Contrasting Interference Functions and Foraging Dispersion in Two Species of Shorebird (Charadrii)

Above a threshold density of ≈ birds ha-1, strong interference occurred between redshank Tringa tetanus (Linnaeus) feeding by sight on the amphipod crustacean Corophium volutator (Pallas). No aggressive interactions occurred between the birds and the probable cause was prey depression. 2. Redshank fed in a square metre of mud that had recently been exploited by another redshank much less often than would be expected by chance. By avoiding areas where prey would hav 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 exploited by another godwit much 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 godwit Limosa lapponica (Linnaeus) feeding on the polychaete lugworm Arenicola marina (Linnaeus) at densities below 300 birds ha-1, even though aggressive interactions occurred between birds.