Scott Carpenter wrote:
>However, for people keeping their own individual lists, probability seems to be pretty decent that the Barnacle Goose at Ridgefield is a wild >bird, and that it mated last year with a minima, and that family unit arrived at Ridgefield on Tuesday. Not certainty, just probability.
>
>On a somewhat related note:
>
>http://www.maavianrecords.com/home/about-species-accounts/barnacle-goose-branta-leucopsis
>
>For those who don't use probability when birding, are you certain that was a Rock Sandpiper you saw on the coast? Which subspecies? Were >those all Purple Sandpipers I saw on Lake Michigan when I lived in Chicago? They probably were all Rocks in the Pacific NW, and all Purples >in Chicago, but I'm not certain. As for the Purple Sandpiper I saw in Texas, I'm just not so sure anymore, but I'll still call it a Purple.



With all due respect, I'll suggest the probability of this goose being an escapee (and the hybrids as well) is more likely than it being a wild bird, though this is just my opinion.? Steve Mlodinow mentioned that that hybrid combination is known from captivity, so that doesn't seem to affect the probabilities.? The group probably did arrive on Tuesday, but I don't think that makes one scenario more likely than another.? For example, maybe they just escaped on Monday.

I'm all for using probability when birding, but sometimes it's not clear what the probabilities really are.? In the Rock Sandpiper example, there's every reason to believe that every "Rock" Sandpiper you see in the Pacific NW is actually a Rock Sandpiper.? So the probability of a particular individual being a Rock is likely close to 100%, while the probability of it being a Purple is almost 0%.? If you identify each one just by range, there's a pretty good chance you'll be correct every single time.? However, I don't think birding by probability works when you're comparing probabilities of several "elaborate" scenarios, each one requiring a guess as to its likelihood.?

For example, what's the probability of a wild Barnacle Goose mating with a wild Cackling Goose, producing hybrid offspring, and ending up in Washington?? What's the probability of a captive Barnacle Goose mating with a captive Cackling Goose, producing hybrid offspring, all of them escaping together, and ending up in Washington?? And what's the probability of a captive Barnacle Goose escaping, joining a flock of wild Cackling Geese, mating with one of those Cacklers, producing hybrid offspring, and ending up in Washington?? No one knows, but they're all unlikely events (because if even one scenario was likely, we'd see a lot more Barnacle Geese around here).? When every possibility is very unlikely and there's essentially no data to work with, it just becomes a matter of opinion which is the most likely, and from my experience, opinions are usually equally split among the "wild" and "escapee" camps.

With that said, there's nothing stopping anyone from counting it on their list.? If your opinion is that it's probably a wild bird, go for it.? I have no problem with that.? In fact, the ABA doesn't have a problem with that (see below).? Hey, I have a few questionable birds myself.? [I don't report list totals to the ABA, so I'm not hurting anyone. :) ]? And FWIW, I chased this Barnacle Goose even after I heard that it wasn't banded.

John Puschock
Wedgwood, Seattle
g_g_allin at hotmail.com
http://www.hotmail.com

*The interpretations of the ABA Recording Rules (http://www.aba.org/bigday/rules.pdf), under Rule 3, section B(ii), state "A species observed far from its normal range may be counted if in the observer?s best judgment and knowledge it arrived there unassisted by man."