This is the time of year we see massive flocks of “black birds” (Starlings, Red-winged Blackbirds, Grackles) wending their way around the landscape in erratic plumes, descending on swamps and fields to feed, and roosting in noisy, dense colonies in the trees.
Red-winged Blackbirds gathered in trees lining some recently plowed fields.
A flock of Red-winged Blackbirds swarmed the cattail marshes at Crex Meadows — looking for what kind of food there?
I always wonder what kind of food birds are finding when they hunker down in the vegetation, probing into dry leaves and stems.
The birds seem to be concentrating their efforts on probing into the bases of the cattails. What would they find there at this time of year when all the vegetation has died back? Inquiring minds want to know — my photography buddy on this field trip insists that I write about it.
A little research into the annual cycle of the Cattail reveals what a wealth of invertebrate life associate with this plant. Its starchy root stalks and rhizomes are fed upon by a variety of critters, but this underwater food source is not what the blackbirds are after. Instead, it might be orb-web spiders and orange garden spiders that have built vertical webs in among the vertical stalks of the cattails at this time of year. Burrowing Water Beetle pupae may be found at the base of cattail stalks, already settled down for their winter diapause, only to be dislodged by the sharp bill of a blackbird. In addition, larvae of the cattail borer moth overwinter in the cattail heads feeding on the seeds all winter — this resource sustains a variety of birds, like Black-capped chickadees, throughout the winter.
A member of a big flock of birds searching extensive areas of potential food resource might locate food more quickly and easily than single individuals searching alone. And of course — there are more eyes to look for potential predators and more victims from which to choose when predators fly by. So dense flocks make a lot of sense at this time of year.
Back Yard Biology 