Differences in foraging behaviour between water shrews: Neomys anomalus and Neomys fodiens

Abstract

The modes and efficiency of foraging in the terrestrial and aquatic habitats in water shrews Neomys anomalus Cabrera, 1907 and N. fodiens (Pennant, 1771) were compared in order to investigate if these species can avoid competition fur food when they occur syntopically. Seven individuals of N. anomalus and five of N. fodiens, caught in the Bialowieza Primeval Forest, were tested individually in the terrarium of size 3 x 0.5 m, containing a 0.25-m-wide `stream' with flowing water of an average depth 25 cm. Six experimental variants, simulating different habitat conditions, were established. Each animal was tested in a given variant during 3 succeeding days for 6 h a day. In total, 738 h of shrews' behaviour were recorded in darkness using 2 infra-red sensitive video-cameras. Results obtained on four N. fodiens tested with similar methods (648 h; Ruthardt 1990) were included for comparison N. anomalus swam and dived significantly shorter than N. jodiens, and they did not take food under water, even when there was no food on land. N. fodiens found and took food placed under water and foraged quite efficiently here. They found on average 17.7% of food portions placed under water in the most similar to natural conditions and 19.4% when there was no food on land. In both species foraging time on land was much longer than in water. The presence of natural structures increased duration and efficiency of foraging, but this influence was stronger in N. anomalus than in N. fodiens. These results and literature data suggest that in the wild: (1) both species forage in shallow water and in muddy grounds of wet habitats (wading foraging mode), and also in drier terrestrial habitats (epigeal and hypogeal foraging); (2) only N. fodiens forage in deep water (aquatic foraging); (3) the competition for food between N. anomalus and N. fodiens may be very weak, when potential aquatic prey are available.