To your cat, they're tasty treats and interesting playthings, but dead birds, whether found or freshly killed, harbor parasites and viruses that have the potential to make your cat sick. Some of these illnesses can even be passed on to humans. Fortunately, however, most healthy adult cats have immune systems strong enough to fight off anything they might contract from a dead bird.
Toxoplasmosis is caused by a parasite that is often carried by a cat's favorite prey animals, like birds and mice. Your cat can become infected by eating a bird it has hunted and killed, or one that is already dead. Healthy adult cats may not show signs of illness and simply become carriers, while cats with immune system deficiencies, and kittens, may become lethargic, lose their appetite and have a fever. In severe cases pneumonia, seizures, blindness and loss of bladder control are possible, although rare.
Toxoplasmosis can be spread to humans through contact with an infected cat's feces. It is not serious and usually doesn't require treatment in a healthy adult, but is dangerous to infants and those with weakened immune systems. People at risk, including pregnant women, should take extra precautions when cleaning the litter box.
Salmonella is a bacterium found in many animals, including birds. A cat can get it by eating a bird or its feces. Also known as songbird fever, salmonella causes fever, lack of appetite, diarrhea and weakness, and in severe cases septicemia, a serious bacterial blood infection. Like toxoplasmosis, it can pass from cats to humans, not only through contact with feces, but also through contact with saliva. Salmonella can also pass from humans to cats and other animals, and back to humans again. Treatment for both cats and humans is focused mainly on gastrointestinal symptoms, although antibiotics are given in severe cases.
Asian bird flu, or H5N1, has been found in cats that have feasted on infected birds; however, the number of cases is low and the cats involved were exposed to large numbers of birds carrying the illness. No cases of cats passing bird flu to humans have been recorded. According to the Arizona Department of Health Services, cats in the United States are not at risk of catching H5N1 from eating dead birds, because it has not affected the wild bird population.
West Nile Virus
West Nile virus is transmitted primarily by mosquitoes. Although birds can be infected, the virus is not passed to cats, even if they eat a sick dead bird. The only known way for cats to become infected is by being bitten by a mosquito carrying the virus; even in such a case, cats do not become very ill. West Nile virus does spread from cats to humans, but humans can also be infected by mosquitoes.