Sunday, August 22, 2010

Shorebird Migration in Connecticut

Larry Flynn emailed me to mention that the shorebird numbers around the Norwalk Islands were much reduced yesterday as compared to previous days. It got me thinking about shorebird movements in CT.

Generally speaking, we think of cold fronts and the northerly winds behind them as mechanisms to concentrate passerines and hawks at migration hotspots during autumn. In Connecticut, shorebird numbers seem to work differently. I and others have observed that shorebird numbers often build to a peak during conditions not conducive to migration (i.e. hot and humid weather with a breeze from the south or east). Then, a strong cold front will clear out these concentrations. The cycle will repeat: numbers build, then the next cold front sweeps them away.

Why? Perhaps during ideal migration conditions, birds moving North to South easily bypass our East-West coastline and continue their migration to Long Island and beyond. Shorebirds just do not seem to pile up against our coastline. Maybe the brief water crossing (Long Island Sound) does not act as much of a barrier for the strong-flying shorebirds, while hawks and passerines try to avoid crossing water when possible. That seems to make sense, but who knows for sure. While fishing mid-sound I often see flocks of shorebirds crossing the sound directly, while the hawks and passerines usually move east-to-west down the coast instead of crossing.

And why do numbers increase during poor migration conditions? Maybe newly-arrived migrants are spread thinly all along the coast when they first arrive on the heels of a cold front, then gradually locate and remain at the best habitat over the next few days until they ride the next
period of north winds to points south. That would account for a gradual build-up over several days at the shorebird hotspots. It should also be noted that shorebirds are more likely to migrate during less-than-ideal conditions (than, say, hawks or songbirds) because they are such strong flyers.

Larry's observations may have reflected those of folks who were shorebirding along the CT coast yesterday, because the prior evening's conditions were fine for migration. A large number of shorebirds may have departed. Or not...these are just general observations and by no means a rule. Also, this applies to numbers but not necessary diversity, which is more dependent on the calendar date. For instance, we are now entering the period of highest shorebird diversity in CT, thanks to the arrival of "grasspipers" such as American Golden-Plover, Baird's Sandpiper, and Buff-breasted Sandpiper.

For those wondering if a reduction of shorebird numbers could put a damper on Sunday's Shorebird Workshop, I wouldn't be too worried. These things vary from day-to-day and location-to-location. Even if shorebird numbers were reduced by the recent north breeze, tomorrow's forecast is for cloudy skies leading to inclement afternoon weather...perhaps the best shorebirding conditions CT has to offer! If you're shorebirding tomorrow, don't let the rain chase you home. In addition to the typical habitat, coastal lawns (Hammo or Sikorsky Airport) or inland fields and pond edges (Rocky Hill Meadows) can be superb during and immediately after rain.

- Nick

No comments:

Post a Comment