PARENT SESSION
Poster Session #43: Avian Ecology.
Thursday, August 9, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Habitat composition determines breeding success of Tengalm's owls under fluctuating food conditions.

HAKKARAINEN, HARRI¹, MYKRA, SAKARI¹, KURKI, SAMI¹, KORPIMAKI, ERKKI¹, NIKULA, ARI², KOIVUNEN, VESA³, ^{1 2 3}

ABSTRACT- The effect of landscape composition on the breeding success of Tengmalm's owl (Aegolius funereus) was studied in western Finland at five different spatial scales (250 - 4 000 m) around the nests during two consecutive three-year vole cycles. Landscape composition had strongest effects on owl breeding in the peak phase of vole cycles. Significant variation in owl breeding occurred along the east-west productivity gradient from farmland predominated areas to barren hinterland. Owls tended to produce earlier clutches on territories predominated by agricultural areas in increasing vole years. Similar trend was observed in the peak phase of vole cycle; owls breeding on barren hinterland seemed to delay breeding compared to owls breeding near agricultural areas. Surprisingly, the nestling survival and fledgling production in the peak phase steeply decreased with increasing proportion of farmland although the clutch size was not significantly related to the landscape composition. Also the clear-cut and sapling areas had a negative impact on fledgling number in the peak phase. Furthermore, during the vole peak years the nestling survival increased from western cultivated areas towards eastern outlying district. These results indicate dramatic and sudden crash of vole populations on farmland predominated habitats during the owl breeding season, where the impact of specialist and generalist predators on vole populations is apparently much higher than on hinterland far away from agricultural areas. This finding gives support for the spill-over hypothesis, according to which predators and their exploitation tends to spill over from luxuriant habitats to the barren habitats in landscape complexes.

KEY WORDS: owls, breeding, habitat