462: Predation Prey plumage adaptation against falcon attack : Nature

Predation Prey plumage adaptation against falcon attack : Nature:

Several plumage types are found in feral pigeons (Columba livia), but one type imparts a clear survival advantage during attacks by the swiftest of all predators — the peregrine falcon (Falco peregrinus). Here we use quantitative field observations and experiments to demonstrate both the selective nature of the falcon's choice of prey and the effect of plumage coloration on the survival of feral pigeons. This plumage colour is an independently heritable trait that is likely to be an antipredator adaptation against high-speed attacks in open air space. …

To confirm the advantage afforded by a white rump to pigeons during a high-speed attack, we captured 756 wild and blue-barred pigeons and switched their rump-patch feathers. We then released these pigeons and monitored predation by three adult peregrine falcons. After plumage transfer, we found that capture rates were reversed (Fig. 1c). The original wild phenotype now suffered predation at the same rate as the unmanipulated blue-barred type, whereas the manipulated blue-barred type now had rates of predation as low as the unmanipulated wild type (P<0.0001). This indicates that the dorsal white rump patch is important for the survival of feral pigeons during attacks by peregrine falcons.

All feral pigeons perform the same evasive roll during predation by falcons (Fig. 1a). The protective white patch may disguise the initiation of the pigeon's evasive roll by contrasting conspicuous (white patch) and cryptic targets (grey wings and body). A fast-flying falcon primed to a conspicuous target centered on the roll might fail to detect the dodge initiated by the cryptic wings as the predator closes from behind. When pursued by predators, schools of fish in open water and many shorebirds also display their dark dorsal and light ventral surfaces in a display that alternates between a cryptic and a conspicuous signal. The use of contrasting patterns as an antipredator mechanism is widespread and may represent a case of convergent evolution. …

In the eastern part of the pigeon's native range in Eurasia, C. livia is sympatric with a subgenus of falcons, Hierfalco, that typically chase their prey in level flight. Pigeons from this region lack the white rump patch. The decline in recent decades of peregrine-falcon populations worldwide relaxed their selective pressure on feral pigeons, but this has now reversed, with falcons recolonizing many of their former haunts. Over the study period, the proportion of wild plumage types in our study population increased significantly relative to blue-barred types (P=0.01), in parallel with a steady increase in predation by peregrine falcons. This suggests that, although pigeon plumage polymorphism persists, falcon predation pressure can lead to an increase in the relative proportion of the wild pigeon phenotype.

Too cool.