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Reversed sexual dimorphism in tawny owls, Strix aluco, correlates with duty division in breeding effort

Sunde, Peter LU ; Bolstad, M S and Moller, J D (2003) In Oikos 101(2). p.265-278
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,... (More)
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. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Oikos
volume
101
issue
2
pages
265 - 278
publisher
Wiley-Blackwell
external identifiers
  • wos:000182800600005
  • scopus:0037499866
ISSN
1600-0706
DOI
language
English
LU publication?
yes
id
a52357e9-783b-4590-b175-aa9946602988 (old id 137322)
date added to LUP
2007-06-25 12:52:00
date last changed
2018-05-29 09:35:12
@article{a52357e9-783b-4590-b175-aa9946602988,
  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.},
  author       = {Sunde, Peter and Bolstad, M S and Moller, J D},
  issn         = {1600-0706},
  language     = {eng},
  number       = {2},
  pages        = {265--278},
  publisher    = {Wiley-Blackwell},
  series       = {Oikos},
  title        = {Reversed sexual dimorphism in tawny owls, Strix aluco, correlates with duty division in breeding effort},
  url          = {http://dx.doi.org/},
  volume       = {101},
  year         = {2003},
}