Date: August 29, 2018
Source: American Ornithological Society Publications
Office
Aerial
insectivores -- birds that hunt for insect prey on the wing -- are declining
across North America as agricultural intensification leads to diminishing
insect abundance and diversity in many areas. A new study from The Condor:
Ornithological Applications looks at how Tree Swallows' diets are affected
by agriculture and finds that while birds living in cropland can still find
their preferred prey, they may be working harder to get it.
The
University of Saskatchewan's Chantel Michelson, Robert Clark, and Christy
Morrissey monitored Tree Swallow nest boxes at agricultural and grassland sites
in 2012 and 2013, collecting blood samples from the birds to determine what
they were eating via isotope ratios in their tissues. Tree Swallows usually
prefer aquatic insects, which they capture in the air after they emerge from
wetlands to complete their life cycles. The researchers suspected that birds
living in crop-dominated areas would be forced to shift to eating more terrestrial
insects, due to the effects of insecticide use and other agricultural practices
on wetland habitat.
Instead,
they found that swallows were eating more aquatic than terrestrial insects at
all sites, and in 2012 it was actually the grassland birds whose diet contained
a higher proportion of terrestrial insects. The results suggest that wetland
habitat may provide a buffer against the negative effects of agriculture.
However, birds living in cropland weighed less on average than their
grassland-dwelling counterparts -- a sign that they may be struggling.
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