Thanks for your thoughts! Actually, the theory originated from such
an examination of the data. However, a partial validation of the
theory would be to predict an invasion ahead of time. I say partial
because we could get a coincidental irruption due to another cause
(probably a one out of three chance).

The lemming-owl relationship was developed before there was real
knowledge of the El Nino cycle which itself could have real impact on
the lemmings. We know that animal population cycles are regulated by
climate changes such as El Nino. Someone out there may have some
literature references for lemmings?

Furthermore we know that El Nino affects weather world-wide. For
example, the warm water effects are limited to an area of the
Pacific Basin, but it affects the Atlantic hurricane season. When
climate is pushed down somewhere globally, it pops up somewhere else
propagating cycles that reach around the world.

I can't postulate the exact mechanism by which El Nino may affect
Snowy Owl irruptions, but by inspection of data from previous years,
it looked like there may be a relationship. To predict it at this
time, would be a possible test.

--Jerry

>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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