Myrtle or Audubon's feeding cow-bird

[Thomas Boysen]

Thought this might be of interest. The poor "mom" was constantly on the move bringing insects for the "little" one.

Captured on Gabriola Island, BC 2 weeks ago on a rocky beach. The throat is mainly white but seems to have a slight yellow tinge on the edge so I can't decie whether it's an Audubon's or a Myrtle Warbler. Maybe someone can help.

Thomas

[John Chardine]

Thanks for posting Thomas. I'll leave it to someone else to comment on the warbler- I am currently away from my resource material and have never seen an Audubon's before.

It is an evolutionary "arms race" between hosts and brood parasites like cowbirds and the European Cuckoo, and some species of hosts have come farther than others. Some reject the cowbird egg outright and just abandon or build a nest floor over top of the egg, including their own. Others ignore and end up feeding a fat parasitic chick like this one. One wonders why evolution had not produced rejectors across the board but it hasn't. In this case the warbler is just performing the rule of thumb- if a bird is food begging to you, feed it (it doesn't matter what it looks like, just feed it). Most of the time this rule works perfectly- the warbler ends up feeding its own chicks. Occasionally the rule fails (as here) bit in evolutionary terms (at least for rejectors) it does not appear to be worth the trouble to develop a system of discrimination.

BTW, the pinnacle of brood parasites has to be the European Cuckoo. The cowbird is an amateur compared to this professional.

[Chris Sloan]

It's an Audubon's - you can see the yellow throat.