Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Animal Ecology

First Advisor

Erwin E. Klaas


I studied the behavior, habitat and perch use, causes of mortality, and time to dispersal of post-fledging American Kestrels (Falco sparverius) during spring and summer 1988-1990 in central Iowa. To monitor kestrel activity, I attached radio-transmitters to 64 birds in 50 nests. All young in the study fledged from nest boxes, most of which (N = 47) were attached to the backs of highway signs along the Interstate-35 (I-35) right-of-way;During the first week after fledging, kestrels spent <1% of their time foraging or flying; the remainder was spent in inactive behavior. Kestrels fledging from nests along the interstate were observed at this time primarily in cropland and along the interstate right-of-way, where they frequently perched on the ground;All but 1 of the 16 kestrels found dead died during the first week after fledging, before flying skills had developed. Mammalian predation accounted for six deaths and was the main cause of mortality. Only 2 of 61 radio-marked kestrels that fledged from nest boxes along the interstate died because of a collision with a vehicle;As kestrels grew older, perch resting decreased whereas perch hunting increased. Post-fledging kestrels fed almost exclusively on invertebrates, and mean hunting success did not exceed 55%;In 1988-1989, I observed social hunting among siblings, families, and also among unrelated kestrels. Social hunting occurred during both perch hunting and ground hunting. Social foraging in these kestrels was imitative rather than cooperative;In 1990 I observed experimentally adjusted broods of two and five post-fledging American Kestrels to test two hypotheses: (1) imitative social foraging increases foraging efficiency, and (2) individuals in large broods will disperse sooner than individuals in small broods. No differences in foraging efficiency or in dispersal time were detected, but sample sizes were small because of high mortality or signal failure among radio-marked birds;Kestrels fledging from nest boxes along the interstate hunted extensively along secondary roads. Mean time until the initiation of dispersal of kestrels along the interstate was 22.7 d after fledging. Band recoveries provided little evidence of natal philopatry.



Digital Repository @ Iowa State University,

Copyright Owner

Daniel E. Varland



Proquest ID


File Format


File Size

87 pages