Song Sparrow nest with Brown-headed Cowbird nestling

I followed a Song Sparrow adult to its nest and discovered four nestlings. One was twice the size of the other nestlings, so I figured it must be a Brown-headed Cowbird.

Chipping sparrow nest containing a cowbird egg

This nest, located about 7 ft from the ground in an Alberta spruce adjacent to my home, contained 4 chipping sparrow eggs and one cowbird egg.