Seems Ive heard some sort of worry about bean eating and chickens. Im assuming here, since Im not a horticulturist, that 'scartlet runners' are the edible ornamental vines by that name. For people, "... this bean is truly a food work horse: you can eat the flowers, the whole bean pod when young, or shell them for the beans when they are bigger. In fact, the starchy roots are still eaten by Central American Indians. They are also one of the heaviest yielding crops (up to about 65lb from a 10ft row) and are not difficult to grow" - -
www.henandharvest.com
The concern as far as I recall is that raw beans have some sort of mildly toxic effect, or something like that. Its not like they'll keel over by tasting one, but seems it's more of a general hand wringing sort of worry. Over on EasyGarden.com, several people swear by scarlet runners for planting around chickens, espousing both the beauty and food value of the vines.
They also warn that you have to protect the young vines from the cluckers, as the ever-ravenous birds will devour them before they can grow to any size! Once you get them established, they are perennial, so be sure you like them where you put them.
Of course, someone will now come along and tell us they are utter poison to chickens....
