Are low reproductive rates characteristic of New Zealand's native terrestrial birds? Evidence from the allometry of nesting parameters in altricial species

Abstract

We investigate the notion that New Zealand's avifauna exhibits a macro‐evolutionary trend towards low reproductive rates by analysing the allometry of nesting parameters for native altricial land birds. We show that egg size, incubation periods, and nestling periods are all strongly correlated with body mass, but clutch size is not. However, egg size more accurately predicts incubation periods, and incubation periods more accurately predict nestling periods, than does body mass. Variation between and within families is explored. Neither divergence per se nor slow rates of reproduction appear related to the taxic level of endemism. “Gigantic” species breed more slowly in proportion to body mass as predicted allometrically, but as a macro‐evolutionary trend, the effect is counterpointed within New Zealand by a parallel trend towards dwarfism. We found that hollow‐ and cavity‐nesting species have longer nestling periods than open‐nesting species. Corvida passerines lay larger eggs, after controlling for body mass, than do Passerida passerines. Most of New Zealand's altricial bird species evolved from Australian colonists. Macro‐evolutionary trends are therefore most likely to be identified by comparison with the Australian avifauna. We present evidence suggesting that New Zealand passerines lay larger clutches than their Australian temperate zone counterparts. A previous study (Trevelyan & Read 1989) suggested that New Zealand birds lay more clutches per year. These findings are inconsistent with suggestions of marked K‐selection in the New Zealand avifauna, but may be explicable under the “bet‐hedging hypothesis” for the evolution of life histories. The notion that New Zealand birds breed slowly may have arisen by comparisons with the avifaunas of the Northern Hemisphere, comparisons that ignore the distinctive life history traits of the avifaunas of tropical and other southern temperate regions.