To lie down (of animals), sit down (of birds).
The carabao is lying down in the mud.
Perhaps that chicken is going to lay an egg; it is sitting down.
Perhaps that cow is sick; it always lies down.
The cows are lying down (collectively) there in the weeds.
For a chicken or bird to take its chicks under its wings, to shelter its chicks, to sit on eggs.
There is a chicken sitting with her chicks (under her wings) under the house.
That chicken is not sheltering its chicks.
That chicken sits on her eggs because she is incubating them.