Foreign Bird Call

Thrushes are our most accomplished singers around here. Their songs are complex, variable, extremely melodic, and endlessly fascinating. The three thrushes we have, in decreasing order of song beauty are the wood thrush, Louisiana water thrush, and the good ol’ American robin. Thrushes are also migrating birds, so we eagerly await their calls each spring and joyfully exclaim our first hearing. 

For years, we’ve thrilled to listen to our best thrush caller—the wood thrush—coming from various places off in the woods. They are the first to call just before dawn and again the last to call after sunset. Their song is a three-part symphony, always repeated in the same order: (1) two low stutter tones, (2) followed by three flute-like liquid notes in varying order, and (3) capped off by a high-frequency trill or tremolo. The third part comes in at least half a dozen varieties, and the bird delightfully mixes them up. I can listen to a wood thrush call out 20-30 times and he never exactly repeats his song.

This year was different, however. There seemed to be only one thrush out there in the woods, and his song was not the same as in the past. Most of the time this guy left off the first and third movements—curtailing it to singing the middle three notes. At other times he’d just sing the final trill. I don’t think it was the same bird we’ve had on the past… moreover, it was only one bird calling from out in the woods during the season. Where were the other thrushes this year? Was this a new guy—either from another territory (with another accent) or maybe a juvenile just learning the song?

Ornithologists know that America’s wood thrush population is alarmingly declining. They breed in the eastern United States and winter in Central America. In both regions, their habitat is disappearing, as forests (its only home) are cut for agriculture and other commercial uses. We feel very fortunate to have had a viable population of wood thrushes around here, these last several years. But maybe they’re dwindling and we’re hearing the last of them now? This year’s lone caller was unsettling. It’s just a matter of time before we will no longer be thrilled by their wonderful song.

I wonder if this year’s single thrush’s different song is because he’s not one of our local birds, but one who has moved in from someplace else. Birds develop regional accents in their calls—especially if they tend to hang around the same location. They learn the local dialect and stick with it. But if a juvenile doesn’t get exposed to its species’ normal song, it’ll develop its own distinctive—and very much simpler—song.

So this lone caller could be a lonely juvenile who did not have mentors around to teach him. Or he could be from another region, and has moved into our territory—either because his native habitat has disappeared, or even that climate warming has driven him a little north this year. (Maybe that’s a Georgia accent I’m hearing?)

We also had fewer Louisiana water thrushes calling out this year, and the calls we did hear were also a little different from the past. So I wonder if we may be experiencing the same thing with both kinds of thrushes: a decrease in population and a subsequent change in calls. I hope not.

When the number of birds declines in an area, the lesser-skilled or less aggressive males begin to predominate for a while. In a normal situation, the best singers prevail, causing the poorer singers to slink off and lose their chance to mate. In any given year, most of the birds who could mate, do not do so, because they get shoved to the margins. But as the population drops off, the less talented (and maybe less fit and healthy) birds get their chance. Maybe that’s what’s going on here?

I can only guess how lonely it must feel to a bird, as the population declines and they find mates increasingly scarce. At first, maybe the less fit birds would flourish, because they have a chance to claim territory they’d otherwise be pushed out of. But as time goes by and the population further decreases, even those who persevere can’t find mates. What’s it like, for those last few birds, as they search in vain? How does the last bird feel? Does he or she sense something wrong?

After a few weeks of the strange-calling wood thrush singing out with his truncated song, we no longer heard him at all. Did he fail to attract a mate? Did the local females reject his call as being just too foreign? Did he move on to yet newer territory, seeking better luck? Later, we heard a few hesitant wood thrush calls far off… too far off to discern which bird it might be.

I pray that this year was just a weird experience, and we may once again hear that old, thrilling call next spring. At some point, however, we (or our survivors) will hear the last thrush call. The termination of a natural phenomenon that’s continued for hundreds of thousands or even millions of years is very sad.