Nesting Kestrels Establish New Record in 2012
- Written by Dick Tuttle
As monitors of a fifty-mile-long roadside nestbox project for American Kestrels (Falco sparverius) in Delaware County, Dick Phillips and I did not know what to expect after a wet and warm winter, but our determined sparrow hawks fledged a record 77 young falcons in 2012 surpassing 76 raised in 2010. From the first egg laid on March 14 to the last fledgling flying from its nest on August 18, nestboxes sheltered eggs or young for 158 days for a typical kestrel nesting season. Hot temperature extremes became a concern but no nestlings succumbed to the challenges of climate change as they thrived inside the project's well ventilated, dry nestboxes. On the other hand, for the second straight season, no clutches of six eggs were laid since three nestboxes held six eggs in 2010. Were there fewer prey items in 2012 to limit food energy for egg production, or did temperature extremes demand that more calories be used for cooling, etc.? Things to think about as the changing climate continue to set records.
For the 2012 season, 19 kestrel nestboxes were offered within 18 possible territories. We had installed two boxes; both numbered as K-1, one-half mile apart within the same territory. The plan was to remove one box after kestrels made their choice. However, our target species rejected both boxes after they apparently found the adjoining habitats to be too overgrown. We removed both boxes on August 22 and reinstalled one in prime kestrel habitat along Harris Road where utility wires string above wide grassy berms.
A Closer Look at the 2012 Nesting Season
Kestrels completed three clutches with four eggs and 15 clutches of five eggs for 18 clutches in 17 boxes. The average number of eggs per clutch was 4.83. Only one clutch failed to hatch after the male disappeared, and after 78 (89.7%) of 87 eggs hatched, 77 (88.5%) fledged, and 98.7% of hatchlings fledged with an average of 4.53 fledglings for successful nests. One box fledged three, six nests fledged four each, and ten families raised five young. The only nestling to die in 2012 might have choked, starved, or suffocated after a snake lodged in its mouth and throat.
When other native species build nests in our kestrel boxes, we attach front panels from bluebird nestboxes to reduce the three-inch entrance to 1-1/2 inches to keep swallows and bluebirds from becoming snacks for kestrels. In 2012, six Tree Swallows from one family and two Eastern Bluebirds grew to fly from their huge natal nest chambers.
Too Many Falcons?
Sometimes, you have to go with your gut-feelings when managing wildlife. We decided to move K-17 from the Delaware Wildlife Area for a very good reason: there might be too many falcon species there for the good of our continent's smallest falcon. K-17 hung from a utility pole between two nestbox grids that I maintain for Tree Swallows along Panhandle and Leonardsburg Roads. Before March 15 each year, I take the grids' 52 nestboxes from winter storage at my home and return them to their permanent pipe mounts in the wildlife area. Three or four times each spring while I am working with my grids across the road from a 50-acre wetland, I hear the squawks of hundreds of ducks and geese as they take to the air all at once, and I smile as I try to find the Bald Eagle that is causing the mayhem and mass flight. Many times, I have failed to locate a flying eagle that should be easy to see, so what else could be causing the fuss?
During early March visits in 2012, a pair of kestrels was part of the life perched on the utility wire that passed over K-17. By April, the kestrels had disappeared and European Starlings had claimed the box. We evicted three clutches of starling eggs before a kestrel egg appeared on May 28, then we counted five cold falcon eggs on June 13 and the male kestrel was nowhere to be seen. The female kestrel stayed all summer but her eggs remained cold. The nest had failed.
Presently, the leading suspect for K-17's failure is Duck Hawks, better known by their modern name, Peregrine Falcons (Falco peregrinus). Peregrines are becoming more common in Delaware County and that is good. Their nickname explains one of the reasons that they would find the wildlife area to their liking since 159 acres of the area are seasonal wetlands managed for migrating and nesting ducks. Where there are ducks, there should be duck hawks. Peregrines also target Mourning Doves sitting on wires, and to a peregrine, a kestrel perched on a wire would also encourage a deep, fast dive for lunch.
Where would non-breeding first and second year peregrines be roosting, and where might breeders find scrapes in tall cliffs above the ground for nests? Across the western edge of Delaware County, tall limestone cliffs parallel the Scioto River and become even taller in Franklin County. Am I making a diction mistake by using "tall" instead of "deep" to describe these cliffs, because I'm talking about stone quarries that hide their walls below the horizon and remain unseen by most of our species. Peregrine Falcons, on the other hand, may be using quarries to roost or nest in. Peregrines try to avoid the murderous Great-horned Owl, so quarries with mature woodlots overlooking cliffs would be unacceptable to a wise peregrine. Well, something to think about, but a gut-feeling nonetheless.
There is a second falcon species that might have been a problem for K-17's kestrels. Bird watchers frequently spot them during their migration as they perch in a stand of cottonwood trees 90 yards from K-17. Merlins (Falco columbarius), nicknamed pigeon hawks, can be seen in the wildlife area between mid-March and mid-May, within the same time period when K-17's first kestrels disappeared in 2012.
So, acting on gut-feelings, we moved K-17 to Cackler Road where it now stands nine-tenths of a mile from K-18. The new location includes a solitary Oak tree that stands ninety yards from K-17's new utility pole. The majestic oak will provide a safe haven for a kestrel while it guards its nest. Also, the Oak's crown will shield our smallest falcon from the speedy, lethal dives of its larger cousin. As Dick and I pulled off the road to install K-17 at its new site on August 22, a kestrel flushed from the electric line strung over a well-manicured grassy berm. We broke into laughter and both announced in our own way, "Buddy, you just got a new nestbox!"
Looking forward to 2013, raptor on!