A Bicknell's thrush. Credit: Courtesy of Bob Duchesne

Most of Maine’s breeding birds are easy to see. Some aren’t. I nominate Bicknell’s thrush as the most difficult to observe.

The quest to locate the elusive bird took me to a mountaintop last weekend, fighting wind and fog, trying to see one.  

I succeeded, barely. One flew by, just as I was steadying myself on a rocky outcropping. In three hours of searching, it was the only one I saw.

But I heard several. They were maddeningly vocal, calling often, rarely singing. Bicknell’s thrushes sing mostly at dawn and dusk, which is annoying. It means your best chance of encountering a singing bird involves hiking a mountain trail, either up or down, in darkness. I’ve done both. I recommend neither. In this instance, I arrived at the summit in midmorning, hoping merely to locate one by its call.

Birds have many vocalizations.

Songs are how we most commonly hear and identify them. It’s the melody they sing to attract mates and repel rivals. Once they’re done raising the brood, most singing stops. They may sing a bit through early July, just to teach the song to their kids. By midsummer, the woods get quiet.

Birds have a repertoire of other characteristic sounds. Many have flight notes and alarm notes, and even some vocalizations used only at night. Most species have call notes, which are used primarily to communicate with others of their own kind.

The Bicknell’s thrush song is beautiful — a melodic series of cascading organ notes. It’s one of the prettiest songs I never heard — not last weekend anyway. However, multiple birds were calling, sometimes quite close. It’s a sharp “WEER,” which is audible at a considerable distance. Loudness is useful in the harsh, high-elevation environment they prefer, where wind is a constant companion.

Bicknell’s thrushes have evolved to succeed in a place where few other species could. Food is scarce, but so is competition. In the end, their specialized habitat requirements may be their demise. As the climate warms, and their mountaintop habitat changes, they’ve got nowhere higher to go. Maine just categorized Bicknell’s thrush as threatened on the endangered species list.

Winter weather on Maine mountaintops is brutal, and summers are short. The vegetation, where it exists, is mostly dense, stunted spruce. It’s impenetrably thick and impossible to bushwhack. The Bicknell’s thrush nesting zone typically begins at around 3,000 feet and extends a thousand feet upslope to where tundra habitat begins. Within this rugged environment, Maine’s breeding populations are small and vulnerable. The more numerous Swainson’s thrushes dominate the forest below this zone.

The range of mountains high enough to support Bicknell’s thrush includes the major peaks of Baxter State Park, the Mahoosuc Range near Bethel, plus several high-elevation mountaintops around Moosehead Lake and the Carrabassett Valley. Access is by hiking trails that cut through the spruces. Or a ski slope. Saddleback Mountain near Rangeley is well-known as a Bicknell’s breeding spot.

Once you’ve hiked up into the breeding zone, it’s still never easy to find Bicknell’s thrushes. They sing from visible perches but call from deep under cover. Like most thrushes, they forage on the ground. They nest deep in the shrubbery. You could be standing right next to one and have no chance to see it.

Worse, Bicknell’s thrush mating habits are unusual and unhelpful.

Most birds compete for mates and defend territories. These thrushes don’t. Both males and females take multiple partners. Singing males overlap with each other without a fight. Males bring food to multiple nests, since they likely have offspring in multiple nests. Females defend a small feeding area for their nestlings, but otherwise don’t quarrel much.

This overtly communal strategy is unique in North America, but it makes sense. Nestlings are apt to be better nourished by adults that cooperate rather than compete for the limited food supply. Besides, in such dense cover, it would be nearly impossible for a male to ensure mate fidelity anyway, so they don’t even try.

This polygamous breeding strategy makes it even tougher on birders. Many other birds will jump into view in reaction to the close-by songs and calls of rivals, but Bicknell’s thrushes have little incentive to challenge each other. There are few predators at elevation, so they don’t pop up and spy for danger much either. There is little for a birder to do except wait them out. That was me last weekend. Three hours on a mountaintop, and all I got was a two-second view of one bird flying away.

I’ll take it.

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.