Breeding dispersal in female North American red squirrels

Although natal dispersal has received considerable attention from animal ec ologists, the causes and consequences of breeding dispersal have remained l argely unexplored. We used telemetry, direct observation, and long-term mar k-recapture (9 yr) to study breeding dispersal in the North American red sq uirrel (Tamiasciurus hudsonicus) at Kluane, Yukon, Canada. We recorded the postbreeding behavior (keep the territory, share it with juveniles, or bequ eath it to juveniles) of mothers from 485 litters, and monitored the fates of eight cohorts of weaned juveniles (680 individuals). The proportion of m others that bequeathed their territory to one of their offspring was roughl y one-third of that keeping or sharing it. Breeding dispersal was a recurre nt phenomenon that characterized a fraction of the population of reproducti ve females every year. Dispersing females did not improve the quality of th eir breeding environment. In contrast, by leaving their territory, mothers allowed some offspring to stay on the natal site, which increased juvenile survival. Breeding dispersal by female red squirrels was thus a form of par ental investment. Dispersing females were older than others, had higher num bers of juveniles at weaning, and moved their breeding sites more frequentl y after reproducing when food availability was high. These patterns are con sistent with the major predictions of parental investment theories. We dete cted no difference in survivorship or future reproduction between dispersin g and resident mothers. Juvenile males dispersed more often than females, b ut not farther. The sex of offspring did not influence whether mothers disp ersed or not. Although we showed that breeding dispersal can have major imp acts on the dynamics of squirrel populations, the relative implications of natal and breeding dispersal for the genetic structure and demography of po pulations and the social evolution of species remain unknown.