In outer space the birds can not fly because there is no atmosphere. The flight of a bird is possible thanks to the "force of lift," A lift force is only achieved when an object, with a specific shape, moves in a fluid, as in the case of the atmosphere.
When birds move with certain speed, the shape of the wings allow that the air to flow faster at the top than at the bottom of the wing. A higher speed in a fluid corresponds to a lower pressure and a lower velocity to higher pressure. So, between the top and bottom of the wing, a resultant force is created, directed upwards, allowing the bird to fly. This same principle is used in the construction of aircraft; in this case the wings and speed of the aircraft are what allow the plane to keep flying.
So in outer space, as there is no atmosphere, it is not possible to have a "force of lift".