Carolina Wren

Thryothorus ludovicianus (Latham)

Previously (Friedmann, 1963:39, 68) this uncommonly selected host had been known on 1 occasion, out of a dozen instances of parasitism, to rear a young cowbird to the fledging stage. A new observation indicates a much greater successful host potential for this wren. Luther (1974) reported a nest in which no fewer than 3 of the young parasites were reared to the fledging stage, an unexpected proof of the ability of a pair of these wrens to raise, not 1, but 3 nestlings, each larger than their own. There were originally 2 young wrens in the nest as well, but they died early in the competition for food with their parasitic nestmates.

At the time of the 1963 compendium (Friedmann, p. 68) only 14 instances of cowbird parasitism on this wren were reported. To these may be added the following. In Anne Arundel County, Maryland, in 1973 and 1974, Paul Woodward, together with Eugene S. Morton, found 13 nests of this bird, 9 in “natural” settings and 4 on manmade structures. Of these, 5 (all nests in natural sites) were parasitized, and each of these fledged 1 or more young cowbirds but no young wrens. The failure of the wren nestlings may be due to the much longer incubation period of their species, giving too great an advantage to the more rapidly developing parasites. In Ontario the Carolina wren appears to be free of cowbird parasitism (16 nests reported to the files at Toronto, none with cowbird eggs).

GRAY CATBIRD