Greetings All

Alternate plumaged Marbled/Long-billed Murrelet ID is extremely difficult. An article by Nick Lethaby a few years back should be reviewed by all interested folks. It was in Birding. Also, a recent (1-2 years) article in Western Birds focusing on the utility of the underwing pattern is worth a read.

The bill length is very difficult to use in the field, and may not be reliable without direct comparison.

There is no consistent posture difference between LBMU and MAMU. The fact is that most photographed LBMUs are being pursued when photographed, and thus have their necks in a stretched/alert position.

A distinctly paler throat is more characteristic of LBMU than MAMU, though to some extent, this is a subjective mark.

An alternate plumaged MAMU should still show some degree of a collar if seen reasonably well

LBMUs can have entirely dark underwings.

Best Wishes and Good Cheer
Steven Mlodinow
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