Abstract
SummaryEvidence for reduction of clutch size in insular passerines is presented. Average clutch sizes for the Catbird, Cardinal and White‐eyed Vireo were reduced 14.0, 18.2 and 30.7%, respectively as compared with coastal North American populations from similar latitudes. Differences are highly significant. Clutch size in the Eastern Bluebird was not reduced. Trends in latitudinal and longitudinal variations of clutch size in North America are examined. With the exception of a slight latitudinal gradient in coastal populations, no consistent trends existed. There is no evidence for reduced variability in clutch size or increased egg size in the Bermudan populations, but both these parameters may show some response to combined effects of latitude and longitude in continental populations.Reduction of clutch size in insular nidicolous birds is consistent with both the Lack‐Ashmole resource limitation hypothesis and Cody's energy allocation hypothesis. In the absence of experimental evidence for life history optimization in response to K‐selection, the modified Lack hypothesis seems sufficient.
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