1972/07/01 by Richard T. Reynolds · 3 citations
Environmental Science · #Avian ecology and behavior #Wildlife Ecology and Conservation #Ecology and Vegetation Dynamics Studies
paper · doi:10.2307/1366283
For several decades the question of the adaptaccipiter hawks, the male actually broods the ive significance of reversed sexual dimorphism young at the nest (Brown and Amadon 1968; (male smaller than female) in the Orders Fal-Liversedge 1962).In response to Cade' s arconiformes and Strigiformes has received congument, I believe the apparent dominance of siderable attention.Numerous theories rethe female is a consequence of, and not the lating to this problem have been proposed (for cause of, sexual dimorphism.In the genus review see Amadon 1959; Cade 1960; Selander Accipiter, where reversed size dimorphism 1966), yet the issue remains unresolved.A reaches an extreme, the female could easily significant point stressed by proponents of overpower and kill the male.The apparent several of these theories is that reversed sexual subordination of the male, then, has probably dimorphism is directly correlated with an evolved concomitantly with the development active predatory existence.This supposition of dimorphism, as a means of maintaining the is based on the observed increase in di-stability of the pair bond.I also question the morphism from vulturine species, through the necessity of female dominance (due to her intermediate mammalian and insect-feeding relatively larger size) in maintaining the male predators, to the extreme found in the highly in his hunting role.In some species, e.g., the active bird-capturing hawks (e.g., certain ac-Sparrow Hawk (F&o sparverius) and the cipiters and falcons ) .Red-tailed Hawk ( Buteo jamaicensis ), the Most of the theories offered in explanation male does most of the foraging during incuof reversed sexual dimorphism can be cate-bation and brooding even though there is little gorized into two groups : ( 1) those which pro-difference in size between the male and female pose that the condition arose as an adaptation (Willoughby and Cade 1964; Austing 1964).reducing intraspecific competition by creating Selander (1966) and others (see above) differential feeding habits of the sexes (Briill have argued that sexual dimorphism has 1937; Hagen 1942; Dementiev 1951; Storer evolved as an adaptation enabling each sex to 1955,1966; Selander 1966) ; and (2) those that exploit different prey species.This would cite the need of female dominance to prevent have selective advantage in that it would dethe occurrence of filicidal behavior by the male crease intraspecific competition thereby allow-(Hagen 1942; Amadon 1959).Another aspect ing denser populations and wider distributions of female dominance, proposed by Cade of the predators.That size dimorphism gives ( 1960), and presently accepted by Brown and rise to differential prey selection is evidenced Amadon ( 1968)) is that dimorphism arose in by Storer' s (1966) work with the three North response to the need of female dominance of American accipiters; Hoglund' s (1946) study the male in order to maintain him in his role of the Swedish Goshawk ( Accipiter gent&) ; as food provider during incubation and raising and Earhart and Johnson' s (1970) work with of the young."A reproductively successful the North American owls.I agree with the pair bond can result only when the female hypothesis inasmuch as there is an advantage falcon is clearly dominant to the male, and to the predator through differential niche utilithe male makes a biologically adequate adjust-zation; however, it reveals nothing as to the ment to his subordinate role in the pairing situ-origin or cause of reversed dimorphism (alation.If this interpretation is correct, then the though Selander suggests that the reversed difference in food habits of the sexes must be condition might be explicable in terms of the considered an obligatory result of their differ-advantages of female dominance).ence in size and not the evolutionary cause of Dementiev ( 1951), Earhart and Johnson size dimorphism" ( Cade 1960).(1970), and Storer (1966) briefly consider the There is, however, no evidence, except per-important point that the agility of a predator haps with the Burrowing Owl, Speotyto cuni-must at least match that of the prey, and that cd&a (see Earhart and Johnson 1970), that the physical adaptations which produce this the male, given the opportunity, would kill and agility-body weight and wing area-are held eat the young.Indeed, in several species of within progressively stricter bounds as the I1911