Portland State University. Department of Biology
Stanley S. Hillman
Date of Award
Master of Science (M.S.) in Biology
1 online resource (46 p.)
Red-tailed hawk -- Reproduction
Various physical and biological factors affecting annual productivity in a Red-tailed Hawk population in north-central Oregon were investigated. The percentage of the population successfully fledging one or more young was the most important factor in determining the number of young fledged per pair in a given year. Neither clutch size nor the number of young fledged per successful nest varied significantly. Percent pair success was correlated with several January weather variables. A cold and dry January is positively correlated with Red-tailed Hawk productivity. This is apparently related to the onset of rapid vegetative growth and this in turn is positively correlated with the timing of the emergence and reproductive cycle of the principal prey, Belding’s and Townsend's ground squirrels, (Turner 1972). Because a cold and dry January delays the emergence of ground squirrels, the period of emergence and dispersal of the young squirrels more closely corresponds to the time of peak food needs of the young Red-tailed Hawks, and greater pair success is observed. This relative abundance of prey appears to be of greater importance than actual abundance.
Red-tailed Hawk productivity was found to correlate significantly with two habitat variables & the presence of adequate numbers of dispersed hunting perches and relative ground squirrel abundance. The presence of one or more perches per sixteenth section provided the best single correlation. Neither territory size nor competition from interspecifically territorial Swainson's Hawks were correlated with productivity of Red-tailed Hawk territories. Red-tailed Hawks with inhabited dwellings within their territories fledged significantly more young than those without.
Janes, Stewart Wayne, "Some physical and biological factors affecting red-tailed hawk productivity" (1979). Dissertations and Theses. Paper 2797.