In the past week, three readers have contacted me with delighted reports of their first red-bellied woodpeckers at their feeders. This southern woodpecker has been expanding into Maine. The species has a stronghold in our state but encountering one is no sure thing.

Red-bellied woodpecker counts are consistent with the pattern of many invading species: two steps forward, one step back. We can see from Christmas bird count records that this species was a rare species on those counts from 1975 until 2003. The number on all of those Maine counts combined vacillated between zero and 10 each year. Then there was a major incursion in the fall of 2004. The total on Christmas bird counts was 64, a spectacular increase. The counts the next three years were lower: 24, 14 and 11. The count in 2009 set a record high with 107 red-bellieds, only to fall to 24 and 46 in 2010 and 2011. Numbers have rebounded since then with 121 sightings in 2012 and 125 in 2014.

We have been expecting this species. Christmas bird counts in Connecticut had 20 to 40 red-bellied woodpeckers until 1985, when 143 were found. Their counts have been increasing since then with slight dips in some years. The 2013 and 2014 counts yielded 1,313 and 1,440 woodpeckers, respectively. Similar population dynamics were found in Massachusetts.

Why are we seeing this northern expansion of red-bellied woodpeckers? This species is common in the southeastern quadrant of the United States, extending as far west as Texas, Oklahoma, Nebraska and South Dakota, and as far north as central Minnesota, Wisconsin, Michigan and western New York state. Red-bellied woodpeckers frequent humid forests, coniferous or deciduous. They adapt well to suburban environments, frequenting suet feeders, but are equally capable of persisting in deep, isolated forests.

The preference of the species for forests may be driving the northern expansion. Although we may bemoan all the real-estate development in the state, the amount of forested land is actually increasing. This increase is largely due to the reversion of former agricultural land to woodlands.

The provision of food at bird feeders and the amelioration of the climate may be facilitating the northern expansion into Maine as well. From Breeding Bird Survey data, we know that red-bellieds are increasing throughout most of their range, particularly at the northern limits of the range. We don’t know why red-bellied woodpeckers are doing so well throughout their range, but increases in population sizes are likely increasing competition, forcing some individuals to migrate northward in search of adequate resources.

I take great pleasure in my occasional encounter with the species in Maine. Hearing one of these woodpeckers takes me back to my childhood in North Carolina, where the distinctive kwirr or churr rolling call and the piercing cha calls were part of the pinewoods symphony. I encourage you to check out the species account at allaboutbirds.com to familiarize yourself with the vocalizations if you don’t know them. Red-bellied woodpeckers are more easily detected by sound rather than by sight. These woodpeckers are noisy creatures and their calls carry well.

With a red forehead, crown and nape, red-bellied woodpeckers are sometimes confused with red-headed woodpeckers. The entire head is red in the red-headed woodpecker.

Because woodpeckers are usually climbing on a vertical surface with their underbelly close to a tree, you might wonder why the red-bellied woodpecker is named for a feature that can’t be easily seen. The explanation stems from the fact that ornithology was once more of a museum science than a field science. Specimens of birds are stuffed and stored on their backs in museum trays. When a museum tray of red-bellied woodpeckers is opened, the reddish cast to the belly feathers is easily seen.

This explanation applies to two other species whose common name is based on hard-to-see field marks: ring-necked duck and yellow-bellied sapsucker.

Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at

whwilson@colby.edu