Effects of territory quality on occupancy, breeding performance and breeding dispersal in Tengmalm's owl

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(1) The occupancy of 104 territories of Tengmalm's owl was studied for 10 years in western Finland. More territories were occupied in only 1 year or in at least 5 years than expected by chance. There were also twenty-nine similar areas with suitable nest-box(es), where no nesting attempts were recorded. (2) Territories were graded according to frequency of use in the 10 years: from 0 (not used), to 5 (used in 5-9 years). On good territories the proportion of pine forest was small, and the proportions of spruce forest and agricultural land were large. The densities of small mammal prey are lower in pine forest than in spruce forest, where small mammal populations are also rather stable. Microtus voles occupy agricultural land and show predictable population cycles. Thus, the owls on good territories benefit from vole peaks by foraging over farmland and shift to alternative prey in woodland during the low phase of the vole cycle. (3) Poor territories supported a breeding pair only in peak vole years, but good ones also in low vole years. Independently of their age both females and males performed better on grades 4-5 than on grades 1-3. (4) Nearly all females shifted territories between successive breeding attempts, but males stayed on the same territory after their first breeding attempt. Females seemed to move to get more experienced mates rather than better territories. The longevity of males was greater on grades 4-5 than on grades 2-3. (5) The mean longevity (1.6 years) of males on their territories was similar to that of sparrowhawks and kestrels in Scotland. Some good territories became vacant every year, but males did not change territories. Because of a scarcity of nest-holes, there are few possibilities for finding a new, good territory with suitable nest-hole(s). There seems to be a strong selection against territory shift among males.

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Reference Code: A88KOR05IDUS

Full Citation: Korpimäki, E. 1988. Effects of territory quality on occupancy, breeding performance and breeding dispersal in Tengmalm's owl. Journal of Animal Ecology 57(1): 97-108.

Location: ANIMAL EF: AEGOLIUS FUNEREUS