Hi Tweets,

In Victoria BC, Kevin Slagboom writes:

>On Sunday, Feb 1st, a male Barn Swallow...Chances are that it's an arrival.
>
>Also on Sunday, a male Rufous Hummingbird...has appearently been here for a few
>days.

>Arrival Dates in Victoria (notes from Brian Gates)
>-----------------------------------------------------------
>Barn Swallow: late march - late april
>Rufous Hummingbird: early - late march

Early? you're not kidding. For Vancouver BC, the averages are:

Rufous Hummingbird: March 11
Barn Swallow: April 07

So, two male Rufous Hummingbirds (RUHU) Selasphorus rufus at
widely-separated locations (couldn't *possibly* be the same bird, hey?), one
of which is an area I would expect early northbound RUHU to appear, Victoria
BC at the S end of Vancouver Island, the other Cougar Mountain WA: I'd say
we're in for an interesting spring with many 'earliest records' about to be
set. Is the Barn Swallow (BNSW) Hirundo rustica a record-early (*Jan*uary?)
arrival or regionally-wintering bird? Hard to say; quite a few BNSW didn't
go very far S this year, it seems, stalling up at southern Oregon and
California.

But this is something I've never quite figured out how to deal with: data
that are waayyy out of pattern: do you include them knowing they're likely a
one-off that's gonna distort whatever means and averages, or do you ignore
them? For example, let's say arbitrarily that this is the pattern of Barn
Swallow arrival, leading to the derived (and equally arbitrary for purposes
of this immediate discussion) average arrival date of April 07 above:

4 12
----|----|----|----|----|----|----|----|----|----|----|----
J F M A M J J A S O N D

then along comes 1998, which leaves the record looking like this:


1 4 12
----|----|----|----|----|----|----|----|----|----|----|----
J F M A M J J A S O N D

which then pulls the average arrival date sometime into mid-March or even
late February, clearly not reflecting reality. I'm sure there's something
simple way to absorb that kind of temporary distortion of the 'normal'
pattern that I'm overlooking here. Anybody with statistics in their blood
(ie, related to that famous Gaul, Vitalstatistix '-) who knows how to fix this?

Michael Price A brave world, Sir,
Vancouver BC Canada full of religion, knavery and change;
mprice at mindlink.net we shall shortly see better days.
Aphra Behn (1640-1689)