The barb pigeon, for example, has wattles resembling those of a chicken, and the trumpeter and swallow pigeons have feathers on their feet. Such species are bred for exhibition. Others, such as tumbler pigeons, are used in aerial performances. Common species are often used in scientific research because of their abundance and availability. Wild pigeons are susceptible to parasites, particularly lice.
Trichomoniasis is a disease caused by a parasite that lives in the bird's liver, throat, and lungs.
Serious outbreaks have killed thousands of mourning doves. They have plump bodies with short necks and small heads. Their legs are relatively short and the feet have four toes. The birds walk with small, deliberate steps and bob their heads distinctively. The Columbidae have a well-developed crop that allows them to collect food faster than they can digest it.