Dynamics of immigration into Yellow-Bellied Marmot colonies

Immigration and recruitment were examined in six colonies of Yellow-bellied Marmots (Marmota flaviventris) for 220 colony-years. Recruitment occurred significantly more often than immigration. Rates of immigration and recruitment were not significantly correlated among colonies nor were either significantly related to the area of the colony. The rates of immigration and recruitment did not differ when the population density of resident females was below the mean, but recruitment was significantly more likely when the population density was above the mean. Immigration was more likely to occur when population density was below the mean, but recruitment did not significantly vary with population density. Recruits were two-years-old whereas immigrants averaged 2.82-years-old. Of 32 yearling females who were potential immigrants to a site, only three became resident and the remaining were transients or peripherals. Two peripheral yearlings and six of 29 peripheral adults eventually became immigrants. Yearlings were more likely to be immigrants if the adult resident females were nonreproductive and if there were no philopatric yearlings present. Immigration and recruitment occurred in the same colony in the same year only eight times. Fitness of adult females is enhanced by recruiting daughters into matrilines consisting of mother:daughter:sister groups. Immigration occurs when empty space is available and there are insufficient recruits to occupy all available space.