High Risk of Lead Contamination for Scavengers in an Area with High Moose Hunting Success

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.

Heads in the sand: public health and ecological risks of lead-based bullets for wildlife shooting in Australia

“…pet dogs) fed the same meat Høgåsen et al 2016). Many vulnerable species of scavenging wildlife (carrion eaters), notably predatory birds, are also at risk of harmful Pb exposure through ingesting bullet fragments (Johnson et al 2013;Legagneux et al 2014;West et al 2017), if shot animals, or parts of them (trimmed tissue or offal), are left in the environment (Craighead and Bedrosian 2008). Experimental studies have shown that avian scavengers do not avoid ingesting bullet fragments in this size range when foraging on carcasses (Nadjafzadeh et al 2015).…”

“…Lead in trimmed tissue and non-consumed body parts (heads, distal limbs, offal) can poison scavenging wildlife that consume the discarded tissues (Hunt et al 2006). Risk of exposure is likely to be high in species that have a propensity to scavenge and those that regularly feed on the carcasses of shot animals (Legagneux et al 2014). Scavenging species are more likely to be exposed if there is intensive shooting within their foraging range and, if wildlife shooting is seasonal, during the peak shooting season (Pain et al 2009).…”

“…searching large geographical areas for fresh carcasses; Baker-Gabb 1984) contribute to potential exposure (Haig et al 2014). Numerous studies have demonstrated harmful Pb concentrations in scavenging birds that consume carrion from animals shot with Pb-based bullets (Helander et al 2009;Finkelstein et al 2012;Haig et al 2014;Legagneux et al 2014;Bakker et al 2017;Ecke et al 2017; Table 2). Lead poisoning has been documented as a major cause of mortality (Hunt 2012;Haig et al 2014) and sublethal poisoning (e.g.…”

Ground Squirrel Shooting and Potential Lead Exposure in Breeding Avian Scavengers

“…For some species that rely heavily on already dead prey and in particular prey that have been shot (e.g. common ravens; [14,66]), we expect that the likelihood of Pb exposure effects in those nestlings would be even higher than for the raptor species modeled in our study. Additionally, the effects of Pb exposure are not limited to those few chosen in our modeling efforts.…”

“…Although avian Pb exposure has been associated with numerous sources such as Pb-based paints [5], mining [6,7], and fishing tackle [8,9], spent ammunition is often the most widespread source of Pb to scavenging birds [10–16]. Carcasses from big game hunting are a well-described vector of Pb exposure to avian scavengers [14,17,18], but other shooting and hunting activities may also cause Pb exposure in avian scavengers.…”