Date of Award:

5-1-1996

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

James A. Gessaman

Committee

James A. Gessaman

Committee

Kimberly A. Sullivan

Committee

John M. Marzluff

Committee

Edward W. Evans

Abstract

The primary focus of my research was to determine the magnitude and causes of mortality of Prairie Falcons (Falco mexicanus) during the fledging-dependence period. In 1992 and 1993, I radio-tagged nestlings prior to fledging and monitored their survival until they emigrated from the study area. Additionally, I quantified parental behavior during the nesting period as well as other factors that have been shown to influence subsequent survivorship. Of the 152 radio-tagged nestlings, 47 died prior to dispersal from their natal territories. Mortality rates were consistent between years, 28% in 1992 and 34% in 1993. The magnitude of mortality varied throughout the fledging-dependence period. Fifty percent of all mortality occurred during the first week after tagging in 1992 in contrast to only 16% during this time in 1993. Predation by Great Horned Owls (Bubo virginianus) was the primary cause of mortality in both years. In 1992, the presence of hematophagous ectoparasites (Hacmatosiphon inodorus) in aeries contributed to the higher death rate during the first week after tagging. Parental behavior during the late brood-rearing period, hatching date, brood size, and fledging mass were not correlated with fledgling mortality. The frequency of predation in this study may have obscured or diminished the influences of these factors. During 1991-1994, the Townsend's Ground Squirrel (Spermophilus townsendii) population experienced a dramatic fluctuation, ground squirrel density was high in 1991, peaked in 1992, then significantly declined in 1993, and remained low in 1994. To ascertain if ground squirrel abundance affected parental and fledgling behavior, I compared measures of behavior and other attributes among years. Attendance rates of male parents in their territories during the early brood-rearing period were significantly higher in 1992, the peak prey year, than in the other three years. Mean prey delivery rates were similar among years, but delivery rates increased as nestlings aged in 1992, whereas the rates decreased as nestlings aged in 1991, 1993, and 1994. Parent falcons may have compensated for low squirrel abundance by securing alternate prey in 1993 and 1994. Differences in ground squirrel abundance had no effect on the length of the fledging-dependence period between 1992 and 1993. However, the length of the staging period, the time between dispersal from the natal territory and prior to emigration from the study area, was significantly longer in 1992 than in 1993.

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