‘Tis the Season…for Rats

‘Tis the season—up on the rooftops, click click click.  No, it isn’t Santa and his reindeer, it’s rats, and they seem to be everywhere this winter.  Rats can squeeze through a hole the size of a quarter. If you’ve ever seen one using your power or phone wire as a suspension bridge to your house, you know how agile they can be.

They’ve even proved to be Olympic class swimmers, with one rat logging an open ocean swim equal to eight lengths of an Olympic swimming pool.  It’s no wonder that rats have managed to inhabit almost every island in the Pacific, either by swimming, or as a stowaway on boats, planes, cargo, and even luggage. 

Although rats seem to like living among people, they are also just as at home in forests and natural areas. 

Conservationists have coined the tongue-in-cheek term “opportunivores,” to describe the feeding habits of rats.  Soap, baby birds, seeds, the insulation on electrical wires, garbage, seedlings, nesting birds, tree bark, catfood—it’s all food to rats.

The impact of rats on native species is becoming clearer every day.   Recent archaeology research on Rapa Nui shows that rats played a huge role in the conversion of the forested island to grassland.  While the people of Rapa Nui may have used trees to move the giant stone moai, it appears that rats ate the seeds that could have regenerated the forest. 

Closer to home Mokoli‘i, also known as Chinaman’s Hat off the coast of O‘ahu, has been home to a population of rats since at least the 1950s.  The islet is also a nesting site for wedge-tailed shearwaters, home to native plants, and shoreline invertebrates like pipipi snails and ‘a‘ama crabs. 

Resource managers saw that the survival rate of shearwater chicks was dropping, until there was one single survivor between 1999 and 2001.  An intensive trapping and baiting project resulted in the capture of eighteen rats.  When the traps were removed, the remaining rats went after the bait until there was clear evidence that the rodents had been eradicated. 

The success of this project was immediately obvious, and it was better than expected.  The number of surviving chicks increased to 126 in 2002 and 203 in 2003.  The native plants no longer looked chewed-on, and even more surprising, was the big increase in the number of shoreline invertebrates.

Conservation and resource management agencies charged with protecting natural resources are looking at the story of Mokoli‘i and other successful rat eradication projects in New Zealand, and are starting to take seriously the damage that rats can do. 

For homeowners this rainy season, we are sure to be overrun with rodents, inside and out.  Tim Lyons of the Hawai‘i Pest Control Association offers some tips:

The key is sanitation, don’t leave food and water out. Each evening, get rid of leftover pet food and water.

Most importantly, call rat control or pest control services for inspection/recommendations; pest control companies will usually give free estimates on control costs.

‘Tis the season, every season, for rats.  Christy Martin is the Public Information Officer for CGAPS (Coordinating Group on Alien Pest Species) based in Honolulu.