in Northern Ireland (K. Thompson, personal communica-

These large-scale killing operations have indicated that there are two potential methods for killing birds with gas mixtures. First, the birds could be carried by hand or in crates out of the house and placed in containers, such as skips or waste bins, which contain lethal concentrations of denser-than-air gases, or crates full of birds could be placed in empty containers and a suitable denser-than-air gas mixture then introduced to them; this method was used in 2005 in the UK to cull a flock of pheasants suspected of having Newcastle disease (T. Pennycott, personal communication). However, as with most other methods, the birds have to be caught and handled, which may compromise their welfare and could compromise the operators ’ health and safety if the pathogen were zoonotic and appropriate protective equipment were not worn. Secondly, the birds could be killed by introducin