Vol. 11 Issue 4, Winter 2006
By Bonnie Eaton
Down through the ages, in cultures around the world, to see a flock of birds was an omen, good or bad, depending upon the species, their color, and in which direction they were flying. Probably knowing this instinctively (as women do), after a highly successful year in 2000, the Dixie Chicks celebrated by each getting a foot tattooed with a flock of birds.
A gathering of birds has sometimes made us nervous — take the playground scene in Hitchcock’s “The Birds.” The great thing about that movie was the phenomenon — based on a short story by Daphne DuMaurier and a true account of birds lost in the fog in Santa Cruz, California — was never explained. In reality, a bird will only attack when it feels its nest is threatened.
Migratory birds do offer some challenges to man in terms of disease. They have been identified as hosts for the mosquitoes that spread West Nile Virus, and last October, officials in Manipur, India were concerned about winter migrating birds flocking to their city. Could this event elevate the possibility of Bird Flu infiltrating their community? So far, Manipur remains free of the epidemic, but with tensions high, they are watchful.
Then consider the plight of Terra Haute, Indiana, where officials are now considering poisoning large numbers of crows early next year. It seems the birds have become a nuisance. Crows have been leaving the rural areas during the harsh winters because of a scarcity of food and gathering in huge numbers to scavenge the garbage-littered urban landscape.
A half-eaten Burger King sandwich looks pretty good when you’re starving. Exactly how they plan to poison the crows and not the other birds, or animals or humans, hasn’t been fully determined, although they claim the pellets will be too large for other birds to consume. According to the local paper, The Tribune-Star, officials would be “monitoring the baiting sites.” Tricky business.
The truth is birds are lovely — lovely to watch and lovely to have as friends. They feed our imaginations in wondrous ways. Swiss psychologist Carl Jung (1875-1961) said that birds represent our thoughts and that birds in flight symbolize changing thoughts. Birds are generally associated with freedom and abandon. How many times have you run outside to see that flock of Canada Geese flying overhead, honking and carrying on, and said to yourself, “Wow, where’s the party?” OK, maybe it’s just me.
Birds of a Feather
Flocking is a behavior that birds have developed for many reasons. For one thing, the winter landscape, especially covered in a thick layer of snow, offers little protection against predators. The trees have dropped their leaves, woodlands become barren, leaving fewer places to hide. By forming a solid visual mass with multiple targets, flocking birds may confuse predators making it more difficult for them to hunt. While it does not completely safeguard each bird, this behavior does offer reasonable protection with birds cooperatively taking turns inside the mass, much like the behavior of swirling fish in the ocean.
Another great benefit to flocking is the ability to spot and communicate food locations. For instance, robins feed primarily on berries in the winter. These foods are abundant where they occur but can be difficult to locate. A large group of birds stands a better chance of finding a food source. While there is some competition in winter between species, many wintering birds forage in mixed-species flocks. Different finch species often associate with other birds, as do sparrows, chickadees, nuthatches, and titmice.
Of course, the downside of this growing community is that competition for food, along with hiding and roosting places, becomes fierce. It often results in loud bickering and aggression. Watch the birds at your feeder as the winter unfolds.
The intensity of aggression varies from species to species, and size does matter, but it usually involves chasing, pecking, and threat displays (horizontal posturing, raised wings and fanned tail). Supplanting is a dance that birds do based on submissive/dominant personalities and traits. It is the end result of learned behavior where one just simply agrees to throw in the towel based on the odds. The minute another more dominant bird arrives, the submissive one at the feeder flies off. Life is good if you’re king of the hill.
Being adaptable is important to survival in the wild. Insect-eating chickadees, titmice and nuthatches are able to change their diet in cold weather to take advantage of seed sources at a feeder. Some birds, like Blue Jays, are omnivorous. Vegetable matter makes up about 75 percent of their diet, although that percentage is higher in the winter. They will eat acorns, beechnuts, many kinds of seeds, grains, berries, and small fruit. Blue Jays are not picky, finding nourishment from almost anything, from roadkill to dumpster trash.
Many birds literally store it up for the winter during the late-summer/early-autumn period. Cache birds include chickadees, jays, titmice and nuthatches. Keep an eye out for the bird at your feeder that flies off with food in its beak. Chickadees may store seeds in several hundred cache sites each day within their permanent winter home range.
