Do trace metals select for darker birds in urban areas? An experimental exposure to lead and zinc

Abstract

Trace metals from anthropogenic activities are involved in numerous health impairments and may therefore select for detoxification mechanisms or a higher tolerance. Melanin, responsible for the black and red colourations of teguments, plays a role in metal ion chelation and its synthesis is positively linked to immunity, antioxidant capacity and stress resistance due to pleiotropic effects. Therefore, we expected darker birds to (1) store higher amounts of metals in their feathers, (2) maintain lower metal concentrations in blood and (3) suffer less from metal exposure. We exposed feral pigeons (Columba livia) exhibiting various plumage darkness levels to low, but chronic, concentrations of zinc and/or lead, two of the most abundant metals in urban areas. First, we found negative and positive effects of lead and zinc, respectively, on birds' condition and reproductive parameters. Then, we observed positive relationships between plumage darkness and both zinc and lead concentrations in feathers. Interestingly, though darker adults did not maintain lower metal concentrations in blood and did not have higher fitness parameters, darker juveniles exhibited a higher survival rate than paler ones when exposed to lead. Our results show that melanin-based plumage colouration does modulate lead effects on birds' fitness parameters but that the relationship between metals, melanin, and fitness is more complex than expected and thus stress the need for more studies.

Speckled and plain regions of avian eggshells differ in maternal deposition of calcium and metals: A hitherto overlooked chemical aspect of egg maculation

“…Several previous studies have shown that the bioaccumulation of various macrominerals and microminerals, in particular Ca, increases with the intensity of pigmentation (derived from various porphyrin and melanin pigments) of avian feathers (Niecke et al 1999, Chatelain et al 2016 and of human hair and skin (reviewed in McGraw 2003). It is therefore assumed that reservoirs of melanin pigments serve as a sink for potentially harmful transition metal ions, adsorbing and harboring the very minerals that helped produce them and thereby offering chemoprotection to adjacent cells and tissues (Larsson 1993, McGraw 2003.…”

Biological responses to environmental contamination. How can metal pollution impact signal honesty in avian species?

“…It seems that highly melanic birds should be favored in an environment with a high level of certain metals (Chatelain et al., 2014). Many birds which adapt to live in European urban areas have melanin‐based plumage coloration (Chatelain et al., 2016). Yet, the mechanism and effect of toxic metals deposition are significantly understudied.…”

“…Elevated levels of toxic compounds were also found in melanized feather parts. Regarding analysis of average effect size for lead, only one of the studies (Chatelain et al, 2016) showed a statistically significant relationship. The remaining studies provided no unambiguous results, probably due to a small sample size.…”

“…Because the data were incomplete, all trace elements (zinc, lead, cadmium, calcium, copper) were examined separately (Table 1; Figure 1). In analysis, following studies were used: Chatelain et al, 2014;Chatelain, Gasparini, & Frantz, 2016;Giraudeau, Chavez, et al, 2015;Giraudeau, Mateos-Gonzalez, et al, 2015;Gochfeld et al 1991;McGraw, 2007;Niecke et al, 2003;Zduniak et al, 2014 . Small sample sizes in the available research result in a high confidence interval.…”

Experimental exposure to trace metals affects plumage bacterial community in the feral pigeon

“…Lead exposure decreases bird immunity (unpubl.) and reproductive success (but there is no effect of metal exposure on bird breeding success; Chatelain et al 2015). Lead, by decreasing bird condition, may affect bird ability to preen, a costly behaviour that helps to regulate feather microbiota (Piault et al 2008, Moreno-Rueda 2010, Leclaire et al 2014b).…”