[Steven Mlodinow]

Greetings All

The Pink-footed Goose (and friends, about 30 Canadas and 5-10 Richardson's Cacklings) spent nearly the entire day in the large pond adjacent to Idaho Creek Wildlife Area. The bird was typically best seen from along Weld County Road 7, and though our cars were sticking a wee bit into the street, no one came to shoo us off; indeed several locals came by for interested and friendly chats. 

The wild vs non-wild question is unknowable. No bands, hind-toes intact. So, at least no slam dunk signs of prior captivity. 

Washington State had two adults appear on its outer coast in December 2003. I was part of the WBRC when we reviewed the birds. Many of us felt the odds of the birds being wild were high, but decided to hold off on accepting the species onto the state list -- waiting to see if a pattern developed

Why did we think the birds had a goodly chance of being wild. 

1) Wild population was quickly increasing and had spread to Greenland

2) We enlisted the aid of some of the country's most respected aviculturalists (and avian curator at the Seattle zoo), and found only one aviculturalist that kept this PF Goose (I can't remember where - but in Canada, 4 birds total, all well ensconced at the time). Don't know why this species is rare in captivity in North America but it is. This is in contrast to Barnacle Goose, which is not rare in captivity.

3) We looked at the migration path of Iceland breeding birds to nw Europe (the species' usual wintering ground). Turn that around 180 degrees (a common misorientation pattern in vagrant birds), travel the same distance, and that puts the birds in central Saskatchewan (as I recall). Continue that same direction... and you are on the Washington coast. Hook up with other geese in Saskatchewan, and you might find yourself in CO. 

Also, I think if you change the breeding location (Iceland vs Greenland), that 180 degree error might land the bird in CO. 

Sadly, the eBird reviewers for WA decided to be very conservative and did not put those well documented birds on eBird, which makes research into these matters more challenging. There were, interestingly, another 2 PF Geese on southern Vancouver Island, BC  (not far from the 2003 WA birds) during the 2016-2017 winter. Same pair??? There are no other accepted PF Geese on eBird west of NY and PA.

Below are stats on the population increase of PF Goose. 

Taxa with rapidly increasing populations are far more prone to vagrancy, explaining why Aleutian Cackling Geese have been found as vagrants far more than minima Cackling Geese over the last decade, despite relatively similar populations and migration distance. 

I hope this provides some illumination if not 100% conclusions

Steve

https://monitoring.wwt.org.uk/our-work/goose-swan-monitoring-programme/species-accounts/pink-footed-goose/

2017	515,852	17.1	1.85
2016	481,341	18.8	1.75
2015	536,871	18.8	1.89
2014	393,170	19.4	2.01
2013	372,074	17.3	2.16
2012	359,175	21.1	2.30
2011	260,325	8.5	1.77
2010	297,798	19.9	2.32
2009	364,212	17.3	1.87
2008	351,188	22.9	2.08
2007	284,405	20.0	2.27
2006	230,123	19.3	2.20
2005	302,774	18.1	1.7
2004	276,644	19.4	2.1
2003	280,998	19.0	2.19

 

[Alec Hopping]

In addition to the WA and BC birds Steve mentioned, there is an additional record from Nebraska in January 2006, which was not accepted because of uncertainty regarding provenance:

https://birds.outdoornebraska.gov/pink-footed-goose/?fbclid=IwAR3OYUI9K3vc69fvsrr5Sh0ioAiRiYNOvSioe3th9tYD6ZzOAp-k9rnvef8

That would make 4 separate occurrences of PFGO west of the Mississippi in the past 15 years. In my opinion, that's fairly solid evidence of a pattern of vagrancy for an infrequently-captive bird, which should probably be about that rare. This is a large goose that breeds in the North Atlantic, regularly shows up in the Eastern US, and by all accounts should be physically capable of making it to Colorado as a natural vagrant. Just food for thought.

Fantastic find Steve!!!

Best,

Alec Hopping