Patterns and causes of breeding dispersal in a declining population of Canada jays, Perisoreus canadensis, over 55 years

Abstract

Breeding dispersal can influence fitness as well as the dynamics and genetic architecture of populations, but the patterns and causes of dispersal in most species are still poorly understood. Here, we used 55 years of re-sighting and breeding data from 530 individually marked adult Canada jays at the southern edge of their range in Algonquin Provincial Park, Ontario, Canada to evaluate factors that influence the probability of breeding dispersal occurrences and distances. Breeding dispersal within the study area was rare, occurring in 3% ( N = 81) of the 2477 cases in which individuals were observed defending a territory in consecutive years, and only 13% ( N = 68) of individuals dispersed at least once in their lifetime (mean age of dispersers = 4.75 ± 2.8). Of the 81 breeding dispersal cases, 68% ( N = 55) involved a single bird, while the remaining 32% ( N = 26) involved 13 cases of a mated pair dispersing together. The probability of breeding dispersal was similar between sexes, but females tended to disperse farther. Surprisingly, almost half of breeding dispersal events occurred during the autumn and winter when all or most food had already been cached. However, 70% ( N = 57) of breeding dispersal events involved settlement on a neighbouring territory, which may have allowed adults to retrieve previously cached food on their original territory. Overall, adults were most likely to disperse locally when they lost a mate, had originally occupied a lower-quality territory, and a vacant position was available nearby. While the distance and rates of breeding dispersal did not change over time ( N = 55), breeding dispersal events caused by mate loss, were highest in years with the steepest population decline, suggesting that a diminishing pool of mate replacements influenced breeding dispersal decisions. • We investigated factors influencing breeding dispersal in Canada jays. • Breeding dispersal was uncommon, occurring in 3% of breeding events. • Individuals usually dispersed to neighbouring territories, near previous caches. • Adult were more likely to disperse locally after experiencing mate loss. • Dispersal from mate loss was highest when population decline was most pronounced.