Data from: Variation in offspring development is driven more by weather and maternal condition than predation risk

<b>Abstract</b><br/>1. Variation in offspring development is expected to be driven by constraints on resource allocation between growth and maintenance (e.g., thermoregulation). Rapid post-natal development decreases predation risk, while inclement weather likely prolongs development. For taxa with parental care, parental behaviour may buffer offspring against some extrinsic drivers. 2. Using a 7-year dataset from an alpine population of horned lark Eremophila alpestris, a ground-nesting songbird in northern British Columbia, Canada, we investigated multiple potential drivers of variation in incubation and nestling development duration. 3. Using path analysis, we evaluated the direct effects of weather, predation risk, and parental care on offspring development, as well as, indirect developmental ‘carry-over’ effects of conditions during incubation on the nestling period. 4. Nestling period duration varied by nearly 100% (7–13 days) and incubation duration by 40% (10–14 days). Cold ambient temperatures late in the nestling period prolonged development by 1 day for every 2 days below 10°C; particularly when combined with heavy precipitation. Rapid nestling development was associated with high predation risk, and prolonging development incurred a nest survival cost (–2.3%/day). Females in good condition created nest environments that promoted rapid nestling development periods (average = 8–9 days) compared to poor condition females during harsh, early-season conditions (10–11 days), indicating buffering capabilities against environmental constraints. Incubation duration was only weakly correlated with fledging age (r = –0.21) suggesting minimal developmental carry-over effects. 5. Given high nest predation risk, immediate fitness benefits can be derived by overcoming environmental constraints and reducing development time. While predation risk was influential, inclement weather and maternal condition had stronger effects on within-population variation in development time. We highlight the importance of addressing multiple drivers of variation in key life-history traits and provide context for understanding life-history theory under changing environmental conditions.