Distribution and feeding ecology of dunlin on seal sands

Abstract

This study describes patch selection by Dunlin, a small, shallow feeding wader, observed feeding on physically heterogeneous intertidal mudflats at Seal Sands, Teesmouth in N. E. England. Seal Sands was not viewed as a homogeneous feeding ground by the dunlin population. The dunlin showed a tendency to congregate on certain subareas, namely Greenabella (A), and Central (C), Banks. The feeding distribution of the dunlin was examined with respect to the substratum characteristics, and it was shown that dunlin concentrated on the soft, wet, muddy substrata. Thus, their feeding distribution was influenced by the stage of the tidal cycle. The tide can affect the dunlins’ distribution both directly, by restricting the space in which they can feed, and indirectly, by affecting the substratum's texture (wetness) and hence the availability of prey within it. In general, the feeding dunlins' microdistribution revealed a preference for the "Film" microhabitat. Hence the birds' feeding activity showed a tidal rather than a diurnal periodicity. The feeding behaviour of dunlin was also influenced by the wetness of the substratum, and thereby the tidal situation. Final conclusions, with regard to the Bill length differences between sexes, and the seasonal change in Body Weight, due primarily to the accumulation and depletion of fat reserves are not presented here in order to emphasizetheir tentative nature, resulting from small sample size. For the same reason, this data was simply presented in appendix IV rather than in the body of the text. The two commonest races of Dunlin on the Teesmouth estuary, Calidris alpina alpina and Calidris alpine schinzii, were both captured during both the spring and autumn migrations. In the latter period, juveniles were in the majority in the captured samples.