Monday, July 18, 2011

Cliff Swallow

Cliff Swallows construct large colonies of mud nests under bridges, culverts, steep cliffs, and under building eaves. The birds in the first photograph were under the Highway 19 bridge in Cannon Falls.

I banded over 500 Cliff Swallows in Aberdeen, South Dakota. They nested under bridges along a creek that ran through town. I found that they moved from bridge to bridge during the summer. I also caught them in Aberdeen in subsequent years, although not often under the bridges where I first banded them.

The Birds of South Dakota, Dave Swanson, Jef Palmer and I cited a Cliff Swallow banded on 14 June 1937 near Sioux Falls, South Dakota that was recovered in West Virginia 16 July 1937. Cliff Swallows breed across most of North America (including Canada and Mexico). They winter from southern Brazil to central Argentina. Do our birds regularly head east before heading to their wintering grounds?

Cliff Swallows are socially monogamous but geneticaly polygamous. That's to say, only one male and one female use a given nest. But both sexes mate with other birds besides their mates. Copulation often occur within the nest. Extra-pair copulations often occur at mud holes where Cliff Swallows collect nesting material. One of these rapes appears to be happening to the right in the photograph below (taken at Sand Lake National Wildlife Refuge near Aberdeen). Males often attack their mate when she returns from mud holes, and forces copulation with her.
According to Brown and Brown (1995), "This may reflect sperm competition...a male's probable defense against extra-pair copulations" that are so frequent at the mud sites. Nevertheless, studies have shown that about half of Cliff Swallow nestlings in any given nest are not related to at least one of the parents. Sometimes the young are related to neither parent!  Females are known to lay in or carry eggs to other, usually nearby nests (
Brown and Brown 1995).  Females that practice this behavior to continue to raise the remaining eggs in their own nests.

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