Friday, January 21, 2011

Small mammals at the bird feeder

While birds are our most conspicuous backyard visitors, the snow reveals signs of a community of mammalian visitors we seldom see. Often we find tiny tracks and a network of tunnels just under the surface. In their yard, our friends Christine and Kyle found similar tunnels, and the tunneler, active in broad daylight last weekend. We were all surprised to learn that the tunneler wasn't a rodent. Instead, it was a Northern Short-tailed Shrew (Blarina brevicauda)!

[click on images to enlarge]
Armed with poison-secreting salivary glands, Northern Short-tailed Shrews are well-known predators of small rodents and invertebrates. They are also known to eat bird seed and are commonly encountered in the vicinity of bird feeders.

One consequence of concentrated small mammal activity in the yard is the attraction of larger predators, as Jo-Ann Ecker of Woodstock, Vermont observed after a snow storm on January 12th. Jo-Ann wrote:
Our Barred Owl waits for white footed mice and voles to appear. I am sure he is successful or else he wouldn't come back.
[click on images to enlarge]

A few years ago, Martha spotted an intact Barred Owl pellet lying beneath a Hemlock in the woods, beyond our yard. When we teased it apart, we found the remains of at least three small mammals.

Two of the partial skulls and a single mandible are from shrews (family Soricidae) of the subfamily Soricinae, also known as the red-toothed Shrews. The reddish colour is the result of iron deposited in the tooth enamel.

The first and third partial skulls are likely from a Northern Short-tailed Shrew. The second (middle) skull is likely from a Meadow Vole (Microtus pennsylvanicus). These two widespread species are common in the area, although the shrew is approaching the northern limit of its Ontario range on the the north shore of Lake Superior.

Just to the south of us, in Northfield, Minnesota, fellow nature blogger Penelope has been documenting the behaviour of a Northern Short-tailed Shrew under her bird feeders.

Here is an excellent series of photos and description of the discovery of a Northern Short-tailed Shrew skeleton in a Saw-whet Owl pellet at the Lake Erie Metropark (MI).

Many thanks to Christine Drake and Jo-Ann Ecker for sharing their terrific photos.


  1. Great post Michael! Excellent photos of the shrew and Barred Owl. I imagine you don't see too many birds at the feeders when he's perched there.

  2. Owls and rodents - wish had those visiting our feeder... well, maybe not the rodents! Nice post.