Date: November 22, 2016
Source: Boise State
University
Milder winters have led
to earlier growing seasons and noticeable effects on the breeding habits of
some predatory birds, according to research by Boise State biologists Shawn
Smith and Julie Heath, in collaboration with Karen Steenhof, and The Peregrine
Fund's Christopher McClure. Their work was recently published in the Journal of
Animal Ecology under the title "Earlier nesting by generalist predatory
bird is associated with human responses to climate change."
Smith and his co-authors
studied the American kestrel (Falco sparverius), also known as a sparrow hawk,
because the bird is widespread and responsive to environmental change. Their
question was whether the warming climate had led to changes in prey abundance
and a corresponding change in when the birds nested.
Their study looked at
kestrels that nested in both non-irrigated shrub and grasslands and those that
nested in irrigated crops and pastures. Using data from remote satellites to
determine the greenness of different types of vegetation they were able to
determine the start of the growing season for different areas. That is
important because peaks in vegetation greenness correspond with peaks in
kestrel prey, like small mammals and insects. They then looked at how that
matched up with kestrel nesting patterns.
Results show that over
the period of 1992-2015, the greenness on irrigated lands occurred earlier
because of earlier planting of crops following relatively warm winters, but
there has not been a change in green-up on non-irrigated lands. Kestrels seemed
to "track" the changes in irrigated lands and were nesting 15 days
earlier than they used to nest. Although this might not seem like much of a
shift, the earliest nesting kestrels can now raise two broods per year instead
of one.
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