an animal's best interests to not defend a territory or to breed at all, but rather to focus its efforts on surviving to the next breeding season. Biologists refer to individuals without a territory during the breeding season as 'floaters'. A new study from The Auk: Ornithological Advances presents some of the best evidence on how changes in environmental conditions, specifically droughts, impact the social and reproductive behavior of birds.

Tad Theimer of Northern Arizona University and colleagues monitored a population of Willow Flycatchers over a five-year period. Each individual in this population was marked with uniquely colored leg bands and its behavior recorded throughout the breeding season. Some of these birds defended territories that contained their nests, while other birds -- the floaters -- moved around the population declining territory and nest. A severe drought that occurred during the study allowed the researchers to examine how these birds respond to changes in the environment. They found there were one and a half times more floaters during the drought than during years with average rainfall, and that these floaters were more likely to survive than individuals that tried to nest. When the researchers compared how many chicks a bird had with their floater status the previous year, they found that territorial birds had more chicks than floaters -- with one exception. In the year immediately after the drought, former floaters produced more chicks.

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Migrating birds 'more reluctant to leave UK' suggests Fair Isle study

27 September 2016

 

Migrating birds such as swallows and house martins are increasingly reluctant to leave the UK and return to Africa, a study on Shetland's Fair Isle has suggested.

The research, published in the science journal Global Change Biology, indicated some were arriving earlier and others were leaving later.

The study used daily observations of birds from Fair Isle Bird Observatory.

The aim was to measure changes over the past 60 years.

Dr Will Miles, of the Fair Isle Bird Observatory, said: "Environmental conditions are changing rapidly at a global scale.

"In response to these changes, the seasonal life-cycles of plants and animals are shifting too, often in dramatic and unexpected ways.

"It's too early to know for sure exactly why bird migrations now last so much longer in spring and autumn, but it's possible that conditions in Europe and Africa have gradually become more favourable for long-distance migration, and the birds are now under less pressure to migrate quickly within a short time window.

"For example, on Fair Isle, swallows and house martins are migrating up to a fortnight later than they did a few decades ago.

"Willow warblers used to migrate within a five-week period in spring but now this species is seen on migration for up to 10 weeks.

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