Sexual Size Dimorphism in Raptors: Intrasexual Competition in the Larger Sex for a Scarce Breeding Resource, the Smaller Sex

Olsen, Penny; Olsen, Jerry

doi:10.1071/mu9870059

Cited by 28 publications

(20 citation statements)

References 16 publications

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“…Our results were consistent with the prediction that ASY female Cooper's Hawks acquire higher quality territories and have higher reproductive success than SY females. These findings support the hypothesis that intrasexual competition for mates and nesting territories does occur among female accipiters (Newton , Olsen & Olsen , Kenward , Millsap et al . ), and that ASY females are most likely better competitors for high‐quality mates/territories.…”

Section: Discussionsupporting

confidence: 88%

Male brood provisioning rates provide evidence for inter‐age competition for mates in female Cooper's Hawks Accipiter cooperii

Lien

Millsap

Madden³

et al. 2015

Ibis

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Life history theory predicts that individuals should maximize lifetime reproductive success (LRS) by breeding as soon as they reach sexual maturity, yet many species delay breeding, either because there are insufficient available mates or breeding sites, or because delayed breeding yields higher LRS. Accipitriform species, such as Cooper's Hawk Accipiter cooperii, exhibit both delayed breeding and delayed plumage maturation. However, in certain circumstances, first‐year females in non‐definitive plumage do breed and apparently compete with older females for high‐quality breeding territories. We predicted that these young females are at a competitive disadvantage compared with older females and that older females would have both higher reproductive success and be able to acquire higher quality nesting territories. We conducted brood counts and measured prey delivery rates by male Cooper's Hawks in an expanding urban population located in Albuquerque, New Mexico (USA), to assess our prediction. We found that older females had higher reproductive success, fledging 1.6 more offspring than younger females, and that they occupied territories where males provisioned at higher rates of 0.37 more prey items per 2‐h period. Our results showed that older females fared better than first‐year females but it is unclear if this is the result of passive or active competition. Older females initiated nesting 14.3 days sooner than first‐year females and thus may have filled vacant, high‐quality territories before first‐year females began seeking mates. Additionally, first‐year females were never observed persistently to confront older females for breeding territories, but they did actively compete against each other. First‐year females may defer to older females who, in a direct competitive interaction, would be most likely to prevail. Thus, delayed plumage maturation in Cooper's Hawks may serve to focus competition for nesting territories within age classes.

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Section: Discussionsupporting

confidence: 88%

Male brood provisioning rates provide evidence for inter‐age competition for mates in female Cooper's Hawks Accipiter cooperii

Lien

Millsap

Madden³

et al. 2015

Ibis

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“…Large female size could also result from intrasexual competition for mates, a hypothesis that also applies to raptors (Olsen and Olsen 1987). Female Great Skuas regularly engage in fights for males.…”

