The most common source of lead poisoning in waterfowl is from the ingestion of lead pellets from shot shells and the resulting absorption of hazardous levels of lead into body tissues. Lead poisoning is more common in species such as mallards, northern pintail, geese, and tundra swans, while frequency decreases in species with more specialized food habits. Raptors, such as eagles, are also often affected by lead poisoning due to the ingestion of lead pellets embedded in the flesh of their prey. Lead poisoning is not considered an appreciable risk to hunters, especially since lead is mostly concentrated in the liver and kidneys of birds, rather than the flesh. A large number of lead-poisoned birds must be consumed in a very short period of time before levels would reach toxicity in humans.
Signs of lead poisoning include weak, erratic flight, inability to sustain flight, or flightlessness; crooked head and neck position; "roof-shaped" wing or wing droop; fluid discharge from the bill; green, bile-filled diarrhea; and emaciated, "hatchet-breast" due to wasting of the breast muscles.
Mercury is a heavy metal that is toxic to vertebrates, and birds can be exposed to high levels due to their feeding behavior. Sources of mercury come from industrial discharge, acid precipitation, and high levels of mercury in fish and sedimentation. Mortality is usually scattered and rarely in the form of a major die-off. Mercury is considered a human health hazard, and hunters should not eat animals with high levels of mercury.
High mercury levels were found in two duck species, northern shovelers and common goldeneyes, at the Great Salt Lake in 2005, and a waterfowl consumption advisory was issued for these species.