Chemical aposematism: the potential for non‐host odours in avian defence

Many birds display plumage coloration and patterns that act as visual aposematic mimetic signals for predators. Avian aposematism can also be communicated via chemical cues, where so-called non-host odours (NHO) emitted from the plumage, uropygial (preen) gland or other sources denote status of dangerous unprofitable hosts ectoparasitic haematophagous arthropods. NHO are in natural concentrations repel nuisance arthropods inhibit their attraction to hosts, opposed being generally unpalatable toxic Birds emit preempt encounters with pathogens they transmit. Nuisance respond avoid exhibit disabling behavioural, anatomical, physiological and/or defences. As distinctive evolved warnings predators, selected advertise semiochemicals. Short-chain (C6–C10) aldehydes some may against a variety In birds, size (and presumably its secretory output) is negatively correlated degree ectoparasite infestation incidence malarial infection, thus implicating secretions defence dipteran vectors haemosporidian pathogens. A field experiment demonstrates volatiles emanating Eurasian Hoopoe Upupa epops deter biting flies. Birds' risky habit plucking hair live mammals incorporating stolen tufts into nests hypothesized serve mechanism appropriating mammalian skin nest Feathers plucked heterospecifics shed snake skins incorporated NHO. Behavioural assays measuring repellence attraction-inhibition needed elucidate avian Experimental efforts underlying defences support entail challenges include enactment variously effective different arthropods, emission ‘understood’, i.e. avoided, by