Section: Norberg 1981) This Increased Efficiency Could Results From Gmentioning

confidence: 99%

Evolution of Reversed Sexual Size Dimorphism in Skuas and Jaegers

Catry

Phillips

Furness

1999

The Auk

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. University of California Press and AmericanOrnithologists' Union are collaborating with JSTOR to digitize, preserve and extend access to The Auk.ABSTRACT.-Skuas and jaegers (Stercorariinae), like other birds with a raptorial lifestyle, display reversed sexual dimorphism in size (RSD) in which females are larger than males. This condition is commonly believed to be associated with the morphology or behavioral ecology of avian predators, and numerous theoretical explanations have been presented to account for its evolution. Most tests of these ideas have been theoretical or based on comparative analyses. We present tests of specific hypotheses of RSD based on field studies of Great Skuas (Catharacta skua) and Parasitic Jaegers (Stercorarius parasiticus) breeding in Shetland. We also present a comparative analysis of foraging behavior and degree of RSD within the Stercorariinae. We found no support for the popular theories that claim that RSD evolved as a result of specialized roles during breeding. Large females were not more fecund, nor were they the main defenders of the nest. Male body size was not correlated with any breeding parameter. In addition, interspecific comparisons did not support the idea that the degree of RSD is related to foraging behavior during the breeding season (as opposed to morphology). Female dominance within pairs did not affect any breeding parameters. Support was found for theories that RSD is linked to sexual selection. Large females had an advantage when pairing with older males, which could be a result of intrasexual competition for mates. There was assortative mating for size, indicating that small males could also have an advantage in pairing, because large males seem to be rejected by small females. Given the disparate results of several previous studies, we conclude that a large body of empirical evidence will be needed before we can draw firm conclusions about the main selective factors that act to maintain current levels of RSD in natural populations of raptorial birds. THE MECHANISMS behind the origin and maintenance of sexual size dimorphism in animals are poorly known (Hedrick and Temeles 1989). Several unrelated groups of birds display reversed sexual dimorphism in size (RSD; females larger than males), suggesting that this condition evolved independently on a number of occasions (Jehl and Murray 1986, Paton et al. 1994). Reversed size dimorphism is a common feature of some avian groups with a raptorial lifestyle, principally the diurnal and nocturnal birds of prey, skuas and jaegers, and frigatebirds. This has led to the belief that the evolution of reversed size dimorphism is linked to the morphology or behavioral ecology of avian predato...

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“…It is not clear if Nothoprocta ornata is a monogamous species with double-clutching (i.e. Moreover, sexual selection may favour bigger females to enhance competitive ability for mates, as it has been proposed for the American jacana (Jacana spinosa; Jenni & Collier, 1972), coucales (subfamily Centropodinae; Andersson, 1994), and raptors (Olsen & Olsen, 1987), and should not be discarded for tinamous, especially because females have an active role in territory defence (Davies, 2002). This evidence suggests that female tinamous may have been selected for their capacity to lay several clutches of eggs in succession, and if this capacity improves with increasing body size, larger females should be expected.…”

Section: Ausal Explanations Of Fssd In Tinamousmentioning

confidence: 99%

“…This evidence suggests that female tinamous may have been selected for their capacity to lay several clutches of eggs in succession, and if this capacity improves with increasing body size, larger females should be expected. Moreover, sexual selection may favour bigger females to enhance competitive ability for mates, as it has been proposed for the American jacana (Jacana spinosa; Jenni & Collier, 1972), coucales (subfamily Centropodinae; Andersson, 1994), and raptors (Olsen & Olsen, 1987), and should not be discarded for tinamous, especially because females have an active role in territory defence (Davies, 2002).…”

Section: Nothocercus Juliusmentioning

confidence: 99%

Female-biased sexual size dimorphism in tinamous: a comparative test fails to support Rensch's rule

Tubaro

Bertelli

2003

Biological Journal of the Linnean Society

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Rensch's rule states that degree of sexual dimorphism increases with body size in species with larger males, and decreases with body size in those with larger females. To test this rule, we assessed the pattern of sexual size dimorphism in tinamous using a comparative analysis of independent contrasts. Tinamous are a monophyletic group of primitive birds comprising at least 47 ground dwelling species with prominent or exclusive paternal care of eggs and offspring. Although the size of females exceeded that of males in most considered species, we found an isometric relationship between males and females, instead of the negative allometric one predicted by Rensch's rule. Previous studies in Strigiformes and Falconiformes found positive allometric and isometric relationships respectively, and, considering these findings with our results, we conclude that Rensch's rule is not supported by birds with exclusively female-biased sexual dimorphism in size.

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Sexual Size Dimorphism in Raptors: Intrasexual Competition in the Larger Sex for a Scarce Breeding Resource, the Smaller Sex

Cited by 28 publications

References 16 publications

Male brood provisioning rates provide evidence for inter‐age competition for mates in female Cooper's Hawks Accipiter cooperii

Male brood provisioning rates provide evidence for inter‐age competition for mates in female Cooper's Hawks Accipiter cooperii

Evolution of Reversed Sexual Size Dimorphism in Skuas and Jaegers

Female-biased sexual size dimorphism in tinamous: a comparative test fails to support Rensch's rule

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