The mystery is: Which types nest in Wisconsin?
What we think of as Red Crossbill appears to actually be a complex of multiple types, each with their own distinctive call note, differing in morphology, and potentially actually different species.
The best way to tell what type you have is to obtain audio of the call note. All you need to do is take audio or video (smartphones work) of red crossbills you hear, and send those files/checklist links to Matt Young at email@example.com or Tim Spahr firstname.lastname@example.org and they’ll analyze and report back. Then report to eBird at type level.
Nesting is getting started right now! Head to your favorite coniferous landscape and keep an ear out. Anytime you are seeing red crossbills, take a video or audio of them. Be alert for behaviors that may indicate nesting like giving flight songs, pairing up, or carrying nest material.
We recently had our first ever breeding confirmation of Type 4, a species whose stronghold is thought to be the Pacific Northwest!
Want to learn more? Here are some resources about Red Crossbills:
Species Survey Strategy: Red Crossbill (and Pine Siskin, another finch to watch for early nesting)
Crossbills of North America: Species and Red Crossbill Call Types (comprehensive summary)
August 2017 Wisconsin Red Crossbill update (The beginning of the big Type 2, 3, 4 invasion)
February 2018 Wisconsin Red Crossbill update (The latest info)