Title

Behavior of Prairie Falcons (Falco mexicanus) During the Nesting and Fledging-Dependence Periods Under Fluctuating Prey Conditions

Document Type

NCA Publications/Journals & Book Chapters

Publication Date

6-1-1996

Journal Title/Publication Source

Bird Behavior

Volume

11

Page Numbers

81-89

Abstract

We studied the behavior of adult and young prairie falcons (Falco mexicanus) during the nesting and fledging-dependence periods over a period of years when the population density of their primary prey, Townsend's ground squirrels (Spermophilus townsenii), dramatically declined. The percentage of time adult male falcons spent in their nesting territories during the early brood-rearing period was significantly higher in 1992, the year of greatest ground squirrel abundance, than in 1991, a moderately high prey year, or in 1993 and 1994, the low prey years. Mean prey delivery rates during the entire brood-rearing period were similar among all years, but rates increased as nestlings aged in 1992, whereas they decreased as nestlings agged in 1991, 1993, and 1994. Prent falcons delivered proportionally fewere ground squirrels and small mammals, but more birds and reptiles in 1993 and 1994 than in 1992. This increased use of alternative prey likely represents compensation for low ground squirrel abundance. The ages at which falcons dispersed from their natal territories were similar between 1992 and 1993. However, low ground squirrel abundance may explain why the length of the staging period (the time between dispersal from the natal territory and emigration from the study area) was significantly lower in 1992 than in 1993.

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Behavior of Prairie Falcons (Falco mexicanus) During the Nesting and Fledging-Dependence Periods Under Fluctuating Prey Conditions

We studied the behavior of adult and young prairie falcons (Falco mexicanus) during the nesting and fledging-dependence periods over a period of years when the population density of their primary prey, Townsend's ground squirrels (Spermophilus townsenii), dramatically declined. The percentage of time adult male falcons spent in their nesting territories during the early brood-rearing period was significantly higher in 1992, the year of greatest ground squirrel abundance, than in 1991, a moderately high prey year, or in 1993 and 1994, the low prey years. Mean prey delivery rates during the entire brood-rearing period were similar among all years, but rates increased as nestlings aged in 1992, whereas they decreased as nestlings agged in 1991, 1993, and 1994. Prent falcons delivered proportionally fewere ground squirrels and small mammals, but more birds and reptiles in 1993 and 1994 than in 1992. This increased use of alternative prey likely represents compensation for low ground squirrel abundance. The ages at which falcons dispersed from their natal territories were similar between 1992 and 1993. However, low ground squirrel abundance may explain why the length of the staging period (the time between dispersal from the natal territory and emigration from the study area) was significantly lower in 1992 than in 1993.