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Feb 19, 2012

How many eggs do Cowbirds lay?

Photo by BarrytheBirder
I ran the photo above in a blog, over a month and a half ago, when a male Cowbird showed up at the feeders at the end of January.   It was followed by two females a week later.   I've always pretty much taken migrant Cowbirds for granted but these newest arrivals were so early and have become such regulars, along with the other winter birds, that I have found myself becoming more interested in this species.   I have done some reading about the parasitism for which Cowbirds are famous and have come upon some interesting things, some of which are downright unpleasant.   But the information that surprised me the most was the fact that Cowbirds lay from 36 to 40 eggs in the breeding season.   I guess I had always assumed that Cowbirds just laid a few eggs in the spring and moved on to enjoy the rest of the summer at their leisure.   Now I realize that there is a heck of a lot of effort in producing  40 eggs, one at a time, in 40 different nests.   It certainly seems to indicate that the Cowbird has some intelligence about the challenge it faces in propagating it species, when so many of its eggs are abandoned or destroyed, by unwilling hosts.   It also seems this bird understands that it can be indiscriminate about whose nest it lays its eggs in, because Cowbird eggs have been found in hundreds of bird species nests and young Cowbirds have been seen being fed by hundreds of different kinds of surrogate bird parents.   Quite remarkable, all and all.   In the  smaller  photo one Cowbird egg is seen  with five Eastern Phoebe eggs.  (Egg photo by Galawebdesign/Wilipedia)
Please comment if you wish.


effie kadoglou said...

cowbirds are then quite unloving parents maybe because they can not feed so many babies,is it true so many ? like chickens but all together ?now comes the good season in Canada and many countries ,here too.have a fine spring Barry with your family !!!!

Balisha said...

We just witnessed a cardinal pair taking care of 4 babies at our feeder. I thought that they were baby cardinals, but a reader left a comment that she thought they were cowbirds. We had the same thing happen last year with another bird too. I have a picture on my blog of the male feeding the baby.

Barry Wallace said...

Hi Balisha. As mentioned, cowbirds can lay up to 40 egggs in a season, usually one to a nest. You appear to have had more than one cowbird egg laid in the same nest, a short time apart. Remarkable, and quite plausible, I suppose. Thanks for sharing this. BarrytheBirder