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

Abstract

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 to offspring, while inclement weather likely prolongs development. For taxa with parental care, parental behaviour may partially buffer offspring against extrinsic drivers like predation risk and severe weather. 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 the duration of incubation and nestling development. 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. 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% per 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 parental buffering capabilities against environmental constraints. Fledging age was weakly correlated with incubation duration (r = –0.21) suggesting minimal developmental carry‐over effects. 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 variation in offspring development. Addressing multiple drivers of variation in key life‐history traits can provide important context for understanding life‐history theory under changing environmental conditions. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13273/suppinfo is available for this article.

Hierarchical fear: parental behaviour and corticosterone release mediate nestling growth in response to predation risk

“…= 0.8) varied among nests. Time of year can influence nestling growth dynamics (Naef-Daenzer and Keller 1999), and parents can vary in their ability to fledge offspring quickly during harsh, early season conditions (de Zwaan et al 2019). Therefore, we predicted the total effect of predation risk on nestling wing growth using the range of observed parental provisioning responses to predation risk at intervals of 1 s.d.…”

“…Extensive snow cover results in compressed breeding seasons (41–57 days) that begin in late-May or early-June and finish by late-July (Martin et al 2017). The nestling period lasts for 7 to 13 days (average = 9.4; de Zwaan et al 2019), and both parents provision nestlings (Goullaud et al 2018).…”

“…and < 1.2 km from all nests. Since cold temperatures can prolong nestling development time, we calculated the number of days with an average temperature below 10 °C prior to the experiment (0 – 4 d post-hatch) and including the experiment (0 – 7 d) to control for the influence of ambient temperature on different stages of development (de Zwaan et al 2019).…”

“…However, high predation risk may select for accelerated development, as nest predation is a cumulative risk that increases with time in the nest (Martin 1995). Nestling development rates occur along a slow-fast continuum, where rapid development is associated with greater predation risk among species (Bosque and Bosque 1995, Remeš and Martin 2002) and within populations (Hua et al 2014, de Zwaan et al 2019).…”

“…Greater site-wide predation risk is linked to more rapid development among and within years for an alpine-breeding population of horned lark ( Eremophila alpestris ) in northern British Columbia, Canada (de Zwaan et al 2019). Here, we experimentally increased perceived predation risk at the nest to investigate the underlying mechanisms for this result by assessing the relative indirect and direct effects on nestling growth.…”