[obol] Re: More on Ankeny NWR Cackling Geese
- From: David Irons <llsdirons@xxxxxxx>
- To: Owen Schmidt <oschmidt@xxxxxxx>, OBOL Oregon Birders Online <obol@xxxxxxxxxxxxx>, Portland Area Birds <portland-area-birds@xxxxxxxxxxxxxxxx>
- Date: Tue, 17 Mar 2015 07:48:22 +0000
Owen et al.
Owen wrote:
I"ve already heard from the USGS bird banding office. The 3 birds we
photographed on 13 March 2015 at Ankeny NWR (Marion County, Oregon) were
1, 2 and 3 years old, 2 females and a male, all banded in western
Alaska by Melissa L. Gabrielson (famous last name). The USGS did not
specify subspecies, as to whether they were minima. Photos and more
details here:
http://oschmidt.net/OwenLSchmidtLLC/MINIMA.html
All of these birds appear to be B. h. minima. Only one of the birds in your set
of photos appears to be in active molt. First winter birds go through a
somewhat protracted molt on the wintering grounds and at this season their
underparts have the look of a snake that has shed part of its skin. The
juvenile body feathers are small and rounded and in fall the hatch-year birds
look very scaly. They also are more brownish on the head and neck, not black
like an adult. As they start acquiring second-generation body feathers they can
look a bit patchy or disheveled. The second-generation feathers are darker,
larger, broader, and more squared-off at the tip. Once fully in, then tend to
give the body a more barred look that results from square tips of the feathers
lining up.
In looking at the dates associated with the neck-collared birds you
photographed, the youngest bird, "P@N," would be most accurately referred to as
an "after second-year" bird (ASY in bandingese). Regardless of hatch date, a
bird's "first" or "hatch-year" ends on 31 December of the year that it hatched.
On 1 January 2014 this bird would have been referred to as after hatch-year
(AHY), or more accurately a second-year (SY) since the approximate hatch date
is known (these birds are banded and collared on the breeding grounds). "P@N's"
second year ended on 31 December 2014 and on 1 January of this year (2015) it
became an after second-year (ASY). I know it seems strange to think of it this
way when the bird only hatched about 20 months ago. In most cases the hatch
date is not known and can only be approximated based on feather age and other
aging criteria. To keep it simple the calendar dates are used to calculate
years.
Looking closely at your top photo (with four birds), the far right bird appears
to be an SY (hatched in 2014). If you look at the belly, you can see the patchy
area with paler scaly-looking feathers well down on the belly. The darker
feathers with pale edges are the new second-generation feathers that are
growing in. Note also that the neck sock and head of this bird has a bit of a
brownish cast to it. Compare its overall plumage to the bird immediately in
front of it, which has a much neater and matched looking set of feathers.
Either this bird is the same age and has already completed its molt or it is
older (ASY). I would guess the latter, as it shows no evidence of molt and the
the head and neck sock seem a little blacker to my eye.
A few years ago, I put together a gallery (link below) of Ridgway's (minima)
Cackling Goose photos taken in the fall. The gallery includes some shots of HY
birds that are still entirely scaly, before the mid-winter preformative molt
started. All of the adults are pristine condition, having just completed a
prebasic molt before leaving the breeding grounds. Based on my observations, it
seems that only the first-winter HY/SY birds have this protracted midwinter
molt on the wintering grounds. They migrate in juvenile plumage and then molt
on the wintering grounds. After second-year (ASY) and older birds have but a
single annual molt that occurs before they leave the breeding grounds each
year. They arrive on the wintering grounds with a brand new set of feathers and
look the same throughout the winter.
http://www.birdfellow.com/photos/gallery/315-ridgways-cackling-goose-variation
Dave Irons
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