Ardea
Official journal of the Netherlands Ornithologists' Union

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Turpie J.K. & Hockey P.A.R. (1996) Foraging ecology and seasonal energy budgets of estuarine Grey Plovers Pluvialis squatarola and Whimbrels Numenius phaeopus at the Southern tip of Africa. ARDEA 84 (1): 57-74
The distribution, behaviour and energetics of Grey Plovers and Whimbrels at the Zwartkops estuary, South Africa, were studied over a period of 14 months, during which time their numbers ranged from winter minima of 21 and 123 respectively to late summer maxima of 603 and 469 respectively. Diet and prey size selection were similar for both species, and bird densities along the estuary were correlated with prey biomass. Individuals of both species established feeding territories during the spring arrival period. Whereas Grey Plovers retained these territories throughout the summer, Whimbrels ceased territorial defence as their numbers on the estuary increased. Daytime energy intake rates were highest in the austral spring and decreased towards the pre-migratory period, but both species fed at night throughout the year. Intake rates were influenced primarily by conspecific density, rather than by patterns of prey availability, suggesting that interference competition plays a role in regulating foraging performance. Nevertheless, seasonal patterns of foraging effort and success suggest that, despite their high foraging densities at the Zwartkops estuary, Grey Plovers and Whimbrels satisfy their energy demands during the non-breeding season more easily than at sites closer to the breeding grounds.


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