Cape Breton's Magazine

> Issue 17 > Page 42 - Great Blue Heron

Page 42 - Great Blue Heron

Published by Ronald Caplan on 1977/8/1 (478 reads)

such as shrews, meadow mice, and young rats, all of which I have found in its stomach. Aquatic insects are equally welcome to it, and it is an expert fly? catcher, striking at moths, butterflies, and libellulae, whether on wing or when it alighted. It destroys a great number of young marsh-hens, rails, and other birds;but I never saw one catch a fiddler or a crab (other observers have added crustaceans to the heron's considerable food list);and the only seeds that I have found in its stomach were those of the great water lily of the Southern States. It always strikes its prey through the the body, and as near the head as possi? ble." Recent observers do not agree with this method of killing. Meyerriecks:"The prey is usually taken in scissors fashion; that is, it is grasped between the mandi? bles." If it is too large to swallow it is usually considerably battered. Lowe: "Normally bodies are dipped in water be? fore swallowing." Pratt on the development of the chick: "Preening of the natal down was seen as early as six days. During the first two weeks of life, the chicks were unable to stand on their feet....At 14 days they could stagger to their feet and by 21 days they could walk firmly across the nest. Nestlings left alone between the ages of 21 and 28 days were seen to threaten egrets flying over...(and) continued to defend the nest until abandoning it.... Nestlings at {'?? weeks) frequently stood on the edge of the nest repeatedly flap? ping their wings. Starting at about age 7 weeks, nestlings took short jump flights of 6-10 ft from the nest to adja? cent branches and back again....At the age of 60 days some of the young took sustained flights around the heronry or out toward the lagoon. Others were ap? parently as late as 69 days at the age of first long flight. They typically re? turned to the nest for two or three weeks after the first long flight and continued to be fed by the adults. Nestlings as old as 11 weeks were seen being fed at the nest. Adult herons were seen standing on two nests soon after the fledglings had left, suggesting that, on some nests at least, the adults continued to arrive for feeding until they found it empty. Nestings abandoned the nest between the ages of 64 and- 91 days...." The heron has few natu? ral enemies and if he survives 6 months, Oliver L. Austin estimates adult mortal? ity at only 30 per cent a year. However, "banding figures show first-year mortal? ity averages 70 per cent." Lowe remarks on cannibalism and intestinal parasites, as well as nest competition for food. In Gape Breton crows, ravens and probably gulls go for the eggs and the young. If a nestling falls. Bent says the adult apparently can? not adjust to rescue or ground feeding • and the abandoned nestling starves. Pratt reported a survival rate of about I.5 young per nest. Pratt: "Nestlings were constantly attended by an adult until they were about 21 days old. When the chicks were between 21 and 28 days, they were left unattended for part of the day....After the chicks passed the age of 28 days, adults were seen at the nest only when feeding the young." The chemistry and stimuli that bound the adult herons to the heronry and the nest have passed. They have spent more and more time away and on their own. They and their young are solitary, self-reliant birds. There is not yet enough evidence to btate that they always return to the same heronry, although ringing in Britain and Germany indicate that certainly some do return to the colony in which they were hatched. And there is even less evidence to indicate whether partners of a pre? vious nesting remate. They migrate south, either singly or in small flocks, and mingle into the southern population un? til the following spring. Heron nests on Cape Breton Island. Information for this article was drawn from the following: Frank A. Lowe, THE HERON; A.C. Bent. LIFE HISTORIES OF N. AMERICAN MARSH BIRDS; A.J. Meyerriecks, COMPARATIVE BREEDING BEHAVIOR OF k SPECIES OF N.A. HERONS; W.P. &T7d.; Cottrille, "Great Blue Heron: Behavior at the Nest;" Helen M. Pratt, "Breeding Biology of...." Thanks to Oliver L. Austin Jr., editor of THE AUK, Ruth Scott, librarian at Acadia, and Cecelia Caplan, Pittsburgh, for supplying xeroxed materials. The drawings are by Richard P. Gross'enheider and William L. Brudon, taken from the Cottrille article. Heron photos by Frank Lowe. And thanks to Linda and Burland Murphy for their help.
Cape Breton's Magazine
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