Lead poisoning of raptors: state of the science and cross-discipline mitigation options for a global problem

Lead poisoning is an important global conservation problem for many species of wildlife, especially raptors. Despite the increasing number of individual studies and regional reviews of lead poisoning of raptors, it has been over a decade since this information has been compiled into a comprehensive global review. Here, we summarize the state of knowledge of lead poisoning of raptors, we review developments in manufacturing of non-lead ammunition, the use of which can reduce the most pervasive source of lead these birds encounter, and we compile data on voluntary and regulatory mitigation options and their associated sociological context. We support our literature review with case studies of mitigation actions, largely provided by the conservation practitioners who study or manage these efforts. Our review illustrates the growing awareness and understanding of lead exposure of raptors, and it shows that the science underpinning this understanding has expanded considerably in recent years. We also show that the political and social appetite for managing lead ammunition appears to vary substantially across administrative regions, countries, and continents. Improved understanding of the drivers of this variation could support more effective mitigation of lead exposure of wildlife. This review also shows that mitigation strategies are likely to be most effective when they are outcome driven, consider behavioural theory, local cultures, and environmental conditions, effectively monitor participation, compliance, and levels of raptor exposure, and support both environmental and human health.

Weight retention and expansion of popular lead-based and lead-free hunting bullets

Hunting bullets are often comprised of a lead core covered with a copper alloy jacket. When the bullet collides with an animal, particles-sometimes millions-can shed from the projectile and embed in animal tissues. Those lead fragments can persist in game meat and remain in the discarded viscera that many wildlife species scavenge. Bullets often differ in design, so it is vital to assess their weight retention and expansion, which affects how much metal they deposit in tissue and how effectively they kill animals. We fired 12 types of hunting bullets into water to measure their weight retention and expansion at 91 m and 238 m (100 and 260 yards). Bullet constructions included copper, tin, bonded lead, partitioned lead, and cup-and-core lead. On average, copper bullets retained >98 % of their weight, whereas cup-and-core lead bullets retained <13-55 %, depending on the brand and shot distance. One brand of bonded lead bullet retained mass (≥96 %) nearly as well as copper bullets, while another brand retained much less (~71 %). Two types of copper bullets expanded similarly between test distances, while a third expanded less at 238 m. Cup-and-core lead bullets often experienced a separation between their copper alloy jacket and lead core. Our data emphasize that lead-based bullets of similar construction can drastically differ in weight retention and expansion.

Animal welfare outcomes of helicopter-based shooting of deer in Australia

Abstract Context Helicopter-based shooting has been widely used to kill deer in Australasia, but the animal welfare outcomes of this technique have not been evaluated. Aim To assess the animal welfare outcomes of helicopter-based shooting of deer in Australia by quantifying the fates of deer seen and shot at, the duration of procedures and the number and location of bullet wounds in deer. Methods Three deer control operations were assessed. These operations targeted: (1) chital deer (Axis axis) in Queensland, (2) fallow deer (Dama dama) in Australian Capital Territory and (3) fallow deer in New South Wales. For each operation, an independent veterinarian conducted ante-mortem (i.e. from the helicopter as shooting occurred) and post-mortem (i.e. from the ground after shooting had ceased) observations. The ante-mortem data were used to estimate the proportion of deer seen that were shot, chase time (CT), time to insensibility (TTI) and total time (TT; CT + TTI). The numbers and locations of bullet wounds were recorded post-mortem. Key results Ante-mortem and post-mortem observations were performed for 114–318 and 60–105 deer, respectively, in the three operations. Shots were fired at 69–76% of deer that were observed. Median CT ranged from 73 to 145 s. Median TTI ranged from 17 to 37 s and median TT ranged from 109 to 162 s. The mean number of bullet wounds per deer ranged from 1.43 to 2.57. Animal welfare outcomes were better in the two fallow deer operations than in the chital deer operation. In both fallow deer operations, most deer were shot multiple times and at least once in the head or thorax. In contrast, chital deer were shot fewer times and less often in the head or thorax, and non-fatal wounding was observed. Conclusions The best animal welfare outcomes were achieved when helicopter-based shooting operations followed a fly-back procedure and mandated that multiple shots were fired into each animal. Implications Animal welfare outcomes for helicopter-based deer shooting in Australia could be improved with a national-level standard operating procedure requiring helicopters to fly back over shot animals and repeatedly shoot animals in the head or thorax.

