Appendix a Evaluation of a Modified Activity Trap for Invertebrate Sampling in Shallow Wetlands

Standard design of invertebrate activity traps limits their use to water depths that exceed the maximum foraging depth of most shorebirds. Assessment of nektonic invertebrate availability in shallow waters is desirable because shorebird diets may include these organisms. Thus, we designed a modified activity trap to assess invertebrate abundance in water depths ≤10 cm. We tested our design by collecting paired activity trap and benthic core samples during spring 1996 in moist-soil impoundments at Back Bay National Wildlife Refuge, Virginia. Twenty-four taxa were detected by 1 or both samplers. Four relatively mobile taxa occurred with greater frequency in activity traps, whereas 3 benthic taxa occurred with greater frequency in core samples. Number of individuals per sample was correlated (r = 0.43 to 0.78, P ≤ 0.004) between samplers for five taxa. Our results indicate that standard invertebrate sampling methods may underestimate availability of mobile taxa. Further, core samples may fail to detect large, mobile organisms that may substantially contribute to the diet of large shorebirds. We recommend that shallow-water activity traps be used as a supplement to benthic core sampling to more accurately describe shorebird food availability.