A Bluebird Day

I try to make a point of getting out into the T.A. Forest at least once a week during a prep block to check trail cameras and note any new happenings in the woods. While walking on the Eastern Trail on a recent warm afternoon, I spotted a small flock of eastern bluebirds (Sialia sialis) feeding along the wood line. Bluebirds are insectivores who generally don't show up until insect numbers are sufficient in the springtime. There are always early arrivals and a select few that will actually hang on for the winter here in Southern Maine. I had a small flock hang around my feeder persisting off suet and sunflower seeds last winter.

The flash of blue from the male against the drab early spring landscape is hard to miss and I was excited to see this omen of spring. The timing of the sighting also lined up well with some vocabulary we have been learning in Maine Fish and Wildlife class. Sexual Dimorphism occurs when there is a distinct difference in appearance between male and female members of the same species. Eastern bluebirds are a classic example of a bird exhibiting sexual dimorphism. Mallard ducks, northern cardinals, and wild turkeys are all examples of Maine bird species exhibiting this trait. As with most sexually dimorphic birds, the male eastern bluebird is more brightly colored. It is assumed that this difference in appearance is a result of tens of thousands of years of natural selection. Females selecting for the bluest of males have created the intense coloration seen today. Because females do the choosing, their coloration has not become as intense as the males'.

 A female eastern bluebird perched on a branch above the Eastern Trail

A male eastern bluebird perched on the eastern trail field fence watching for insects along the ground