Small-Mammal Shooting as a Conduit for Lead Exposure in Avian Scavengers

Lead (Pb) exposure is a widespread wildlife conservation threat. Although commonly associated with Pb-based ammunition from big-game hunting, small mammals (e.g., ground squirrels) shot for recreational or pest-management purposes represent a potentially important Pb vector in agricultural regions. We measured the responses of avian scavengers to pest-shooting events and examined their Pb exposure through consumption of shot mammals. There were 3.4-fold more avian scavengers at shooting fields relative to those at fields with no recent shooting, and avian scavengers spent 1.8-fold more time feeding after recent shooting events. We isotopically labeled shot ground squirrels in the field with an enriched ¹⁵N isotope tracer; 6% of avian scavengers sampled within a 39 km radius reflected this tracer in their blood. However, 33% of the avian scavengers within the average foraging dispersal distance of nests (0.6-3.7 km) were labeled, demonstrating the importance of these shooting fields as a source of food for birds nesting in close proximity. Additionally, Pb concentrations in 48% of avian scavengers exceeded subclinical poisoning benchmarks for sensitive species (0.03-0.20 μg/g w/w), and those birds exhibited reduced δ-aminolevulinic acid dehydratase activity, indicating a biochemical effect of Pb. The use of shooting to manage small mammal pests is a common practice globally. Efforts that can reduce the use of Pb-based ammunition may lessen the negative physiological effects of Pb exposure on avian scavengers.

A comparison of fragmenting lead-based and lead-free bullets for aerial shooting of wild pigs

In response to the health threats posed by toxic lead to humans, scavenging wildlife and the environment, there is currently a focus on transitioning from lead-based to lead-free bullets for shooting of wild animals. We compared efficiency metrics and terminal ballistic performance for lead-based and lead-free (non-lead) bullets for aerial shooting of wild pigs (Sus scrofa) in eastern Australia. Ballistic testing revealed that lead-based and lead-free bullets achieved similar performance in precision and muzzle kinetic energy (E0) levels (3337.2 J and 3345.7 J, respectively). An aerial shooting trial was conducted with wild pigs shot with one type of lead-based and one type of lead-free bullets under identical conditions. Observations were made from 859 shooting events (n = 430 and 429 respectively), with a sub-set of pigs examined via gross post-mortem (n = 100 and 108 respectively), and a further sub-set examined via radiography (n = 94 and 101 respectively). The mean number of bullets fired per pig killed did not differ greatly between lead-based and lead-free bullets respectively (4.09 vs 3.91), nor did the mean number of bullet wound tracts in each animal via post-mortem inspection (3.29 vs 2.98). However, radiography revealed a higher average number of fragments per animal (median >300 vs median = 55) and a broader distribution of fragments with lead-based bullets. Our results suggest that lead-based and lead-free bullets are similarly effective for aerial shooting of wild pigs, but that the bullet types behave differently, with lead-based bullets displaying a higher degree of fragmentation. These results suggest that aerial shooting may be a particularly important contributor to scavenging wildlife being exposed to lead and that investigation of lead-free bullets for this use should continue.

Animal welfare testing for shooting and darting free-ranging wildlife: a review and recommendations

Several important techniques for managing wildlife rely on ballistics (the behaviour of projectiles), including killing techniques (shooting) as well as capture and marking methods (darting). Because all ballistic techniques have the capacity to harm animals, animal welfare is an important consideration. Standardised testing approaches that have allowed refinement for other physical killing and capture methods (e.g. traps for mammals) have not been applied broadly to ballistic methods. At the same time, new technology is becoming available for shooting (e.g. subsonic and lead-free ammunition) and darting (e.g. dye-marker darts). We present several case studies demonstrating (a) how basic ballistic testing can be performed for novel firearms and/or projectiles, (b) the benefits of identifying methods producing undesirable results before operational use, and (c) the welfare risks associated with bypassing testing of a technique before broad-scale application. Following the approach that has been used internationally to test kill-traps, we suggest the following four-step testing process: (1) range and field testing to confirm accuracy and precision, the delivery of appropriate kinetic energy levels and projectile behaviour, (2) post-mortem assessment of ballistic injury in cadavers, (3) small-scale live animal pilot studies with predetermined threshold pass/fail levels, and (4) broad-scale use with reporting of the frequency of adverse animal welfare outcomes. We present this as a practical approach for maintaining and improving animal welfare standards when considering the use of ballistic technology for wildlife management.

Unleaded hunting: Are copper bullets and lead-based bullets equally effective for killing big game?

Semi-jacketed lead-cored or copper-based homogenous rifle bullets are commonly used for hunting big game. Ever since their introduction in the 1990's, copper-based bullets have not been widely accepted by hunters due to limited supply, higher expense, and the perception that they exhibit inferior killing efficiency and correspondingly higher wounding rates. Here, we present data showing that animal flight distances for roe deer, red deer, brown bear, and moose dispatched with lead- or copper-based hunting bullets did not significantly differ from an animal welfare standardized animal flight distance based on body mass. Lead-cored bullets typical fragment on impact, whereas copper-based bullets retain more mass and expand more than their leaden counterparts. Our data demonstrate that the relative killing efficiency of lead and copper bullets is similar in terms of animal flight distance after fatal shots. Hunters that traditionally use lead bullets should consider switching to copper bullets to enhance human and environmental health.

