Site tenacity and nomadism in Tengmalm's owl (Aegolius funereus (L.)) in relation to cyclic food production

Abstract

In northern Sweden breeding males of Tengmalm's owls (Aegolius funereus (L.)) were site tenacious during and between the peaks of the vole (staple food) cycles, but females only during the peaks. Most of these adults shifted nest boxes between successive years. They selected nest boxes randomly in a radius of 3 km. Juveniles, in contrast to site tenacious adults, dispersed outside their natal area. The females moved longer than the males prior to their first breeding. Five adult females were found to be nomadic. One of these nomadic females previously bred site tenaciously as long as food was abundant. Juveniles and adult males were not found to be nomadic. Emigration of adult females and juveniles occurred most frequently when vole populations declined. The breeding population increased sharply and received immigrants suggesting that nomadism may be essential in the population dynamics. Site tenacity and nomadism are discussed in terms of costbenefit to males and females, respectively. Emphasis is on the main functional roles of males (feeding femle and young) and females (incubation).

Female offspring desertion and male-only care increase with natural and experimental increase in food abundance

“…Over-winter survival of Tengmalm's owl females has not been estimated, but Hakkarainen et al (2002) found that annual survival in adult males ranged from 25 to 76 per cent, depending on food abundance. If they survive through the winter, female Tengmalm's owls have a good chance of breeding every year, in contrast to males, who typically do not breed every year (Lö fgren et al 1986;Korpimäki et al 1987;Sonerud et al 1988). We suggest that the late deserting females, with low body reserves, deserted to increase their own chances of survival to the next breeding season.…”

“…Adult male Tengmalm's owls are territorial and resident, and typically do not breed when food is scarce (Lö fgren et al 1986; but see Hipkiss et al 2002). By contrast, adult females are nomadic, concentrating and breeding where prey is abundant, and they may breed every year (Lö fgren et al 1986;Korpimäki et al 1987;Sonerud et al 1988). Individuals of both sexes usually (more than 95%) change mates between breeding seasons, even if their previous partner is still alive (Korpimäki 1988(Korpimäki , 1989K.…”

Conservation assessment for the northern goshawk in southeast Alaska.

“…The pattern is similar to the more extensively documented pattern observed in boreal owls (Aegolius funereus). In this northern owl, food stress favors nomadism and nest site scarcity favors site tenacity, resulting in different movement patterns for males and females: females exhibited nomadism and males exhibited site tenacity (Lundberg 1979, Lofgren et al 1986). …”

Monitoring habitat quality and condition of Queen Charlotte saw-whet owls (Aegolius acadicus brooksi) using vocal individuality.

“…Some factors affecting breeding site fidelity are breeding success in the previous year, age (Newton 1993), sex of the bird and food availability (Lofgren et al 1986). Thus, birds that have had an unsuccessful breeding attempt at a given site in the past tend to switch to a different territory (Newton 1993).…”

“…1986), and high food availability tends to be associated with greater breeding success (Korpimaki 1992). As habitat quality can be associated with resource availability and reproductive success, both of which seem to be related to site fidelity (Bried and Jouvetin 1999, Gavin and Bollinger 1988, Lofgren et al 1986). Thus, it may be possible to deduce habitat quality from monitoring levels of site fidelity across different habitat types by comparing sites that have an overall greater level o f fidelity to those with lower re-occupancy rates.…”