Date: 11/7/17 10:02 pm From: Christian Nunes <pajaroboy...> Subject: [cobirds] More Red Crossbill Info
As others have noted on the forum, there's a perceptible Red Crossbill incursion occurring across the region this fall. I'd like to stress the importance of recording crossbill calls. A simple voice memo from a smart phone can be uploaded and analyzed with free software (e.g. Ravenlite) or simply uploaded to eBird where a spectrogram will be produced automatically. If the recording is of high enough quality, the shape of the crossbill's call notes can be seen without any extra manipulation.
The recent eBird article on crossbill types is by far the most succinct and useful resource yet published on the web. By comparing the shape of the call notes on a spectrogram, the identification of precise types becomes almost easy.
Type 2 (Ponderosa Pine) and Type 5 (Lodgepole Pine) are the common breeding types in CO, and Type 4 (Douglas-fir) are irruptive. Other types wander into the state less frequently, most notably Type 3 (Western Hemlock). Several others are possibilities (maybe Types 7 & 10?), but we'll never document them without good recordings.
Some recent observations and recordings of Type 4 (Douglas-fir) crossbills from CO: