Here in SF, I've heard two distinct call types over the past years. I can't
do justice to them through written alliteration, and currently don't have
access to sonograms or recordings of the 8-9 call types from around the
continent. The majority of the birds in the city use a single call, a relatively
straightforward "jip-jip". The other call was clearly different, and the first
time I heard it, I wondered if I was indeed hearing a crossbill, and was able
to confirm a single bird (female plumage) giving it. I've only heard that
call here one other time, unsighted, so it may be a singleton of a different type
hanging with our flocks, or different birds that happened to wander through
town while I was listening. I'll have to check if all of the call types are
available on the web, and hope the odd caller returns, so I can try to match it
up. I've rarely heard any crossbill songs in the city, only calls.
Our birds occur regularly in western GG Park, Sutro Heights, Land's End and
throughout the Presidio, and irregularly on Mount Davidson and Twin Peaks.
Both of the odd calls occurred in the Presidio. Over many years of birding the
East Bay hills, I've never heard or seen a crossbill in any of the extensive
conifer forests there.