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.

Highlights

  • For species living in seasonal environments, reproductive success can be maximized by timing reproduction to coincide with annual peaks in resource abundance (Lack, 1968; Nussey et al, 2005; Parmesan, 2007; Perrins & McCleery, 1989; Van Noordwijk, McCleery, & Perrins, 1995)

  • We investigate the mechanisms behind these patterns by quantifying the extent to which different aspects of incubation behavior vary, exploring whether this variation can be explained by temperature cues, and determining which aspects of incubation behavior are important in improving synchrony with the caterpillar peak

  • This study examined whether incubation behavior is used to improve the timing of hatching relative to peak resource abundance, and which temperature cues best predict within-­year variation in incubation

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Summary

| INTRODUCTION

For species living in seasonal environments, reproductive success can be maximized by timing reproduction to coincide with annual peaks in resource abundance (Lack, 1968; Nussey et al, 2005; Parmesan, 2007; Perrins & McCleery, 1989; Van Noordwijk, McCleery, & Perrins, 1995). Variability in the relative onset of incubation has been demonstrated across a diverse range of bird species (e.g., Paridae and Anatidae) and can vary by up to a week either side of clutch completion (Álvarez & Barba, 2014; Cresswell & McCleery, 2003; García-­Navas & Sanz, 2011; Hepp, 2004; Loos & Rohwer, 2004; Lord et al, 2011; Matthysen et al, 2010; McClintock, Hepp, & Kennamer, 2014; Stenning, 2008) Such changes are known to have knock-­on impacts on reproductive success. To what extent do these three aspects of incubation behavior (relative onset, duration, and intensity) contribute to improving synchrony between timing of chick hatching and the caterpillar peak?

| METHODOLOGY
Findings
| DISCUSSION
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