“America’s Smallest Falcon is Getting Smaller,” an article appearing in the spring issue of Living Bird Magazine, references a paper co-authored by Visiting Assistant Professor of Biology Christopher Briggs.
The paper, “Morphological changes in American kestrels (Falco sparverius) at continental migration sites,” was published in the July 2018 issue of Global Ecology and Conservation. It presents the results of a study of American kestrels showing a decline in both the population and the size of these birds.
Briggs and his fellow researchers analyzed 20 to 40 years of count and banding data from seven North American raptor migrations sites. For all sites, they found a significant decrease in the number of migrating birds during the last decade, and for some sites much longer.
The study also examined two key factors of overall bird size — mass and wing size. Changes in the size of kestrels varied with location as well as bird sex and age with the overall trend showing a decline.
The authors concluded that the “declines in body size at the majority of sites are consistent with the hypotheses that food availability, impacts of a changing climate, or predation risk may be contributing to population declines.”
Living Bird Magazine is a publication of The Cornell Lab of Ornithology.
This summer, Briggs will travel to northern California to continue research on Swainson’s hawks. The project is in its 41st year — Briggs has participated since 2001.
Briggs and other researchers will join a team from James Madison University to use multispectral sensors on drones to investigate the efficacy of treating alfalfa fields with zinc phosphide to kill ground squirrels. They will then determine whether reducing prey affects hawk reproduction.
The researchers will also put out another satellite transmitter to help them determine where juvenile Swainson’s hawks spend the first few years of life, adding to their previously collected data.