different eggs in same nest

found different eggs in this nest. I am a new birder and found this strange.thank you

Savannah Sparrow nest with cowbird eggs

A Savannah Sparrow nest containing multiple Brown-headed Cowbird eggs.

bluebird feeding a cow bird on top of bird house

a bluebird raised a baby cow bird from a egg that had been laid in its nest by a cow bird

Spring time at Sapsucker Woods

I found this beautiful nest while hiking in May 2014 at Sapsucker woods. It looks like a cowbird decided to lay her egg in the bluebird egg nest. (I’m pretty sure these are bluebird eggs.)

Looking out the window

Carolina Wrens built a nest between my storm window and living room window. Unfortunately the solo wren I thought they fledged was a cowbird.

Cornell Lab of Ornithology

Cornell Lab of Ornithology