Column: A few migrants return despite the wintry world
We’re back from a trip to warm, Caribbean climes. I admit that I leave home with some reluctance as I enjoy the subtle seasonal changes this time of year.
However, we returned to the same wintry world we left other than a few more buckets hanging from sugar maple trees.
The redpoll gang that descends on our feeders most mornings are still here, not yet motivated to head back north.
As for returning migrants, postings to NHBirds, the Internet listserv of notable goings-on in the bird world, report turkey vulture sightings and red-winged blackbirds. Right on schedule.
The most notable report is of an American woodcock in Hampton, and the photos posted to NHBirds suggest a major thaw hit the New Hampshire coast.
This most odd shorebird species feeds on earthworms for the most part, far from any shore. Returning robins trot sodden fields and lawns by day while woodcocks emerge from cover at dusk to work those same areas and also to roost there overnight.
Instead of rapidly trotting shoreland edges as other shorebirds do, woodcocks step slowly on short legs probing for worms with long bills perfectly engineered for the task.
Despite their earthworm diet, woodcock males often return north when there’s lingering snow and frozen ground.
For most migrants, the older, more experienced and therefore dominant males are the first to return. They get to pick prime territories and are a good example of “the early bird that gets the worm.” However, in the case of woodcocks and the literal, not figurative, worm, I’m not so sure the early bird gets many worms . . .
One change that’s noticeable despite persistent snow is the lengthening daylight, and it’s that shifting light level that in large part governs the bird world. “Photoperiod” or “photoperiodism” is the concept: the effect that seasonally increasing or decreasing light has on plants and animals.
Out in the henhouse, we lengthen photoperiod by a light on a timer and “the girls” keep on laying.
For birds, increasing light triggers a hormonal response centered in the pituitary gland. Birdsong is stimulated along with a significant physiological change preliminary to breeding. What atrophies in the off-season as photoperiod decreases, enlarges in spring. Impressively so!
It’s a sophisticated system that ensures that young and ravenously hungry birds hatch when insects are abundant — and earthworms are a lot easier to find. Days are longer, too, providing more daylight for foraging.
Our time away was far to the south, and I began wondering about photoperiod close to the equator when there isn’t much of a seasonal shift in day length. What triggers hormones that in turn enable the biology of breeding?
Pam Hunt at New Hampshire Audubon said, in her usual straight-to-the-point manner, “Good question.” We humans haven’t figured it all out. Often it’s a region’s rainy versus dry season that triggers hormonal changes. Rain brings food, whether it’s insects or nectar followed by fruits and seeds. Different species, depending on their primary food, nest in different stages of food production.
Studies suggest that birds are very sensitive to photoperiod: They don’t need much of a change to detect a shift.
In equatorial rain forests, where rainfall and photoperiod are constant, the trigger is harder to figure out. The solution for some species is an extended nesting season with several broods. With unchanging daylight, temperature and food resources, there’s no need to compress the process into four months.
At our latitude, birds have at least one brood and many species have two. The size of the broods typically is larger, also. Southern latitudes have greater nest predation (lots of snakes!), and smaller broods spread out over time is a smarter strategy than “putting all your eggs in one basket” —literally, again.
As for the woodcock pictured here, photographer and experienced birder Len Medlock captured more than a photo in his posting to NHBirds. Woodcocks feed during the day, but under cover and well camouflaged by their plumage. Sightings are rare.
Here’s Len’s posting:
“JoAnn O’Shaughnessy called me early this evening to watch an American Woodcock in her backyard (I zoomed out of the house, sans wallet and a warm coat, fueled with tremendous excitement. Heck, I even said “Peent!” out loud in the car, repeatedly). I’ve spent nearly 10 years trying just to see them during the day (yup, I’ve stumbled upon them and flushed a few accidentally, and spent countless hours rummaging through brush), but a chance to snap a photo of one still blows my flippin’ mind. Folks, I can barely contain my excitement — indeed, this bird rocks my world so much, more than any other, and it shocks me to the core that I was actually able to see it. Thank you, JoAnn! I’m never washing my eyes again [smiley face].”
Coming soon to a snow-free patch of field near you: the “Peent!” of a displaying American woodcock male in the faded light of dawn and dusk.
Backyard Birder by Francie Von Mertens appears every other week in the Monadnock Ledger-Transcript.