There are two common dowitchers in the Bay Area: The Long-billed Dowitcher, and the caurinus subspecies of the Short-billed Dowitcher. Thus, our challenge is narrowed down to separating these two taxons, and we can pretty much ignore the other two subspecies of Short-billed Dowitchers.
The first dowitchers arriving in July and August are adult female Short-billed Dowitchers in breeding plumage. Most of the Long-billed Dowitchers don't arrive until October, although a few trickle in earlier. Most of the adult dowitchers have molted into alternate plumage by October. Juveniles arrive in September - October, and some don't lose their colorful juvenile plumage until December. For explanations of characteristics below, see references to left.
|Bill length to head length||avg 1.9||avg. 1.6|
|Base of bill vs height after nostril||about 1.1||about 1.6|
|Loral Angle||about 5 deg.||about 15 deg.|
|Color of breeding plumage belly||Red-orange||White|
|Juvenile tertials||Gray with narrow edging||Broad cinnamon edging and internal marks|
For me, dowitchers are one of the most difficult shorebird ID challenges. Here is some useful material.
Pekka Sarvela, Dowitcher Bills 1995 (a discussion that shows the longest bills belong to LB Dowitchers, and the shortest to SB Dowitchers).