Abstract: Prey density explains seasonal patterns of occurrence of Sanderling Calidris alba on a sandy beach in Ghana

Yaa Ntiamoa-Baidu1,2, Jones Quartey1 and Alfred Ali Nuoh1

1 Centre for African Wetlands, University of Ghana, Legon, Accra, Ghana

2 Department of Animal Biology and Conservation Science, University of Ghana, Legon, Accra, Ghana

A 20-year monthly counts of non-breeding populations of Sanderling Calidris alba on the Ghana coast showed a clear seasonal pattern of occurrence. Sanderlings start arriving on the Ghana coast from August, numbers peak in September/October, and by November, the numbers remaining is 30-40% of the peak observed in the northern autumn. Evidence from ringing recoveries indicates that Sandelings leaving the Ghana coast go further down to the south western coast of Africa. A second peak is observed in February/March during the northward migration to the breeding grounds in some years, but not in others. To explain the factors accounting for the observed patterns, we studied the relative abundance of prey items on the most important site for Sanderling in Ghana, the Esiama beach, a 13 km beach between the Amansuri and Ankobra estuaries in the western region of Ghana.  We took core samples of benthos at 500 m intervals of the beach once a month between March 2011 and December 2012. Seven groups of invertebrates were recorded: Amphipoda, Nemertea, Glyceridae, Terebridae and Donax pulchelus, but the species that occurred with any degree of abundance and constituted the bulk of the prey for Sanderling was D. pulchellus.  The size (length) of D. pulchellus recorded ranged from 2.2 mm-11.79 mm, mean 7.76 mm (SD 1.31). Densities varied from 0.015 -0.44 per cm2 at the two estuarine ends of the beach to 2.65 per cm2 on the sandy beach.  D. puchellus showed two peaks of occurrence, August to October and March/April, which coincide with the periods that Sanderling numbers are highest at the site.

Key words: Non-breeding Sanderling populations, prey abundance, Donax pulchellus

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