Dispersal tendency and duration of life of littermates during population fluctuations of the vole Microtus townsendii.

In increasing and peak populations of the vole Microtus townsendii, littermates, whether they did or did not disperse, tended to have similar lifespans. Identifiable families tended to survive or disperse as a unit. Tendency to disperse from peak populations was non-randomly distributed among litters, and littermates dispersed at the same age.