Jerry and Tweeters,

It would be very easy to test your theory of Snowy Owl invasions
corresponding to El Nino years by looking at past data. I would suggest that
data for Washington be combined with those from southwestern BC. Some
invasions have virtually stopped at the US/Canada border; i.e., lots of
Snowy Owls in the Fraser Delta but very few in Washington.

The Vancouver area (especially the Ladner Christmas Bird Count) has had very
consistent peaks of Snowy Owls every 4-5 years, going back to 1966, except
for a couple of winters in the last 15 years when the expected influx failed
to materialize.

Snowy Owl invasions are generally believed to peak in winters after lemming
populations in the breeding areas have crashed. For the Pacific Northwest,
this would be Snowy Owls breeding in western Alaska and possibly northern
Alaska. It seems possible that El Nino-related weather trends could be
related to lemming numbers, although I don't know that anyone has tried to
show this. On the other hand, lemming cycles and El Nino cycles could be two
completely unrelated 4-year cycles. The Arctic tundra is far to the north of
areas usually considered to be affected by El Nino, although it's possible
that weather trends even there could be related to El Nino.

Just thinking out loud,

Wayne C. Weber
Delta, BC
contopus at telus.net



-----Original Message-----
From: tweeters-bounces at mailman2.u.washington.edu
[mailto:tweeters-bounces at mailman2.u.washington.edu] On Behalf Of Tangren
Family
Sent: January-02-10 8:46 AM
To: tweeters at u.washington.edu
Subject: [Tweeters] predicted Snowy Owl invasion

A couple years ago we discussed on tweeters whether the El Nino cycle
had an effect on Snowy Owl numbers in Washington. The current El Nino
is now beginning to show its appearance in our area:


http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/enso
disc.html

Following the scientific method, it might be interesting before the
fact to speculate on what might be possible: there is evidence that
in the falls coming after sufficiently strong El Nino events there
are corresponding good flight years for Snowy Owls in Washington.

Thoughts?

--Jerry Tangren
East Wenatchee, WA
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