More is known about the ecology of the coyote than any other carnivore. Coyotes are primarily nocturnal and are most active in the early evening. There is a second, minor peak of activity shortly before dawn. Some individuals are active during the daylight hours, especially juveniles during summer. Coyotes are usually solitary, although pairs may hunt together during the breeding season. Larger aggregations usually represent family groups or several males courting estrous females. Dens are constructed by coyotes in rangeland, in protected areas adjacent to farmland, on brushy hillsides, in thickets, and under rock ledges. Abandoned badger, fox, rabbit or woodchuck dens may also be used. A typical den has more than one entrance and is 1.5-6 m long. It serves primarily as a nest chamber. A female Coyote may prepare several dens and move the litter from one to another before the young disperse. Studies have indicated that daily movements of both males and females average about 4 km. However, one Coyote moved about 160 km. Density of coyotes depends on numerous variables but tends to be 0.2 to 0.4 coyotes per square km. Coyotes are highly vocal (the word "coyote" is derived from the Aztec word "coyotyl," meaning "barking dog"). There are doglike barks and squeals in addition to their characteristic howl. All told, 11 distinctive sounds, all presumably used to communicate with other Coyotes, have been categorized.
The size of Coyotes varies geographically. Adults may attain the following dimensions: total length 1050-1400 mm; length of tail 300-400 mm; length of hind foot 175-220 mm; length of ear 80-130 mm; weight 12-18 kg. Females average slightly smaller than males. In captivity, Coyotes may live as long as 18 years. However, few wild animals live longer than 6 or 8 years.
Coyotes are opportunistic omnivores, eating a wide variety of plant and animal foods, but focus on small mammals and carrion. Much of their diet consists of mice, rats, rabbits, squirrels, and whatever dead animals they find. Ground-nesting birds also are eaten. Various fruits, berries, seeds, and grasses are consumed when available. Deer that are eaten are usually carrion; Coyotes rarely capture a healthy adult individual.
Adult coyotes have few natural predators. In areas where wolves occur, wolves may kill some and outcompete others. In fact, extirpation of wolves is thought to be one cause of the current abundance of Coyotes. Pumas are known to kill Coyotes, but this probably is not a common occurrence. Most mortality of Coyotes likely results from injuries and hunting.
Female Coyotes are monestrous, the period of heat lasting from 2 to 5 days. Courtship may begin 2 or 3 months before estrous, which occurs in late winter or early spring. Breeding usually occurs sometime between mid-February and mid-March. Gestation lasts about 9 weeks, and the average litter size is 6.
The same pair of individuals may breed year after year, but do not necessarily remain together for life. Gestation varies from 58 to 65 (average 63) days. Litters range in number up to nineteen (probably a combined litter from two females), but average 4 to 7 pups, the size varying with the abundance of prey. The young are born blind, weigh about 250 grams, and are 160 mm long. Their eyes open 14 days after birth. After about two weeks, both parents regurgitate partly digested food for the pups. They begin to eat solid food when they are about three weeks old and are weaned between the fifth and seventh weeks. The young first leave the den when they are two to three weeks old, and disperse when they are six to nine months old. Males may help the female and young by providing food and grooming the young. Coyotes reach adult weight at about nine months. Females and males may breed as yearlings but unless prey are abundant, yearling females do not produce litters.