Dennis Wrote:

>Even if we agree on the semantics, there's plenty of room to discuss the
>facts, I think!

>I'd call Barn Owls quite nocturnal. They come out typically when it's
just
>about too late to see them. They're supremely adapted for nocturnal
>hunting and, I would say, are even more nocturnal than Great Horned, which
>quite frequently come out early enough to grab the last (entirely diurnal)
>squirrels before they go to bed. Food-habit studies would easily define
>the hunting times for owl species, as indicated by the proportions of
>diurnal and nocturnal prey.

I certainly agree that Barn Owls are nocturnal and yet I've watched them
(on the Riefel Refuge, for example) coursing weedy fields in the middle of
overcast days in winter. Perhaps they're driven by hunger.

>Burrowing Owls are largely nocturnal in the tropics but probably
>increasingly diurnal at high latitudes. Nevertheless, they are also
>primarily nocturnal in Washington. The reason you see them out during the
>day so much is that the male is out of the burrow and conspicuously
>perched, more or less guarding his territory at that time.

Good point. I've seen them hawking insects by street light in Arizona.

>Short-eared Owls really match up with "crepuscular" best, as that seems to
>be the peak hunting time for them, although they definitely hunt at any
>time of day as well. Snowy Owls probably fall in this category during the
>winter. Most of their hunting is while at rest, so you don't see them
>flying around looking for prey like Short-ears do.

I apologize for not looking at much of the literature first. Snowy Owls
obviously have to hunt in broad daylight above the Arctic Circle in summer.
When we see them down here in Fall & Winter they're invariably "at rest"
during the day. The implication, mentioned by someone else, was that they
hunted at night. Here's the puzzle: there have been several references,
recently and in the literature, to Snowy Owls feeding on Buffleheads,
specifically, and other ducks, in general. It would seem extraordinary
that a Snowy Owl could catch a duck. Are they perhaps opportunistic
carrion feeders?

>Northern Pygmy-Owls are our only fully diurnal common owl, at least from
>studies of their prey. They can be active (calling) at night, too, but I
>don't know if they feed then. Hawk Owls are quite diurnal, too. Look at
>the heads of owls; the more distinct the facial disk, the more sound is
>probably used in hunting. Of course, sound can be used during the day
too;
>Great Gray Owls, with their huge facial disks, often hunt diurnally.

>I've often wondered what the highest-latitude "nocturnal" species such as
>Boreal Owls do when it's light all the time. I guess they must hunt in
the
>daytime.

Indeed, just like Snowy Owls.

>And, about those semantics--I think "diel" means "having a 24-hour cycle,"
>not "active both day and night." Any organism that has behaviors (i.e.,
>activities) that vary regularly around 24 hours has a diel cycle. It can
>be diurnal or nocturnal.

That would be circadian, as well. Hmmmm, maybe we don't have a term for
"active during the day or night." I've always used "diel" in that regard
for lack of a better word.

Herb Curl

h.curl at hazmat.noaa.gov "You may be only young once but you can be
Hazmat/NOAA, 7600 Sand Pt. Wy., NE immature the rest of your life."
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