Contrasting interference functions and foraging dispersion in two species of shorebird (Charadrii)

1. Above a threshold density of approximate to 100 birds ha(-1), strong int erference occurred between redshank Tringa totanus (Linnaeus) feeding by si ght on the amphipod crustacean Corophium volutator (Pallas). No aggressive interactions occurred between the birds and the probable cause was prey dep ression. 2. Redshank fed in a square metre of mud that had recently been exploited b y another redshank much less often than would be expected by chance. By avo iding areas where prey would have been recently exploited, the feeding rate of redshank was up to three times faster than it would have been had they not avoided other foraging redshank. 3. Bar-tailed godwit fed in a square metre of mud that had been recently ex ploited by another godwit much more often than would be expected by chance in randomly moving birds. They tended to flock while foraging and showed no tendency to avoid areas where prey would have been recently exploited. 4. There was no evidence that interference occurred between bar-tailed godw it Limosa lapponica (Linnaeus) feeding on the polychaete lugworm Arenicola marina (Linnaeus) at densities below 300 birds ha(-1), even though aggressi ve interactions occurred between birds.