Audubon places an egg on the rock surface. Why show it? Was he aware that these birds can avoid rearing a complete brood by carrying an egg--or even laying it--next door where a neighbor will involuntarily incubate and rear it? (See brood parasitism, which reduces parental effort at a cost to competitors, below.)
But Audubon might not have seen many of these birds nesting, for this is primarily a western species whose range expanded eastward presumably much later with the building of highway culverts that provide nesting sites for colonies. Audubon may simply have wanted viewers to know what the eggs of these birds look like. But, he did another interesting thing: He placed a male at the entrance of one of the nests. Both males and females incubate the eggs and will respond to an alarm call by moving to the entrance. Might this bird's mate have called when spotting another female nearby—one seeking an unguarded nest to parasitize?
Campus LocationsThis long-winged songbird is a common resident from late February into September, foraging aerially throughout campus. 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 (see van de Woestijne photo, below).
Campus sustainability
Why did the swallows move? A number of years ago the Arcade's wooden ceiling was stained during refurbishing and may be a factor. Also, years ago droppings beneath the nests were considered a nuisance remedied by hosing down the mud nests. Campus biologists succeeded in having this curtailed, but many of the birds may have stopped returning to the sites. The swallows of Capistrano, for example, stopped returning to the mission after nests were removed during renovations. Only a swallow vocalization project using speakers playing swallow courtship calls enticed birds to return to the mission.
Another factor may be involved: The swallows are thought to get mud for their nests from the edge of Lagunita when it has some water, from puddles below sprinkler heads, and from other sources of reliably damp soil. Lower lake levels and drought may make mud a limiting resource here.
Beecher et al., 1985; Brown, 1986; Brown and Brown, 1986; Withers, 1977.
Carel Brest van Kempen's photo of a Cliff Swallow nest above the nest of a Common Raven in Wyoming illustrates an improbable nesting association and contrasting specialization in nesting materials and sites. See Carel's blog (which featured this photo in 2001) and his website.
Johanna van de Woestijne's photo of a House Sparrow appropriating a used Cliff Swallow nest at Shoreline Park, Mountain View, CA also shows how the swallows navigated past netting and spikes in order to nest. Where nets and spikes fail to deter nest-building, Johanna suggests installing a catch plate or shelf for swallow droppings below preferred nesting sites to eliminate the nuisance factor. Where that fails, redireting swallow nesting efforts to alternative sites using teflon paint on the surfaces in question and building suitable artificial eves in alternative nearby sites may reduce the possibility of power washing sites before nestlings fledge. This site in the Quad, with remains of a nest, appears to have been sprayed with a a coating to deter future nesting. See more of Johanna's photographs.
DW watercolor of Cliff Swallow in the Quad