On the water depth in diving sampling sites of Tachybaptus ruficollis

In a remnant wetland of Central Italy, we carried out a yearly pilot study on some aspects of diving ecology and behavior of the little grebe (Tachybaptus ruficollis). During the 2005 period, this species occurred in the study area from October to June, when the maximum water depth in wetland channels was deeper than 30 cm. Density of the little grebe resulted significantly correlated with maximum water depth in channels. In diving sampling sites the water depth was 77.62 cm in average (+/- 28.89) and, during the study period, it was not correlated with maximum water depth in channels. In January-March period, when maximum water depth was deeper than 110 cm in average, the median values of water depth in diving sampling sites was significantly lower, when compared to the median values of water depth in channels. Water depth in sampling sites appeared relatively constant around a yearly cycle and independent to maximum water depth in channels. These data corroborate the hypothesis that in a wetland with a heterogeneous pattern of water depth, little grebe individuals avoid diving in wet areas with too deep water (i.e., > 1 m) because in these conditions individuals could face a too high energetic cost for acquiring food resources.