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‘Frequent Fliers’: American kestrels take to the skies in new study

Two kestrels on a wire
Photo by Neil Paprocki

The American kestrel is a beautiful and familiar sight across North America, and especially in the raptor-rich state of Idaho. Yet despite their ubiquity, there is still much that is not known about the small falcon, especially in terms of how the species moves and adapts to environmental change.

“I came to Boise State because I was drawn to the focus on raptor research, and in particular to Julie’s [Heath] research on the impacts of global change on American kestrels,” said raptor biology alumna Hanna McCaslin (M.S. ‘19).

McCaslin and her mentor, biology professor Julie Heath, have been studying kestrels in the Boise area, using nest boxes and banding procedures. While the data collected from these boxes were useful for the area, they only showed a fraction of the greater picture of kestrel dispersal.

“Dispersal is the movement of an organism from where it was born to where it breeds, and is important because dispersal movements are critical for facilitating gene flow between populations, which can influence how well a species will be able to adapt to environmental change,” explained McCaslin.

McCaslin wanted to know to where and how far kestrels in North America where flying, and to be able to learn what might be shaping those dispersals. To tackle this knowledge gap, Heath and McCaslin teamed up with new biology faculty member Trevor Caughlin to create a comprehensive study of kestrel dispersal across the continent.

“Banding data and other long-term data sets are powerful tools for studying populations at large scales, and we wanted to understand kestrel dispersal at a larger scale than what we are able to capture with local studies,” said McCaslin.

kestrel in flight
Photo credit, Neil Paprocki

Across Canada and the United States, thousands of researchers and permitted bird-banders have been collecting information on kestrels for decades and submitting it to the Bird Banding Laboratory, which is affiliated with the United States Geological Survey.

“We studied kestrel dispersal using banding data collected by many researchers from 1961-2015 to capture dispersal at a large scale, and to understand the frequency and distances of kestrels dispersing more than 30 kilometers. We also sought to understand if factors related to global change, like temperature and land cover, influence dispersal distance,” said McCaslin

The team discovered that dispersal of more than 30 kilometers (long distance dispersals) were influenced by temperature and migratory strategy, and made up nearly half of the dispersals accounted for in the study. Data analysis also found that shorter dispersals were linked to sex and population density.

“Our findings indicate that long-distance dispersal is relatively common, and suggest that long-distance and short-distance dispersal may be distinct processes in kestrels. This result is particularly important because it indicates that environmental change may influence the two differently, which may have implications for how kestrels adapt to global change,” said McCaslin.

While at Boise State, McCaslin’s research was supported by the Michael W. Butler Award for Ecological Research through the Department of Biological Sciences and Trustee Fellowships in Raptor Research from the Raptor Research Center. Additionally, McCaslin was awarded a National Science Foundation Graduate Research Fellowship during her final year as a master’s student.

Now a doctoral student of ecology at Colorado State University, McCaslin hopes that the team’s discovery will continue to shape future research, and also prove useful for Heath’s ongoing collaborative research project called Full Cycle Phenology.

“I hope that these results will encourage other researchers to examine long-distance dispersal in their study organisms, because it may give us new insight into how species might adapt to global change.”

This study was published in the Journal of Animal Ecology, and can be found at: Journal of Animal Ecology: Long-distance natal dispersal is relatively frequent and correlated with environmental factors in a widespread raptor.

Support for this kestrel research was provided by a Department of Defense Strategic Environmental Research and Development Program (SERDP) grant awarded to Heath.