Options for shorebird-exclusion devices for pitfall traps on sandy shores

Abstract ContextPitfall trapping is a standard technique for indexing surface active invertebrates on beaches, and underpins the study of sandy shore ecology. However, pitfall traps may pose a risk to the flightless young of beach-nesting birds, which may fall into such traps and potentially die. AimThe aim of the present study was to compare the invertebrates captured in standard pitfall traps with those captured in pitfall traps fitted with one of three potential shorebird exclusion devices. Ideally, the traps with exclusion devices would perform similarly to the standard traps (to enable inter-study comparability) and would detect ecological gradients, such as those evident in invertebrate assemblages between the beach and foredune. MethodsA systematic array was deployed, using 64 pitfall traps of four types: three types with bird-exclusion devices (a mesh cover, a fence around the rim and a low roof); and a standard pitfall trap with no exclusion device. Pitfall traps were stratified across two habitat types (upper beach and foredune) and were simultaneously deployed to control for environmental and other variables. ResultsEach trap type was broadly comparable in terms of the assemblage of invertebrates recorded, with two exceptions: (1) there was a slightly lower species diversity in mesh than in roofed traps; and (2) the assemblage captured differed between roofed and fenced traps, with the former trapping more isopods and amphipods. No trap type differed from control traps, and all differentiated an ecological gradient between beach and foredune. Thus, any trap design option we tested met our criteria. Conclusions and implicationsThe present study shows that bird-exclusion devices for pitfall traps need not compromise trap performance, comparability or utility.