A flurry of wingbeats caught my peripheral vision as I was lowering
my binoculars from scanning the Bay. The flock settled behind nearby ledges, at
the edge of the moors, an odd place for the Purple Sandpipers that forage at
the tide line. Nevertheless I folded the camera tripod legs and clambered over
the rocks for a look. The birds took off down the coastline in a purposeful but
jumbled group showing nothing like the tactical precision of sandpipers. They
disappeared around the bend toward the grout pile. Besides their bobbing, finchy flight they flashed
remarkable white patches under wings. Kay and I packed off in pursuit.
Snow Buntings were on my short list of winter delights at
Halibut Point. In seven years of exploration I hadn't seen one yet. Sibley's Field Guide to Birds offers the
tantalizing note that they can be "common but irregular" in the northern
states on open ground such as beaches and fields, foraging for seeds. After
hastening along the shoreline we went up toward the grassy areas by the quarry.
Park Supervisor Mark Peterson told us he'd just gotten a picture with his cell
phone of what he was pretty sure were Snow Buntings. They've been scurrying
around the Visitors Center parking lot for a couple of days. I had the classic
twin reactions, "You're kidding!" and "Of course!"
A good look at Snow Buntings shows the tufts of feathers
that help keep their legs warm, similarly to Snowy Owls. Both these species
spend most of the year in tundra latitudes. The Buntings are usually back there
by March, when much of the breeding male's plumage turns white to match its
surroundings. To the extent that feather patterns govern sex appeal, I think we
have the better pleasure with these off-season highlights of cinnamon and
chestnut.
The fact that their migration to the Arctic is entirely
nocturnal has intrigued research biologists to study the Snow Bunting's
navigational systems. We may not know
exactly how, but it's clear they find their way home by orienting to the
geomagnetic energy fields of the earth and to celestial cues in the sky. This summary
of experimental results adds to the curious allure of both nature and science.
Orientation tests were
conducted with snow buntings (Plectrophenax nivalis) exposed to artificially
manipulated magnetic fields, during both spring and autumn migration.
Experiments were run under clear sunset skies and under simulated complete
overcast. The birds closely followed experimental shifts of the magnetic fields
during both seasons regardless of whether they had access to celestial cues.
Clear-sky tests in vertical magnetic fields resulted in a significant bimodal
orientation, the directionality of which was almost identical during spring and
autumn. When the snow buntings were deprived of celestial directional
information and tested in vertical magnetic fields, they failed to show any
statistically significant mean directions in either spring or autumn. The
results demonstrate that snow buntings possess a magnetic compass and suggest
that magnetic cues are of primary importance for their migratory orientation
while on passage through temperate-zone areas. However, the axial orientation
in vertical magnetic fields under clear skies may indicate an involvement of
celestial cues as an auxiliary source of directional information.
R. Sandberg and J. Pettersson, "Magnetic orientation of snow buntings (Plectrophenax
nivalis), a species breeding in the high Arctic: passage migration through
temperate-zone areas," Journal
of Experimental Biology vol. 199 no. 9, 1996.
