We can only guess how they got there, but it’s likely that their former guardian tried “returning” these birds to the wild. This is a dangerous misconception since Silkie and Red Star chickens aren’t wild in the first place. They’re domestic breeds: dependent on humans for their care, and at risk of starvation, attack from predators, or being hit by a car if left to fend for themselves.
These two might have belonged to a backyard flock. Red Stars like Rainbow are used for egg production; Silkies like Unicorn are ornamental breeds and may also be raised for meat. Not all places are zoned for roosters, though; some chicken keepers may order female birds, only to be surprised when surprise roosters start to crow. If it’s illegal to keep roosters on their land, they may kill these birds or set them free.
Unicorn and Rainbow, a bonded pair, were set loose on their next adventure together. But without help—and soon—they might not survive on their own for very long.