Methheads make and or smoke METHANPHETAMINES...it's just hydroxal compound off of Mah huang, or Ephedrine...very easy to make, but very dangerous as well...
METHANE, is a gas that is produced by bacteria & solid animal wastes...one reason you don't wanna light a smoke on an outhouse...it's a clean burning fuel, giving off four carbons per every hydrogen burnt, unlike propane, which has 1.5-2 carbons givin' off per every hydrogen burnt. 'Bout the only thing cleaner than methane, is hydrogen itself...
& yes, it would take quite some chickens to be worthwhile, however, chicken reproduction is pertty fast, so somone with a lil' gumption could easily grow enough chickens to produce to enough methane, but still, its a viable source of free reusable energy...once yer methane production is done, you can use the left over sludge as fertilizer...