There are many factors affecting birds such as habitat loss through intensive agriculture, pollution, climate change and predation. Waterbirds, especially ducks, geese and swans, are also known to mistakenly ingest lead shot as grit in an effort to aid digestion. This then enters the gizzard and the lead pellets are ground down, which makes the lead particles easier to absorb. In some cases, a single lead pellet is enough to cause poisoning for 2-3 weeks leading to death in mallard and some small waders (Bellrose, 1959; Mateo, 2009). The numbers and trends of waterfowl populations at different scales are known to be associated with their ingestion of lead shot (Anderson et al. 2000; Samuel & Bowers 2000; Stevenson et al. 2005; Mateo et al. 2014; Pain et al. 2015; Meyer et al. 2016; Green & Pain 2016, Andreotti et al., 2018).
Studies have also shown that terrestrial huntable birds can also ingest lead shot, including Red grouse (Thomas et al., 2009), Pheasant (Butler et al., 2005), Red-legged Partridge (Butler et at., 2005) and Grey Partridge (Potts, 2005) in the UK, and Red-legged Partridge in Spain (Ferrandis et al., 2008). An assessment in France categorised lowland galliforms as having a “minor to moderate exposure” risk to lead shot (Portier, 2016).
Lead ingestion from ammunition (see also section on ‘Non-lead bullets’) has been reported in various raptors and scavenging species in Europe. Studies show that certain species can ingest lead through eating non-retrieved game or offal containing lead fragments in discarded gut piles. The following recent studies provide more information on the ingestion of lead (from ammunition) in raptors and scavengers in Europe:
For game shot with a rifle using lead bullets, the greatest levels of lead will be in the meat around the wound channel and typically in the heart and lungs. Misplaced shots or shots which hit bones can also result in high levels of lead in the abdominal organs.
Disposal of lead contaminated tissues in the field can result in lead poisoning of avian and mammalian predators and scavengers such as eagles, bears and wild boar, and even hunting dogs. Scavenging birds such as vultures, golden eagles and white-tailed sea eagles are also at risk (Margalida et al., 2008; Hernández and Margalida, 2009; Berny et al., 2015, Isomursu et al., 2018).