Devin R. de Zwaan, Alaine. F. Camfield, Elizabeth C. MacDonald and Kathy Martin
Among vertebrates, there is incredible diversity in development rates of young animals among populations, and even among individuals of the same population. We still understand very little about what causes this variation, particularly in habitats where predation, weather and parental care may all have big impacts on development rate.
During periods of greater predation risk, offspring should develop faster to leave the nest and evade predators. However, cold, stormy weather may slow development by restricting food availability or increasing thermoregulatory costs. Parents may have the ability to buffer offspring against both effects. Songbird offspring in particular are entirely dependent on the parents for survival while in the nest, as they provide food, warmth, and protection from predators.
We investigated what drives variation in offspring development within an alpine population of horned larks Eremophila alpestris in Northern British Columbia, Canada. In this population, the incubation period varies by 40% (10-14 days) and the nestling period varies by nearly 100% (7-13 days). Weather and predation risk are highly variable above the tree-line (> 1600 m), providing the perfect context to address individual responses to an uncertain environment.
Cold ambient temperatures prolonged the nestling period, but only when occurring later in development. During this later development period, nestlings are largely responsible for providing their own warmth and may have to invest limited energy into thermoregulation rather than growth, prolonging time within the nest. As expected, greater predation risk was linked to more rapid nestling development. However, temperature had a stronger effect on offspring development than predation risk. Finally, early in the season during cold, snowy conditions, females in good condition were able to create nest environments that encouraged rapid nestling development compared to poor condition females, indicating an ability to buffer offspring against harsh conditions.
By addressing several influential drivers simultaneously, this study improves our understanding of the relative importance of environmental constraints on offspring development, providing critical insight into how individuals may respond to rapidly changing environmental conditions.