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Optimization of Territory Shape in Heterogeneous Habitats: A Field Study of the Red-Capped Cardinal (Paroaria gularis)

Perri Eason
Journal of Animal Ecology
Vol. 61, No. 2 (Jun., 1992), pp. 411-424
DOI: 10.2307/5332
Stable URL: http://www.jstor.org/stable/5332
Page Count: 14
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Optimization of Territory Shape in Heterogeneous Habitats: A Field Study of the Red-Capped Cardinal (Paroaria gularis)
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Abstract

1. Models were developed to examine two factors that may influence optimal territory shape in heterogeneous habitats, resource availability and defence costs. These models were tested in a study of a population of red-capped cardinals (Paroaria gularis, L.) in Manu National Pari, south-eastern Peru. 2. Cardinals defend territories along the shores of oxbow lakes and rivers, with each territory containing two short stretches of shore that are on opposite sides of the water. 3. Analysis of samples of arthropod prey showed no differences between the two shores, allowing the foraging model to be rejected and indicating that resource distributions do not determine the shape of the cardinals' territories. 4. The probability of detecting an intruder on the same shore decreased with increasing distance from the territory owner. Intruders on the shore opposite the territorial pair were more likely to be detected immediately than were intruders on the same shore. Intruders detected immediately were easier to evict than intruders that were not detected immediately, and intruders tended to avoid the shore opposite the territorial pair. 5. The data supported the defence model: reduction in defence costs due to increased intruder detectability appears to be the factor that favours the inclusion of two shores in each cardinal territory. 6. I suggest that in patchy habitats, the effects of defence costs may result in territories that are suboptimally shaped for foraging, and that defence considerations should be included in future studies of territory shape.

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