The American Kestrel (Falco sparverius) is a small falcon whose population is declining across North America, but drivers of this decline have yet to be identified. Conservationists have called for greater understanding of kestrels' migratory connectivity to identify potential causes of decline that may occur during various parts of their annual cycle. For many bird species, the most common and direct way to determine migratory connectivity is by attaching a tracking device that documents their locations over time. However, American Kestrels present a challenge when attaching tracking devices due to their small size and aggressive biting capabilities. We used two attachment methods (backpack and leg-loop harnesses) commonly used for raptors on a wintering population of American Kestrels in north Texas to test whether there were differences in observed return rates the following year. Of 20 American Kestrels fit with devices, significantly more of the kestrels fit with backpack harnesses were observed the following winter than the birds fit with leg-loop harnesses. Eight of the 10 kestrels we fit with backpacks were observed to return to their winter territories compared to only two of 10 kestrels fit with leg-loops. Overall return frequency data of kestrels with both harnessing methods (50%, n = 20) was similar to the frequency we observed on marked birds without devices (52%, n = 190), though this was heavily skewed due to the high return of birds with backpack harnesses (80%). Although our sample size was limited, the disparity between the return rates of birds with the two harness types suggests that backpack harnesses are the preferred method of attaching tracking devices to American Kestrels, and also potentially to similar small raptor species.
Same-sex copulations by raptors, and birds in general, have been rarely reported. In American Kestrels (Falco sparverius), there have been no previous reports of a female copulating with a female. Here, we summarize our observations of a pair of female kestrels that were documented to copulate repeatedly with each other over a 5-wk period in north Texas. Two females were first observed together on 17 March 2020, when they copulated 23 times. That same day, we trapped and marked both females with coded anodized color bands. Between 17 March and 20 April 2020, we observed the pair copulate an average of 9.2 times/hr (7 d of observation, 7.9 hr), with both kestrels being present during 74.9% of our observations. The kestrels alternated which bird was in the top position during copulations, with the female with band code E/17 on top during 55.8% of copulations (n = 45) and female E/20 on top during 44.2%. One or both kestrels vocalized during 75.6% of copulations. We recorded other behaviors typical of breeding kestrels, including nest-site inspection, territorial defense, and an apparent aerial courtship display. Contrary to published speculations on same-sex pairs in birds, our observations do not support the hypothesis that the females typically adopt separate sex-specific behavioral roles. We propose probable benefits of a female-female pairing may include (1) stimulating ovulation, (2) sharing incubation and provisioning duties that could result in a greater number of young fledged, and (3) the ability to more easily defend and hold territory by two females, which typically hold higher-quality territories than males in American Kestrels.
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