The Reality of Rats in an Urban Ecosystem

Seattle is a city with all the wonders of different cultures, a vibrant economy, and the wonderful parks that Seattle Parks and Recreation (SPR) stewards. With that population and development also come the trash we create and the rats that thrive with that waste. These animals can be a real nuisance, and SPR is constantly seeking the best methods to manage their population.

SPR uses an Integrated Pest Management (IPM) system to handle all pests. IPM is a tiered method that starts with using cultural methods first, such as picking up litter, installing appropriate waste cans, cleaning up encampment areas, and designing parks to reduce burrowing areas for rats.

But even with these deterrents, rats still find ways to thrive in our urban ecosystems. The next method in our IPM program is to use biological methods. In the case of managing rodents, supporting a robust raptor population is one of the best ways to keep their population in check. To have a healthy population of birds of prey, we need healthy habitats and, as we learned from chemicals like DDT, limited use of pesticides that eventually rise up the food chain to negatively impact predators.

And still rats will remain in our parks! In the past SPR has implemented the traditional system of dealing with rats that involves hiring contractors to place poison traps. These traps work well but introduce poisons into the environment - these poisoned rats are then often eaten by scavengers like crows, causing harm to the very predators that help control rat populations.

SPR piloted a new process that manages our city's rat population without the use of poisons: carbon dioxide injections into rat burrows. This started as a partnership with Birds Connect Seattle at Cal Anderson Park and was wildly successful. Simply put, CO2 is injected into burrows, killing rats humanely in place. No poison necessary, and thus no negative ecosystem impacts.

The pilot expanded to Woodland Park, where SPR initially removed trash from encampments, eliminated hiding spots, identified burrow areas, and then injected CO2. Over 200 burrows were found in the area, and monthly inspections took place after our initial management. Currently very few new burrows have been found and new waste bins keep attractants down.

Now SPR has expanded this process system-wide with 50 parks receiving monthly inspections and applying CO2 injections when needed by a local contractor. At times, baiting stations are used to determine the extent of a rat problem in a park, and then the issue is addressed when required.

Sometimes additional efforts are needed, especially in parks where SPR doesn't control the food sources. One example is in Freeway Park where nearby dumpsters offer an endless food supply for rats. Also, the design of the historic and innovative park creates many places where rats can burrow. Prefontaine Park has similar challenges. In these cases, SPR has placed Xcluder geomesh, a product that prevents burrowing while allowing plants to flourish.

SPR is a learning organization, and we continually seek to improve our methods to manage rats while minimizing our impact on the environment. We work collaboratively with other City departments and King County as part of the Seattle Rodent Work Group to assess current methods and seek new strategies to address this problem. Through these conversations and innovations our goal is to create a safe and healthy park environment for the public and a thriving ecosystem in our city.