Latitudinal Variation in Life History Traits and Incubation Patterns of Yellow Warblers (Setophaga petechia)

We studied Yellow Warblers breeding in arctic habitat in Inuvik, NT and temperate habitat in Revelstoke, BC, and use data from 21 populations spanning 0°N to 68°N to evaluate latitudinal trends in life history traits. We observed latitudinal gradients in clutch size, nest success, annual productivity and adult survival that were in accord with predicted shifts towards faster life histories at the higher latitudes. However, we only detected weak latitudinal declines in incubation and nestling periods. Incubation periods were similar in arctic and temperate habitats, despite Inuvik females maintaining colder and more variable nest temperatures during incubation. This suggested that the effect of temperature on incubation periods was limited and/or may have been counteracted by other factors. We conclude that multiple environmental factors likely influence and select for variation in life history traits and that the expectation for a general shift in life history traits may be oversimplified.