Practicality and humaneness of euthanasia of pest birds with compressed carbon dioxide (CO₂) and carbon monoxide (CO) from petrol engine exhaust

Feral birds degrade the environment and have an adverse impact on human health, welfare and economy in many parts of the world. In eastern Australia, common myna (Acridotheres tristis), common starling (Sturnus vulgaris) and house sparrow (Passer domesticus) have recently become targets of community groups seeking to control impacts by selective live-trapping. We sought a safe and practical euthanasia method that could be recommended to such groups for humanely destroying trapped birds. We compared the practicality and humaneness of the following two commonly available inhalant euthanasia agents: (1) carbon dioxide (CO₂) from cylinders and (2) carbon monoxide (CO) from cooled exhaust from idling petrol engines. Test birds were euthanased in conditions that promoted calm (small groups of birds; small covered chambers with perches). Video recordings were analysed in real time and at 1/10 speed for signs of distress, and times to recumbency and last movement. In all, 25 mynas and 24 starlings were euthanased with CO₂, and 32 mynas, 30 starlings and 8 sparrows with CO. Times to recumbency for birds euthanased with CO₂ varied from 20 to 85s and time to last movement from 65 to 153s. For birds euthanased with CO, these times were 7180s and 43240s respectively. Mynas and starlings euthanased with CO₂ showed substantially more signs of distress (gaping and head-shaking) before recumbency than did birds euthanased with CO, although this was less pronounced if the concentration was increased slowly. No signs of distress were observed in any birds euthanased with CO, irrespective of the rate at which the concentration was increased. CO produced a comparably rapid, and more humane death than did CO₂ in birds of all three study species. The study indicated that, with simple precautions to avoid accidental exposure, CO in cooled exhaust from petrol engines provides a safe, rapid and humane agent for euthanasing mynas, starlings and sparrows, that is readily available at a very low cost. We tested only three species, and the results suggested that it would be useful to re-examine the embargo against animal euthanasia via engine exhaust, that exists in many jurisdictions.