And they DANCE!
But a study by University of Rhode Island researchers has
found direct evidence of a species – the American woodcock, a migratory
shorebird from eastern and central North America – that overlaps periods of
migration and reproduction, a rare breeding strategy known as “itinerant
breeding.” Their work, backed by collaborators across the East Coast, was
published in the biological sciences journal Proceedings of the Royal Society B.
“I think this is a very exciting moment for bird researchers,” said Colby Slezak, a URI Ph.D. student in biological and environmental sciences who led the study.
“It’s interesting to see that these
distinct periods in a bird’s annual cycle are not so cut and dried. We often
think of migration, breeding, fall migration and wintering as separate events.
But woodcock are combining two of these into one period, which is interesting
because both are so energetically expensive.”
“Each year the period of migration is distinct from the period of breeding in the vast majority of migratory birds, presumably because doing so at the same time is simply too costly,” said Scott McWilliams, URI professor in natural resources science and principal investigator on the study.
“This paper provides the best documented case of a migratory bird that is an
itinerant breeder. Such itinerant breeding is exceptionally rare, and
documenting exceptions often proves the rules of nature.”
The American woodcock – also called a timberdoodle, bogsucker, night partridge, and Labrador twister, among many more – is a migratory shorebird that occurs throughout eastern and central North America but its populations have been declining over the past half century.
The species
is known for its long, needlelike bill that can extract earthworms from deep in
the ground and the males’ elaborate mating dance and “peent” call to attract
females, Slezak said.
While there are about a dozen bird species in the world
believed to be itinerant breeders, the study is the first to show direct
evidence of the rare strategy. “They’ve suspected other species of being
itinerant breeders, but this is the first time we’ve had detailed GPS-tracking
data and on-the-ground verification of nests to confirm that this was
happening.” said Slezak, of Broadalbin, New York.
To do that, the study benefitted from the work of scores
of biologists from federal, state and non-governmental agencies along the
American woodcock’s flyway, from the southern U.S. into Canada, who tagged more
than 350 females with GPS transmitters between 2019 and 2022. That initiative
was part of the University of Maine’s Eastern
Woodcock Migration Research Cooperative.
Slezak, whose work on the study was part of his dissertation research, organized and analyzed the tracking data and alerted collaborators along the bird’s range to verify possible nesting locations.
URI
graduate students Liam Corcoran, Megan Gray and Shannon Wesson also worked on
other aspects of the woodcock project, all part of a collaborative research
program with biologists from the Rhode Island Department of Environmental
Management Division of Fish & Wildlife.
“I was looking for really short movement patterns during
the breeding season to find suspected nests,” Slezak said. “Relying on all of
these collaborators from across the East Coast, I would reach out to them to
tell them there was a suspected nest. They would travel out to the sites,
sometimes quite far. It was amazing that we got the buy-in that we did.”
Based on GPS tracking of more than 200 females, the URI study found that more than 80% of the tagged females nested more than once during migration – some up to six times. During northward migration, females traveled an average of 800 kilometers between first and second nests, and shorter distances between subsequent nests, the study said.
During 2021-22, URI
researchers oversaw onsite verification of 26 nests from 22 females. Four
females nested more than once, three of which migrated a substantial distance
northward after their first nest attempt, the study said.
“There are many records of woodcock males singing along
their migration routes, which has always been a mystery because it’s
energetically expensive,” said Slezak. “With this new data on females, we’re
seeing that females are also nesting in the south early, moving north and
nesting as they go. So, these males are probably getting breeding opportunities
along the way.”
While migration and reproduction take a lot of energy,
American woodcock reduce the cost in other ways, Slezak said. They have shorter
migration distances than other species and have the flexibility of using
various young-forest habitats. Also, females are larger than males and their
eggs are small relative to the size of the females.
“A lot of birds probably can’t do it because they don’t
have these lower reproductive costs that woodcock have evolved to do,” he said.
Another evolutionary driver of itinerant breeding in
woodcock could be predation. While they use a variety of habitats – wetlands,
young forests with different tree types – they often nest near edges of open
fields, leaving them prone to numerous predators.
“We think most of these post-nesting migratory movements
are in response to predation events,” he said. “They’re sitting on the nest and
something comes and eats the eggs. The female takes off and keeps migrating
north before trying to nest again. What we don’t know is: if the female has a
successful nest, does she stop nesting the rest of the year?”
Despite steady declines in woodcock populations and their
preferred young forest habitat over the last half century, the study offers a
glimmer of hope for woodcock, and other itinerant breeders facing the
challenges of ongoing human development and climate change.
“Itinerant breeders may be more flexible in their
response to environmental change because they are willing to breed in a wide
variety of places,” said Slezak. “So as long as some suitable habitat remains,
the consequences may be less.”
