Interesting discussion. I wonder which is the ruling factor for the owls. El Nino
or Lemmings or rather the absence of them and what link, if any, El Nino has to
the owl's food source cycles.

Roger Craik
Maple Ridge BC

Tangren family wrote:

> >
> >In the Vancouver, BC area, since the mid-1960s, peak Snowy Owl
> >numbers have occurred in the following winters: 1966-67,
> >1970-71, 1973-74, 1977-78, 1980-81, 1984-85, 1992-93, 1996-97,
> >and 2004-05. In some cases, there was an "echo" flight as large
> >as, or nearly as large as, this peak flight the following year (e.g.
> >1971-72, 1993-94, 2005-06). The expected invasions of 1988 and 2000
> >did not materialize; there was a small flight in 2000, but no birds remained
> >over the winter near Vancouver, although there were a few in the Puget
> >Sound area.
> >
> >This looks suspiciously like a 3-4 year cycle to me.
>
> With the salient exception of 1977, the numbers at Ladner/Vancouver
> follow the trend that flights occurred in years when the Oceanic Nino
> Index was dropping. 1977 was in the middle of an almost two year warm
> period. I had overlooked 1977 in Mike's data.
>
> >
> >There is a tendency for every 3rd invasion or so to be much larger than the
> >others. The biggest flights in the last 40 years were those of
> >1973, 1984, and 1996. (No, 2005 does not compare with the
> >numbers seen in those years.) Mike Patterson is correct when he says
> >that he sees evidence of a 9- to 12-year cycle in numbers (not a lack
> >of cycles, as Kerlinger et al. claim). However, part of the reason he
> >fails to recognize the less dramatic 3-4 year cycle is that in these
> >flight years, few or no birds get as far south as Oregon, and in
> >some of them, none get south of the Canada/US border on the west coast.
> >It may be that 1988 and 2000 were also flight years, but that in
> >those years, few owls got even as far south as Vancouver.
>
> I count nine possible episodes in 40 years in Mikes's data.
>
> >Does the El Nino cycle (yes, a 3-4 year cycle, on
> >average) affect weather in a predictable way as far north as the
> >Arctic tundra? Perhaps. However, I'm not aware that anyone has
> >shown convincingly that it does. Maybe someone will take up the
> >challenge soon.
>
> El Nino is just a part of the interconnected global weather
> cycles--but the most prominent aspect. Furthermore the Index is a
> measurement only. It just happens that in 8 out of 9 Snowy Owl years
> the Index has the same pattern.
>
> >
> >Wayne C. Weber
> >Delta, BC
> >contopus at telus.net
>
> --Jerry <tangren.family at verizon.net>
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