Rat and Mouse Identification and Behavior: Is it a Roof Rat, Norway Rat or House Mouse?

To work out the best strategy for managing a rodent problem, accurate identification is important, as is understanding their behavior.

1. Norway Rat Identification

Norway Rats (Rattus norvegicus) also known as common rats, sewer rats or brown rats, are the larger of the two pest rat species, and have distinct features which we can use to identify them:

• coarse reddish-brown to grey fur, with grey belly fur and grey feet
• large, stock, heavy-set build
• blunt nose (snout or muzzle)
• small eyes
• short thick ears with fine hair, the ears do not reach past their eyes
• head and body length of 20–27 cm (8–11 in)
• tail length of 16–20 cm (6–8 in), tail length is shorter than the combined length of the body and head. A simple field identification test (for non-living rodents!) is to pull the tail toward the head. If the tail extends past the snout, it’s a roof rat, if it doesn’t, then it’s a Norway rat.
• weight of 200–500 grams (7–18 oz)
• banana or sausage-shaped droppings (with rounded ends), around 20-25 mm (3/4-1 in) long.

Other Characteristics:

• Habitat: Norway rats are ground dwelling rodents that can climb if they need to, and are excellent burrowers and swimmers. They often dig into rubbish and under buildings or concrete slabs. They thrive particularly well in areas where garbage is not properly contained. They frequently travel 30-50 m (100–150 feet) from their nests in search of food or water.
• Food: Norway rats usually prefer to eat fresh meat, fish, and grain. They consume 30 grams (1 ounce) per day of food from various sources. Being omnivores they will eat both plants and animal matter, including vegetables, weeds, earthworms, crustaceans, nuts and fruit. These rats will eat almost anything, including garbage or decayed food. Because they must have water to survive, Norway rats also consume around 30 grams (1 ounce) of water per day.
• Lifespan and Breeding: Norway rats live between 9-12 months. Females can produce 5-6 litters per year, with an average 8-10 pups per litter. Sexual maturity is reached at 3-4 months, and females have a gestation period of 21 days.

2. Roof Rat Identification

Roof Rats (Rattus rattus), also known as ship rats or black rats, are smaller than the common Norway rat, and are often bred for the pet trade. They have distinct features which we can use to identify them:

• fine grey, black or brown fur, with occasional white belly fur and pink feet
• small, slender, streamlined build
• pointed nose (snout or muzzle)
• large eyes
• large, thin, almost hairless, translucent ears, the ears extend past their eyes.
• head and body length of 14-20 cm (5.5–8 in)
• tail length of 25 cm (10 in), the tail is longer than the combined length of head and body.
• weight of 200-300 grams (7–11 oz)
• spindle-shaped droppings (having tapered or pointed ends), up to 12 mm (1/2 inch) long.

Other Characteristics:

• Habitat: Roof rats are usually found in built-up areas or near coastal areas. They are excellent climbers and prefer to nest off the ground in attics, roof spaces, wall voids, hollow trees, and in the thatch and dead fronds of palm trees. They prefer to travel off the ground and enter houses from nearby trees or along power lines, and will range 30-50 m (100–150 feet) from their nesting locations in search of water or food.
• Food: Roof rats generally prefer to eat vegetables, fruits and grain, but will eat any type of human, pet, or livestock food. They consume 15-30 grams (1/2-1 ounce) per day of food from various sources. They are omnivores and will feed on insects or meat if necessary. Because they must have water to survive, roof rats also consume around 30 grams (1 ounce) of water per day.
• Lifespan and Breeding: Roof rats live between 9-12 months. Females can produce 4-5 litters per year, and average 6-8 pups per litter. Sexual maturity is reached at 3-4 months, and females have a gestation period of 21 days.

3. House Mouse Identification

House Mice (Mus musculus) are much smaller than rats and can be easily distinguished from young/juvenile rats, as mice have large ears and eyes, and a pointier nose. They have distinct features which we can use to identify them:

• brown or grey fur, with uniformly colored body (backs and bellies are fairly similar in color), and pink feet
• small slender build
• pointed nose (snout or muzzle)
• large eyes
• large, hairy ears,
• head and body length of 8-10 cm (3–4 in)
• tail length of 8-10 cm (3–4 in), the tail is the same length as the combined length of head and body.
• weight of 14-20 grams (0.5–0.7 oz)
• small spindle or irregular-shaped droppings, about the size of rice grains, typically 3-6 mm (1/8 to 1/4 in) long.

Other Characteristics:

• Habitat: House mice normally live outdoors if conditions are suitable, but can successfully live their entire life indoors, behind walls, in false ceilings, floor voids, cabinets, furniture and similar enclosed spaces. They often seek warmth in appliances that operate continuously such as stoves, refrigerators, air conditioners, and coolers. They will travel 3-10 m (10–30 feet) from their nests in search of food or water. Rats prey on mice and compete for the same food and shelter, so removing rats often results in higher and more visible mouse populations.
• Food: House mice prefer to feed on grains but usually eat a wide variety of foods, such as fruits, nuts, animal feed and cereals. They can usually obtain all the water that they need from their food if it has high moisture, and only need to drink water if they are eating dry food. House mice require only 3 grams (1/10 ounce) of food and 1.5 grams (1/20 ounce) of water daily if needed.
• Lifespan and Breeding: House mice live approximately 12 months. Females can produce 6-10 litters per year. Sexual maturity is reached at about 6 weeks, and females have a gestation period of 3 weeks.

