Tractor: moveable, with the implication it will be moved frequently.
Stationary coop: permanently in one place.
(there are also a few coops that people drag from 1 location to another every year or so, but that is pretty uncommon and not relevant to most BYCers situations)
Tractor pros: chickens can always have fresh grass, grass is not killed
soil does not get packed or poo-poisoned
minimal if any worm egg buildup
can move according to seasonal changes, e.g. shady locations in hot weather, sun the rest of the year
can be used to let chickens work over garden plots
often cheaper to build
Tractor cons: can never be as predatorproof as a fixed coop can, and some are *very* non predatorproof
can never be as large as a fixed coop can, most are suitable for only 3-6 chickens (other than
more-crowded meat-chicken tractors)
cannot be very satisfactorily winterized in serious-winter climates; some tractors are hard to
winterize even for modest winters
it is only moveable if ground permits, meaning during mud or snow season it may be stationary
whether you like it or not
electricity dependant on (not entirely safe) extension cords; can't plumb in water except by
running a hose
may have to get moved a lot more frequently than you expect (e.g. every day) and even then
you are likely to have a visible "tractor trail" across your lawn, involving scratched-down
turf and poo deposits.
Stationary coop pros:
can be any size you want, tiny to huge, for any number of chickens and as much space-allowance
per chicken as you want
can be really seriously pretty predatorproof if you desire
can be built to provide really good wintering conditions no matter how severe your winter
can run proper hardwired safe electricity, and even a water faucet, if desired
walk-in coops can easily be converted to other uses e.g. playhouse, workshop, storage, goats, etc
if needs change
Stationary coop cons:
often built more expensively (even for the same size coop), although that is not strictly *necessary*
unless run is *enormous*, it will go to bare earth and get muddy and stomped-down and poor soil quality
worm eggs will eventually build up in the run to some degree or another
difficult or impossible to take with you if you move to another property
In my opinion, being as I feel that except in unusual circumstances chickens really deserve to have a lot more space than most BYCers allow (because they really do behave differently at larger space allowances), I am not a fan of tractors except as "day tractors" or if they house only a few chickens. (The largest practical size of tractor, even if you're doing it hoop style, is around 10x15 or so, and that won't work well for many people... and personally I would not put more than 6-8 chickens in there and not for a Northern winter or where there's lotsa predators around. Personally I would not put more than 2-3 chickens in a 4x8 tractor and that's IF the indoor part is up above the run so that total square footage is greater than the footprint. Of course others may feel differently, I'm just stating my own feelings here)
I am particularly not a fan of tractors used as winter housing in Northern climates. It can be done in the sense of the birds can pull through but it is not easy on the chicken owner and it is certainly not easy on the *chickens*, and IMO should be avoided if at *all* possible.
OTOH in a year-round mild climate where good predator protection comes from other sources and chickens are going to be kept in small (rather than large) groups, there are definitely a lot of advantages to a tractor; or for summer-only use for very small flocks in the North.
JMHO,
Pat