Browsing by Author "Nelson, Robert Wayne"
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- ItemEmbargoBehavioral ecology of coastal peregrines (Falco peregrinus pealei)(1977) Nelson, Robert Wayne; Myres, M. TimothyA long-term study, 1968-75, of Peregrine Falcons at Langara Island, British Columbia, produced much information on the behavior and ecology of this population. An ethogram summarizes descriptions and functions of 43 behavior patterns in courtship, 32 in territorial advertisement and defense, and 15 in self, nest and food defense. Males are more active in courtship, territorial advertisement and defense. Mainly same-sex intruders are chased, but males also evict females. Nine hypotheses of sexual size dimorphism are considered. I conclude that aerial combat with dangerous weapons selects for smaller males, better combatants; the proportion of aerial to ground fighting sets the lower limit to the size of males. The annual schedule of courtship, incubation, nestling, fledgling, and dispersal phases is described. Seasonal changes in courtship are not proximate causes of egglaying. Photoperiod is an early timer for laying. Ambient temperature is a "final" timer, initiating rapid follicle growth ea. two weeks before Egg 1 is laid. Early egglaying gives juveniles more experience before autumn-winter hardships. Productivity over eight years averaged 1.76 fledglings per territorial pair, and 2.32 per successful pair. Average breeding spans were: males, 6.0 years; females, 3.5 years (survival rates: 0.85, 0.75). A first year survival rate of ea. 0.45-0.55, and a floating population at least 50% of the size of the breeding population were estimated. The Langara falcons declined from ea. 21-23 pairs in the early 1950s to 5-6 pairs in 1968-?5. This decline paralleled a seabird decline, apparently throughout the Queen Charlotte Islands. Falcons amalgamate territories by means of pseudopolyandry; an orderly population decline results, toward a new "equilibrium" with the prey base. Peregrines occupy Type A, B-A, and B territories, from 0.3-0.5 km to ca. 15 km in diameter. Individuals establish and adjust territory size in relation to available food. They harvest on a conservative sustained-yield basis. The result is the "natural conservation" of V. C. Wynne-Edwards, but the cause is individual selection. Peregrines demonstrate Bergmann's Rule. Larger birds live in cooler climates and have higher mortality rates and larger clutch sizes. Clutch size offsets natural mortality plus provides a floating population of optimum size. Peregrines evolved a strategy which does not produce the most fledglings at independence (e.g. D. Lack), but which balances the survival of parents and the number and quality of fledglings. Smaller broods will produce young with better survival rates and competitive abilities. When balanced with quantity, and combined with philopatry, this strategy tends to increase genetic fitness.
- ItemEmbargoSome aspects of the breeding behaviour of Peregrine falcons on Langara Island, B.C.(1970) Nelson, Robert Wayne; Myres, M. TimothyThe behaviour of Peregrine 'Falcons (Falco ueregrinus pealei) in the breeding season was studied on Langara Island, in the Queen Charlotte Islands group of British Columbia in 1968, 1969 and 1970, for a total of almost twelve months .in the field. In 1968 one pair of falcons and their young was observed closely from coastal rocks and from a blind overlooking the nest ledGe at Area A. In 1969 another pair was studied in similar fashion at Area B. In all three years observations were made on several other pairs and their young. The Peregrine Falcon has a vocabulary of at least twelve separable calls. Adult Langara Island Peregrine Falcons appear not to migrate. In 1969 a pair was observed through the Preincubation Phase. The male seems to take the initiative at this period, stimulating the female by his flight behaviour, Ledge-demonstration displays and Male-ledge displays. If disturbed at a prospective nest ledge, the falcons my quickly abandon it in favour of another ledge some distance away. Transfers of food from the male to the female were first observed almost a month prior to egg-laying. Food-transfers are similar to those seen between adults and fledglings. During parts of courtship, the female exhibits nestling-like behaviour. The significance of markedly lethargic behaviour in the female prior to the laying of the eggs is discussed. During incubation, the majority of hunting is done by the male in twilight before dawn. During the daylight hours he retrieves food for himself and the female from caches on the cliff. Only the female incubates at night. Although the male plays a role in daytime incubation, the amount of time that he devotes to this is small. This is thought to be partly explained by his inability (due to his smaller size) to brood nestlings effectively. The female broods the nestlings for about a week after hatching, but continues to brood them at night for some time longer. When the nestlings become too large for this, the female continues a nightly 'guard duty' at the ledge. Feeding behaviour of nestlings gradually develops from a stage in which the parents feed the gaping young, through a stage in which the young take food from the parent's beak, to a stage in which food is sometimes forcibly seized from the parent. The young falcons first fly at 41-44 days of age, and become adept at flying within a week. From then on they receive most of their food from the parents in the air, usually by means of foot-to-foot Food-transfers. The parents frequently attempt to hide from their young for long periods. The fledglings 'play’ with each other and make play-attacks at inanimate objects, followed by mock-attacks at possible prey, and finally actual attempts to hunt for themselves. But they continue to be dependent on the parents for at least six weeks after first flying. The Langara Island falcons have been found to contain considerable amounts of chlorinated hydrocarbons. These are probably already affecting their ability to raise young, and possibly also some aspects of their behaviour.