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Sunday, December 9, 2012

Nomads

Well, these aren't great pictures or recordings, but this is an interesting species and phenomenon, so I thought it would be worth posting about.

When I walked outside of our house in Sebastopol on 7 December 2012, I heard Red Crossbills (Loxia curvirostris) calling overhead.  I ran inside to get my recorder and ended up with a couple of short recordings.  It's hard to see the treetops in our yard (redwoods), but when the flock flew off I could see that there were about 10-12 birds.

Then when I walked outside in Yachats, Oregon, on 8 December 2012, I heard Red Crossbills calling overhead again.  This time I saw two very large flocks of 40-60 birds each.

This morning I managed a few images before we left Oregon.  Here's a landscape shot with two birds perched at the top of a tree (left side of photo).


Crossbills are medium-sized finches.  As their name suggests, their most distinctive feature is their crossed bill — the upper and lower mandibles are curved and cross at the tip.  You can just barely see this in the silhouette below.


To help visualize the bill, here's an illustration:

Figure from Benkman, C.  1993.  Adaptation to single resources and the evolution of crossbill (Loxia) diversity.   
Ecological Monographs 63(3): 305-325.


This bill shape is useful for prying open the scales of conifer cones to reach the seeds inside.  (There is a much more involved story about bill sizes, food preferences, and call notes of Red Crossbills, but that'll have to wait for another time.)

Crossbills "follow the cones" — they are nomads, wandering to find good cone crops (e.g., spruce, pine, douglas-fir, hemlock).  They're most often associated with northern areas (taiga forests in Alaska and Canada) and montane coniferous forests, but some years they're forced to search widely for food and they show up in areas where they're not regularly seen.  They're considered uncommon residents in Sonoma County.

Adult males are red, while the females are greenish yellow.  Although it was too dark this morning to get good pictures, adjusting the exposure on the computer provided a hint of coloration (next photo).


The appearance of Red Crossbills in this area is unpredictable.  But this may be a good winter for them, so keep your eyes and ears open!

Here are two recordings from Sebastopol, CA, on 7 December 2012.  You can hear quite a few species, but try to focus on the short call notes that are sometimes written as jip-jip, jip-jip-jip.  [You may need to turn up your volume.  And if you don't see these sound clips in the e-mail message, just click on the title of this post to go directly to the web page.]
 
P.S.  Matt Young from the Cornell Lab of Ornithology's Macaulay Library has confirmed these as Type 3 Red Crossbills.


1 comment:

Anonymous said...

the recordings came through very well - have seen white winged but not red crossbills this year....c