Cliff Swallow (Petrochelidon pyrrhonota)
   
 
Narrative and Science Lens
 

   Audubon places an egg on the rock surface. Why show it? Was he aware that these birds can get out of rearing a complete brood by carrying an egg--or even laying it--next door to have a neighbor involuntarily incubate and rear it? Such brood parasitism reduces parental effort a cost to competitors.

But Audubon might not have seen many of these birds nesting, for this is a western species whose range expanded eastward, presumably much later with the building of highway culverts that provide sites for colonies to nest. Audubon may simply have wanted viewers just to know what the eggs of these birds look like. Still, he did another interesting thing: He placed a male at the entrance of one of the nests. Both males and females incubate the eggs, but will respond to an alarm call by moving to the entrance. Might this bird's mate have called him when spotting another female nearby—one who might be looking for an unguarded nest to parasitize?
 
  Campus Locations
This small, dark-throated, square-tailed, pale rumped, short-billed, long-winged stocky songbird is a common resident from spring through fall, foraging aerially throughout campus. Large colonies in the Main Quad comprise most of the campus's breeding population, although a few pairs build their mud nests on residences and other structures. Nests are occasionally appropriated by House Sparrows.
 

Campus sustainability

  These birds prefer nest sites with an overhang (or position within a colony where they can share sides with neighboring nests), which reduces their nest-building effort and energy investment. These birds formerly nested within the arcade. Now, they are more apt to nest on the Quad gates, as seen here, which share characteristics with the cliffs that give these birds their name. Also, a number of years ago the arcade ceiling was stained and perhaps mud does not adhere well to the refinished surface.

Years ago droppings beneath the nests were considered a nuisance and nests were routinely washed away. Campus biologists succeeded in having the practice curtailed. The dropping, were not just those of Cliff Swallow adults exiting the nest. By the time they’re a week old, nestlings back up to the nest entry and defecate out the entrance. Prior to that, their parents carry the dropping out for them, usually releasing them at the entrance. Such cleanliness leads the birds to reuse the nests yearly and accounts for the nuisance factor. The swallows of Capistrano are apt to return to their colony--and their nest--yearly, but if it’s been removed, may XXXX.

The birds are thought to get the mud for their nests from Lake Lagunita, from puddles below sprinkler heads, and from other sources of reliably damp soil. In drought, mud may be a limiting resource.
  What you can do
  1. Report mud-gathering activity to help determine favored "mud puddles".
  2. In dry springs see if “mud puddles” can be maintained during nesting (the birds need to repair nests from time to time).
  3. Survey areas near the Quad that might provide good alternative nesting sites.
  4. Design a nest support that could be evaluated and tested to encourage nest-building in an area with low foot traffic.
 

5. Help determine if nesting in the arcade should be encouraged to return, at least in part, to its historic role.

  Science
       Essays from The Birder’s Handbook:
            Parasitic Swallows; Parent-Chick Recognition; Coloniality; Brood Parasitism
       References:
       Videos:
  Art
       Photos:
            Tom Grey (gathering mud, nesting)
          Carel (nesting above Common Raven nest)
       Drawings and Paintings:
            DW drawing after Audubon
          DW watercolor of Cliff Swallow in Quad
 
  To add reports or images please submit them via the Art at Exits home page