Opportunism

By Bob Engel, Marlboro College Professor Emeritus of Biology and Environmental Scienc

Guilford, Ct.:  I was pinching myself — no, I was feeling downright smug — as I walked out the old tram line into the marsh.  It was my kind of early winter morning, sunny and 62.  Nobody has said anything about the strong El Nino in a while, but here it was, providing a quarter of the planet with what is to come on a global scale. Happy holidays!  Record rain and record heat greet us this December.

A kingfisher rattled and flew off.  S/he might stay for the whole winter, as might the thirty or so geese a few hundred meters away.  I had just seen hundreds of geese on a grassy common in nearby Milford.

The birds are doing what they ought to.  Why give into your decaying instincts and fly all the way to the Chesapeake or beyond when you can get it all in New England?  They are behaving optimally (not wasting energy) and opportunistically (taking what they need where they can get it).

Photo by CSZMURLO

Photo by CSZMURLO

The Canada goose is the poster child for opportunistic movement in the winter.  Yes, there are some populations that dutifully move all the way to the Gulf, no matter what.  But there are increasing numbers of birds that stop where the grass is green and the snow has not piled up.  A lot of birds do that.  Herons, many ducks, and kingfishers are just looking for open water, not South Carolina marshes.  Many Red-tailed hawks don’t go any further south than open ground.  Rodents oblige by being rodents, they have to feed every day, snow cover or not.

And so it goes.  Some “migratory birds” only move as far as they have to.  The Audubon Christmas Bird Count is this Saturday (December 19) and it will be interesting to see who was still here, basking in a winter that (in Albany) is currently 500+ heating degree days below the thirty year average.

Something like these events is currently playing out at our feeder.  I adore chickadees and I feed them.  Jays, however, are not welcome.  I admire their smarts, but not their greed.  And, because they cover a lot of ground, jays are prime participants in the movements of the Hemlock-killing wooly adelgid.  So I cage the feeder, making it a semi-permeable device that welcomes only small birds.  Two week ago, three titmice showed up.  Titmice have a tough time up here in Marlboro, so it’s always a treat to see or hear one.  These three stayed because of the inexhaustible food and because they fit through the screen.       

And then we went to NYC and coastal Connecticut.  The feeder ran dry on our first day away.  With our return two days later, the chickadees were almost as happy to see us as was our cat, but only one titmouse remained.  The other two, like the cloud of 100+ waxwings that were here eating crab apples for three weeks, have hit the road.  Maybe the two deserters are at another, more reliable feeder just a couple of miles away?  Maybe they’re in Guilford?  Their movements will be on the order of a few miles instead of a few hundred or even a thousand miles, but they are still behaving opportunistically (and nomadically).

Opportunistic birds exploit resources that are riskier and more variable in space and time.  In a sense, Red-bellied woodpeckers and Carolina wrens, now here all year long, are opportunistic, pushing the limits, but with the climate changing, the risk gets smaller, and all kinds of ranges are changing.