Pigeon odor varies with experimental exposure to trace metal pollution

Trace metals are chemical pollutants that have well-known noxious effects on wildlife and that are current major environmental issues in urban habitats. Previous studies have demonstrated their negative (e.g. lead) or positive (e.g. zinc) effects on body condition, immunity and reproductive success. Because of their effects on condition, trace metals are likely to influence the production of condition-dependent ornaments. The last decade has revealed that bird odors, like mammal odors, can convey information on individual quality and might be used as secondary sexual ornaments. Here, we used solid-phase microextraction headspace sampling with gas chromatography-mass spectrometry to investigate whether plumage scent varied with experimental supplementation in lead and/or zinc in feral pigeons. Zinc supplementation (alone or in combination with lead) changed the proportion of several volatiles, including an increase in the proportion of hydroxy-esters. The production of these esters, that most likely originate from preen gland secretions, may be costly and might thus be reduced by stress induced by zinc deficiency. Although lead is known to negatively impact pigeon condition, it did not statistically affect feather scent, despite most of the volatiles that increased with zinc exposure tended to be decreased in lead-supplemented pigeons. Further studies should evaluate the functions of plumage volatiles to predict how trace metals can impact bird fitness.