Temporal constraints influence reproductive characteristics that are related to the pace-of-life continuum in geese

Abstract

Among avian species, particularly those with altricial young, life-history strategies are characterized by a ‘slow’ pace-of-life at lower latitudes, where relatively low annual investments in reproduction are traded-off for increased survival. Evidence for this pattern in precocial species, however, is equivocal, and questions about ecological drivers of latitudinal variation in reproduction remain. To better understand spatial variation in pace-of-life and related reproductive traits across bird species and to test a hypothesis that might explain observed spatial patterns, we analysed breeding data from closely related Canada Geese Branta canadensis and Cackling Geese Branta hutchinsii, hereafter Canada-type geese, comprising eight sub-species from 16 sites across a broad gradient of latitude (32°N to 69°N) and season length. Unlike the pattern reported for many altricial species, Canada-type geese did not show reduced annual fecundity at lower latitudes, and instead this reduced reproductive investment was at higher latitudes. For three of five reproductive traits, the relative influence of growing season length (GSL; an index of the time available to breed) was greater than that of latitude. A shorter GSL resulted in later nest initiations, shorter pre-laying intervals and higher seasonal rates of clutch size decline. Our results suggest that these and other species of geese are able to circumvent nutritional and temporal constraints imposed by shorter GSL by storing and using nutrient reserves for egg laying and incubation. Relative flexibility in reproductive traits may permit Canada-type geese to accommodate predicted increases in climatic variability, compared to species with more rigid reproductive strategies.