Very, very, very broadly, and depending on all sorts of variables,
mid-morning and mid-afternoon. That's because the big numbers are
Broad-Wings, which basically vacate the continent en mass over a very
short period of time in early fall. In Mass., something like 90 percent
of the BWS seen over the entire 30 years of data have been seen between
Sept. 10th and 20th.
BWs use thermals to get height, then glide as far as they can before
picking up another thermal. Their "goal" is to get as far as possible
towards central America as fast as possible while expending as little
energy as possible-- so soaring and gliding rather than flapping.
The result of that is that when weather conditions are good -- those
crisp fall days with lots of sun -- very strong thermals are created
that take the birds in the middle of the day so high that they're often
out of view. The "mid-day lull" is a well-known cliche in
hawk-watching. In mid-morning and mid-afternoon, the sun angle is lower
and the thermals not as strong, so they don't get as much height and
that keeps them at a lower height.
But again, that's not a rule, just a statistic. You can have huge
flights visible at any time of day. One of the truly addictive things
about hawkwatching during BW season is you can have an empty sky for
hours, and then they start coming in and just pour through so you get
hundreds or thousands over the course of a couple of hours, and then the
spigot shuts off completely and the sky is empty again for the rest of
the day. I once experienced an estimated 8,000-bird flight compressed
into an hour and a half, and no more than 100 birds of various species
spread over the rest of the day.
On 9/19/2013 9:41 AM, Willem Leenstra wrote:
> Is there a time of day when the numbers are higher than others? Broadly
> speaking, that is, morning vs. evening?
> On 9/19/2013 1:34 AM, Jane Stein wrote:
>> Mt. Wachusett