Abstract
Top predators and scavengers are vulnerable to pollutants, particularly those accumulated along the food chain. Lead accumulation can induce severe disorders and alter survival both in mammals (including humans) and in birds. A potential source of lead poisoning in wild animals, and especially in scavengers, results from the consumption of ammunition residues in the tissues of big game killed by hunters. For two consecutive years we quantified the level lead exposure in individuals of a sentinel scavenger species, the common raven (Corvus corax), captured during the moose (Alces alces) hunting season in eastern Quebec, Canada. The source of the lead contamination was also determined using stable isotope analyses. Finally, we identified the different scavenger species that could potentially be exposed to lead by installing automatic cameras targeting moose gut piles. Blood lead concentration in ravens increased over time, indicating lead accumulation over the moose-hunting season. Using a contamination threshold of 100 µg.L−1, more than 50% of individuals were lead-contaminated during the moose hunting period. Lead concentration was twice as high in one year compared to the other, matching the number of rifle-shot moose in the area. Non-contaminated birds exhibited no ammunition isotope signatures. The isotope signature of the lead detected in contaminated ravens tended towards the signature from lead ammunition. We also found that black bears (Ursus americanus), golden eagles and bald eagles (Aquila chrysaetos and Haliaeetus leucocephalus, two species of conservation concern) scavenged heavily on moose viscera left by hunters. Our unequivocal results agree with other studies and further motivate the use of non-toxic ammunition for big game hunting.
Highlights
Lead bioaccumulation is a threat to both human [1] and wildlife health [2,3]
Because blood lead concentration of individuals sampled during the moose hunting period at the two study areas were similar (F1,111 = 1.97; P = 0.17, after controlling for date with year consider as a random factor, test performed during the moose hunting period), we pooled all samples gathered during the hunting season for subsequent statistical analyses
During the moose hunting period, we found that blood lead concentration in the common raven increased over time in both years (F1,137 = 16.23; P,0.001; Fig. 1)
Summary
Lead bioaccumulation is a threat to both human [1] and wildlife health [2,3]. Lead has irreversible negative effects on general health, reproduction and behaviour and can potentially lead to death [3]. Sub-lethal toxic effects are exerted on the nervous system, kidneys and circulatory system, resulting in physiological, biochemical, immunological and behavioural (e.g., locomotor) changes [3,4,5,6,7]. Trophic interactions via facultative scavenging can impact ecosystem stability and persistence [12,13]. Because of their position at the top of the food chain, predators and especially scavengers are vulnerable to the bioaccumulation of pollutants [10]. Lifetime cumulative of sublethal lead exposures may have more dramatic consequences for wild animals than recent exposure [14]
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