I don't enjoy taking down my own bird, but it is good to look thru a broad spectrum of information rather than focusing on the decisions of the IL Bird Records Committee, assuming such is actually final.
The Greenland population, distinctly the most proximate to the US and Canada numbered at only 9000 in 1959 to 28000 by the mid-1970s and 70,500 about 10 years ago. So, yes, the chance of vagrancy has increased.
But where to?
This species is a short-distance migrant. Going from Greenland to eastern Canada and the ne. USA would make sense and might result from mirror image migration from the species' usual Greenland to Scotland route, but more likely results from birds joining Greenland-breeding Canadas, which do winter in northeastern (not western Great Lakes) USA and Canada. Why would a population that rarely winters as far south as the north of France stray to places such as California, New Mexico, and southern Texas. Is the grass not lush enough farther northeast?
Unfortunately, I don't have the recent spread of data as some states validate Barnacle Goose on eBird and others don't (I do believe all should be validated, unless incorrectly ID'd or known escapes so that any pattern could be teased out)
But as of the early 1980s, as many Barnacle Geese had been reported from Oklahoma as Maine, New Hampshire, and Vermont combined. There were 16 records from IL, WI, and MI compared to about 25 from all of New England despite a significant bias against these birds being reported away from the northeast.
And if one was to compare the pattern of occurrence away from the eastern seaboard (as of the early 1980s), there were as many records from June as from February. Hardly a natural looking pattern.
So, let's look at some Barnacle Goose cohorts. Pink-footed Goose has a similar breeding and wintering range to Barnacle Goose and had a similar population increase, from about 20,000 in the 1930s to 350,000 in the early 2000s.
The Greenland breeding population of Greater White-fronted Goose has a population of about 25,000, steady or slightly down over last 20-30 years.
Pink-footed Goose has but two records (one from near Victoria BC and the other from the outer coast of WA) that are west of central PA and easternmost ON listed on eBird. The total number of records from North America is also far fewer than those for Barnacle Goose.
In parallel, the number of Pink-footed Geese in captivity in North America is tiny (rather close to zero, for some reason) compared with that of Barnacle Goose, which is "Generally for sale at cheap prices and is easy to breed" (Reeber's Waterfowl of North America, Europe, and Asia). Coincidence?
Greater White-fronted Goose (Greenland flavor) has only once been recorded (to eBird) w of Ontario, in TN. It is occasionally kept in captivity, which may explain the TN record and those from FL.
So, if you are not asleep or at a different post yet...
Yes, Barnacle Goose might actually occur in CO, wandering here from Greenland. However, the odds look quite low at this time.
Sleep Well
Steven Mlodinow
Longmont CO
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