Under the bridge

 

Do you have any guesses about which species of bird made this nest? 

Here's a perfect description of the nest:

"Their adherent nests are composed of a mud shell lined with plant fibers, typically placed over water and plastered to a vertical wall within a few centimeters of a protective ceiling."

Did you guess swallow?  If so, that's a good guess...but note that the nestlings in the picture above are black and they have fairly large bills, unlike swallows.  Note that finding the bills (yellowish/pinkish in color) is the easiest way to count the nestlings.  (There appear to be at least three nestlings, and perhaps more if some are hidden.)

Warning: The next picture will reveal the owner of the nest.

 

This adult Black Phoebe (Sayornis nigricans) had just caught a fly and was preparing to bring it to these nestlings.

Here are a few fun facts about Black Phoebe breeding behavior:

- It takes 1-3 weeks for the female to build the nest

- Building a nest close to a "protective ceiling" may help to discourage avian predators

- Clutch size varies between 1-6, with a mean of 4

- The female incubates the eggs for ~16 days

- Both parents feed the young in the nest for ~18 days

- Nestlings are primarily fed bees/wasps, flies, and butterflies/moths

- After leaving the nest, the young will stay with the parents for another 7-10 days

These pictures were taken near Falletti Park in Cotati on 31 May 2015.

P.S.  Facts above from The Birds of North America account by B.O. Wolf.