Friday, January 16, 2004
Biodiversity Corner Great Blue Heron
When and where seen: On December 30, Warren Lyman photographed this Great Blue Heron at the Cranberry Bog. He often sees the bird at the southern outlet from the upper pond (the one closest to Martin Street) where it seems to be finding food in the fast moving water below the outfall.
Appearance: That solitary tall elegant blue-gray bird with an S-shaped neck standing in the water is probably a Great Blue Heron. It is the largest heron in North America. An average adult is around 46 inches from the tip of its long yellow bill to the tip of its tail. It has long legs and a long neck. The wingspan is six feet. The adult has a white crown — so this one at the Cranberry Bog may be a juvenile. It has the darker crown typical of juveniles and its neck lacks the shagginess typical of adults. Also, it is not showing either the black shoulder, or the black plumes that extend beyond the back of the head of the adult.
Range, Habitat and Nesting: Great Blues are found throughout much of North and Central America. Their breeding range extends into southern Canada. They live near lakes, ponds and coastal marshes where they can fish. Their primary food is fish and they seem to take any species they can catch. They also eat frogs, lizards, snakes and aquatic insects. They hunt for food either by slow stealthy stalking or by standing still and waiting for the food to come to them. A. C. Bent describes the more common standing-still method this way: "Standing as still as a graven image in shallow water, where fish are moving about, it waits patiently until one comes within reach, when a swift and unerring stroke of its well-trained bill either kills or secures the fish." Great Blues like to build their large stick nests in colonies, very high in trees, often using trees in swamps or standing water. There may be several nests in the same tree. A typical nesting habitat is the one on Route 110 in Westford near Kimball's. Heron nesting sites are often referred to as "rookeries." You won't find rooks there but occasionally great horned owls will use an abandoned heron nest. There is a recent report (January 2001) of this occurring in the heron rookery at Littlefield Road in Boxborough.
Word for the day: Eurythermal: tolerant of wide temperature ranges. Great Blues are eurythermal.
References: USGS Patuxent Wildlife Research Center, www.mbr-pwrc.usgs.gov; David Allen Sibley, The Sibley Guide to Birds; A. C. Bent's Life Histories of Familiar North American Birds, published in 1937, available on-line — ask Google to find it.
It's not too late for a New Year resolution to write a column, or tell me what you are finding, or send me a photo. It's easier than losing weight and more fun than balancing your checkbook. The only requirements are that the subject exists in the wild and was seen in Carlisle. Send a note to Kay Fairweather at 392 School St, Carlisle MA 01741 or to email@example.com.
© 2004 The Carlisle Mosquito