Individual fitness and the effects of a changing climate on the cessation and length of the breeding period using a 34‐year study of a temperate songbird

Abstract

Studies of the phenological responses of animals to climate change typically emphasize the initiation of breeding although climatic effects on the cessation and length of the breeding period may be as or more influential of fitness. We quantified links between climate, the cessation and length of the breeding period, and individual survival and reproduction using a 34-year study of a resident song sparrow (Melospiza melodia) population subject to dramatic variation in climate. We show that the cessation and length of the breeding period varied strongly across years, and predicted female annual fecundity but not survival. Breeding period length was more influential of fecundity than initiation or cessation of breeding alone. Warmer annual temperature and drier winters and summers predicted an earlier cessation of breeding. Population density, the date breeding was initiated, a female's history of breeding success, and the number of breeding attempts initiated previously also predicted the cessation of breeding annually, indicating that climatic, population, and individual factors may interact to affect breeding phenology. Linking climate projections to our model results suggests that females will both initiate and cease breeding earlier in the future; this will have opposite effects on individual reproductive rate because breeding earlier is expected to increase fecundity, whereas ceasing breeding earlier should reduce it. Identifying factors affecting the cessation and length of the breeding period in multiparous species may be essential to predicting individual fitness and population demography. Given a rich history of studies on the initiation of breeding in free-living species, re-visiting those data to estimate climatic effects on the cessation and length of breeding should improve our ability to predict the impacts of climate change on multiparous species.

When to start and when to stop: Effects of climate on breeding in a multi‐brooded songbird

“…Our selection analyses showed that the fitness consequence of breeding phenology in multi‐brooded species was complex, and that ABS was more associated with start and end date than with duration. However, studies of other multi‐brooded bird species have reached the opposite conclusion that duration is more important than start and end date in determining ABS (Dunn & Winkler, ; Møller, ; Tarwater & Arcese, ). The inconsistency between our results and those of other multi‐brooded species may potentially be explained by differences in nest predation rates between species.…”

“…For example, when individuals start breeding will generally be affected by weather in early spring (Møller, Fiedler, & Berthold, 2010), but when they stop is likely to be dependent on weather conditions much later in the season (Tarwater & Arcese, 2018;Weatherhead, 2005). As a result, any focus on start date alone may miss important effects of climate on end date, and hence on the overall duration of the breeding season (Mares, Doutrelant, Paquet, Spottiswoode, & Covas, 2017;Tarwater & Arcese, 2018). Determining exactly which climate variables at exactly which periods in the year are the best predictors of breeding phenology traits can therefore be a substantial challenge.…”

“…Determining the selection acting on phenology may also be substantially more complicated in multi-brooded species, in which annual breeding success (ABS) may be affected by each or all of the breeding phenology traits (start, end, and duration of the breeding season) and their potential interactions (e.g., Møller, 2007;Tarwater & Arcese, 2018;Townsend et al, 2013). Just as in single-brooded species, an earlier start date may be associated with higher ABS in multibrooded species: for example, high quality individuals may occupy superior territories and hence breed earlier than low quality breeders (Brinkhof, Cavé, Hage, & Verhulst, 1993;Christians, Evanson, & Aiken, 2001;Hatchwell, 1991;Parsons, 1975), which could lead to early breeding being associated with higher ABS (McLean, Lawson, Leech, & van de Pol, 2016).…”

Individuals’ expected genetic contributions to future generations, reproductive value, and short-term metrics of fitness in free-living song sparrows (Melospiza melodia)

“…On Mandarte, among‐year variation in local environmental conditions and population density drives considerable among‐year variation in song sparrow reproduction and survival (Arcese et al. ; Wilson and Arcese ; Tarwater and Arcese ), inducing substantial among‐cohort variation in mean lifespan and LRS (Lebigre et al. ; Wolak et al.…”

“…On Mandarte, among-year variation in local environmental conditions and population density drives considerable amongyear variation in song sparrow reproduction and survival (Arcese et al 1992;Wilson and Arcese 2003;Tarwater and Arcese 2018), inducing substantial among-cohort variation in mean lifespan and LRS (Lebigre et al 2012;Wolak et al 2018). Total adult population size consequently varied substantially among years (arithmetic mean: 73 ± 29 SD individuals, range: 33-128, Supporting Information S1).…”