A large influx of American Robins has occurred in Maine in the past couple of weeks. Some observers report flocks of 75 birds. The arrival of robins is often taken to be a sign of spring but don't be fooled. These robins are almost certainly birds from the north that have been pushed south by lack of food. If you see a bunch of robins, take a close look at them. Some of them will likely have the dark back of the Newfoundland race of American Robins.

Most birds are remarkably tolerant of cold weather as long as they have sufficient food to support their increased metabolic demands in the winter. Common Redpolls can winter as in latitudes as high as 70 degrees North as long as they can find enough seeds. When seed production is low, they are forced to move south and we get to enjoy seeing these delightful sprites. Similarly, American Robins can tough out the winter in the Maritime Provinces and Newfoundland as long as sufficient fruit is available. When the fruit is depleted, the robins have no choice but to move south in search of food.

OWLS

The heavy snowpack, and more importantly, the ice layers in the snow pack pose a huge challenge to our larger owls that depend on rodents and other small mammals for food. A number of birders have observed Barred Owls in the daytime in the past couple of months. Their daytime activity is almost surely a sign of the owls' difficulty in finding food. The scarcity of available food makes it necessary for owls to forage both during the day and night.

At our feeding station in South China, we were treated to the presence of a Northern Saw-whet Owl. It was perching on a feeder pole, no doubt waiting for a vole or shrew to come out of snowpack to feed on some of the seeds that had fallen from the bird feeders.

RECORDS

We certainly haven't lacked for snow across the state this winter. Northern Aroostook County has been hit quite hard. As of this writing, Caribou has had 137 inches of snow this winter, 59 inches above normal, and is on a pace to set a new yearly snowfall record. With records on my mind, I thought a consideration of some bird records might be of interest.

The largest living bird is the Ostrich, a flightless bird that tips the scales at 345 pounds and reaches a height of nine feet. But that pride of place is unwarranted. The heaviest birds we know of were the elephant birds found in Madagascar until they went extinct around 1600. Those birds topped out at 1,000 pounds. Their eggs had a two-gallon capacity and were in fact used as buckets by the Malagasy people. The tallest bird was one of 24 species of flightless moas found in New Zealand. Those were all exterminated by the year 1500. Dinornis means terrible bird, not a very fitting name for a leaf-eater.

How about the largest bird capable of power flight? That record belongs to the Great Bustard, a Eurasian grassland bird. Individuals may weigh as much as 46 pounds. However, the fossil record has even larger birds that we believe could fly under their own power. Four species of vulture-like birds called teratorns are known from North and South America, first appearing about 25 million years ago. The largest, Argentavis magnificens, had a wingspan of 26 feet.

At the other end of the spectrum, the smallest bird is the Bee Hummingbird found in Cuba. An adult weights only 1.6 grams, half the weight of a penny.

Humans are fascinated by speed records. For birds, the fastest speed ever measured was achieved by a Peregrine Falcon. The bird was in a stoop, making its body aerodynamically smooth and thus able to knife through the air with a minimum of friction. That diving bird was clocked at 117 mph.

It is appropriate that the speed record for flapping flight is held by a swift. The White-throated Needle-tailed Swift can achieve a speed of 107 mph. Red-breasted Mergansers are no slouches, though. These birds have been timed at 100 mph in level flight.

The birds that have the heaviest flight muscles relative to their body weight are the hummingbirds. That fact is not surprising because hummingbirds generate lots of power (upward lift and forward thrust) on the upstroke as well as the downstroke.

Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at whwilson@colby.edu Previous columns and other information on Maine birding can be found at his blog: http://www.mainebirds.blogspot.com/

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