Apr 14, 2012

Tale of two woodrats

Dusky-footed woodrat.

Unless we're presented with a major disaster, like an oil spill, most of our wildlife rescues involve a single injured or ill animal. It's concerning, then, when we find more than one casualty at the same location, especially when the cause of their demise is not readily apparent.

This week, we recovered two dusky-footed woodrats from a property near Elkhorn, CA. One was freshly deceased, the other, dying. These two animals brought the total number of woodrat casualties from that area, in six months, to 4. What is even more alarming about that number, is that the species is in jeopardy.

Neotoma macrotis luciana, the Monterey dusky-footed woodrat, one of 11 subspecies of dusky-footed woodrats that inhabit the Pacific coast, is considered a Species of Special Concern by the California Department of Fish and Game. Loss and fragmentation of their distinct habitats - dense oak woodlands, riparian, and cooler chaparral ecosystems, has been identified as a major reason for their decline. In the Northeastern part of the United States, researchers have cited the raccoon roundworm as a significant cause for the decline in the Allegheny woodrat.

The two woodrats discovered near Elkhorn were both adults, measuring approximately 8" from tale base to snout. They had the distinctive woodrat fur, grayish brown with tawny undertones, white feet and undersides. 

This handsome American native can be distinguished from its distant relative, the Norway rat, by its blunt nose, and long whiskers. Woodrat's tales are more furred than scaly, and they have extraordinarily large, round ears. They differ, dramatically, in behavior, as well.

Dusky-footed woodrats are best known for their large stick houses, which can reach 6' in height and last for decades. Each structure is divided into chambers for various uses, including a separate area where they create a debris pile and latrine. The species is meticulous about cleanliness. They also have a creative side.

Woodrats, or packrats, as they are often called, adorn their debris piles, or middens, with 'little treasures' - oddities they collect from their environment. These decorations can include plant material, pebbles, bones, and human artifacts. Inspection of ancient woodrat middens have given scientists a look back in time, some tens of thousands of years!

Dusky-footed woodrats also line their homes with leaves. Of particular interest is their use of bay leaves. Research suggests deliberate use of the aromatic foliage around their sleeping quarters to reduce ectoparasites. Click HERE for more on this unusual behavior.

The dusky-footed woodrat social structure is also unique. They have evolved to live in loosely-cooperative, matrilineal societies. When pups are weaned, males disperse away from their birth den, while females move to adjacent stick houses, remaining close to their mother. When the matriarch dies, one her daughters inherits her stick home. A single woodrat home can be maintained by several generations of the same family, for decades.

The property where the rats were discovered offered plenty or woodrat habitat with dense foliage and numerous oak trees, but both animals were found out in the open, during the day. A clue. Neither presented with external injuries. Another clue. We suspected rodenticide.

The carcasses were shipped to the California Department of Fish and Game Wildlife Investigations Laboratory in Davis where necropsies revealed large amounts of blood in the lungs and in the abdomen, suggesting anticoagulants - rodenticide use in the woodrat's home range.

After some investigating, we found that neighbors had recently set poison bait stations on their land to control a Norway rat infestation. We explained that bait boxes kill indiscriminately, and pose a threat to all the area's predators, too, including their cats and dogs. We have offered them alternatives to help them solve their Norway rat problems sustainably.

Please read more about how rodenticides pose a threat to non-target animals at these links:

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