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Effect of age on the fishing ability of sandwich terns Sterna sandvicensis
In: Ibis. British Ornithologists' Union/Wiley: London. ISSN 0019-1019; e-ISSN 1474-919X
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| Trefwoorden |
Sterna sandvicensis Latham, 1787 [WoRMS]
Marien/Kust |
| Abstract |
The fishing ability of first-winter and older Sandwich Terns was compared at foraging sites used by both age-groups on the coast of Sierra Leone between January and March 1970 when first-winter birds were about 7–9 months old. The methods used for measuring various parameters of fishing ability are described. It was found that a significantly larger proportion of plunge dives by the older age-group yielded prey although the difference between the two age-groups was only slight.There were no major differences between the age-groups in diving rates or in size of fish captured. Older birds tended to dive from higher than first-winter birds.By driving shoals of small fish to the surface, predatory fish enhanced the fishing success of both age-groups on certain days. Where man's beach seining operations yielded a superabundance of small fish near the tideline, these were captured equally well by both age-groups.First-winter birds were not seen being fed by older birds, and although food-begging behaviour was observed once in late January it is clear that the first-winter birds were self-sufficient for food by the time this study was made.Some implications of the observed differences in fishing success are discussed. It is suggested that, after fledging, Sandwich Terns gradually gain the judgment and skill necessary to dive profitably from increasing heights and so learn to exploit prey in a greater range of water depth as they get older. |
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