1 2Trace metals are chemical pollutants of prime concern nowadays given their implication in 3 several human diseases and their noxious effects on wildlife. Previous studies demonstrated 4 their negative (e.g. lead, cadmium) or positive (e.g. zinc) effects on body condition, immunity 5 and reproductive success in birds. Because of their effects on bird condition, trace metals are 6 likely to influence the production of condition-dependent plumage colours, that may be used 7 in mate choice. In the feral pigeon (Columba livia), we investigated iridescent colouration in 8 response to lead and zinc experimental (i.e. metal supplementation in standardized 9 conditions) and natural exposure (i.e. metal concentrations in feathers of wild urban 10 pigeons), and melanic feather colouration in response to experimental lead and zinc 11 exposure. Both studies (i.e. experimental and correlative) consistently showed that lead 12 exposure decreased iridescent neck feather brightness independently of colour morph. 13Moreover, lead, when provided alone, decreased melanic feather reflectance in the middle 14 wavelengths while zinc supplementation increased melanic feather reflectance in the violet-15 wavelength. In conclusion, our study suggests that the colouration of iridescent and melanic 16 feathers depends on the exposure to pollutants. Whether trace metal exposure affected the 17 ability of birds to produce melanin pigments, to grow the microstructural feather elements 18 required for maximum colour display, or to cope with bacteria that degrade feather 19 microstuctures remains unclear. Future studies should investigate whether these metal-20 induced modifications of plumage colouration affect behaviours involved in sexual selection. 21 22 23

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.