birdsoup

The Brown-headed Cowbird is an appropriately named bird – a black bird with a brown head.  I saw my first cowbird of the year today.  They are early returning migrants and can usually be found in flocks of grackles and starling.  I know they have been in the area for a while but I just hadn’t seen one.  Maybe I just didn’t go birding often enough.

Cowbirds have a terrible reputation and are universally disliked.  The reason behind this loathing is simple:  they are nest parasites.  In practice that means they lay their eggs in the nest of other birds and let those birds raise the cowbird’s kids.  Often they lay eggs in the nest of a tiny birds, such as a warbler.  New-born cowbirds are physically larger than adult warblers.  But the adult warblers have such a strong parental instinct that they feed this hungry, giant baby at the expense of their own smaller, weaker young.  Young cowbirds also destroy warbler eggs or kill the hatchlings.

Cowbird nest predation is one of the major concerns for the continued existence of Kirtlands Warbers, the rarest of all warblers with a total population of only hundreds of individuals.  Scientists found cowbird eggs in more than half of all Kirtland Warbler nests.

 It is somewhat easier to tolerate cowbirds if you understand how they developed their nasty habit.  Cowbirds used to follow the buffalo herds.  As buffalo roamed they flushed a lot of insects, which the cowbirds devoured.  Buffalo herds are constantly on the move.  If the cowbird took a few weeks off to build a nest and raise young, the buffalo would have moved on and might be 50 miles away. 

It was better to stay with their source of food and let someone else raise the kids