Little egrets colonised the UK from the 1990s and have become established wetland birds, but face welfare risks from organochlorine and heavy metal contamination through fish prey and disturbance at roost and breeding sites.
Little egrets accumulate methylmercury from fish prey, with high mercury individuals showing neurological impairment and reduced reproductive success. Roost disturbance at night causes energy-expensive flush responses and may prevent roosting in key sites during cold weather. Chicks in colonial heronries are vulnerable to predation during disturbance-induced adult flushing. Egrets fishing in polluted urban waterways face higher contamination loads than those using cleaner agricultural or nature reserve wetlands. Road strikes during low-level hunting flights cause acute trauma.