Ecology & Behavior of Roof Rats

Like Norway rats and native rats, roof rats are nocturnal (active at night). The most significant behavioral difference between the species, which has implications for control methods, is the aerial nature of roof rats. Roof rats prefer to forage for food above ground in elevated areas indoors and outdoors. They are agile climbers and travel through trees and along vines, wires, rafters, and rooftops. They often use trees and utility lines to reach food and to enter buildings, but can also be found foraging in dense ground cover. Like Norway rats, roof rats can swim and may use sewer systems to disperse to new areas.

Roof rats may nest in your neighbor’s yard but find food in your yard. Outdoors, they can travel several hundred feet in a single night to find their survival resources. They prefer to nest in secluded areas above ground in such places as attics, soffits, overhead garage storage, in the vine cover of fences or buildings, and in wood piles or other stored materials where harborage can be found. They favor dense non-deciduous trees or trees with hollow cavities and the crowns of palm trees, especially when old fronds are not removed. Roof rats sometime burrow in the ground especially in hot, dry environments. In these areas, they may use trees, materials stored on the ground, concrete slabs and sidewalks to support shallow

Roof rats have a high reproductive potential and may breed year-round in warmer areas. Females produce 5 to 8 pups per litter with a possible 4 to 5 litters per year.

Food Habits

Roof rats are omnivores (plant- and animal-eating). They are very fond of fruit, especially oranges (Figure 2). In addition to citrus they will feed on fruit-producing ornamentals, dates, stored food, birdseed in feeders, insects, snails, and garbage. These rats will also feed on stored food and livestock feed and will contaminate much more than they actually eat. They obtain much of their water requirement from their food, but unless their diet includes a sufficient amount of succulent plant material,they will require a source of free water such as landscape irrigation.

Roof rats generally begin searching for food shortly after sunset. These rats may cache or hoard considerable amounts of solid food, which they will eat later. These food caches may be located in attics, in dense vegetation such as hedges, or in a variety of other hiding places generally near their nests.

Roof Rat Signs

Roof rat signs include smudge marks on surfaces from oil and dirt rubbing off their fur as they travel (Figure 3). Because of their propensity to climb, look for these smudges up high on structures, e.g. between rafters, as opposed to marks along walls near the floor which could be made by other rodent species. Because they are often living overhead, between floors or above false ceilings, there is less tendency to see signs of roof rat tracks, urine, and droppings.