Robins migrate only as far south as they need to, or are forced to by bad weather or food shortages. During ice storms, when berries and fruit are covered in a thick coating of ice, many robins flock together and move south. If robins stay for the winter, they stick to the woods and thickets where they can find food. With the onset of warm weather, they seem to reappear out of nowhere on our lawns eating their favorite foods including earthworms, grubs, caterpillars, and other insects.
Native songbirds that are residents of Loudoun during winter include the Tufted Titmouse, Blue Jay, Northern Cardinal, White-breasted Nuthatch, Dark-eyed Junco, White-crowned Sparrow, White-throated Sparrow, Carolina Chickadee, and Eastern Bluebird.
‘Let’s Spend the Night Together’
The nights are cold in winter and conserving energy is of paramount importance. As the outside temperature decreases, birds first fluff their feathers, then, as the temperature continues to plummet, they withdraw their feet and tuck their heads under their back feathers. Many species of birds have hidden fat reserves which warm their bodies. Shivering increases their metabolic rate.
House Sparrows are able to withstand a temperature of minus 13 degrees Fahrenheit. Chickadees and titmice, which do not have a lot of extra body fat, rely on a method of induced hypothermia which would be highly dangerous in humans. They reduce their nightly metabolic energy loss by decreasing their body temperature 17 – 21 degrees below their daytime temperature of 107 degrees Fahrenheit. This represents an energy savings of about 23 percent per hour. As the nighttime temperature continues to drop, these birds do not enter a deeper hypothermia but maintain their hypothermic temperature at around 80 – 90 degrees Fahrenheit by shivering.
Hole-nesting birds such as titmice, woodpeckers, nuthatches, and chickadees tend to roost alone in cavities or in nest boxes, although chickadees will also roost under eaves or in clumps of dead oaks. Many wintering birds roost together for warmth. House Sparrows share their body heat at night under eaves or in vines around buildings. Eastern Bluebirds and some nuthatches conserve heat by huddling tightly. Crows, starlings, robins, and finches choose sheltered habitats such as dense deciduous trees or conifer stands. Studies have shown that these sites offer a slightly slower rate of nighttime cooling.
What is really interesting, though, is that some species, such as starlings and blackbirds, show no evolutionary adaptation to surviving the cold winter months at all. Instead, they depend upon the benefits of roosting in a large flock, sometimes as many as several thousand birds.
We Have Lift Off
In the warmer months, many birds defend themselves in pairs against the world. After the breeding season, birds form flocks while feeding or roosting. Birds that migrate will be gearing up for the long journey ahead. Timing of migration is a mix of internal stimuli which results in a feeding binge to put on fat. Once the flock is gathered, the feeding continues while the birds wait for suitable weather conditions. So while the birds’ internal clocks may be releasing all the appropriate hormonal triggers, the availability of food and the presiding weather conditions (they need a good tail wind) decide when the migration starts.
Little is known about how birds navigate. Some scientists are exploring the use of cell phone technology to track their behavior. Experiments show that most migratory birds have a built-in sense of direction and know innately which direction they need to travel. Some birds appear to use landmarks, and obviously at a height of several thousand feet they can see a considerable distance. In one study, young crows born and raised in Alberta, Canada, and then kept caged until after all the population had flown south and the first snows had fallen, flew straight to Oklahoma where the rest of their flock was.
Birds seem to have discovered the great aerodynamic advantage in flocking together for migration. Take for instance the perfectly executed V formation of migrating geese. As each bird flaps its wings, it creates an uplift for the bird immediately following.
By flying in V formation, the whole flock adds at least 71 percent greater flying range than if each bird flew on its own. When a goose falls out of formation, it feels the drag and resistance of trying to go it alone and quickly gets back into formation to take advantage of the lift resulting from the group. When the head goose gets tired it rotates back in the wing, and another goose flies point.
Some migrating birds fly longer distances, some shorter. For geographical reasons — mountains, coasts and rivers — many migrating birds travel certain general flyways or routes. In the United States, there are four main flyways: the Atlantic, Mississippi, Central and Pacific flyways.
Birds of prey, swallows and crows migrate by day. Thrushes, warblers, cuckoos and woodpeckers migrate by night. Wildfowl migrate both day and night. Most songbirds migrate at night.
Thus, flocking is a behavior with many benefits for birds. And when you think about it, we aren’t so very different ourselves. We practice the old adage that there is strength in numbers. We frequently fly south for the winter. We have even been known to ask around, “Hey, where’s the best steak in town?” And when we get there, we are handed a vibrating device, told to take a seat by the drafty entrance, and huddle together for warmth.