Why do birds arrive at different times on their breeding grounds, and why are there differences in when they lay eggs, and in when those eggs hatch? Is the timing of these events genetically hardwired or are these behaviors driven by the variation in environmental conditions these birds face?

To untangle the environmental and genetic factors affecting American Kestrel phenology (the timing of life cycle events), we monitored American Kestrel presence and breeding activity in nest boxes across the United States. These 246 nest boxes across 12 Department of Defense (DoD) sites encompassed a wide geographic area where vastly different environmental conditions and genetically distinct sub-populations likely occur (Read our fall blog post to see the variety of habitats across nest box sites).

To uncover what was going on inside the nest boxes, we used a combination of in-person visits (where biologists peeked inside nest boxes to see nest contents), and remote monitoring using trail cameras in nest boxes to capture time lapse images of nest contents.

Preliminary review shows that kestrels used >40 nest boxes across eight DoD sites in the 2018 breeding season.

Map of DoD sites where nest boxes have been installed: Yakima Training Center, WA; Camp Pendleton, CA; White Sands Missile Range, NM; Fort Hood, TX; Fort Riley, KS; Eglin AFB, FL; Big Oaks National Wildlife Refuge, IN; Fort Bragg, NC; Fort Drum; NY and two sites with pre-existing nest boxes: Dugway Proving Ground, UT; and Lucky Peak; ID. Orange bird symbols represent sites where American Kestrels were present in at least one nest box in 2018. Brown house symbols represent sites where no American Kestrels were present in nest boxes.

From trail cam photos and in-person visits, we collected timing information such as: the date kestrels arrived in nestboxes, when they laid eggs, when eggs hatched, and when nestlings fledged out of the nest box.

Using real-time information from cellular cameras and from communication with DoD biologists, our BSU crew conducted trips to DoD sites with nest boxes occupied by American Kestrels. We captured adult and nestling kestrels to attach unique identifying bands, take measurements, and collect genetic samples (from feathers) and isotopic samples (from claw clippings).

From April to mid-July 2018, our BSU crew banded, measured, and took samples from ~50 American Kestrels on the breeding grounds across six DoD sites (Fort Wainwright, AK; White Sands Missile Range, NM; Camp Pendleton, CA; Yakima Training Center, WA; Fort Bragg, NC; and Fort Riley, KS). DoD biologists at Lucky Peak, Idaho and Dugway Proving Ground, Utah independently captured and sampled an additional >20 kestrels. These samples will be used to help build the American Kestrel Genoscape, and to determine which individuals remained on the breeding grounds during the winter season (residents), and which individuals ventured south (migrants).

In addition to our kestrel breeding phenology data, our nest box monitoring efforts provided all kinds of fascinating data on predation, egg infertility and abandonment, and other species’ nesting phenology. Species using nest boxes ranged from starlings to flycatchers to owls; to squirrels and hungry snakes snacking on nestling birds; to infestations of wasps, ants, and kissing bugs. Although we were grateful that nest boxes provided easy hands-on access to breeding kestrels, we soon realized that they also provided refuge for many species that you’d rather not get your hands on!


From top left to bottom right: Rat snake in Eglin AFB, FL nest box; gopher snake in Camp Pendleton, CA nest box; European Starling in Yakima, WA nest box; Tufted Titmouse feeding nestlings in Fort Bragg, NC nest box; Eastern Bluebird feeding nestlings in Fort Hood, TX nest box; Western Screech Owl brooding nestlings in Fort Hood, TX nest box; Great-crested Flycatcher incubating eggs in Eglin AFB, FL nest box; Red Squirrels nesting in Fort Drum, NY nest box; flying squirrel in Fort Bragg, NC nest box.

In summary, the first breeding season of the Full Cycle Phenology project has been an unbelievable success and a major learning experience! Despite dealing with frustrating camera failures, nest predation, major insect infestations, and extreme weather events on DoD sites, we have made huge strides towards better understanding the variation in kestrel breeding phenology.

Stay tuned for more updates on our research as we head into fall migration season!

Time lapse video of American Kestrel nest in Yakima Training Center, Washington (video credit: Katie Callery)

This research is supported by the U.S. Department of Defense, through the Strategic Environmental Research and Development Program (SERDP RC-2702).

Special thanks to the 19 DoD biologists and volunteers across 12 DoD sites who monitored nest boxes and provided invaluable on-the-ground help with logistics, camera troubleshooting, and species identification.

Post by-Anjolene Hunt

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