Northern Prairie Wildlife Research Center
American Kestrels require open terrain for hunting, and the grassy rights-of-way are ideal for this purpose. While driving the interstate, it is not uncommon to see a kestrel hovering above a right-of-way or perched on a power line searching for prey. The nest boxes are predator-proof because raccoons and other predators are unable to climb the steel posts which support the signs.
In Iowa nest box use by kestrels averages 50%, and young are sucessfully raised in about 70% of these boxes. European Starlings occupy most of the boxes not used by kestrels. With an average of three young kestrels raised in each successful kestrel nest box, each year the Iowa program yields about 105 young for every 100 nest boxes in place.
Dan Varland studied the behavior and survival of young kestrels leaving their nest boxes along I-35 for his doctoral research in Animal Ecology at Iowa State University. Dan followed the young by attaching radio-transmitters to them just before they left their nests. Dan attached transmitters to a total of 61 birds during each of three summers, 1988 - 1990. He found that the young left the interstate right-of-way soon after they could fly and went to nearby areas to hunt and for cover. Only 2 of the 16 young kestrels found dead were killed as a result of collisions with vehicles along the interstate, indicating that traffic was not a major source of mortality.