For the Birds Radio Program: Flocking
Do birds of a feather flock together? And why, and why not?
(Recording of Canada Geese)
“Birds of a feather flock together.” That simple adage is true for many birds during migration and winter. Canada Geese are the birds most Americans think of first when they hear the word flock–families of geese join with relatives to form flocks which migrate together. The conspicuous line or ‘V’ that geese make is well known to be energy-efficient–the lead bird cuts into the air like the motor of a boat, and the other birds follow literally in its wake, where air resistance is least. Cranes, cormorants, some shorebirds, and even gulls take advantage of this ‘V’ formation on migration flights, but the call of migrating geese is so haunting that they get most of the attention.
Broad-winged Hawks form spectacular migrating flocks, called kettles, especially at Hawk Ridge, but these birds don’t stay in their flocks except during actual flights. If you’re at the ridge in early morning in September, you can see one or two flying laboriously past. As the sun warms the earth as the morning proceeds, thermals begin developing, and one of the early flyers will eventually discover a nice thermal. Once it start circling, other broad-wings notice it and join, not for the company but for the thermal, which carries them up high enough to allow them to fly without flapping for a long distance before they lose so much altitude that they need to find another thermal. They migrate all the way to Central and South America, which is a long way from north country–this unique method of migration saves them a tremendous amount of energy. But during summer and winter they keep pretty much to themselves.
Chickadees move in flocks throughout the winter, and roost together in tree cavities on the coldest nights. By day the group has an easier time discovering both food supplies and predators, and by night the many birds huddled together stay warmer than solitary birds could. Many other species are known to huddle together for warmth–in England a flock of over 60 Winter Wrens crowded into a tiny nest box every night during a cold snap. Nuthatches, creepers, swallows, and other species do the same–once in a while a bird is crushed or suffocated in so tightly packed a group, but overall there is surprisingly little mortality–and very little evidence of cabin fever.
Oddly enough, it isn’t just in cold climates that birds huddle together at night–several tropical species also huddle together in tree cavities. So there must be other benefits to birds besides warmth.
Flocking often increases certain behaviors–crows attack owls more furiously when other crows join in; chickens eat an average of 53% more grain when set in a pen with three other hungry chickens; and anyone who’s fed gulls at fast food joints knows that their calls quickly attract more gulls, and the closer one gull comes to your hand, the closer others will come until they’re practically sitting on your head. People display flocking behavior, too–in snowstorms it brings out the best, but the rest of the time it’s called ganging up or mob rule.
(Recording of a Ring-billed Gull) This is Laura Erickson, and this program has been “For the Birds.”