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.