Although most cervids are polygynous, some species are monogamous (e.g., European Roe deer). The breeding season of most cervids is short, with females coming into estrus in synchrony. In some species, males establish territories, which encompass those of one or more females. Males may then mate with those females who have territories within his own. In some cervids, females may form small groups known as harems, which are guarded and maintained by males, and in other species males simply travel between herds looking for estrus females. Sexual segregation is not uncommon in cervids; however, in some species permanent mixed-sex groups result in male-male competition for potential mates. In sexually segregating species, males join females only to copulate, leaving at the end of breeding season. Males establish dominance hierarchies among themselves, with the most dominant males achieving the most copulations. Males may hold dominance over a harem or territory and are often challenged by rival males. Male cervids significantly decrease forage intake during breeding season, which, in conjunction with being continually challenged by rivals males, ensures that dominance by any one individual is short lived. Antler growth is dependent on individual nutrition and evidence suggests that the size and symmetry of male antlers serves as an indicator of mate quality for females.
Mating System: monogamous ; polygynous
Cervids living in temperate zones typically breed during late autumn or early winter. Seasonal breeders at lower latitudes, such as the chital, breed from late spring into early summer (e.g., April or May). Conception usually occurs during the first estrus cycle of the breeding season, and those that do not conceive will re-enter estrus every 18 days until they become pregnant. Species living in tropical climates, such as grey brocket deer, often do not have a fixed breeding season, and females may come in to estrus multiple times throughout the year. Gestation in cervids ranges from 180 days in Chinese water deer to 240 days for elk, with larger species tending to have longer gestational periods. Roe deer are the only cervid known to have delayed implantation. Cervids typically have from 1 to 3 offspring, and often, not all fetuses are carried to term, as the number of offspring born each year is dependent on population density and resource abundance. Age at weaning varies among species, with smaller species nursing for only 2 to 3 months and larger species nursing for much longer. For example Bornean yellow muntjacs are weaned by about 2 months of age and North American moose are weaned by about 5 months, however, erratic nursing may continue for up to 7 months after birth.
Body weight is more importance in determining sexual maturity in cervids than actual age; therefore, an individual's reproductive activity is dependent on environmental conditions and resource quality and abundance. Due to the energetic costs of lactation, this is especially true for females. In males, testes begin producing hormones at the end of the first year, and consequently, antler growth occurs during the end of the first year or the beginning of the second. However, because male-male competition plays a dominant role in cervid mating behavior, most males do not mate until they can outcompete rivals for access to females.
Although some cervids are solitary, most are gregarious and live in herds that vary in size from a few individuals to more than 100,000 (e.g., caribou. Average group size depends on the demographic composition (i.e., sex and age) of the immediate population, the degree of inter- and intraspecific competition, and resource quality and abundance. Habitat segregation in cervids tends to peak during calving and significantly decreases soon afterward. Most species are polygynous, and males use their antlers in combat to obtain and defend females. Sexual-size dimorphism is common in cervids. Males are larger than females in most species, and sexual dimorphism is more pronounced in the most highly polygynous species. Cervids have a number of glands on their feet, legs, and faces that are used during intraspecific communication. Males of many cervid species significantly decrease forage intake during mating season, and evidence suggests that feeding cessation in males is linked to various physiological processes associated with chemical communication during the breeding season.
Key Reproductive Features: iteroparous ; seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous
As with many artiodactyls, cervids can be classified as either hiders or followers. Altricially born cervids are highly vulnerable to predation for the first few weeks of life. As a result, mothers hide their young in the surrounding vegetation as they forage nearby. Hider mothers periodically return to their young throughout the day to nurse and clean their calves. Females that give birth to multiple offspring hide each individual in separate locations, presumably to decrease the chance of losing multiple young to a predator. Once young become strong enough to escape potential predators they join their mother during foraging bouts. Some species are precocially born and are able to run only a few hours after birth (e.g., Rangifer tarandus). These species are often referred to as followers.
Lactation is one of the most energetically expensive activities possible for female mammals and lactating cervids are often not able to consume enough food to maintain their body weight, especially during the first weeks of lactation. Typically, young are weaned earlier in smaller species; however, sporadic nursing may occur for up to 7 months after birth. Young cervids may stay with their mother until she is about to give birth to the subsequent season’s offspring. In many species, females stay within their mother’s range after maturation, while males are forced to disperse. In most species, males do not provide any parental care to their offspring.
Parental Investment: female parental care ; pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female); post-independence association with parents