Several times each winter the phone rings, and a concerned voice asks for help. The caller reports feathers under his feeders. Not clumps of feathers, which would indicate a hawk kill, but a scattering of feathers directly beneath the feeders.
I'm always ready with an explanation because I experienced this and solved the mystery years ago.
The first time I noticed a few suspicious feathers under my feeders, I found hidden among the litter of sunflower seed shells small, one-inch holes in the ground. Could mice be responsible for the feathers I'd found? I decided to find out.
I pulled up a chair to a window so I could see the ground around the feeders. After about 30 minutes, movement at one of the holes caught my eye. A small head emerged, and I grabbed my binoculars for a better look.
It was not a mouse. The long, pointed snout and beady little eyes told me it was a shrew. Now I knew what was eating the goldfinches. I really shouldn't have been surprised. Small, mouse-like mammals, shrews are voracious predators that often kill prey larger than themselves.
Smallest mammal: Pygmy shrews, the smallest mammal in North America, weigh two to four grams (about the weight of a dime) and a single one eats more than twice its weight in food every day.
The species I watched in my backyard was a short-tailed shrew. I could tell by its size - about four inches - and its short, one-inch tail.
Short-tailed shrews are abundant and widespread in the eastern U.S. They inhabit both deciduous and coniferous forests as well as old fields, thickets and hayfields. Just last week I caught one in a mouse trap in the cellar.
Their only habitat requirement seems to be a thick layer of leaf litter that keeps the surface of the ground moist. The thick mat of sunflower hulls under the feeders certainly qualified.
Shrews eat mice, small birds, insects, earthworms, snails, slugs, and insect larvae. Though they prefer animals, they also eat fungi, nuts, and berries.
No doubt the ground around the bird feeders makes an excellent place to hunt. There is always a supply of food. After digging its burrow, a shrew needs only to sit at its entrance and wait for an unsuspecting bird to hop by. A shrew strikes quickly. It grabs its prey and bites furiously.
Short-tailed shrews have a special adaptation that enables them to take prey larger than themselves. They are poisonous - one of nature's few venomous mammals. Behind their lower front teeth are glands that release a powerful venom. It flows along a groove in the teeth and enters the wound as the shrew bites. The victim's struggle ends quickly.
The toxin usually just immobilizes rather than kills. In humans the venom causes swelling and some pain that may last a day or more.
In nature's grand scheme, shrews kill relatively few birds, so birdwatchers need not fear that the birds in their backyards will disappear. In fact, shrews are good to have around.
They help control insect and rodent populations. Some evidence suggests that short-tailed shrews may also eat gypsy moth caterpillars.
If feathers mysteriously appear in your backyard this winter, look for shrew holes. Be alert, and you may even catch a glimpse of this beady-eyed killer.