Start by building a cuckoo bird.
Of course you could build any kind of critter.

Here's one solution ...

Using colored paper or sheets of foam rubber Foamies,
cut out these parts and hot glue them together.

If you think you're a hot shot inventor,
try hot gluing the pieces together
so the duck has a 3 dimensional quality.
You could glue pipe cleaners between the foam
rubber pieces. Then you would have flexible
joints and could put your wild thing in
many different positions.

Now you need to build a contraption on
your door to make the duck fly up
when someone opens the door.

Look for some small screw eyes, black sheet rock screws
and some 2"x8" (roughly) wood scraps.

Drill holes. Then put a screw eye in as follows:

Get on a chair and place the
wood shim high on your door frame.
Drill through the two holes in the wood shim
and into the side of the door frame.
Put the screws in.

Drill a hole for a screw eye
in the top corner of your door and
screw in the screw eye.

Finally, get some thread or fishing line.
Put the loose end of the spool through the screw eye
on the wood shim and then tie that end
to the screw eye on the door.

With the door shut, cut the thread about
one foot from the floor.
Attach this end to your bird and watch
your wild thing fly when you open the door.

You may need to glue some weight to the cuckoo bird
to make sure it comes down when the door closes.