"Colorado Mockingbird"? Stubborn and won't sing?

I need some help with this question I found. It says: Try all you want, you'll never get a "Colorado Mockingbird" to sing. Give me the name of this stubborn "bird". Does anyone know what bird this is? I have tried forever looking on the internet to find the answer but I cannot. Any help would be greatly appreciated. Kelly

Kelley - great question! "Colorado Mockingbird" is old cowboy slang for burro or donkey. And getting a donkey to do anything would be difficult! ~KB