This is bird note.

Imagine you're a cliff swallow, soaring and swooping on a long flight from South America in the spring.

Sounds pretty nice.

But when you arrive in North America to nest,

the dirty work begins.

To build a mud nest under the eaves of a barn, you and your mate have to find a mud puddle or creek.

Next, start scooping up mud with your beak.

You build the floor first. Press a row of mud pellets against

the wall, 4 to 5 inches beneath an overhang, making a slight crescent shape. Once the floor extends far enough out, build the sides up.

To finish, give the roof a rounded taper, like the top of a jug. The opening, just wide enough to wiggle in and out, angles downward.

Finally, line the inside with dry grass for the eggs.

After days of work and 1,000 mouthful of mud, your nest is complete and it's just one part of a large colony.

Nesting on vertical... a large colony.

Nesting on vertical human structures like bridges, culverts and buildings has helped the species expand its range.

Even in new habitats, Cliff swallow construction skills get the job done.

For Bird Note, I'm Michael Stein.