LIFE-HISTORY TRAITS OF OPEN-NESTING VS CAVITY-NESTING BIRDS

We re-examined the longstanding dogma that cavity-nesting birds have larger clutch sizes than open-nesting species because of lower nest predation rates, which allow longer developmental periods. We provide data on nesting success of open-nesting species plus excavator and nonexcavator species (cavity-nesters that do vs. do not create their own cavities) of birds that coexist in the same habitat and use natural nest sites; studies were conducted in central Arizona in high-elevation forest drainages from 1987 to 1989. In comparisons among species, nest success increased in the order open-nesting < nonexcavator << excavator species. Length of the nestling period increased, whereas number of broods decreased, with increased nest success across these nest types. Contrary to conventional expectation, clutch size did not increase directly with increased nest success and length of the nestling period, and these patterns were not simply a result of phylogenetic effects. A literature review of data on adult survival in land birds indicated that nonexcavators have significantly lower adult survival than the other two nest types. The lower adult survival of nonexcavators was associated with greater annual productivity than for the other two nest types. Annual productivity appeared to be associated with nest site attributes, whereas number of brood attempts was related to nest failure rate. Clutch size was a byproduct of annual productivity and number of brood attempts. Thus, the long-standing paradigm relating clutch size directly to nesting failure and developmental period was not supported.