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The technique is fairly simple: the animal is placed in an enclosed space into which carbon dioxide gas is added at a controlled rate. When the animal breathes this gas, it quickly loses consciousness and then dies. The entire process takes about five minutes.
Carbon dioxide (CO2) is a colorless, odorless gas. It's called an "inhalant agent" because the animal must breathe it in. CO2 affects the nervous system, the lungs, and the heart.
Carbon dioxide chambers work well to humanely kill birds, rodents, and most small mammals. But you may encounter problems if you try this technique on animals that are old, very young (less than 2 weeks old), weak, or sick with a respiratory disease, because they're often resistant to the effects of carbon dioxide. If possible, choose another technique to humanely kill animals that breathe slowly (such as reptiles or amphibians) or are very good at holding their breath (such as beaver and diving birds). Under these circumstances, CO2 might take too long to be considered a best practice.
Commercial carbon dioxide chambers are often made of metal and have windows for monitoring the animal, but the chamber can be made of many materials, such as plywood or plastic. Coolers, garbage cans, and other containers have been converted into chambers. The best chambers are clear or have windows so you can monitor the animal, and are also easy to clean and transport.
You may want to have several chambers of different sizes and designs, and a portable model. For example, bats can be more humanely killed in a small chamber that fills faster. A small, clear plastic container with two holes drilled into it (one for the tube feeding the gas, and a vent hole) would work well.
One NWCO has rigged a garbage container on wheels to serve as both an enclosed trap and carbon dioxide chamber. He sets a cage trap within the chamber, then, after capturing the animal, wheels the can to a place where he can safely and discreetly attach the carbon dioxide tank and kill the animal. This combination of a trap within the CO2 chamber also offers a safety advantage, because there is no handling of the animal. Consider such an approach, especially when dealing with sick, rabies suspect, or highly aggressive animals.
There may be a market niche for those willing to provide on-site wildlife euthanasia services, especially in areas where other techniques that are generally accepted by the public, such as shooting, aren't legal or practical. With care, carbon dioxide chambers can be safely transported.
Homemade CO2 chamber
|Many commercial coolers come with a drain hole at the bottom. Attach the hose to the drain hole. If your model lacks a drain hole, you can drill it out. To add a window to your chamber, drill through the cooler using a jigsaw. Cut a piece of plexiglass to fit, then attach to the cooler using epoxy.|
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