Editing Owl (section)

=== Sexual dimorphism ===
[[File:Owl. Birds - defenders of the forest. USSR stamp. 1979.jpg|thumb|A stamp from the Soviet Union, 1979]]
[[Sexual dimorphism]] is a physical difference between males and females of a species. Female owls are typically larger than the males.<ref name=":0">{{Cite journal|title = Adaptive advantages of reversed sexual size dimorphism in European owls|last = Lundberg|first = Arne|date = May 1986|journal = Ornis Scandinavica|volume = 17|issue = 2|pages = 133–140|doi = 10.2307/3676862|jstor = 3676862}}</ref> The degree of size dimorphism varies across multiple populations and species, and is measured through various traits, such as wing span and body mass.<ref name=":0" />

One theory suggests that selection has led males to be smaller because it allows them to be efficient [[Foraging|foragers]]. The ability to obtain more food is advantageous during breeding season. In some species, female owls stay at their nest with their eggs while it is the responsibility of the male to bring back food to the nest.<ref name=":2">{{Cite journal|url = https://sora.unm.edu/sites/default/files/journals/wilson/p0387-p0406.pdf|title = The evolution of reversed sexual size dimorphism in hawks, falcons and owls: a comparative study|last = Krüger|first = Oliver|date = September 2005|journal = Evolutionary Ecology|volume = 19|issue = 5|pages = 467–486|doi = 10.1007/s10682-005-0293-9|s2cid = 22181702}}</ref> If food is scarce, the male first feeds himself before feeding the female.<ref name=":1">{{Cite journal|url = https://sora.unm.edu/sites/default/files/journals/wilson/p0387-p0406.pdf|title = The evolution of reversed sexual dimorphism in owls: an empirical analysis of possible selective factors|last = Mueller|first = H.C.|date = 1986|journal = The Wilson Bulletin|volume = 19|issue = 5|page = 467|doi = 10.1007/s10682-005-0293-9|s2cid = 22181702}}</ref> Small birds, which are agile, are an important source of food for owls. Male burrowing owls have been observed to have longer wing chords than females, despite being smaller than females.<ref name=":1" /> Furthermore, owls have been observed to be roughly the same size as their prey.<ref name=":1" /> This has also been observed in other predatory birds,<ref name=":2" /> which suggests that owls with smaller bodies and long wing chords have been selected for because of the increased agility and speed that allows them to catch their prey.{{citation needed|date=July 2019}}

Another popular theory suggests that females have not been selected to be smaller like male owls because of their sexual roles. In many species, female owls may not leave the nest. Therefore, females may have a larger mass to allow them to go for a longer period of time without starving. For example, one hypothesized sexual role is that larger females are more capable of dismembering prey and feeding it to their young, hence female owls are larger than their male counterparts.<ref name=":0" />

A different theory suggests that the size difference between male and females is due to sexual selection: since large females can choose their mate and may violently reject a male's sexual advances, smaller male owls that have the ability to escape unreceptive females are more likely to have been selected.<ref name=":1" />

If the character is stable, there can be different optimums for both sexes. Selection operates on both sexes at the same time; therefore it is necessary to explain not only why one of the sexes is relatively bigger, but also why the other sex is smaller.<ref>Székely T, Freckleton R. P., Reynolds J. D. (2004) Sexual selection explains Rensch's rule of size dimorphism in shorebirds. ''PNAS'', '''101''', N. 33, p. 12224–12227.</ref> If owls are still evolving toward smaller bodies and longer wing chords, according to V. Geodakyan's Evolutionary Theory of Sex, males should be more advanced on these characters. Males are viewed as an evolutionary vanguard of a population, and sexual dimorphism on the character, as an evolutionary "distance" between the sexes.  "Phylogenetic rule of sexual dimorphism" states that if there exists a sexual dimorphism on any character, then the evolution of this trait goes from the female form toward the male one.<ref>Geodakyan V. A. (1985) Sexual dimorphism. In: Evolution and morphogenesis. (Mlikovsky J., Novak V. J. A., eds.), Academia, Praha, p. 467–477.</ref>