On a summer night just before sunset on the summit of Mount Mansfield, biologist Nathaniel Sharp and a crew of volunteers are getting ready to try to catch Bicknell鈥檚 thrush.
鈥淚f you even give, like, a poor impression of a whistle, sometimes you鈥檒l get them to come and check you out,鈥� Sharp said, playing a recording of the bird鈥檚 call 鈥� a sharp 鈥淰reet!鈥� that ends on a down note.
If you鈥檝e spent time on a high peak in the Adirondacks or the summit of Mount Mansfield at dawn or dusk, it might sound familiar to you. So too might its song.
鈥淚t鈥檚 just this beautiful 鈥� sort of cascade of whistles and buzzes and flute-y notes,鈥� Sharp said. 鈥淚f we鈥檙e lucky, we鈥檒l hear that going off on the mountain later this evening.鈥�
These dainty looking songbirds that fit in the palm of your hand travel thousands of miles every year to nest and raise their young in some of the most rugged places in New England.
But their populations are declining, and scientists like Sharp are trying to learn more about them in hopes they can reverse the trend.
Tonight, the crew 鈥� led by the Vermont Center for Ecostudies, where Sharp works 鈥� is hoping to find Bicknell鈥檚 thrushes wearing tiny backpacks outfitted with GPS trackers.
To catch the birds, they string up long nets along the maze of hiking trails around Mount Mansfield鈥檚 ridge.
After the sun goes down, they split up to hike around and find out what birds they caught. A chorus of birdsong starts to swell as the sun drops.
鈥淏icknell鈥檚 thrush 鈥� yeah 鈥� there鈥檚 nothing like hearing that up on the mountain,鈥� Sharp said. 鈥淪o hopefully we get lucky and hear some late-singing males tonight.鈥�
It will be a good sign if the scientists do hear them, because these birds appear to be in trouble.
Researcher Chris Rimmer has been studying Bicknell鈥檚 thrush and leading this project for Vermont Center for Ecostudies for about 30 years.
鈥淏icknell鈥檚 thrush [populations] are declining at about 4% per year, which is a pretty steep rate of decline,鈥� he said, taking a break from setting nets.
The songbirds spend their lives flying between two kinds of islands 鈥� they spend summers on tall alpine summits in southern Quebec and New England like Mount Mansfield, and spend winters in the cloud forests of the Dominican Republic.
鈥淲hat I hope is that 50 or 100 years from now, you're going to be able to stand here on Mount Mansfield and still be able to hear the swirling, ethereal song of Bicknell鈥檚,鈥� Rimmer said. 鈥淚s that realistic? I don't know.鈥�
Rimmer says for reasons scientists don鈥檛 yet understand, there are a lot more male birds than females in the adult population. The theory is that the females aren鈥檛 surviving the winters, and that this imbalance is causing their populations to dwindle.
The goal with attaching these tiny backpacks to the birds is to find out where they're overwintering in the Dominican Republic, so the Vermont scientists can work with colleagues in the Caribbean to protect those forests from being cut down.
The scientists are also experimenting with even lighter trackers that could let them learn exactly where birds are spending their time, without having to recapture them to collect the data when they return to New England.
They hope to publish their findings in the coming years.
The thrushes also face some longer-term challenges here in New England.
鈥淭hese montane forests, as we call them, the dominant tree here is the balsam fir, which is right above me here,鈥� Rimmer said, gesturing to a wall of stubby trees along the side of the trail.
Bicknell鈥檚 thrush nest in balsam fir trees, he says, which are very sensitive to hot summer weather. Research has shown that for every degree Celsius of warming New England sees, the trees鈥� range could move up in elevation by about 500 feet.
鈥淭here's already evidence of this, empirical evidence, that the hardwood forests are beginning to encroach upslope,鈥� he said.
This is a concern because mountains here in the Northeast are only so tall. According to Rimmer, would just about eliminate the birds鈥� habitat across the region. And this is the only place in the world where they raise their young.
Back on the trails, the sun is setting. And in the gloaming, a volunteer gently removes a juvenile Bicknell鈥檚 thrush from a net 鈥� the first of the night.
鈥淭his little guy hatched out on the mountain four weeks ago or so,鈥� he says, gently holding the bird鈥檚 feet between his fingers as it flaps its wings and ruffles its feathers. 鈥淲e鈥檒l put a band on it, and then, in early September, it鈥檒l look up one night and decide it鈥檚 time to go down to the Caribbean.鈥�
Right now, the researchers can only hope this little bird survives the test of its first winter. In the meantime, they鈥檙e racing to figure out exactly where it鈥檚 going, so scientists there can protect it.
