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Factors Governing the Hunting Behaviour and Selection of Food by the Great Tit (Parus major L.)

T. Royama
Journal of Animal Ecology
Vol. 39, No. 3 (Oct., 1970), pp. 619-668
DOI: 10.2307/2858
Stable URL: http://www.jstor.org/stable/2858
Page Count: 50
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Factors Governing the Hunting Behaviour and Selection of Food by the Great Tit (Parus major L.)
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Abstract

(1) This paper deals with the underlying mechanisms of the hunting behaviour and selection of prey species by great tits feeding their young at the nest, and is based on observations made mainly in mixed broad-leaved woodland in Wytham near Oxford, England, and partly in larch plantations in Yamanaka, Japan, using both automatic cameras (41 000 photographs taken) at ten nests for 150 nestling-days and direct observations at six nests for 63 nestling-days. (2) A brief description of general tendencies in nestlings' diet as observed by various authors in different parts of the world is given first, as an introduction to this study. The major prey species in the breeding season are invariably Lepidoptera, particularly the larvae. (3) Apart from spiders taken during the first few days after hatching, the composition of prey species in the diet of nestlings has no particular relation to their age. It is suggested that spiders are of particular importance, from a nutritional point of view, at a certain stage of the chicks' growth. The nestlings were regularly fed with grit and snail shell, whose function seems to be related solely to mechanical grinding of food in the gizzard. (4) The seasonal succession of the prey species in the nestlings' diet throughout the breeding season is described, and the collection sites for many of the prey species are discussed. (5) Factors governing the utilization of prey species by tits to feed their young are highly complicated and are discussed first in terms of observed facts. On the whole, there seems to be no direct correlation between the biomass of the prey in the habitat and the tits' selection. The occurrence, in the nestlings' diet, of many lepidopterous species coincided with their time of pupation, which suggests that the behaviour of the prey has some importance in relation to their exposure to predation by tits. The effects of taste and conspicuousness of the prey species and of alternative prey occupying different micro-habitats are discussed in relation to the hunting efficiency of tits. (6) The factors governing the utilization of prey by tits are discussed further with the aid of a theoretical model. Tinbergen's theory of search images is critically reviewed, and an alternative theory proposed. The model is based on one fundamental assumption: that the predator tries constantly to maximize its hunting efficiency within its limited ability to perceive the abundance of food in various parts of the hunting area. (7) The concept of `profitability', defined as the amount of food the predator can collect for a given amount of hunting effort, is introduced into the model, and the relationship between the profitability and the density of a given prey species is investigated. From this model, some conclusions are drawn, and tentatively tested against the available observations. As the profitability of a prey species is determined not only by the density but also by the size of the prey and the method of hunting of the predator, and as the predator tries to get the most out of the whole complex of prey populations in the habitat, a direct correlation between the numbers of a given prey taken by the tits and its density cannot be expected. Instead, it is shown that the tendency expected from this model fits, without apparent contradictions, both Tinbergen's observations and my own. (8) It is also shown that the size of prey has some bearing on the selection of food by tits and influences differences in the composition between the diets of adults, fledglings and nestlings. (9) Some suggestions are made in concluding remarks as to the aspects of the problem which need to be considered in future studies.

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