Studying variation in bird eggs

House sparrow eggs(Enlarge) ©Janet Allen
House sparrow eggs…and one cowbird egg!

The Cornell Lab of Ornithology is studying the variation in eggshell patterns and color by examining house sparrow eggs, which are quite varied. The researchers note that eggshell coloration and pattern may vary with available calcium, sunlight patterns, or habitat quality, and are expected to differ seasonally and geographically as well.

House sparrows aren't native to this continent and are a detriment to our native species. They (and European starlings) are not legally protected as are our native birds, so they provide a good opportunity to study variations in eggs without harming native birds.

The Lab asked people to send in photos of the eggs on white paper, noting the date and place, including a coin in the photo for size comparison. Since we routinely remove house sparrow eggs from our nest boxes anyway, this was a good opportunity to make the best of a bad situation.

After sending in the photo, I was contacted by Cornell. They noticed that the egg in the middle of the top row was actually a cowbird egg!

Eggs in the nest ©Janet AllenEggs in the nest

Here's what the eggs looked like when they were in the nest.

The whole nest ©Janet AllenThe whole nest

Here's the whole nest after we removed it from the nest box.

Although we don't enjoy disturbing any bird's nest, we believe we have an ethical responsibility to help native birds by decreasing the house sparrow population.