Sexual dimorphism (1 Viewer)

Some birds have striking sexual dimorphisms, while others are practically indistinguishable by gender. Is there a clear delineation of the species that do and do not have sexual dimorphism? E.g., do they all happen to fall into the same families? Or are there other characteristics that seem to be associated with the presence or absence of sexual dimorphism?

There are several groups where some species have strong sexual dimorphism and other species have very little (at least as judged by the human eye). Contrast for example Lesser Antillean Bullfinch with Barbados Bullfinch and Greater Antillean Grackle vs its Lesser AG counterpart.

Niels

Black capped chickadees?
White breasted nuthatches are kind of hard to tell....

dbooksta said:

Some birds have striking sexual dimorphisms, while others are practically indistinguishable by gender.

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Humans can't see UV light. Birds can.
Muir D. Eaton (2005). Human vision fails to distinguish widespread sexual dichromatism among sexually “monochromatic” birds. PNAS vol. 102 no. 31

Based solely on human vision there are some basic general rules in sexual dimorphism in birds. Species that a polygamous tend to be more sexually dimorphic than monogamous species. It is generally believed that this mainly is the result of two primary counteracting mechanisms: Getting as many females as possible for the male (colorful plumage an advantage) and sitting on a nest without being taken by a predator (dull plumage an advantage). In polygamous species the male has to get as many females as possible but doesn't help with the upbringing of the young. In monogamous the male stays with one female but helps with the upbringing of the young. Sexual dimorphism is reduced in both monogamous and polygamous species where voice is of greater importance than plumage. These are only guidelines that are useful in most cases but there are plenty of exceptions.
Sexual dimorphism in size typically follows a comparable pattern: In polygamous species the males will often be larger (fighting with other males for females). In monogamous species the female will sometimes be larger (need the energy to produce the eggs). This can be enhanced in species where there is potential prey competition between the sexes. In most eagles, hawks and relatives females are significantly larger than males and also tend to take larger prey.

Related to UV light. It'll be interesting to see how many near-identical species really aren't that similar. It has already been shown that some Empidonax flycatchers and female Sporophila seedeaters have differences in UV
http://onlinelibrary.wiley.com/doi/10.1111/j.1600-048X.2010.05205.x/abstract
http://pubs.er.usgs.gov/publication/70004700

Sexual dichromatism

Huang & Rabosky 2015. Sex-linked genomic variation and its relationship to avian plumage dichromatism and sexual selection. BMC Evol Biol 15: 199. [abstract] [pdf]

Dale et al

Dale, Dey, Delhey, Kempenaers & Valcu (in press). The effects of life history and sexual selection on male and female plumage colouration. Nature. [abstract]

Gilbert (in press). Sexual selection makes female songbirds drab. Nature. [article]

McMaster University, 4 Nov 2015: Female Birds Can’t Shake Their Colorful Fathers, and Other Lessons From Studying 6,000 Species.

Max Planck Society, 4 Nov 2015: Are females glamorous because males are?

See also: Birds & Birding > Are taxonomists sexist?

Richard Klim said:

Dale, Dey, Delhey, Kempenaers & Valcu (in press). The effects of life history and sexual selection on male and female plumage colouration. Nature. [abstract]

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[pdf]
(Probably not supposed to be "visible", as if you enter the research group's domain [through the front door], you are directed to the publisher's website. But Google finds it readily.)

Flight initiation distances

Møller, Samia, Weston, Guay & Blumstein (in press). Flight initiation distances in relation to sexual dichromatism and body size in birds from three continents. Biol J Linn Soc. [abstract] [pdf] [supp info]

Drury & Burroughs

Icteridae > Nest shape & sexual dichromatism.

Angélica Hernández-Palma. Light matters: testing the “Light Environment Hypothesis” under intra- and interspecific contexts. Ecology and Evolution, Early View.

[article]

Isabel López Rull, Leticia Nicolás, Nadia Neri-Vera, Víctor Argáez, Margarita Martínez, Roxana Torres. Assortative mating by multiple skin color traits in a seabird with cryptic sexual dichromatism. Journal of Ornithology, First Online: 23 May 2016.

[abstract]