An analysis of clutch‐size in New World passerine birds

Variation in clutch‐size among New World passerine birds was analysed with respect to four variables: body‐mass, geographic latitude, the frequency of nest predation, and the structure of the nest. Data were analysed separately by averaging traits at three taxonomic levels: species, genus, and subfamily. Allometric scaling with body‐mass did not account for significant variation in clutch‐size regardless of the taxonomic level of analysis. Latitudinal effects on clutch‐size were highly significant at all taxonomic levels. For species building small‐pensile nests and open‐cup nests, nest predation had a significant partial effect on clutch‐size, with latitude held constant. When nest predation and latitude were held constant, clutch‐size was significantly different among species building small‐pensile nests, open‐cup nests, and domed nests. These results suggest that New World passerine clutch‐size is related to at least three variables: latitudinal effects, nest predation, and nest structure.