Bird watchers excited about arrival of spring

Spring in Maine may be dolefully known as “mud season,” but to birdwatchers it is one of the most exciting seasons. At first, each week brings another few returning migrants back to us.

As the season progresses, the trickle turns to a flood, and every day migrants are pouring back into the region. Most will settle here, but some will continue ever northward, completing a marathon journey none of us can imagine.

Many people keep lists of when each migrant is spotted every year. It is intriguing and enjoyable to note how close the return dates are compared to previous years, as well as to track unusually early appearances or vagrants who’ve flown off course.

One interesting report concerned a pine warbler spotted in Knox County last week. At first I was very surprised, because most warblers don’t begin to arrive until May. Most winter in Central and South America. A few warblers also extend their winter ranges into the southern United States. Diet dictates this seasonal location; most warblers are insectivorous and would not be able to survive here in the winter.

Hardier birds, such as the yellow-rumped warbler, will switch over to a winter diet of fruit. In particular, this warbler is able to digest the hard waxy coating of bayberries.

The pine warbler does the yellow-rumped one better: It also regularly eats seeds, and will visit backyard feeding stations during the winter, consuming suet as well. Its winter range is almost entirely confined to the southeastern United States, and they’ve been reported to winter as far north as Maryland, sometimes farther.

Reading this, I realized that it isn’t so unusual for this bird to be seen here in Maine at this time. Besides the yellow-rumped, it is the earliest warbler to arrive in spring and the latest to leave in autumn. However, arrival dates for this bird usually range mid-to-late April, so the individual spotted in Knox County is a month early.

As its name suggests, the pine warbler breeds primarily in pine-dominated or mixed-pine and hardwood forests. During migration, though, it can be seen anywhere, and at this time they are easily spotted as they perch at the tops of still scantily clad deciduous trees. Even unseen, they can be identified by their song, which is sometimes a lazy, slightly slurred, musical trill. It is easy for me to connect this sound with the image of sun-washed pine boughs swaying gently in the breeze.

In appearance, pine warblers are not as flashy as most warblers. They are olive-green above with gray wings and a pale yellow wash extending from their throats down to their bellies, which are white, as are their undertail feathers. Faint olive streaks are visible along their sides and flanks, and they have two white wing-bars. Their faces sport bright yellow “spectacles,” and dark olive-yellow check patches.

As is the case with other warblers, the male’s coloration is brighter and more contrasting than the female’s, but in pine warblers the difference is slight. I look forward to seeing and hearing my first pine warbler of the season, as I do other birds. I wonder who will show up next.

Chris Corio, a volunteer at Fields Pond Audubon Center in Holden, can be reached at fieldspond@juno.com