Ecological factors influencing the occurrence of ‘flash marks’ in wading birds

Abstract

1. Although the plumage of birds is important for flight and thermoregulation, it is also employed in inter‐ and intraspecific communication. The role in communication of particular plumage features can be studied by experiment or, as here, by correlational analysis. 2. The study was carried out on the 210 species of wading birds, such as plovers, sandpipers, thick‐knees and allies, that are placed within the traditional order Charadriiformes. 3. Species differ in the location and extent of ‘flash marks’, patches of white on the plumage that are typically conspicuous when the bird flies. These patches occur, in various permutations in different species, on the wing (primaries, secondaries, coverts), back, rump and tail. 4. Within a phylogenetic framework, it was asked which of several broad ecological variables (migration, habitat choice, feeding technique, propensity to flock) were correlated with the occurrence of flash marks. Only flocking correlated significantly. In particular, taxa that flock have flashier backs and coverts than their non‐flocking relatives. 5. Three non‐exclusive explanations for this correlation are: (i) individuals that take flight to avoid a predator may benefit from signalling their take‐off to flock mates which themselves then take flight; (ii) flash marks could enhance the confusion effect within flocks, making it more difficult for a predator to single out an individual; and (iii) flash marks may facilitate co‐ordinated flight within flocks.