Understanding Rat and Mouse Behavior

Rats and mice exhibit a variety of behaviors that make them highly adaptable and often elusive to humans. By understanding these habits, we can better manage their populations and mitigate infestations. Below are some key aspects of rat and mouse behavior, from their nocturnal activity patterns to their highly developed sensory abilities.

Nocturnal Habits: Rats and mice are nocturnal animals, mainly active at night to feed under the cover of darkness and avoid being seen. They will only be active during the day when food is scarce, there is an overpopulation of rats, or when poison has been used and the population is sick.

Stealthy Behavior: Rats and mice prefer to travel along edges for safety, such as beside walls or objects, and avoid crossing open spaces like the middle of a room or yard, as this exposes them to predators. Their secretive behavior allows them to go unnoticed, and they are usually only discovered when their populations grow large enough to leave obvious signs of their presence, potentially leading to an infestation.

Curiosity: Rats are extremely cautious and avoid new objects in their environment, a condition known as neophobia (fear of the new). They always travel along established tracks and may wait up to two weeks before approaching traps or bait stations. Mice, on the other hand, are very curious and like to explore, investigating changes and new objects in their surroundings. This curiosity makes them easier to trap as they are more likely to wander from their usual paths.

Senses: Rats and mice possess a range of highly developed senses that help them navigate their environment, find food, and avoid danger.

• Hearing: Rats and mice have excellent hearing and can detect high-frequency (ultrasonic) sounds outside the human hearing range (20 Hz to 20 kHz). The hearing range of rats is approximately 250 Hz to 80 kHz, with the greatest sensitivity between 8 and 38 kHz. Mice can hear from 1 kHz to about 100 kHz.
• Smell: Their keen sense of smell helps them locate food, recognize territory, and sense danger.
• Touch: They use their sensitive whiskers (vibrissae) to enhance their sense of touch, enabling them to navigate and detect environmental changes in the dark.
• Taste: Rats and mice also rely on their keen sense of taste to avoid harmful substances. Because they cannot vomit, lacking the necessary anatomical structures and reflexes, they are more vulnerable to toxins they ingest, making their ability to detect them through taste crucial.
• Eyesight: Despite their highly developed senses, rats and mice have poor eyesight and depend more on their other senses. They use their vision primarily for detecting contrasts, patterns, and movement rather than seeing fine details or colors. Both rats and mice have dichromatic vision, meaning they can perceive only two primary colors. Their eyes have photoreceptor cells (cones) sensitive to ultraviolet (UV) light with peak sensitivity around 358–359 nm, and green wavelengths around 509–510 nm. The ability to detect UV light helps them navigate their environment, find food, and detect predators. In comparison, humans have trichromatic vision and can see red, blue, and green wavelengths of light but cannot perceive ultraviolet light.

Physical Flexibility: Rats and mice can fit through any gap or hole larger than their skull.

• Mice are highly flexible and can squeeze through very small openings. The average mouse’s skull is about 9-10 mm wide (around 3/8 inch), allowing them to get through gaps or holes slightly larger than that. Younger and smaller mice can even squeeze through gaps as small as 6 mm (1/4 inch) in diameter.
• Rats are larger with bigger skulls and bodies, but they can still squeeze through surprisingly small openings. The average rat’s skull is about 15-20 mm wide (9/16–3/4 inch), so they can fit through any gap or hole larger than their head, typically around 20-25 mm (3/4-1 inch) in diameter or wider.

Identifying Signs of Rat and Mouse Infestation

As rats and mice are nocturnal and rarely seen during the day, their presence can be recognized by various signs of their activity:

