Five Young Kestrels in Box
2013 Last Egg Laid
The last egg laid has a lighter shell. Most kestrel clutches are completed within nine days time.

For the past 21 years, nestboxes have been maintained and managed for American Kestrels (Falco sparverius) along roadside routes throughout the northern region of Delaware County, Ohio, making it possible for 859 young kestrels to have a chance at life. In 1991, the Ohio Department of Natural Resources, Division of recycling and Litter Prevention awarded a grant to the Delaware General Health District to promote recycling throughout the county’s schools by convincing caring students to generate money to finance materials for kestrel nestboxes by selling recycled cans and other materials. With the cooperation of the Ohio Department of Highways, the Delaware County Bird Club constructed and mounted the first ten boxes to the backs of highway traffic signs before the 1993 nesting season. Kestrels attempted one nest in 1994 and it failed. The 1995 season saw two attempts and the project’s first five falcons fledged from one nest. During the early years, the kestrel population grew as they adapted to nesting along busy highways, but after two traffic accidents smashed sign-mounted boxes in 1999, all agreed that safer and more peaceful habitats were in order. Consolidated Electric Co-op offered to allow the project’s nestboxes to hang from their utility poles located in quieter habitats along country roads.

Five young kestrels huddle as they await their leg bands. Brown wing tips on two visible nestlings identify them as females. These birds are young enough to act “tame” during banding.
Five young kestrels huddle as they await their leg bands. Brown wing tips on two visible nestlings identify them as females. These birds are young enough to act “tame” during banding.

Today, of 18 nestboxes making up the project, only one box in Gallant Woods Preserve hangs from its own pole. Each spring, Dick Phillips and I begin monitoring the boxes by the third week of March to make sure that no other species has excavated the white pine bedding from any of the boxes. After we make sure all boxes are ready for our falcons, we then try to monitor the boxes once every two weeks in order calculate hatch dates so we can predict when the nestlings will be old enough to receive leg bands. Kestrels lay eggs on alternate days and incubation starts after the next to last egg appears in a clutch, then after 27 to 30 days of incubation by both parents, hatchlings start life outside their eggs. Two weeks after hatching, emerging wing feathers reveal the sex of the nestlings; females have brown primary wing feathers and the males show gray wings. From 14 to 21 days of age, the young birds can be safely banded without their human handlers bleeding on their feathers. Even though their talons are always needle sharp, half-grown kestrels are not strong enough to cause injury to bare hands and forearms. Also, their nervous systems are not developed enough for them to express extreme fear and aggression. Young kestrels fledge after 30 days of nest life, and if leg banding events are timely, then all participants remain happy.

Keeping accurate records over the years also makes it possible for astounding facts to emerge. Since 1994, 227 nests have started with eggs and 202 nests produced fledglings for a nest success rate of 89%. In other words, nearly nine out of every ten nests have been successful. Of 1055 eggs laid, 875 (82.9%) hatched and 859 (81.4%) matured to fledge.

So, what is the most astounding fact to emerge? Since the project’s beginning, among all eggs that hatched, 98.2% of hatchlings matured to fly on their own from their nests. I am confident of this value since we completely excavate used nests in late summer or fall in order to add new white pine bedding, and we thoroughly search for remains of young that might have died and were eaten by their siblings. Leg bones with bands are easily found encased in the old nest material, but fortunately, such finds are rare due to the skill and dedication of kestrel parents.

The 2013 Season

The 2013 season was fairly typical with 147 days from the first egg on March 19 through August 12 when the last youngster fledged. No boxes produced two broods, which usually results in the last fledgling leaving as late as August 26.

All sixteen nests with eggs raised young. Seventy-six eggs were laid, 71 (93.4%) hatched and 70 (91.1%) fledged, or stated another way, 98.6% of hatchlings grew to fledge. Of the sixteen nests, twelve had clutches of five eggs and four nests started with four eggs. The average number of eggs per nest was 4.75 and the average fledged per nest was 4.38, all quite typical.

In 2013, there were no clutches of three eggs, nor were there any large clutches of six eggs. In 2009, two nests had six eggs, and in 2010, three families started with six eggs. For the last three seasons, no clutches of six have been counted. Considering two prey items whose remains are commonly found in kestrel nests, meadow voles and grasshoppers, one has to wonder how each year’s weather affects kestrel prey populations and their degree of influence in determining clutch sizes among kestrels.

Still Learning from Mistakes

Steel Cable on Box K16
Steel cable, a winch, a sandwiched pole, and a sliding baffle makes monitoring K-16 easy, but a changing habitat might require a new location for this once productive box. The entrance seen in this photo is really one of two decoy holes painted on to attract distant kestrels.

At the end of the 2012 season, we moved two nestboxes to better habitats, and one box in particular, K-17, we moved to avoid other falcon species that we thought might be interfering with our kestrels. In 2013, K-17 started out hanging in the wide-open spaces along Cackler Road in Delaware County where utility wires stretched over wide, grassy berms. We were excited about K-17’s new habitat because we thought that a large, majestic Oak tree that stood ninety yards away would provide a peaceful place for a kestrel to perch while it guards its nestbox. Well, we forgot to ask the neighborhood Red-tailed Hawks (Buteo jamaicensis) for their opinion.

On April 8, a female kestrel sat in the box, and I did not bother her further as I closed the lid to her nest chamber. During the following weeks, we counted no eggs, egg remains, or adult kestrels, but we did remove three successive clutches of European Starling eggs. Why didn’t the kestrels nest? Well, for the rest of the season, both Dick and I saw the best reason sitting in the large Oak tree. Three different times, I alone saw a Red-tailed Hawk perched in the Oak, and once it was busy eating prey. Needless to say, at the end of the season, we moved K-17 three utility poles to the east to avoid conflict between our smallest falcon and our largest Buteo. Will we find nesting kestrels in K-17 in 2014? We will see, but so far, kestrels have been seen hanging out near the shuffled box.

The second kestrel box that we moved in 2012, K-1, raised four in 2013 as it now stands with no woodlots or large trees nearby. The only nestbox whose habitat is not desirable to raise kestrels is K-16 in Gallant Woods Preserve. The habitat is presently being managed as prairies and there are many mature trees standing along the grassland’s border. K-16 did not raise kestrels in 2013, but we will give it one more year before we make a decision about relocating it. Presently, K-16 is very visible to the public, so it helps promote the conservation effort of erecting nestboxes for our small raptors.

Helping North America’s smallest falcon continues to be a challenging highlight of each nesting season. Raptor on!