Hi Tweets,

On our flu-delayed San Diego/Borrego Springs trip we had good birding,
113 species. In San Diego we saw lots of terns --Caspians, Royals, and a
Gull-billed. Least were said to be there, but we didn't see them. While
on the San Diego River estuary we ran into difficulties separating
Common and Forsters terns, both of which were said to be there. They
are the same size and have about the same color for bills and legs, in
flight both show a deeply-forked tail, and standing in the NG Guide to
the Birds of North America they seem to have identical markings. Is
there a reasonable way to tell which is which? (For example, the
wingspan of the Common is said to be 31" and the Forsters 30," but
that's not reasonable in the field because of differences among
individuals of both species.) Does one have to try to hear the
difference in calls above the roar of traffic on the San Diego bridges?

Paul Webster
PWebst25 at concentric.net