[CT Birds] Red Crossbill analysis; Types 3 and 4

[Nick Bonomo]

Hi CTBirders,

As was previously posted here and on other listservs, the species we
currently know as Red Crossbill may in fact consist of up to 9 good
biological species in the United States and Canada. Check these links
for the previous post and more crossbill info.

http://lists.ctbirding.org/pipermail/ctbirds_lists.ctbirding.org/Week-of-Mon-20071112/004070.html
http://research.amnh.org/ornithology/crossbills

Last month I was able to get my hands on a mini-recorder and a shotgun
microphone (thanks Noble Proctor), and I have since recorded
crossbills on three occasions:
Dec 2 – East Shore Park; 2 birds (both TYPE 4)
Dec 7 – Hammonasset State Park; 42 birds (one TYPE 3, the rest TYPE 4)
Dec 8 – Hammonasset State Park; about 30 birds (one or two TYPE 3, the
rest TYPE 4)

Computer analysis has revealed the following thus far. The two East
Shore Park crossbills were TYPE 4 birds. Early returns on the
Hammonasset crossbills are that the flock is largely made of TYPE 4
birds, but at least one TYPE 3 was present on the 7th and 8th.

I will continue to sort through the Hammonasset recordings from the
7th and 8th to see if I've missed anything. This may take a while as
it can be difficult to identify every note when a flock of 30 birds is
calling at once. But the early returns are both very interesting and
exciting, and I figured that birders would want to know this before
the crossbills depart the region. Hopefully the crossbills will
persist through the winter, in which case I will continue to record
them when possible.

A few folks have asked about the process of recording and identifying.
In the field, the birds were recorded using a mini tape recorder and a
shotgun microphone. I moved the tape from the mini-recorder to a home
stereo system. I then used an audio cable ($6 from Radioshack) with
1/8-inch 'minijacks' on each end to connect the stereo to my computer
(from the headphones jack on the stereo to the line-in jack on my
laptop). Using the free software Audacity, I transferred the audio
from the stereo to the computer and saved the file in .wav format. At
this point, you have a .wav file with a bunch of flight calls
interspersed throughout. From there, I used the software Thrush-x
(also free) to automatically detect the bird calls from my audio file;
this software also breaks the larger file into many smaller files that
each contain one or more bird calls (ideally, crossbill flight calls).
Next, the software GlassOFire (you guessed it….free) produces a
sonogram for each small file. These visual 'sound maps' are
instrumental in positively identifying each flight call. There is more
sophisticated software out there somewhere (though probably not free),
which I hope to get my hands on soon.
For anyone interested in trying this, here is a great resource:
http://oldbird.org/

Once you have your recordings and sonograms, it's time to identify
them to type. I have used two resources to match the CT crossbills to
type. The first is the Evans & O'Brien "Flight Calls of Migratory
Birds," available from http://oldbird.org/ and some bird stores. This
resource has audio examples and sonograms of types 1-4 (the ones known
to occur in the east). Second, the crossbill audiovisual guide (linked
at the beginning of this message) provides information on types 1-7
and is also very helpful. Crossbill researchers Jeff Groth and Matt
Young have confirmed my results.

If anyone would like to hear and "see" examples of the Connecticut
crossbills, let me know and I'd be happy to send the small audio files
(.wav) and sonograms (.jpeg). The difference between the type 3 and 4
birds is quite drastic.

As far as field birding goes, if anyone wants to try to pick out a
type 3 crossbill at Hammonasset without the help of a computer, it
might be doable with preparation. I got lucky at Hammo on the 7th and
had a type 3 bird and a type 4 bird calling quite loudly while the
rest of the flock was silent. At the time I knew enough that it was
not a type 4, but needed the computer analysis to figure out which
type it was. Of course you need to differentiate the flight call from
the various calls the crossbills give while feeding and chattering
(note: they often give the flight call while perched in the few
seconds before they take flight and after they land).

Nick Bonomo
Orange, CT