Incubation behavior adjustments, driven by ambient temperature variation, improve synchrony between hatch dates and caterpillar peak in a wild bird population

Abstract

For organisms living in seasonal environments, synchronizing the peak energetic demands of reproduction with peak food availability is a key challenge. Understanding the extent to which animals can adjust behavior to optimize reproductive timing, and the cues they use to do this, is essential for predicting how they will respond to future climate change. In birds, the timing of peak energetic demand is largely determined by the timing of clutch initiation; however, considerable alterations can still occur once egg laying has begun. Here, we use a wild population of great tits (Parus major) to quantify individual variation in different aspects of incubation behavior (onset, duration, and daily intensity) and conduct a comprehensive assessment of the causes and consequences of this variation. Using a 54‐year dataset, we demonstrate that timing of hatching relative to peak prey abundance (synchrony) is a better predictor of reproductive success than clutch initiation or clutch completion timing, suggesting adjustments to reproductive timing via incubation are adaptive in this species. Using detailed in‐nest temperature recordings, we found that postlaying, birds improved their synchrony with the food peak primarily by varying the onset of incubation, with duration changes playing a lesser role. We then used a sliding time window approach to explore which spring temperature cues best predict variance in each aspect of incubation behavior. Variation in the onset of incubation correlated with mean temperatures just prior to laying; however, incubation duration could not be explained by any of our temperature variables. Daily incubation intensity varied in response to daily maximum temperatures throughout incubation, suggesting female great tits respond to temperature cues even in late stages of incubation. Our results suggest that multiple aspects of the breeding cycle influence the final timing of peak energetic demand. Such adjustments could compensate, in part, for poor initial timing, which has significant fitness impacts.

Diurnal patterns of ambient temperature but not precipitation influence incubation behavior in Great Tits

“…We showed, that local ambient temperature and time of day affected duration of single offbouts and nest attendance of females. Contrary to our expectations, female Great Tits made more frequent and longer off-bouts when local ambient temperatures were low (but see Cresswell and McCleery 2003;Simmonds et al 2017). The probability that females stayed in the nest box increased with increasing local ambient temperature.…”

“…Thus, high food availability during incubation period might affect hatching date of nestlings. Indeed, female Great Tits seem to adjust their incubation behavior, and thereby breeding success, by varying clutch size and/or onset of incubation to synchronize the hatching of nestlings with a peak of food abundance (Cresswell and McCleery 2003;Simmonds et al 2017).…”

“…Temperature profiles and off-bouts were confirmed visually using the software Raven, a product of the Bioacoustics Research Program at Cornell Laboratory of Ornithology. We were aware that incubation might have begun prior to clutch completion (Cresswell and McCleery 2003;Stenning 2008;Álvarez and Barba 2014b;Simmonds et al 2017), but we had to standardize the data before analyses. Thus, we defined the onset of incubation as the first day after the last egg was laid (clutch completion, see also Kluijver 1950).…”

“…A variety of factors are assumed to affect incubation behavior, e.g., stage of incubation (Álvarez and Barba 2014b;Basso and Richner 2015), clutch size (Thomson et al 1998), predation risk (Conway and Martin 2000b), male feeding behavior (Bambini et al 2019), phenology (Cresswell and McCleery 2003;Simmonds et al 2017) and weather conditions. Birds that employ uniparental incubation face a trade-off between maintaining egg temperature and their own body condition during incubation period, as they have to leave the nest repeatedly (Kluijver 1950) to avoid depleting stored resources (Reid et al 2002).…”

Testing the effect of quantitative genetic inheritance in structured models on projections of population dynamics

“…Further to the environmental drivers included in our models, we also found a quadratic effect of synchrony with caterpillar prey on reproductive success and survival. This is what we would expect from mismatch theory (Cushing , Johansson et al ) and previous work looking at hatch date synchrony (Simmonds et al ), both breeding too early or too late reduces reproductive success and female survival. We would expect both of these effects due to mismatch reducing the amount of food available to chicks and increasing stress on females.…”