It’s Sunday, which means we get another batch of themed bird photos from John Avise. John’s narrative and IDs are indented, and you can click on the photos to enlarge them.
Brood Parasitism (also known as “egg dumping”)
This is a phenomenon in which a female lays one or more of her eggs in the nest of another bird, leaving the duties of incubation and hatchling rearing to the duped foster parents. Brood parasitism can be intraspecific (when the brood parasite and the host belong to the same species) or interspecific (when the brood parasite and the host belong to different species). Brood parasitism may also be facultative (when the brood parasite dumps her eggs only occasionally) or obligatory (when the brood parasite always employs this lifestyle). Here in Southern California we have two obligate interspecific brood parasites: the Pin-tailed Whydah (Vidua macroura) and the Brown-headed Cowbird (Molothrus ater), neither of which apparently ever rear their own young.
The Whydah is native to sub-Saharan Africa where it uses Estrildid finches as its parasitized hosts. In Southern California, the introduced Whydah uses another introduced species, the Scaly-breasted Munia (Lonchura punctulata) as its primary host. This Munia is an Estrildid finch that was introduced to California from its native home in Southeast Asia.
The Brown-headed Cowbird is native to North America where it parasitizes a wide range of native host species, sometimes so severely that it can seriously impair normal reproduction by its host. Indeed, brood parasitism by the cowbird can be so detrimental to the nesting success of other native species (including some endangered ones) that wildlife managers here in Orange County sometimes set out special traps to try to capture and eradicate the nest-parasitic cowbirds.
This week’s post shows these two obligate brood parasites and some of their commonly employed host species. All photos were taken in Southern California.
Pin-tailed Whydah adult male:
Pin-tailed Whydah female:
Pin-tailed Whydah juvenile:
Scaly-breasted Munia adult:
Another Scaly-breasted Munia:
Scaly-breasted Munia juvenile:
Brown-headed Cowbird male:
Brown-headed Cowbird female:
Brown-headed Cowbird juvenile:
Common Yellowthroat (Geothlypis trichas) male (this species is a commonly parasitized host for the Brown-headed Cowbird):
Common Yellowthroat female:
Bell’s Vireo (Vireo bellii) (this endangered species is another commonly parasitized host for the Brown-headed Cowbird):
Another Bell’s Vireo:
Seems unfair to punish the cowbird for going about its naturally evolved business. Maybe if there weren’t 8 billion humans and all our trash, tractors, cars, chainsaws, bulldozers, pesticides, and invasive species, the other birds wouldn’t be too stressed to cope. I’d gladly trade 7 billion of those people for more birds…But my misanthropy aside, I still find it fascinating that the imprinting instinct is not strong in brood parasites and that they still recognize their own species when mating time comes around.
In the East, the real promoter of cowbird range spread is the cattle industry. Cowbirds evolved around bison, feeding on the insects that they stirred up as they moved and fed, and that were attracted to their dung. Cattle became a satisfactory substitute, when the bison were wiped out,and cowbirds expanded their range to the east, taking advantage of cattle herds in cleared land there.
Diminution of forested area in the East also promotes cowbird parasitism of other species’ nests. They don’t like to go too deeply into forested areas, but will parasitize nests near the verges. And with the jigsaw nature of forest cover these days, woodlands seem to be all edge – there aren’t so many extensive woodlands to serve as refuges for the parasitized species.
ETA – great pictures, Dr. Avise
The adult male Pin-tailed Whydah is quite a looker—I live in California and had no idea it existed here. Perhaps it’s more common in southern CA? Anyway, superb pictures as usual!
Wonderful post… thanks!
Another great themed set of photos, John! For anyone interested in brood parasitism I’d strongly recommend Nick Davies excellent book “Cuckoo: Cheating by Nature”.