Cause they can both fly
how are trains and airplanes alike
Planes are man made, birds are not. They both have wings.
To provide the lift that is required to glide through the air without plummeting to the ground.
They have both fly alike
birds
planes
Both are simple machines
Sex
They both make noises.
there wings
planes birds stars and what not
I think it's just the order the objects are thought of when guessing at what "that object in the sky" is. Planes are often named after objects other than birds. Cherokee's, Cessna's, Mooney's and Lear all all examples of planes not named after birds.