|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|
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.