Bwack, Pluck, Bwack, Pluck...
Okay, this special day is just strange. I agree with you on that. Two obvious questions arise.
- How do you tune your guitar to a chicken?
- How did someone come up with this idea?
I'll try to answer both questions for you, but I won't promise the results will be satisfying.
Tuning your guitar to a chicken assumes that you have both a guitar and a chicken available. Many people own (or have access to) a guitar. Not so many also have a chicken at hand. (I think a rooster, as opposed to a female chicken, is acceptable.)
So we'll say you have a guitar and that you 1) own a chicken, 2) live near a chicken, or 3) can take your guitar where it will be near a chicken.
Once the two are both in earshot, I guess you wait for the chicken to say "bwack" and tune your lowest guitar string (normally tuned to E) to that sound. You might have to "sing" the "bwack" yourself and extend the note so that you can actually hear a pitch. This is possible.
After tuning that first string, I think you have to tune the rest of the strings to each other, as is often done anyway. I seriously doubt the chicken is going to provide bwacks at different pitches.
I wonder if Johnny Cash ever tried this.
As to how someone invented this January 20 special day, I'll only be able to make some wild guesses.
Illegal substances are a possibility but certainly not necessary.
Perhaps the creator of the day actually heard a melodic chicken. I suppose they could exist. If you listen to a chicken long enough, you will hear different "pitches" amongst their sounds - just not the ones you'd normally use for guitar tuning.
Maybe this day was originally something like killing a chicken with a guitar, but someone thought that was too weird or gruesome and changed it to this kinder, gentler day.
Whatever the case may be, celebrate it if you can. Approximations are probably in order today. Tuning any instrument to any animal (living or artificial) is okay in my book.
Addendum: There are way too many search results on Google image for "chicken guitar".