By Ian Sinclair
Характеризует 750 видов южноафриканских птиц, включая не только резидентные и размножающиеся, но и большинство мигрантов. Фотографии, многие их которых демонстрируют птиц в полете, иллюстрируют разнообразие форм и раскрасок.
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Additional info for A Photographic Guide to Birds of Southern Africa
7°lmin), correlating with the relative solubility and expected distribution pattern of fatty acids downstream from a prey source. This means that a flatworm would be most likely to localize the region of the least soluble fatty acid, which would normally be found at the site of a resource. 2 Directional sources Distant orientation, based on directional information sources, is accomplished by moving along a stimulus trail, up a stimulus gradient, or toward a visual object, or by moving up a current which mayor may not carry a stimulus.
4 SUMMARY AND CONCLUSIONS Resources and their distributions change over the short term and over the long term, thus requiring the temporal organization of searching activities. This organization can be based on a searching rhythm, stimulation from the presence of resources or resource cues, or physiological state. An animal's physiological state can modify response thresholds to resource cues, thereby increasing or decreasing the likelihood of searching for a given resource. 5 Assessment mechanisms: resource, patch and habitat selection An animal can assess the quality of a resource unit so as to restrict its search to the best habitats, patches or resources by comparing what it 'knows', its reference, with information perceived at the resource unit.
This means that the proportion of localized cockles successfully Scanning mechanisms 43 opened increased with cockle density. At densities of 450 per m2 nearly one out of every two pecks was successful. In darkness, cockles are localized by rapid and continuous up and down movements of the bill. A bird takes one or two steps forward, then places its bill into the substrate and walks in a straight line, while the bill makes quick ('sewing') movements in the substrate. This process may proceed for a length of about 150 cm, and if the bird changes direction the bill is retracted from the substrate first and then reinserted after the change of direction.
A Photographic Guide to Birds of Southern Africa by Ian Sinclair