About us: We own the Wild Birds Unlimited nature shop in East Lansing, Michigan,
a store that provides a wide variety of supplies to help you enjoy the birdwatching hobby.

This blog was created to answer frequently asked questions & to share nature stories and photographs.
To contribute, email me at bloubird@gmail.com.

Saturday, May 5, 2012

Weird Egg Abnormality: One blue egg & a small pink egg in the same nest

I found a small nest in a pine tree. It has one very small pink egg and a slightly larger blue egg (not a robin). Does anyone know what kind off bird layed these? ~ Illinois
House Finch eating seed cylinder on Wild Birds Unlimited Dinner Bell feeder
There are a lot of birds that lay blue eggs. For example, bluebirds, robins and other thrushes all have blue-colored eggs. House Finches also have blue eggs that are smaller than a robin’s egg and like to nest in pines or hanging wreaths or plants.

Normal House Finch clutch of eggs
Blue eggs develop after the deposit of biliverdin while the eggshell is forming during the last 5 hours before the egg is laid. Biliverdin is a breakdown of hemoglobin and diverting these chemicals for the use in coloring eggs may be costly for females.

If there is a temporary impairment of the reproductive tract, a common abnormality that results is a “runt” egg. These eggs are noticeably smaller and can be a different shape or color too. Runt eggs are not necessarily the first or last egg and occur in clutches across a wide variety of bird species.

There are some studies that find younger birds tend to have runt eggs more often than older birds. These small eggs do not hatch due to some internal abnormality but the other eggs in the clutch should develop just fine.
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