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Inside Front Cover - The Life of the Great Blue Heron

Published by Ronald Caplan on 1977/8/1 (1310 reads)
 

The Life of the Great Blue Heron We commonly know the heron as a solitary creature. But the birds we see in Cape Bre? ton are those that have migrated north for the breeding portion of their year. And it takes a strong seasonal alteration for the heron to permit another heron near, and to remain close during the period of nest- building and repair, mating and raising the young. A complicated system of behavioural patterns and physiological changes has de? veloped within the species to communicate to one another their preparedness to have another near. Frank Lowe writes of colour changes in the European heron • the eyes and bill become blood-red just before pairing and when only recently paired. When nesting has further advanced the colour returns to normal. But "the bills and eyes of the he? rons whose nests have been destroyed be? came red again when they paired anew." Before actually occupying the nest, it is reported that the herons assemble and stand on some piece of ground near the heronry. This is a period of sorting out, wherein what Lowe calls their "somewhat primitive dance" takes place. Audubon described it in 1840: "About sunrise you see a number arrive and alight either on the margin of a broad sand bar or on a savannah. They come from different quarters, one after an? other, for several hours;and when you see kO or 50 before you, it is difficult for you to imagine that half that number could have resided in the same district. Yet-in the Floridas I have seen hundreds thus col? lected in the course of a morning. They are now in their full beauty, and no young birds seem to be among them. The males walk about with an air of great dignity, bidding defi? ance to their rivals, and the females croak to invite the males to pay their addresses to them. The females utter their coaxing notes all at once, and as each male evinces an equal desire to please the object of his affection, he has to encounter the enmity of many an adversary, who, with little at? tention to politeness, opens his powerful bill, throws out his wings, and rushes with fury on his foe. Each attack is carefully guarded against, blows are exchanged for blows; one would think that a single well- aimed thrust might suffice to inflict death, but the strokes are parried with as much art as an expert swordsman would em? ploy; and although I have watched these birds for half an hour at a time, I never saw one killed on such an occasion; but I have often seen one felled and trampled upon, even after the incubation had com? menced. These combats over, the males and females leave the place in pairs. They are now mated for the season, at least I am in? clined to think so, as I never saw them as? semble twice on the same ground, and they become comparatively peaceful after pairing." Other more recent observers indicate it is not quite so neat as Audubon presented it. Lowet there will be periods "when there will be herons on the field and at some of the nests; such is the case until the occu? pation of the colony is complete. It is im? possible to say whether each newcomer spends a probationary period in the field, or whe? ther the late arrivals go directly into the treetops....The probable explanation of these gatherings is that the birds await the attainment of the physiological condi? tion necessary for successful reproduction: close sociality may stimulate reproductive development (Fraser Darling)." Lowe:"In the reproductive cycle of the heron the nest has greater significance than in many species. It is a near-perma? nent structure to which the birds go each spring; in cases where no existing nest is available a token foundation of a few sticks is made. The nest usually endures for many years, its demensions increasing until its vast bulk, having become too great a weight or too great a wind-stop, finally crashes." The nests we've seen in one typically secluded heronry in Cape Breton, were of a rough branch and twig construction. According to Bent, in nest building "the birds often break the twigs off the trees rather than pick them off the ground. (Pratt observed a heron flying into the heronry carrying a twig • so they do oc? casionally bring in nesting materials.) New nests of the year are often so frail that the eggs can been seen through them from below. The older nests, which have been added to each year, are much larger, thicker HERON

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