May 9, 2018 by Samantha Knight
And Ryan Norris, The
Conversation
With the arrival of spring, we
look forward to the return of hundreds of species of migratory songbirds from
their wintering grounds.
Sparrows, swallows, warblers and
thrushes, among other songbirds, will be returning from their wintering sites
anywhere between the southern United States and distant South America.
Some of these birds will return
with a small "backpack" that has recorded their entire migration from
their North American breeding grounds to their wintering grounds and back.
Birds provide important ecosystem
services, such as preying on insects, dispersing seeds, scavenging
carcasses and pollinating plants. Unfortunately, there have been dramatic
declines in many migratory songbirds over
the past few decades, with some of these populations dropping by more than 80
per cent.
If we are to find ways to slow or
reverse these declines, we must first figure out what's causing them. Climate
change, habitat loss and
predation by cats are among the leading causes of bird declines.
But with the vast distances these
birds move over the course of the year, it can be difficult to pinpoint the
main cause for a given species —and where it's occurring.
Migratory connections
To answer this question, we need
to know where individual birds spend their time throughout the year.
We have a good idea of the range
—or the total area —the birds occupy during the breeding and wintering periods.
But ranges are composed of many populations, and we still have a very poor
understanding of how individuals within each of these populations are connected
between seasons.
Individuals from different
breeding populations may remain segregated during the winter. For example, some ovenbirds
winter in the Caribbean whereas others spend their winters in Mexico
and Central America.
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