The animal that Danny brought into camp that day in 1988 was the first live individual of Rhynchomys isarogensis ever seen by biologists. As our group of Americans and Filipinos crowded around, we felt the elation that makes the hard work of scientific field studies worthwhile. First whooping and hollering, then shushing each other to keep from startling the little animal, we all peered through the wire mesh of the cage-trap with something that felt a great deal like reverence. We had rediscovered a "lost" species. Over the next two days, we did as we typically do with live mammals of species that we have never seen before: We gave it water and some nesting material, and samples of everything we thought a rodent might eat from the surrounding forest.
Small seeds, acorns, several small reddish fruits, and some tender young leaves were sniffed hopefully by the little animal, but clearly were not what he was hoping for. Raw and cooked rice, bread, dried mangoes, dried fish, oatmeal, and peanut butter drew the same response. He would hop over to the side of the cage each time we held something out for him, then, almost visibly disappointed, would hop back to his nest. Hard-shelled beetles, ants, and a lightning bug drew no interest. He took a grub from the end of a pair of tweezers and ate it without any sign of enthusiasm. After 24 hours, we began to worry that he must be getting hungry.
At that point, Leoning, a subsistence farmer from Negros who had worked with us for several years, kicked over a rock next to the table, uncovering a couple of squirming earthworms. Almost as a joke, he picked one up and held it out for the little animal, who rushed to the side of the cage, pounced on the worm, held one end in his teeth while he shucked off the dirt with hispaws, and then swallowed it like a long piece of spaghetti.
Shouting and laughing with excitement, we spread out to find more worms. In short order the animal devoured a half-dozen more, tearing the larger ones into pieces before swallowing them. Rhynchomys isarogensis had proven itself to be a primary vermivore—one of the few speciesof mammals to live on almost nothing but earthworms.
The Isarog shrew-rats, as we now call them, make tiny trails in the forest a few inches wide, carefully cleaned of debris. They patrol the trails day and night, and when they find an earthworm, they pounce quickly, using the long, narrow snout to poke down into the moss to get a good hold, then lift the worm high as they quickly dig it out.
This species has evolved in a direction that few biologists might have expected, but one that makes a great deal of sense: Its unusual prey is one of the most abundant resources in their habitat. That habitat is unusual in several additional ways. It has exceptionally high numbers of unique species of animals and plants, and remarkably high rainfall that promotes the development of dwarf trees, heavy moss cover, and a thick layer of soil rich in decomposing leaves, branches, andmoss. |
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