Origins of lead in populations of raptors

Abstract

Although poisoning from anthropogenically derived lead threatens wildlife of many species, routes of lead exposure are unclear and rarely empirically tested. We used blood lead concentration and isotope ratio ( 207 Pb/ 206 Pb) data from populations of four species of raptors from across North America to test hypotheses associated with lead exposure via inhalation versus ingestion. Mean variation in blood lead concentration among cohort siblings was non-zero at nests of ferruginous hawks Buteo regalis and osprey Pandion haliaetus (P < 0.001 and P < 0.001), indicating exposure via episodic ingestion. However, within-nest variation in blood lead concentration was not significantly different from zero among cohort siblings at nests of bald eagles Haliaeetus leucocephalus and golden eagles Aquila chrysaetos (P = 0.014 and P = 0.023), consistent with exposure via continuous inhalation. Isotope ratio data corroborated the lead concentration data and within-nest average and variance of blood lead concentrations were positively correlated (r = 0.70 to 0.94), indicating episodic ingestion. This study provides some of the first empirical population-level data to evaluate mechanisms of lead exposure and demonstrates the importance of lead ingestion to avian predators and scavengers.

High Frequency of Lead Exposure in the Population of an Endangered Australian Top Predator, the Tasmanian Wedge‐Tailed Eagle (Aquila audax fleayi)

“…A very high proportion (95%) of nestlings we tested had been exposed to lead. Although this rate is higher than that reported for other raptors (Harmata 2011; Katzner et al 2017; Bruggeman et al 2018; Herring et al 2020), that most exposure was at a low level is consistent with findings for other raptors (Carlson et al 2012). Nestling raptors can be exposed to lead from inhalation, ingestion, or maternal transfer (Pattee 1984; Katzner et al 2017; Bruggeman et al 2018).…”

“…Analyses of isotope data focused on the lead 207/206 ratio. This ratio is used most commonly in research investigating sources of lead exposure in birds (Finkelstein et al 2012; Behmke et al 2015; Katzner et al 2017).…”

“…Wedge-tailed eagles, like other raptors, are thought to mainly provision their nestlings with live-caught prey (Olsen 2005); however, exposure through consumption is still possible due to prey species surviving being shot and containing lead ammunition (Pain et al 2015). Similarly, the high blood lead concentrations found in 2 nestlings are indicative of ingestion, rather than inhalation or maternal transfer (Katzner et al 2017), and therefore suggest that adult Tasmanian wedge-tailed eagles do bring lead-contaminated food to their young (be it scavenged or live caught).…”

“…Scavenging bird species are particularly prone to poisoning from these fragments, because they are often the first species to locate a carcass, the bullet wound provides an easy access point for feeding, and their highly acidic digestive tracts break down lead effectively (Beasley et al 2015; Nadjafzadeh et al 2015). Lead exposure has been reported in 34 raptor species (Pain et al 2009, 2019), ingestion has been identified as the route of exposure (e.g., Katzner et al 2017), and the link between lead‐based ammunition and exposure is evidenced by increased lead concentrations in raptors during the hunting season (Kelly and Johnson 2011; Cruz‐Martinez et al 2012; Garbett et al 2018), isotopic similarities between lead in tissues and those of ammunitions (Finkelstein et al 2012; Ishii et al 2017), and the presence of lead ammunition in regurgitated pellets and the alimentary canals of a range of raptor species (e.g., Donázar et al 2002; Helander et al 2009).…”

Feeding Ecology Drives Lead Exposure of Facultative and Obligate Avian Scavengers in the Eastern United States

“…Of the contaminants present in ecosystems, lead is one of the most frequently documented (Franson and Pain 2011). The pathway by which most birds are exposed to anthropogenic lead is by incidental ingestion (Katzner et al 2018). This occurs via unintentional ingestion of lead particles in the form of fragmented projectiles, fishing equipment, and paint (Sileo and Fefer 1987; Cruz‐Martinez et al 2012; Finkelstein et al 2012).…”