Animals that are ready to go shortly after birth are called precocial. This includes chickens and most of the equines.
If you've ever seen a newborn foal stand up for the first time, it's clear that's a built-in behavior. Standing up on those long spindly legs usually works the first time. So does walking, and within hours, running.
Lying down, however, is not built-in. I've seen a foal try to get back down on the ground, which is clearly trial and error, often ending in a fall. There's no evolutionary pressure to have that work right the first time.
If you've ever seen a newborn foal stand up for the first time, it's clear that's a built-in behavior. Standing up on those long spindly legs usually works the first time. So does walking, and within hours, running.
Lying down, however, is not built-in. I've seen a foal try to get back down on the ground, which is clearly trial and error, often ending in a fall. There's no evolutionary pressure to have that work right the first time.