A Bird in the Bush

My curiosity got the best of me and I contacted, Mitch, a representative of the St Louis Audubon Society, for information on the nest I found in the garden (see post from 13 May). I discovered the nest when a smallish brown bird flew away with frantic calls as I approached the tree. The egg really looked too large for the small bird. I sent photos and a description of the encounter.

Mitch kindly referred me to Dave, a local expert on birds' nests and their eggs.

Dave sent the following information:

The photos are clearly of a Robin''s nest and egg. Based on your description of the smaller brown bird you observed at this nest, I offer the following scenario:
The Robins built the nest and the female laid the first egg. The female will normally lay four eggs total to complete the clutch before she starts incubating them. A Brown Headed Cowbird (the one you saw) tried to lay her egg in the Robin's nest but was driven off before she could lay one. Cowbirds do not build their own nests, but a single female will lay about 20 eggs in other birds' nests and have those birds hatch out and care for their young. Cowbirds like to lay their eggs in nests containing only one to two eggs.Robins are good about fending off Cowbirds. Smaller birds don't fare as well.
Because of the disturbance and with only one egg involved, the Robins apparently abandoned the nest.Because it is early in the nesting season, I'm sure the Robins will re-nest in a new location. They do not reuse their old nest. There are many factors that result in nest failures and Cowbirds are just one of these obstacles.

I hope it was early enough that the Robins did return and finish laying their eggs. I would much rather have resident Robins than Cowbirds. I am waiting for a report from the house next door.