The transition to non-lead sporting ammunition and fishing weights: Review of progress and barriers to implementation

This review presents evidence of lead exposure and toxicity to wildlife and humans from spent shotgun and rifle ammunition and fishing weights, and the barriers and bridges to completing the transition to non-lead products. Despite the international availability of effective non-lead substitutes, and that more jurisdictions are adopting suitable policies and regulations, a broader transition to non-lead alternatives is prevented because resolution remains divided among disparate human user constituencies. Progress has occurred only where evidence is most compelling or where a responsible public authority with statutory powers has managed to change mindsets in the wider public interest. Arguments opposing lead bans are shown to lack validity. Differing national regulations impede progress, requiring analysis to achieve better regulation. Evidence that lead bans have reduced wildlife exposure should be used more to promote sustainable hunting and fishing. Evidence of the lead contribution from hunted game to human exposure should shape policy and regulation to end lead ammunition use. The Special Issue presents evidence that a transition to non-lead products is both warranted and feasible.

Rationale for the regulated transition to non-lead products in Canada: A policy discussion paper

Lead gunshot, rifle bullets, and fishing weights are still allowed in Canadian provincially-regulated hunting and fishing, despite the contribution to lead exposure in humans, wildlife, and the environment. Non-lead gunshot and fishing weights are required in Canada only for waterfowl hunting, and angling in national parks and national wildlife areas. Lead wheel weights are also allowed and comprise a majority of the Canadian market. Effective non-lead substitutes for these products exist, and are already required in various American and European jurisdictions. Several analyses commissioned by the Canadian government in 2018 identified the problems of lead exposure attributable to these four lead products. Lead is already listed under Schedule 1 of the Canadian Environmental Protection Act (CEPA) that authorizes the government to undertake measures to reduce exposure. CEPA could require, simultaneously, use of non-lead ammunition, fishing weights and wheel weights at the national level, following an appropriate phase-in period. The low provincial and territorial licence fees for hunting and fishing in Canada would offset any costs associated with use of lead substitutes. Costs for non-lead wheel weights would comprise a small percentage of the costs of new vehicles and new tire purchases. This regulatory initiative would complement other Canadian national bans on lead products. Because there is no safe threshold level for blood lead, use of non-lead products would benefit the health of humans, scavengers, upland game species, and fish-eating birds.

Mercury and lead exposure in avian scavengers from the Pacific Northwest suggest risks to California condors: Implications for reintroduction and recovery

Mercury (Hg) and lead (Pb) are widespread contaminants that pose risks to avian scavengers. In fact, Pb exposure is the primary factor limiting population recovery in the endangered California condor (Gymnogyps californianus) and Hg can impair avian reproduction at environmentally relevant exposures. The Pacific Northwest region of the US was historically part of the condor's native range, and efforts are underway to expand recovery into this area. To identify potential threats to reintroduced condors we assessed foraging habitats, Hg and Pb exposure, and physiological responses in two surrogate avian scavenger species (common ravens [Corvus corax] and turkey vultures [Cathartes aura] across the region between 2012 and 2016. Mercury exposure near the Pacific coast was 17-27-fold higher than in inland areas, and stable carbon and sulfur isotopes ratios indicated that coastal scavengers were highly reliant on marine prey. In contrast, Pb concentrations were uniformly elevated across the region, with 18% of the birds exposed to subclinical poisoning levels. Elevated Pb concentrations were associated with lower delta-aminolevulinic acid dehydratase (δ-ALAD) activity, and in ravens there was an interactive effect between Hg and Pb on fecal corticosterone concentrations. This interaction indicated that the effects of Hg and Pb exposure on the stress axis are bidirectional, and depend on the magnitude of simultaneous exposure to the other contaminant. Our results suggest that condors released to the Pacific Northwest may be exposed to both elevated Hg and Pb, posing challenges to management of future condor populations in the Pacific Northwest. Developing a robust monitoring program for reintroduced condors and surrogate scavengers will help both better understand the drivers of exposure and predict the likelihood of impaired health. These findings provide a strong foundation for such an effort, providing resource managers with valuable information to help mitigate potential risks.

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

Lead (Pb) is a toxic element banned from fuel, paint and many other products in most developed countries. Nonetheless, it is still widely used in ammunition, including rifle bullets, and Pb-based bullets are almost universally used in Australia. For decades, poisoning from Pb shot (shotguns) has been recognised as a cause of disease in waterfowl and Pb shot has been subsequently banned for waterfowl hunting in many jurisdictions. However, the risks posed by Pb-based bullets (rifles) have not been similarly recognised in Australia. Pb-based rifle bullets frequently fragment, contaminating the tissue of shot animals. Consuming this Pb-contaminated tissue risks harmful Pb exposure and, thus, the health of wildlife scavengers (carrion eaters) and humans and their companion animals who consume harvested meat (game eaters). In Europe, North America and elsewhere, the environmental and human health risks of Pb-based bullets are widely recognised, and non-toxic alternatives (e.g. copper-based bullets) are increasingly being used. However, Australia has no comparable research despite widespread use of shooting, common scavenging by potentially susceptible wildlife species, and people regularly consuming shot meat. We conclude that Australia has its collective ‘head in the sand’ on this pressing worldwide One Health issue. We present the need for urgent research into this field in Australia.