The importance of nighttime length to latitudinal variation in avian incubation attentiveness

Abstract

Avian incubation provides an opportunity to test how parental behavior and ecological conditions interact to shape variation in offspring traits along geographic gradients. In particular, the duration of the incubation period is shorter at higher latitudes, but the degree to which this pattern arises from genetic divergence in rates of growth and development versus from parentally‐mediated variation in egg temperatures is controversial. At higher latitudes parents have higher daytime incubation attentiveness, i.e. they spend a greater proportion of the day on the nest. However, interpreting latitudinal variation in behavior is complicated by latitudinal patterns in ambient temperature and day length. Here, we use 24‐h video recordings to compare the incubation behavior of orange‐crowned warblers Leiothlypis celata in California and Alaska and test how attentiveness varies between populations and as a function of temperature. Birds in Alaska had higher nest attentiveness during the day, despite experiencing similar ambient temperatures. However, when analyzed over 24‐h, the longer nighttime period in California almost entirely canceled out daytime attentiveness differences between populations, and differences in 24‐h attentiveness were small. Our work highlights how incorporating nighttime incubation behavior qualitatively alters latitudinal patterns of attentiveness, and how lower ambient temperatures cannot account for the higher attentiveness in a high latitude population. These populations differ in their incubation period lengths, and differentiating between evolved versus environmentally‐induced variation in offspring growth and development will help understand the fitness consequences of variation in developmental periods.

Intraspecific variation in incubation behaviours along a latitudinal gradient is driven by nest microclimate and selection on neonate quality

“…This study is the first to quantify intraspecific variation in a suite of incubation behaviours (traits that trade‐off with other life‐history traits) along a large latitudinal gradient; incubation period duration, daily nest attentiveness and cumulative nest attendance were all positively correlated with latitude. Several studies have examined interspecific variation in these traits (Chalfoun & Martin, 2007; Martin et al., 2007; Martin & Schwabl, 2008), but few previous studies have reported intraspecific latitudinal variation in incubation behaviours (see Ardia et al., 2006; Sofaer et al., 2020) and none have compared populations at more than two study sites. The available intraspecific latitudinal comparisons of incubation periods are in species with intermittent incubation and reported results opposite of our patterns; both orange‐crowned warblers Leiothlypis celata and house wrens Troglodytes aedon had longer incubation periods at low‐latitude sites compared to high‐latitude sites (Dobbs et al., 2006; Sofaer et al., 2020; Tieleman et al., 2006).…”

“…Several studies have examined interspecific variation in these traits (Chalfoun & Martin, 2007; Martin et al., 2007; Martin & Schwabl, 2008), but few previous studies have reported intraspecific latitudinal variation in incubation behaviours (see Ardia et al., 2006; Sofaer et al., 2020) and none have compared populations at more than two study sites. The available intraspecific latitudinal comparisons of incubation periods are in species with intermittent incubation and reported results opposite of our patterns; both orange‐crowned warblers Leiothlypis celata and house wrens Troglodytes aedon had longer incubation periods at low‐latitude sites compared to high‐latitude sites (Dobbs et al., 2006; Sofaer et al., 2020; Tieleman et al., 2006). Similarly, interspecific studies have documented longer incubation periods in tropical species compared to temperate species (Martin, 2002; Martin et al., 2007; Martin & Schwabl, 2008).…”

“…Daily nest attentiveness was positively correlated with latitude in burrowing owls, and nest microclimate explained a significant proportion of that variation, largely corroborating previous studies. Diurnal nest attentiveness was higher at high‐latitude sites than at low‐latitude sites in two species of warblers (Rohwer & Purcell, 2019; Sofaer et al., 2020). However, 24‐hr nest attentiveness was similar between sites for one of the species (Sofaer et al., 2020) and the difference in nest attentiveness between the two study sites for the other warbler species was fully accounted for by variation in ambient temperatures and male feeding rates.…”

“…Visual inspection of the data revealed that percent daily nest attentiveness during the incubation stage followed a strongly left‐skewed distribution. Therefore, we used a beta distribution to model variation in these data after first applying a transformation to slightly compress the range of the proportional response variable and eliminate values of 0 and 1 (following the approach of Smithson & Verkuilen, 2006; Sofaer et al., 2020). We then modelled daily nest attentiveness as a function of the linear and quadratic effects of clutch size, Julian date, mean daily nest temperature, latitude and a categorical variable indicating whether the nest was warmer or colder than above‐ground ambient temperature.…”

Adaptation and constraint shape the evolution of growth patterns in passerine birds across the globe

“…Thus, a pressure to finish development early and/or allow for re-nesting after failure within a short breeding season might be a strong selection on fast development. Indeed, within-species studies demonstrated that northern populations have shorter incubation and nestling periods, faster growth and higher brood mass for the same age than southern populations [ 64 , 69 – 72 ]. Additionally, faster growth in northern temperate species can also be explained by the increased length of daytime during breeding period.…”