Age-Dependent Response of Migrant and Resident Aegolius Owl Species to Small Rodent Population Fluctuations in the Eastern Canadian Boreal Forest

Abstract

ABSTRACT We investigated the relationship between late summer abundance of small rodents and fall migrant abundance of two nocturnal avian predators, the Boreal Owl (Aegolius funereus) and the Northern Saw-whet Owl (A. acadicus), during their fall movement/migration. In the eastern Canadian boreal forest, Boreal Owls are considered resident (with irruptive movements to the south thought to occur during periods of low prey availability), and Northern Saw-whet Owls migratory. Data on late summer abundance of small rodents collected between 1995 and 2004 were used to develop an index of prey availability. Data on the number and age of irrupting/migrating owls were collected between 1996–2004 (mid-September to late October) using audiolures and mist nets. Our study revealed strong evidence of (1) a negative relationship between the abundance of small rodents and movement of Boreal Owls and (2) a positive relationship between the abundance of small rodents and the number of migrating juveniles and second year ...