Shorebirds use stopover sites throughout the Lower Mississippi Alluvial Valley (LMAV) to fuel their southern migration. At these stopover sites shorebirds exploit macroinvertebrates as their primary foraging material during migration. Studies from coastal areas suggest that shorebirds can significantly deplete macroinvertebrate abundance and biomass at stopover sites. Whether these results are true for the LMAV remains to be evaluated. An exclosure experiment was conducted on five National Wildlife Refuges (NWRs) stretching 400 km throughout the LMAV to see if shorebird foraging impacted macroinvertebrate community composition, abundance and standing stock biomass. Macroinvertebrates were sampled in the late summer of 2001 and 2002 from exclosure areas and open areas and compared using 2-sample paired t-tests. Community composition was relatively similar between the five refuges sampled. Macroinvertebrate abundances ranged from 300 to 433,000 individuals/m² with a mean of 66,500 (±6000) individuals/m².

Shorebird foraging had no significant impact on abundance. Macroinvertebrate biomass ranged from less than 0.1 to greater than 24.4 g ash free dry mass (AFDM)/m² with a mean of 3.43 (±0.35) g AFDM/m². With the exception of one sampling date, 21 August 2001 at Bald Knob NWR, shorebird foraging did not significantly impact macroinvertebrate biomass. On the exceptional date, the difference was due to a reduction of Chironomidae larvae, which was neither the most abundant macroinvertebrate present nor the macroinvertebrate comprising the highest biomass. Results of this study suggest that, at present, shorebirds do not have a significant impact on foraging material in the LMAV flyway during their southern migration. However, with continued degradation to other interior regions and increased promotion of shorebird management in the LMAV, the potential exists for shorebirds to increase in numbers high enough to cause significant impacts in the future.