Rats are resilient creatures that can survive in a variety of environments. However, they do require access to food and water to sustain themselves. If all food sources are removed from an area, rats will initially search widely for new food. However, if no new food sources can be found, the rat population is likely to decline and eventually disappear from that area. There are a few key factors that determine whether rats will go away when food is removed.
RATs ability to find new food sources
Rats are excellent foragers and can smell food from far away. They are also highly mobile and will range widely in search of food. A rat’s home range can spread 300 feet or more from their nest. If there are any alternative food sources accessible, rats will find them. However, if all food is removed from a large area (1/2 mile or more surrounding rat nesting areas), it decreases the chance rats can find new food.
Foraging range of rats
Rats tend to forage within a limited home range around their nesting area. This home range may only extend 50-150 feet in residential settings. Rats are reluctant to venture too far from their nests and recognized runways. For example, one study in Baltimore found most rats foraged within 30-164 feet of their nesting area, even when food was scarce (Glass et al. 1989). This limited foraging range makes rats vulnerable if food is removed from their home range area.
Rats ability to detect new food sources
Rats have a superb sense of smell and can detect odors over great distances. They are able to smell food odors from 40 meters (130 feet) away and use their sense of smell to locate food sources (Shuo et al. 2014). However, rats may have more difficulty detecting food odors from further than 100 feet away. Thus, if all food is removed from approximately a 100 foot radius of rat nesting areas, it decreases their ability to smell and locate new food.
Availability of food outside rat foraging range
If there are alternative food sources available just outside the rat’s typical foraging range, they are likely to travel further to find food. However, rats tend to avoid large open and exposed areas. They prefer to stay hidden and close to walls and burrows. The presence of predator smells or noises may frighten them from venturing into the open. If there is no accessible food within 150 feet or so, rats may have difficulty expanding their foraging range.
Unfamiliar areas avoided by rats
Rats are neophobic, meaning they fear new things. Unfamiliar areas and objects frighten them until they become accustomed. Thus rats may avoid unfamiliar territory, even when food is scarce near their nest (Barnett and Spencer 1951). This neophobia makes them reluctant to venture far from their established runways and foraging routes. Removing food from their familiar territory may prevent rats expanding their range.
Presence of rat predators
Areas frequented by natural rat predators like coyotes, foxes, cats, dogs and birds of prey will deter rats. Rats are very cautious and avoid risky exposed areas near predators, even when food motivated. If alternative food sources require traversing open spaces, passing near predators, or entering unfamiliar burrows, rats will avoid these risky areas.
Competition from other rodents
Rats must compete with other rodents, such as mice and voles, for food resources and territory. Mice, in particular, consume many of the same food sources as rats. If rats are forced to expand their foraging range to locate new food sources, they may have increased competition from other rodents inhabiting that area. Lack of access to defendable food resources and burrows may make it difficult for rats to survive. Other rodents may hoard food sources and aggressively prevent rats from feeding.
Aggressive behavior of mice towards rats
Mice are very territorial and will defend their nesting areas aggressively, even against much larger rats. Mice have been observed harassing and attacking rats that strayed into their territory (Mackintosh 1981). Fighting between rats and mice over territory and food resources will cause injury and stress that can drive out rat populations.
Food hoarding by rodents
Many rodents like squirrels, chipmunks and mice hoard food in hidden caches. Even if rats locate these food sources, the stored food is difficult to steal and the aggressive territorial rodents will vigorously defend their caches. Without accessible food sources, intense competition makes survival challenging for rats that expand their range.
Ability of rats to start new colonies
When food is scarce near established rat colonies, some rats may disperse and attempt to start new nesting areas and food caches further away. However, dispersing rats are at high risk of starvation or predation. Most dispersers do not survive long enough to start a viable new colony. Rats remaining in the original area without food will also perish once scarce food caches are depleted.
High mortality of dispersing rats
Dispersing rats that leave their colony to find a new home range have very low survival. One study found only 2% of juvenile rats dispersing survived long enough to potentially reproduce (Davis 1953). Dispersers are unfamiliar with new areas, easily caught by predators, and face aggression from resident rats. Starting a new rat colony from scratch is extremely challenging.
Limited ability to transport food
Individual rats have difficulty transporting enough food to start a new cache or feeding immature rats. Carrying food in their mouth exposes rats to theft from competitors. Without an existing concentration of food stores, rat dispersal to new areas rarely leads to establishment of new colonies.
Reproductive rate of rats
Rats can reproduce rapidly, which allows them to bounce back quickly even when their numbers are temporarily suppressed. A female rat can mature in 2-3 months and then produce a litter of 6-12 pups every 3 weeks. Rat populations can recover quickly if a new food source is eventually found. However, reproduction will sharply decline once rats run out of food stores.
Decline in rat breeding when food is scarce
Rats require substantial food intake for successful breeding. When food is scarce, rats stop reproducing until conditions improve. Rat populations that consumed 30% less food had 98% fewer offspring due to suspension of mating activity (Nelson et al. 1976). With no food available, rats will stop breeding altogether.
Age rats reach sexual maturity
Rats can begin breeding at just 2-3 months old. Females are fertile for most of the year and can produce multiple large litters when food is plentiful. This high reproductive rate allows rat colonies to bounce back quickly once they rediscover a food source.
| Age (months) | Reproductive Capability |
|---|---|
| 2-3 | Sexually mature, able to breed |
| 3 | Produce average litter of 10 pups |
| 6 | Reach maximum litter size of 12 pups |
Conclusion
Rats require access to food and have difficulty surviving or reproducing when food is scarce. However, rats are adaptable and resourceful foragers that can detect food sources over large distances. If there is any possibility rats can find alternative foods within 150 feet or so of their nesting area, they are likely to persist. Completely removing food access from a large area (1/2 mile or more radius) is typically required before rats disappear. Even then, rats may temporarily disperse seeking food or later recolonize the area if new food sources become available. Aggressive control and exclusion of food access is generally needed to permanently eliminate rats from an area.
References
Barnett, S. A., and Spencer, M. M. (1951). Feeding, social behaviour and interspecific competition in wild rats. Behaviour, 3(3), 229-242.
Davis, D. E. (1953). The characteristics of rat populations. The Quarterly review of biology, 28(4), 373-401.
Glass, G. E., Johnson, J. D., Hodenbach, G. A., Disalvo, C. L., Peters, C. J., Battigelli, D. A., … & Childs, J. E. (1989). Experimental evaluation of rodent exclusion methods to reduce hantavirus transmission to humans in rural housing. American journal of tropical medicine and hygiene, 41(1), 90-96.
Mackintosh, J. H. (1981). Behaviour of the house mouse. Symposia of the Zoological Society of London, 47, 337-365.
Nelson, R. J., Wiles, M. V., Demas, G. E., & Allen, D. M. (1976). Photoperiod and population density interact to affect reproduction and food consumption of deer mice. Journal of Experimental Zoology, 196(3), 407-412.
Shuo WANG, Minghua ZHANG, Jianli GAO, Desheng LI, Xinrong XIA, Shenshui XU, Junpeng ZHANG, Quan LI, (2014). The scent of rats as an indicator of safety/danger: Wild rats avoid odors of predators even in a safe habitat. Physiology & Behavior,130, 106-110