Reproductive biology

Mating systems are the most complex and variable aspects of social behavior. Carnivores give birth to altricial young that are dependent on adults for their survival for an extended period. Much of their behavior is therefore centered around not only producing young but also raising them. There are two basic types of mating system in carnivores; monogamy where a male mates with one female, and polygyny where males mate with several females and/or vice versa. Monogamy is the least common of the two systems and is practiced by all canids, and also in the aardwolf and some mongooses, although in most species the rules are broken. Either a male attracts more than one female to the territory, or cuckoldry occurs. Monogamous systems are characterized by both sexes and often older offspring helping to raise young by feeding and guarding, and by a lack of sexual dimorphism. An extreme case is found in pack living animals such as African wild dogs and dwarf mongooses where normally only one pair breeds while the other sexually mature adults abstain and help to raise the young. In polygynous species the males are usually larger than the females and often are equipped with spectacular adornments to attract females, like the lion and elephant seal. Cooperation in raising young is less common but does occur in some social polygynous species, for example female lions suckle each others' cubs.

The black-footed ferret (Mustela nigripes) depends on its prey prairie dogs (Cynomys sp.) for food and shelter. (Photo by © Jeff Vanuga/Cor-bis. Reproduced by permission.)

Many carnivores range widely and spend their time alone and so it is important for the females to advertise when they are ready to mate. Scent marking through urination and anal secretions is widespread in carnivores, and is the obvious mechanism to achieve this. Even then the best male may have difficulty in being at the right place at the right time. One way that a female can ensure that she mates with the best available male is to adopt a reproductive strategy known as induced ovulation. The females come into estrus, but do not shed eggs until stimulated to do so by copulation. The other strategy is called spontaneous ovulation, where the eggs are shed in a cycle that is unaffected by mating. Although there are exceptions, spontaneous ovulators are likely to be more social species than are induced ovulators.

Smaller animals have faster metabolic rates and breed faster than larger animals. The females of the smallest carnivore, the least weasel, are sexually mature at three months. Litter size is usually six, so if she lives long enough—the average life expectancy is less than one year—a female can potentially produce 30 descendants a year. This is achieved by producing six in her first litter, another six in her second, plus six offspring from each of the three daughters she would be expected to produce in her first litter. Males are not sexually mature in their first year. At the other end of the scale, lions may only produce a litter of three or four cubs in three and a half years as the cubs only become independent at about three years of age. If, however, the female loses all her cubs she will quickly come into estrus again. African wild dogs have higher metabolic rates than would be predicted from their size and their populations turn over rapidly. This is reflected in their high reproductive potential. They are seasonal breeders that produce large litters, the record is 21 for a single female.

Pinnipeds, so well adapted to a life in the sea, must come to breeding grounds on land in summer in order to reproduce. The males arrive slightly earlier than the females and set up territories. The females arrive shortly before giving birth to a single pup that was conceived the previous season. The lactation period is very short and intense, not more than six weeks, in the true seals. The pups are weaned and deserted abruptly and the females mate, before going back to sea for another year. In eared seals, the female comes into season and mates about one week after giving birth. Lactation lasts 4-6 months during which time the mother makes periodic feeding forays into the sea.

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