Ardea
Official journal of the Netherlands Ornithologists' Union

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Tinbergen J.M. (1976) How Starlings (Sturnus vulgaris L.) apportion their foraging in a virtual single-prey situation on a meadow. ARDEA 64 (3-4): 155-170
This study deals with the question of whether free living Starlings (Sturnus vulgaris L.) spend more time foraging in places with more food in a field situation. As in fact they do, the next problem is to investigate the mechanism. Special attention is given to the profitability idea of Royama (1970). Observations were collected in two seasons, and data from egg-laying and incubation phase are presented here. The place selected for intensive study was close to the nesting colony, but consisting only of a part of the foraging area used by the Starlings. In this area the major prey was the larvae of Tipula paludosa. This study area was divided in plots of 20 x 20 m. Per plot the dry weight of insect prey, the grass length, the moisture-content and the distance to the colony was measured. Starlings were observed from a hide on a tower. The time spent foraging; the number of visits and the intake rate were estimated per plot. The observations revealed that in both years the Starlings spent more time on plots with more food (Fig. 3). In one season distance to the colony and moisture-content of the soil played a role in determining foraging time as well. The positive relation between foraging time and food quantity resulting from more frequent visits to places with more food, and not by a longer duration of visit (Fig. 5). It is argued that this means that the birds obtain information about the profitability of the place during a visit and use this information later in choice of foraging site. In both years intake rate was higher in places where most visits occurred, although this trend was not significant (Fig. 6). So far as the data go, they do not conflict with Rayama's model that birds should chose the best places to forage on the basis of intake rate, at least when hunting for the same prey at different sites, as in this study.PrFont34Bin0BinSub0Frac0Def1Margin0Margin0Jc1Indent1440Lim0Lim1This study deals with the question of whether free living Starlings (Sturnus vulgaris L.) spend more time foraging in places with more food in a field situation. As in fact they do, the next problem is to investigate the mechanism. Special attention is given to the profitability idea of Royama (1970). Observations were collected in two seasons, and data from egg-laying and incubation phase are presented here. The place selected for intensive study was close to the nesting colony, but consisting only of a part of the foraging area used by the Starlings. In this area the major prey was the larvae of Tipula paludosa. This study area was divided in plots of 20 x 20 m. Per plot the dry weight of insect prey, the grass length, the moisture-content and the distance to the colony was measured. Starlings were observed from a hide on a tower. The time spent foraging; the number of visits and the intake rate were estimated per plot. The observations revealed that in both years the Starlings spent more time on plots with more food (Fig. 3). In one season distance to the colony and moisture-content of the soil played a role in determining foraging time as well. The positive relation between foraging time and food quantity resulting from more frequent visits to places with more food, and not by a longer duration of visit (Fig. 5). It is argued that this means that the birds obtain information about the profitability of the place during a visit and use this information later in choice of foraging site. In both years intake rate was higher in places where most visits occurred, although this trend was not significant (Fig. 6). So far as the data go, they do not conflict with Rayama's model that birds should chose the best places to forage on the basis of intake rate, at least when hunting for the same prey at different sites, as in this study.


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