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Sökning: WFRF:(Sunde Peter) > (2003-2004) > (2003)

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1.
  • Sunde, Peter, et al. (författare)
  • Diurnal exposure as a risk sensitive behaviour in tawny owls Strix aluco?
  • 2003
  • Ingår i: Journal of Avian Biology. - : Blackwell. - 0908-8857. ; 34:4, s. 409-418
  • Tidskriftsartikel (refereegranskat)abstract
    • Tawny owls Strix aluco generally roost in cryptic locations during the day. To test the hypothesis that this cryptic behaviour is an effort to avoid mobbers or avian predators, we measured diurnal behaviour and cause-specific mortality of radio-tagged birds. Non-breeding adults (assumed to be well fed individuals, optimising their own survival) roosted in less exposed locations than adults with young and newly independent juveniles. Parents roosted in the most exposed sites when their young were immature and vulnerable to depredation, probably to guard offspring. Newly independent juveniles apparently selected roosting sites in exposed places to get access to food, as this behaviour was associated with lower perching heights and higher prey abundance beneath their roosting sites. They also perched in more exposed sites, closer to the ground, in summers with low prey abundance compared to summers with high prey abundance. After previous encounters with goshawks Accipiter gentilis, dependent juveniles roosted in less exposed places compared to other young. The increased risk of being mobbed was highly significant with increasing roosting exposure. Once an owl was mobbed, the intensity of the mobbing correlated positively with the mass of the mobbers, but mobbing birds never killed any owls. In contrast, diurnal raptors caused 73% of natural owl deaths (n = 15) and the depredation rate by raptors was 3.8 times higher in population classes that generally roosted in more exposed locations than did non-breeding adults. We therefore suggest that depredation by diurnal raptors is the main factor shaping the diurnal behaviour of tawny owls.
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2.
  • Sunde, Peter, et al. (författare)
  • Reversed sexual dimorphism in tawny owls, Strix aluco, correlates with duty division in breeding effort
  • 2003
  • Ingår i: Oikos. - : Wiley-Blackwell. - 1600-0706. ; 101:2, s. 265-278
  • Tidskriftsartikel (refereegranskat)abstract
    • Even though most bird species with a raptorial feeding habit express varying extents of reversed sexual dimorphism (RSD: females bigger than males), the evolutionary basis for its maintenance, as well as its possible secondary consequences for the ecological adaptations of the different sexes, is debated. We studied pairs of tawny owls, Strix aluco (females 20% heavier than males), throughout the year by telemetry to test whether any inter-sexual differences in movement patterns, resource partitioning and breeding effort correlated with RSD. Females were larger than males in all body size measures and were 16% heavier than would be expected from the difference in wing length alone. In accordance with predictions from flight economics, males moved longer distances per time unit than females, in particular during the post-fledging season, when they also fed chicks more often than the females. Males had larger home ranges than females during the post-fledging period, whereas the sexes had home ranges of equal size during the non-breeding season. Until 10 days after fledging, females foraged much closer to the offspring than males, apparently balancing their distance to offspring between the needs of offspring guarding and foraging. In males, the parent-offspring distance only increased with decreasing brood condition. The sexes did not differ in habitat use or feeding habits, rendering no indications of food niche partitioning. The study provides further evidence that selection for males to be light and energetically efficient foragers is the main evolutionary force behind RSD in raptorial birds, even when the prey base is confined by territoriality.
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  • Resultat 1-2 av 2
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tidskriftsartikel (2)
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refereegranskat (2)
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Sunde, Peter (2)
Bolstad, M S (2)
Desfor, K B (1)
Moller, J D (1)
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Lunds universitet (2)
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Engelska (2)
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Naturvetenskap (2)
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