Wednesday, November 15, 2017

Brief Stop at Rocky Mountain Arsenal

November 15, 2017

Richard Stevens:

While out doing chores, I stopped by Rocky Mountain Arsenal (Adams) to update the status on the reported Tundra Swan and Common Loon.  It was cooler today with temperatures only reaching 59 degrees.  A windy day with anemometer readings 11-12 mph and gusts to 22 mph.

I scoped Lower Derby Lake at least three times.  The Tundra Swan swam along the northern shore (opposite of my location).   Field marks:

Neck length/body length ratio: if its neck laid back it would not cover 75 percent. 

Angle of Body Major Axis: straight line through base of neck and through tail; Trumpeter Swan almost level or slightly upslope, Tundra Swan much more sloped.

Head Profile and Bill Shape:
some Trumpeter Swan have flatter head while Tundra Swan appear rather smooth curved

distance from bill tip to eye is about two times the distance from eye to nape; while Tundra Swan only 1 to 1.5 times

Trumpeter Swan upper mandible is straight while Tundra Swan it is usually curved

Tundra Swan yellow lore is lacking in Trumpeter Swan

A great treatment and additional information on Trumpeter Swan verses Tundra Swan is in "Colorado Field Notes" November, 2017 issue
(see Colorado Birding Society's website on how to obtain)

No loon, scoter, Greater Scaup or other uncommon waterfowl was found.  Nearby Lake Ladora was similar.  Most common duck species were on Lower Derby; it is a good place to study them.

No Short-eared Owls appeared as I drove the DIA Owl Loop (Adams/Denver).

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