The bird's speed is 5 mph. If
the speed of the wind across the ocean is greater than or equal to 1 mph towards the direction the bird is flying*, the overall speed of the bird will be greater than 6 mph,
and it can easily reach the other side of the ocean without resting.
So that means
the speed of the ocean wind at that time must have been at least 1 mph in the same direction the bird was flying.
And hence the bird reached the other side of the ocean without resting.
This picture illustrates the point:
*Or greater than or equal to √2 mph to any angle not more than 45˚ from the direction of bird's flight. If greater than 45˚, it needs to be more than √2 mph, depending on the angle.