Today’s Sunday, ergo we have a themed bird post from biologist John Avise. John’s notes and IDs are indented, and you can enlarge his photos by clicking on them.
Avian Sexual Dichromatism
Sexual dichromatism is a difference in plumage coloration between males and females, typically due to sexual selection via male-male competition and/or female preferences during mate choice. Many bird species are sexually dichromatic. Ducks (including Jerry’s beloved Mallards) offer great cases-in-point. In most ducks, breeding drakes are brightly colored whereas hens are dull brown and well camouflaged. But many other kinds of birds are sexually dichromatic too. This week’s post highlights several species in the taxonomic order Passeriformes in which males are much brighter than females. I took these pictures near my home in Southern California.
House Finch (Carpodacus mexicanus) male:
House Finch female:
Blue Grosbeak (Guiraca caerulea) male:
Blue Grosbeak female:
Red-winged Blackbird (Agelaius phoeniceus) male:
Red-winged Blackbird female:
Vermillion Flycatcher (Pyrocephalus rubinus) male:
Vermillion Flycatcher female:
Western Bluebird (Sialia mexicana) male:
Western Bluebird female:
Western Tanager (Piranga ludoviciana) male:
Western Tanager female:
Hooded Oriole (Icterus cucullatus) male:
Hooded Oriole female:
Lesser Goldfinch (Carduelis psaltria) male:
Lesser Goldfinch female:
Lazuli Bunting (Passerina amoena) male and female:
House Sparrow (Passer domesticus) male and female:
I learned not long ago that male house finches can vary in color from yellow to red depending on their diets, although I’ve never seen a yellow one in person.
“My” second brood (from nests in the hanging baskets under my deck) will fledge in another week or two.
Wonderful photography, John!
Question for John: I notice that you included Lesser Goldfinches in your photos. We have lots of these here at our feeders seasonally from late winter to late spring, and from mid fall to early winter. The males seem to be seasonally dichromatic, whereas the females remain the same. When they first arrive in the late winter, they all look the same, but as the days get warmer and longer, the males begin to show breeding plumage.
What, in your opinion is the evolutionary purpose of seasonal dichromatism, vs. males remaining the same color all the time? American Goldfinches don’t seem to change the way Lesser Goldfinches do, although we don’t get all that many of those here, so it would be hard to tell from just my location.
Thanks,
L
In my experience, American Goldfinch males are seasonally dichromatic too. I presume that for these and other seasonally dichromatic species, it behooves a male to brighten during the breeding season to attract mates, but then to return to a duller plumage during the non-breeding season to be less conspicuyous to predators. Also, manipulative experiments with several dichromatic species have enabled scientists in specific instances to test whether a male’s bright colors are uesful in male-male competition or in female choice. For example, when the shoulders of Red-winged Blackbird males were artificially painted black, those males lost much of their ability to defend their breeding territory against non-painted males. In other words, without bright shoulders their status became lower in the male “pecking order”.