Thanks Ian. Very useful info, as I’d never heard of Civil Twilight.

RESIST

> On May 10, 2018, at 4:17 AM, Ian Worley <[log in to unmask]> wrote:
> 
> The Sunset View Cemetery Whip-poor-will is back again.  Probably arrived a week ago, but I didn't have the chance to check before last night.
> 
> First song began at 8:40pm, two minutes after the end of Civil Twilight.  Typical of behavior when first arriving the bird sang short bursts (10-20 seconds) of song, moving to a new location every 2-3 minutes.  When first heard it was about 600-700 feet south of the of the cemetery, and then worked its way to various locations at and near the back end of the cemetery.
> 
> When within about 500 feet of me, I could easily hear the "tic" note that sometimes precedes each repetition within the song. This note adds an extra rhythmic "down-beat" to the extended song as a whole.  Always a delight to hear it accentuating the song.
> 
> The start time for vocalizing of 8:40pm was two minutes _after_ the posted end of Civil Twilight (which for humans is when our eyes switch from using cones to using rods, and colors are exchanged for grays).  On this date the posted end of Civil Twilight was 33 minutes after the posted sunset time for the location.
> 
> Slightly over a week ago at the Snake Mountain Road, Weybridge site, the start time for vocalizations was 8:24pm.  This was two minutes _before _the posted end of Civil Twilight at 8:26pm (31 minutes after the posted sunset time).
> 
> The Weybridge site is on the east face of Snake Mountain, and thus the real end of Civil Twilight there would be sooner than the listed time, due to the shadowing of the mountain.  The Waltham site looks across the Champlain Valley with a far distant horizon to the west.  On a very clear night, such as last night, the real end of Civil Twilight would be slightly later than the posted time, and in fact the Whip-poor-will began two minutes after the posted time.
> 
> Pretty neat, and a very useful tool when seeking to confirm the presence of Whip-poor-wills, especially late in summer and early fall when that is the only time they might vocalize (very close to the end of Civil Twilight), and then with but a single song often only 2-4 seconds in duration.
> 
> Ian