At Powdermill for analysis we use civil twilight
Best,
Mike
Sent from my iPhone
On Sep 27, 2009, at 3:18 PM, Harry Lehto <hle...@utu.fi> wrote:
Hi,
in discussing night flight calls I am a bit confused about the
concept of "night". Astronomically, I have no problem with the true
night, and the various twilights. If the limit of "night" is taken
at sunset/sunrise, then various day birds fall into the category of
night flight calling birds even if they are not proper night
migrants. Tits (chikadees), crows and finches start to vocalise
before well sunrise, during the civil twilight, and gererally they
do not crowd the sky in the deep hours of the night.
There appears also to be an assymetry between dusk and dawn. During
the same light conditions the duirnal birds at dusk tend to be much
quiter than at dawn, so this is not that miuch of a problem in the
evening.
My question is when do you guys consider the night over?
Regards
Harry
hle...@utu.fi
Finland
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