Aspects of the Population Biology of Tundra Peregrine Falcons, Falco peregrinus tundrius
Johnstone, Robin Mark
A population of tundra peregrine falcons (Falco peregrinus tundrius) was studied over 4 breeding seasons at Rankin Inlet, NWT, Canada. These data were combined with data from the 10 previous consecutive seasons. As the study area and methodology was consistent during the entire study, I summarized and analyzed information from all 14 years to investigate paradigms in avian biology. The toxicological assessment of peregrines and their prey revealed that the population is still likely to experience some contaminant related reproductive failure, however, the levels are not high enough to seriously affect production of the population. Contrary to predictions, no improvement in shell thickness was detected between decades and residue levels changed little. Results suggest that peregrines accumulate organochlorines on their wintering rounds, but also from contaminated aquatic species that range only within North America. The parentage of 55 peregrine broods (144 young total) was examined using both single-locus minisatellite and microsatellite DNA profiling to: (1) investigate the accuracy of traditional measures of an individual's reproductive success; (2) test predictions of the Paternity Assurance Hypothesis (PAH) in a dense raptor population; and (3) assess whether non-territorial adult peregrines contribute to their lifetime reproductive success before holding a territory. A low frequency (1.3% of young) of extra-pair paternity (EPP) was detected; justifying the use of traditional measures of reproductive success. Infrequent EPP is consistent with other studies of raptors, but fits poorly with the predictions of the PAH. Inconsistencies with the PAH, and the mechanism of social dominance and territoriality is discussed. The pattern of nesting territory occupancy and reproductive performance over 14 years was analyzed to identify the importance of density-dependent processes in regulation of the population, and test the predictions of two hypotheses explaining density-dependent fecundity. Breeding attempts at preferred (frequently occupied) territories produced young more often than attempts at avoided (infrequently occupied) territories supporting the hypothesis that occupation frequency is an indirect measure of habitat quality. Density-dependent fecundity was the result of proportionally more breeding attempts occurring at infrequently occupied territories where the frequency of failure was high; production at preferred territories did not decline with increasing density. This was consistent with the predictions of the "habitat heterogeneity" hypothesis, but not the "interference" hypothesis. 14 adult peregrines were removed from their territories for 24 hours to test whether breeding densities were limited and elucidate the relative importance of territory quality and territoriality in population limitation. Replacements at 11 territories provided evidence of 'floaters' and population limitation. All six vacancies for females, at 5 good and one poor quality territories, were filled; males were replaced at four good quality territories but only one of four poor quality territories. Mechanisms of population limitation are discussed. I analyzed capture and resighting records of colour-banded adult peregrines collected from 1982 to 1995 to provide accurate estimates of survival using Cormack-Jolly-Seber capture-recapture methodology and traditional turnover methodology. Results were indicative of little or no difference in survival between males and females. Differences between estimates from the two methods were minimal. Estimates represent minimum survival because of the confounding effects of emigration. Limitations and practical difficulties in the estimation of survival among peregrines and other raptors are discussed.