There are many different kinds of bird nests, and one that I find especially interesting is the mud nest. I came upon cliff swallows building their mud nests last week in a cove of San Francisco Bay.
I was walking in a residential neighborhood at the shoreline, when I noticed two or three dozen cliff swallows swooping around the water’s edge. That day we had particularly low tides. In fact, in the four months I’ve been traversing this path, I have never seen so much exposed mud.
The swallows were taking advantage of the mud opportunity afforded by this perigee phase of the moon (unusually close to earth).
In an area where there are usually ducks and cormorants swimming in the lapping water, this sight of the swallows fluttering in the mud slowed my disciplined pace.
I watched as the swallows used their bills to dig up little dabs of mud. Bills loaded with mud, they flew off to a nearby waterfront house; all flew to the same place, the underside of one house.
Superior flyers that they are, the swallows didn’t even pause at the extensive nets lining the underside, presumably installed to prevent this very activity. They effortlessly navigated through the net holes to the house’s beams.
One after another, each individual delivered their mud pellets, turned around and glided right back to the tidal mud, and scooped up more. This went on for at least 15 minutes.
There was no way to see or photograph the nests without a boat. But cliff swallow nests look like this.
They’re gourd-shaped, mud enclosures with a single opening.
Named for their behavior of building on cliffs, the cliff swallow has adapted, in the absence of cliffs, to building on human structures. They build under bridges, on highway overpasses, and other man-made structures, like houses.
Sometimes cliff swallows build fresh new nests, and sometimes they use old nests. They are colonial nesters and their living quarters can grow quite expansive. This swallow is known for their big communities, the species of the legend, the returning swallows of San Juan Capistrano.
There are about 80 species of swallows across the globe, occupying every continent except Antarctica. They don’t all build mud nests. The violet-green swallow, for example, is a cavity nester. I have witnessed their nest-building skills every spring in nest boxes on our property.
Barn swallows, the most widespread swallow in the world, also collect mud pieces for use in their nests. As their name suggests, they typically build in a barn or stable. Their mud nests are cup-shaped, usually built on a beam. Just like the cliff swallows, barn swallows require fresh mud for their nesting venue, and consequently nest near water.
Another swallow we encountered that day at the waterfront were the northern rough-winged swallows. They prefer to nest around water too, but build tunnels in the ground instead of nests.
Wherever you are, it’s always rewarding to observe birds building nests–the materials they choose, the places they set up house, and the devotion they declare in starting a new generation.
A toast to the mud-nesters: here’s mud in your eye.
Photo credit: Athena Alexander unless otherwise specified