birdsoup

 Last Saturday 10,000 migrating hawks were counted at the Chestnut Ridge Hawk Watch.  Yesterday, exactly one week later, we saw no hawks.  Zero.  Not a single one.

 I joined Sandy Morrissey to take a group of kids from the Young Birders Group to the Hawk Watch hoping to awe them with the spectacle of a sky full of hawks.  But none.  No hawks to be seen.  Fortunately, kids are so flexible they did not mind.  They transferred their energy and enthusiasm into finding frogs, toads, salamanders and a zillion earthworms and were happy. 

 Why were there so many hawks one week and none the next? 

 There are two primary reasons.  The first and greatest cause is weather.  On the first Saturday the weather was ideal for migration.  For several days bad weather had been holding up hawks preventing them from migrating.  But on Friday night, a front came through.  The weather cleared and a nice tail wind picked up adding up to perfect conditions for a big hawk flight.

 Weather for the second Saturday was gloomy with possible rain.  It was muggy and very overcast so the sun could not break thru to create rising “thermals” of hot air. (Hawks like to soar on these thermals to conserve energy during migration.)  So, like humans faced with the prospect of bad weather, the hawks just stayed put.

A second reason is that different species of hawks migrate at different times.  The peak of Broad-winged Hawk migration is mid-September.  That is a part of the reason we saw so many on the first Saturday.  The chart below illustrates the typical timing of hawk migration in Westchester.  The thickness of the horizontal line reflects the quantity of hawks that are moving at a given time.  A thicker line means you are likely to see more of that species.  As you can see, the most Broad-winged Hawks are expected in mid-September, and by end of October you probably won’t see any.