Tigers, like most mammals, utilize their lungs to respire gaseous oxygen from the atmosphere using diaphragm muscles to inhale and exhale. Tigers rarely use their sense of smell for hunting; their olfactory senses are used to scent-mark territory and for mating. The feline leukemia virus is a common ailment among tigers that causes respiratory problems.
Tigers are normally solitary animals who mark their territory by spraying urine on plants. Scents identify tigers by sex and whether or not the animal is from nearby or far away. When an outsider tiger smells another specimen's urine, the intruder knows that this territory is already claimed. Tigers smell each other by wrinkling their noses while the tongue is exposed from the mouth. This facial expression allows the felines to enhance their sense of smell to identify the owners of territory.
Females spray more urine than normal when they are ready to mate. When males pass through a female's territory, the scent of urine is stronger during mating times. This stronger urine scent indicates a female is ready to conceive.
National Geographic asserts that there are fewer than 2,500 tigers left in the wild due to hunting, habitat loss and human encroachment. Tigers are the largest felinoid species on Earth that have distinctive red-orange coats with black stripes.