Hispid Cotton Rat - Timing of Major Life Events

Timing of Major Life Events

Some studies have suggested that hispid cotton rats are mainly nocturnal, but activity has been observed at all hours. Activity patterns appear to be influenced by both biotic and abiotic factors. Hispid cotton rats are active year-round.

Hispid cotton rat populations usually exhibit a bimodal breeding season, with peak litter production occurring in late spring and in late summer-early fall. Rose reported reproductive peaks in March and June for hispid cotton rats; all of trapped females were pregnant from March through July, but none were breeding in November and December. They do not breed in the coldest winter months. In Kansas breeding is restricted to the frost-free months.

A nest is constructed by the female either on the ground surface or in a burrow. Nests are cup- to ball-shaped and woven of grasses. Hispid cotton rats in the northern parts of their range make nests that are thicker and denser, but not larger, than those of southern hispid cotton rats.

Gestation in hispid cotton rats lasts approximately 27 days. Litter sizes range from 1 to 15 young, with larger litters more typical of northern populations and also of late-season litters. Neonates are well developed; they are mobile and lightly furred but the eyes are not open. The eyes open approximately 18 to 36 hours after birth. Hispid cotton rats are weaned in 10 to 15 days and reach minimum adult size by about 41 days.

Some male hispid cotton rats are sexually mature by 60 days, some females are receptive by 30 to 40 days. The earliest recorded pregnancy was at 38 days. Hispid cotton rats have been noted as one of the most prolific mammals in the Southeast. Females bear two to several litters per year depending on latitude and local weather. Females mate within 24 hours of giving birth.

Hispid cotton rat populations are largely sedentary; population density depends mainly on current reproductive effort and not as strongly on immigration. In Kansas remnant prairie, hispid cotton rat population density was highest in fall and early winter and lowest in spring and early summer. In the northernmost parts of hispid cotton rat range, severe weather is associated with rapid hispid cotton rat population declines and local extinctions. In Kansas, most hispid cotton rat mortality was associated with severe weather in March and April. Populations in the northern part of hispid cotton rat range experience dramatic declines in the nonbreeding season. In many areas local extinction is frequent . In Georgia, hispid cotton rat spring abundance in old fields was lowest following drought and extreme winter cold. The reductions in hispid cotton rat populations were associated with sharp declines in vegetative biomass and cover.

In Georgia, a density of 15 hispid cotton rats per acre was considered the predator-limited carrying capacity. Mammalian predators did not have a substantial effect on hispid cotton rat population density. At densities higher than 15 per acre mortality was high; below 15 hispid cotton rats per acre predator-caused mortality was low. Schnell concluded that when diverse and mobile predators are present they are more important than food, social interaction, or weather in limiting hispid cotton rat density. Also in Georgia, 1-acre (4,000 m2) field enclosures protected from avian predators (covered with a net) were monitored for the effect of avian predators on breeding hispid cotton rat populations. The presence of the cover had no effect on seasonal recruitment or spring-summer mortality; however, autumn-winter mortality was greatly reduced with the cover in place. It was therefore suggested that avian predators are more important than mammalian predators. In addition, it was concluded that nonbreeding (winter) populations suffer substantial losses from predation whereas breeding populations are either able to compensate by replacing lost individuals, are less vulnerable to predation, or both.