1. Droppings and Urine: Rodent droppings are a common sign of infestation. Fresh droppings are black, shiny, and putty-like, while old droppings are gray, dusty, and crumble easily. Rodents urinate while running, leaving characteristic streaks that glow blue-white under ultraviolet (UV) light.
2. Odor: A musty, urine-like odor often indicates the presence of mice rather than rats.
3. Gnawed Objects: Rodents gnaw at thing daily to keep their teeth short and sharp. Look for teeth marks on food, building materials, wires, and beams. Teeth gnaw marks appear as two grooves, those from adult mice measure 1-2 mm wide, while adult rat gnaw marks are 3.5-4 mm wide. Fresh gnaw marks are light-colored and splintery, while old marks are smooth and darker.
4. Entry Holes: Rats and mice will also gnaw holes in walls. Mouse entry holes are usually around 4 cm (1-1/2 in) in diameter or less, while rat entry holes are 5 cm (2 in) or larger.
5. Runways: Rats use the same paths or runways between their harborage (nest) and food or water sources. Outside, these paths are 5-7 cm (2-3 in) wide and appear as smooth, hard-packed trails under vegetation. Indoors, runways are usually found along walls.
6. Rubmarks: Rodents leave greasy smears (rub marks) along runways, walls, and baseboards from the oil and dirt on their fur. New rub marks are soft and smudge easily, while old marks are brittle and flake when scratched.
7. Tracks: To detect rodent activity, spread fine material like flour or talcum powder along runways. Footprints and tail drag marks will show in the powder. Mouse footprints appear as small dots, while rat footprints look like actual feet and may include a tail drag mark.
8. Nests: Rodents build nests from shredded paper, fabric, or other soft materials. These nests are often found in hidden areas like attics, basements, or behind appliances.
9. Sounds: Scratching, scurrying, or gnawing sounds, especially at night, can indicate rodent activity.
10. Burrows: Norway rats often dig burrows along walls near building foundations, in earth banks, under debris, rubbish and concrete slabs, or in gardens. These burrows can be identified by their entrance holes that are around 7 cm (3 in) wide, with freshly dug dirt scattered in front of the opening, and smooth, hard-packed soil runways leading to it indicate an old established colony.
11. Damaged Goods: Chewed packaging, gnawed food containers, and damaged goods are signs of rodent activity.

Additionally, pets like cats and dogs may become agitated or focused on areas where rodents are present. If pets are persistently sniffing at a wall, pawing under the refrigerator, or staring at a heating vent, they might have detected rodents.

The sighting of live rats or mice is a sure indication of their presence, but if they appear in the daytime, this can indicate that large populations are present (an infestation), or that they are affected by disease or poisoning. Mummified rodent carcasses may indicate a previous infestation although many fresh carcasses suggest recent disease or poisoning.

For more information, see article – How To Tell If You Have Rats and Mice in Your Home or Garden

References

• IPM for Rats and Mice – Utah State University Extension, Pest ID Handbook, https://extension.usu.edu/planthealth/schoolipm/files/pest-id-handbook/Rats_and_Mice_2012_IPM_Manual.pdf
• Mouse and rat biology and behaviour. (n.d.). CALS. https://cals.cornell.edu/new-york-state-integrated-pest-management/outreach-education/whats-bugging-you/rodents/mouse-and-rat-biology-and-behaviour
• IPM Action Plan for Rodents | School Integrated Pest Management. (n.d.). https://schoolipm.tamu.edu/forms/pest-management-plans/ipm-action-plan-for-rodents/
• Is There a Mouse in the House? Eliminate Mice with IPM. (n.d.). https://extension.psu.edu/is-there-a-mouse-in-the-house-eliminate-mice-with-ipm
• ENY-224/DH044: Rat and mouse control. (n.d.). Ask IFAS – Powered by EDIS. https://edis.ifas.ufl.edu/publication/DH044
• Non-Chemical Rodent Control | Extension | University of Nevada, Reno. (n.d.). Extension | University of Nevada, Reno. https://extension.unr.edu/publication.aspx?PubID=3224
• RATS and MICE: Get Them Out of Your House and Yard, Warnell School of Forestry & Natural Resources, University of Georgia Cooperative Extension, https://secure.caes.uga.edu/extension/publications/files/pdf/C 970_1.PDF
• Controlling Rats – G1737, University of Nebraska–Lincoln Extension, https://extensionpubs.unl.edu/publication/g1737/2007/pdf/view/g1737-2007.pdf
• RATS AND MICE Fact Sheet, Cairns Regional Council, Queensland Government, https://www.cairns.qld.gov.au/__data/assets/pdf_file/0007/523384/Rats_and_Mice_Brochure-_CRC.pdf
• Gerald H. Jacobs, John A. Fenwick, Gary A. Williams; Cone-based vision of rats for ultraviolet and visible lights. J Exp Biol 15 July 2001; 204 (14): 2439–2446. doi: https://doi.org/10.1242/jeb.204.14.2439
• Thomas W. Cronin, Michael J. Bok; Photoreception and vision in the ultraviolet. J Exp Biol 15 September 2016; 219 (18): 2790–2801. doi: https://doi.org/10.1242/jeb.128769
• Celia D. Escabi, Mitchell D. Frye, Monica Trevino, Edward Lobarinas; The rat animal model for noise-induced hearing loss. J. Acoust. Soc. Am. 1 November 2019; 146 (5): 3692–3709. https://doi.org/10.1121/1.5132553
• Reynolds, R. P., Kinard, W. L., Degraff, J. J., Leverage, N., & Norton, J. N. (2010). Noise in a laboratory animal facility from the human and mouse perspectives. Journal of the American association for laboratory animal science, 49(5), 592-597.

Further Resources

For more information on rat and mouse control, see the following articles:

1. How To Tell If You Have Rats and Mice in Your Home or Garden
2. The Best Ways to Trap Rats and Mice That Really Work
3. How To Make Safe and Effective Rat and Mouse Baits Using Baking Soda
4. Spice Up Your Rodent Defense With Potent Chili Capsaicin-Based Repellent Sprays
5. Using Live Catch Traps for Humane Rat and Mouse Control