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Cited by 368Animal Behavior and ReproductionAvian ecology and behaviorEvolutionary Psychology and Human Behavior

Evolution of reversed sexual size dimorphism and role partitioning among predatory birds, with a size scaling of flight performance

ANDERSSON, MALTE, NORBERG, R. ÅKE·1981·Biological Journal of the Linnean Society
DOI 10.1111/j.1095-8312.1981.tb00752.x
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Abstract

To explain the adaptive significance of sex role partitioning and reversed sexual size dimorphism among raptors, owls and skuas, where females are usually larger than males, we combine several previous hypotheses with some new ideas. Owing to their structural and behavioural adaptations for prey capture, predatory birds have better prospects than other birds of defending their offspring against nest predators. This makes sex role partitioning advantageous; one parent guards the offspring while the other forages for the family. Further, among predators hunting alert prey such as vertebrates, two mates because of interference may not procur much more food than would one mate hunting alone. By contrast, two mates feeding on less alert prey may together obtain almost twice as much food as one mate hunting alone. For these reasons, partitioning of breeding labours might be adaptive only in predatory birds. An initial imbalance favours female nest guarding and male foraging: the developing eggs might be damaged if the female attacks prey; their mass might reduce her flight performance; she must visit the nest to lay; and the male feeds her before she lays (‘courtship feeding’). Increased female body size should enhance egg production, incubation, ability to tear apart prey for the young, and, in particular, offspring protection in predatory birds. Efficient foraging during the breeding period then becomes most important for the male. This imposes great demands on aerial agility in males, particularly among predators of agile prey. Flight performance decreases with increasing size in five of six aspects explored. The male must therefore not be too large in relation to the most important prey. For these reasons, he should be smaller than the female. Among predatory birds, size dimorphism increases with the proportion of birds in the diet, which may be explained as follows. Adult birds have mainly one type of predators: other predatory birds. Because almost only these specialists exploit adult birds, they carry out most of the cropping of this prey. A predator of easier prey competes with many other kinds of predators, which considerably reduce prey abundance in its territory. This is not so for predators of adult birds. Further, because birds are extremely agile, the specialized predator can hunt efficiently only within a limited size range of birds, whose flight skill it can match. Increased size dimorphism among these predators therefore should be particularly important for enlarging the combined food base of the pair. A bird specialist may consume much of the available prey in the suitable size range during the breeding period. When the predator's young are large enough to defend themselves, the female aids better by hunting than by guarding the chicks. It is advantageous among bird specialists if she hunts prey of other sizes than does the male, who has by then reduced prey abundance in his prey size class. But among predatory birds hunting easier prey the female gains little by hunting outside the male's prey spectrum, because other kinds of predators will have reduced the prey abundance outside as well as inside the male's preferred size range. Intra-pair food separation through large sexual size dimorphism therefore should be particularly advantageous among predators of birds. This may be the main reason why the degree of size dimorphism increases with the dietary proportion of birds.

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Research works printed but not linked: 18

  1. AMADON, 1959, The significance of sexual differences in size among birds, Proceedings of the American Philosophical Society, 103, 531
  2. BALGOOYEN, 1976, Behavior and ecology of the American kestrel (Falco sparoerius L.) in the Sierra Nevada of California, University of California Publications in Zoology, 103, 1
  3. BRULL, 1937, Das Leben deutscher Greifvögel
  4. CADE, 1967, Ecological and behavioral aspects of predation by the Northern Shrike, Living Bird, 6, 43
  5. DEMENTIEV, 1951, Birds of the Soviet Union, 1
  6. BLOTZHEIM, 1971, Handbuchder VögelMitteleuropas. Vol. 4. Falconiformes
  7. HAGEN, 1942, Totalgewichts-Studien bei norwegischen Vogelarten, Archiv für Naturgeschichte, 11, 1
  8. HALD-MORTENSEN, 1974, Nest and nest site of the sparrowhawk Accipiter nisus-and some comparisons with the goshawk A. gentilis, Dansk Ornithologisk Forenings Tidsskrift, 68, 91
  9. JAKOBER, 1980, Flügellängen und Gewichte einer südwestdeutschen Population des Neuntöters (Lanius collurio) unter Berücksichtigung der geschlechtsspezifischen Arbeitsteilung während der Brutperiode, Vogelwarte, 30, 198
  10. NELSON, 1975, Breeding biology of frigatebirds-a comparative review, Living Bird, 14, 113
  11. NELSON, 1978, The Sulidae
  12. OPDAM, 1975, Inter- and intraspecific differentiation with respect to feeding ecology in two sympatric species of the genus Accipiter, Ardea, 63, 30
  13. SCHMIDT-BEY, 1913, Neckereien der Raubvögel nebst Gedanken über die Entstechung ihrer secondären Geschlechtsunterscheide, Omithologische Monatsschrift, 38, 400
  14. SEARS, 1976, Behavioral evidence on skimmer's evolutionary relationships, Auk, 93, 170
  15. SIMMONS, 1972, Some adaptive features of seabird plumage types, British Birds, 65, 465
  16. STORER, 1955, Weight, wing areas and skeletal proportions in three accipiters, International Ornithological Congress 1954, 11, 287
  17. WHITE, 1971, Cliff-nesting raptors and ravens along the Colville River in arctic Alaska, Living Bird, 10, 107
  18. WILLOUGHBY, 1964, Breeding behavior of the American Kestrel (Sparrow Hawk), Living Bird, 3, 75

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Authors
ANDERSSON, M., & NORBERG, R. Å.
Affiliations
University of Gothenburg (SE)
ORCID
ANDERSSON, MALTE
Venue
Biological Journal of the Linnean Society
Publisher
Oxford University Press (OUP)
Published
1981-03
Volume
15
Issue
2
Pages
105-130
ISSN
0024-4066 (ISSN-L)
DOI
10.1111/j.1095-8312.1981.tb00752.x
OpenAlex
W2001353176
Semantic Scholar
412ca86ceeba5dfc33cb31c38ab6e0e238a61892
Cited by
368
References
74
Citations by year
2026: 6 · 2025: 5 · 2024: 3 · 2023: 1 · 2022: 12 · 2021: 9 · 2020: 6 · 2019: 7 · 2018: 5 · 2017: 16 · 2016: 7 · 2015: 8 · 2014: 17 · 2013: 9 · 2012: 8
FWCI
6.94
Type
journal article
Language
en
Open access
closed
Licence
doi.wiley.com/10.1002/tdm_license_1 (tdm, 12602 d)
Locations
Biological Journal of the Linnean Society (publishedVersion)
Topics
  • Life Sciences › Agricultural and Biological Sciences › Ecology, Evolution, Behavior and Systematics › Animal Behavior and Reproduction
  • Physical Sciences › Environmental Science › Ecology › Avian ecology and behavior
  • Social Sciences › Psychology › Experimental and Cognitive Psychology › Evolutionary Psychology and Human Behavior
Keywords
reversed sexual size dimorphism, raptors, owls, skua, flight performance, body size scaling, nest guarding, courtship feeding, foraging efficiency, prey size, interspecific competition, egg production, offspring protection, body length, wing span, wing aspect ratio, wing loading

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