You know the basics on the differences between Norway rats and roof rats: one is typically on the ground, the other generally is up high. In the US, Norway rats are widespread, but roof rats generally are southern and along the seaport cities. There are other key differences you may not know or think of that can help you manage both these species.
- Roof rats can handle the cold. Even though roof rats are tropical in origin, they are now present in many areas of the world and can tolerate some pretty cold temperatures. Roof rats are established on Macquarie Island, where temperatures range from 36-47oF. While temps rarely fall below freezing, they also don’t get above 50oF, so it’s not too warm. In cooler regions, roof rats will burrow instead of nesting up high in trees. Roof rats can tolerate those cooler regions, but they do prefer warmer spots. With ongoing climate change and global temperatures increasing, we can expect to see the range of roof rats expanding as conditions become more favorable.
- Norway rats are great swimmers. Roof rats prefer to be up high and do not swim well. The excellent swimming capabilities of Norway rats could be one reason they have expanded worldwide. Scientists tagged a Norway rat and dropped it on an uninhabited island. They wanted to look at where it went and what it did to understand more about how an invasive species starts to colonize. However, the rodent had different plans. It swam over 400 yards across the ocean to a nearby island. It took the scientists 18 weeks to recapture it. They finally caught it in a trap baited with penguin meat. To the pest management professional, this means you may have to look farther and harder to find burrows and food sources.
- Norway rats outcompete roof rats. Most studies indicated that food is the primary limiting factor for individual and population growth for both species. Norway rats are better at getting to that food, feeding on it, and growing just a bit faster than roof rats. Norway rats have slightly bigger litter sizes, so their populations grow faster than roof rat populations. Roof rats were actually present in the US first, but when ships brought over the Norway rats, they quickly started taking over, and roof rats were pushed south and to the coasts.
- But they can be found together. As previously mentioned, Norway rats outcompete roof rats, now we are saying that they can be found together. In areas that have both species (again, the southern states and coastal areas), if food is plentiful, both Norway and roof rats can be found in the same locations. They are typically taking advantage of different heights: Norway rats down low to the ground, roof rats up high in the trees and roofs. Trapping data out of New Orleans, LA has shown both species in traps placed very close to each other. As long as food resources are abundant, they can occupy the same general area.
It takes knowledge and experience to be a pest management professional. Knowing the pest, its preferences, and the biology can help put traps and stations in just the right spot for maximum efficacy. VM Products can help you with all of that, so contact us for more info.