Conventional wisdom holds that migration and reproduction are two separate phases of the annual cycle of migratory birds. After all, flying hundreds or even thousands of miles uses up a lot of energy, as does raising the next generation. Doing both at the same time can seem exhausting.
but sometimes evolution Let us be surprised. In fact, scientists have identified about a dozen species, including the yellow-billed cuckoo, orchard harrier and tricolor blackbird, whose migratory and breeding periods they believe overlap. So far, there is only indirect evidence for this extremely rare phenomenon known as mobile reproduction. In a new study, however, a team of researchers tracking the migration of American woodcocks has collected what they say is the first concrete evidence of itinerant breeding around the world.
A study of more than 200 GPS-tagged female woodcocks found that about 80 percent nested more than once during spring migration, with some nesting six times.combination [migration and breeding] Colby Slezak, Ph.D., said it seemed nearly impossible.candidate at the University of Rhode Island and lead author of a paper published in Proceedings of the Royal Society B. But this shows that it is possible, at least in the case of snipe.
Previous studies of other species have identified movement patterns used by birds to breed as they migrate, but this new paper is the first to document birds nesting in multiple areas during migration. “This is definitely the new gold standard in mobile breeding research,” says Daniel Baldassarre, an ornithologist at the State University of New York at Oswego who has studied mobile breeding in Finopepla but didn’t. participate in this study. It is unprecedented to track so many individuals moving across a landscape and ultimately show that they are making individual reproductive decisions.
To reach their conclusions, the Rhode Island team worked with scientists from three dozen institutions and organizations to capture female woodcocks and equip them with GPS transmitters. Scott McWilliams, an ecologist at the university and a co-author of the paper, said this approach was only possible only recently through improvements in tracking technology that produce small enough to fit on the birds. Class emitter. “If we were talking about doing this five years or more ago, it wouldn’t be possible,” he said.
Using computers to track the GPS-tagged birds, Slezak discovered a movement pattern that he believed indicated the female was building a nest.He then recruited local Partners along the migratory route visit parts of these sites and confirm whether there are well-camouflaged nests. He said the men were actually looking for these nests in grass and bushes, so it wasn’t an easy task. These birds are not large and very striking. I mean, they look brown in a brown landscape.
After confirming that the movement patterns he observed were indeed signs of nesting, SlezakAbility to confidently identify nest locations among a full range of tagged birds. On average, females travel about 500 miles between their first and second nesting, but in some cases they travel even further, up to 1,400 miles. The distance between subsequent nests is usually a little over 100 miles.
The findings help solve a long-standing mystery surrounding the breeding and migratory behavior of woodcocks. For example, why do males strive to perform elaborate courtship dances not only after arriving at their destination in the northern forests, but also during their migrations from the Southeast and the Gulf Coast? Why are females found nesting further north in southern states later that same year?
The findings help solve a long-standing mystery surrounding the breeding and migratory behavior of woodcocks.
Evidence of mobile breeding provides answers to these questions, but the cause of this behavior remains uncertain. One possible explanation has to do with the harsh reality of the breeding time of the American Woodcock: Among the North American species that breed earliest each spring, some individuals begin nesting as early as January and migrate north as the winter snow melts, leaving the birds Categories are exposed to the environment. As ground nesters, their eggs are also vulnerable to predators. Through itinerant breeding, a female can nest multiple times with multiple males without the bird forming a pair bond, giving it a better chance of success.
At the same time, the researchers note that this strategy makes sense because the cost to the female per nesting attempt is relatively low.Part of the reason is that her eggs are very small, which means they don’t require much energy to produce. Additionally, young woodcocks are precocious, meaning they can leave the nest within a few hours of hatching. After about a week, the chicks are able to feed themselves, and after about a month they are fully independent. Nest building is not particularly energetically demanding for the female, as woodcocks simply create a shallow depression in the leaf litter.
The team’s findings could also be valuable for conservation. American woodcock populations have been declining for decades, largely due to changes in land use that make their young forest habitat harder to find. The findings suggest protecting potential nesting habitat along the birds’ migration routes is an ideal way to help them rejuvenate, Slezak said. He said that as we now know, management needs to be done more broadly and collaboratively.
At the same time, Baldassare said, the ability to nest multiple times during migration may help woodcocks and other mobile breeders cope with changing threats in a rapidly changing world. By definition, their migration and breeding behaviors are less rigid than typical migratory birds, which should allow for some adaptability, he said. Mobile breeding may be a lifeline to maintain the survival of their populations.
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