NESTS AND NEST SITES OF THE SAN-MIGUEL-ISLAND SONG SPARROW

Nests and nest sites of the San Miguel Island (SMI) Song Sparrow (Melo spiza melodia micronyx) are described; nests are compared with those o f 16 other races of Song Sparrows. Bush lupins (Lupinus albifrons), co yote brush (Baccharis pilularis) and golden bush (Haplopappus venetus) were the shrubs used most commonly as nest sites by Song Sparrows on SMI. As a result of its location, the nest was effectively concealed f rom gray foxes (Urocyon littoralis), the major predator of this sparro w. Nest and nest site also moderated the combined chilling effects of cool air temperatures and strong northwesterly winds on the eggs and n estlings. Even in the absence of these moderating effects of the nest site, the energetic cost of incubation, estimated at 41-53% of the spa rrow's resting metabolic rate, was modest. Twenty-nine percent of the canopy above the nest was open and as much as 73% of the nest cup was in the sun at midday, a time when surface temperatures of foliage, nes t and nestlings sometimes exceeded 40 C. Whereas this exposure did not apparently reduce fledging success, it may explain why the incidence of addled eggs was so high in this population of Song Sparrows compare d to others. Significant differences existed among races of Song Sparr ows in the size, porosity and insulation of the nest. In most cases, t hese differences were not related to the latitude of the races' nestin g areas.