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  • Hello! I'm curious when it comes to distinguishing M. ciliolabrum vs M. californicus, is muzzle length referring to the base of the muzzle to the tip? Or is it the width of the muzzle across? I've seen other western bat keys that use the latter to distinguish the two species. Thank you! Taylor

    MYCI and MYCA are very difficult to positively distinguish even in hand. The muzzles are a little subjective, especially if you don't have both bats side-by-side. In SE AZ I find the tail tip to be relatively easy and reliable: if the tip is 2mm past the tail membrane, it's MYCI. If the membrane just ends in the tip, then MYCA. If you happen to have a good bat acoustic microphone setup handy such as SonoBatLIVE+ Pettersson M500-384, then as a double check try to get a good recording preferably 5-10 seconds after releasing the bat. MYCA generally has a Fc of ~50kHz where MYCI will be distinctly lower at ~35-45 kHz. You actually could see this with a simpler detector such as a Batscanner. I recommend the Bat Survey Solutions AZ field workshop where you'd catch dozens of both: https://batsurveysolutions.com/collections/frontpage