Tuesday, February 11, 2014

Down to Seeds and Stems

We've had generous numbers of American Robins (Turdus migratorius) around the Pennypack Preserve all winter.  There are always robins here during the winter, but we seem to have more than the typical number this winter - despite the fact that there's more snow and longer-lasting snow cover than usual.

Because the snow has lasted so long, I (and other birders) have been wondering what the robins have been eating.  Though they are insectivores and carnivores during the growing season, they rely on fruits and berries during the winter.  However, they long ago stripped all the crabapple trees and holly shrubs of their berries.  What's left?

When Mary and I took a walk on Sunday afternoon, I noticed a small group of robins perched in a tree, flitting from branch to branch.  When I pulled up my camera with the telephoto lens, it became clear what was happening: the robins were eating fruits of invasive alien Asian bittersweet.

I knew that robins ate bittersweet arils (along with the berries of invasive Japanese honeysuckle and the hips of alien multiflora rose), which helps to spread the plants, but this is the first time I had seen them in action.  In addition, one of our strategies for managing our preserve is to try to eliminate as many of these alien plants as possible, so I feel a little guilty about reducing the winter birds' food sources.  On the other hand, the birds can always seek food in warmer climes, can't they...
The image above depicts an Eastern Bluebird (Sialia sialis) nesting box adorned with an icicle.  Bluebirds, also thrushes like robins, switch their diet in winter, too, and we host many bluebirds in the preserve as well.
Submitted by
David Robertson, Executive Director