“…Timing of breeding is one of the most important determinants of organismal fitness. Across a broad variety of taxa, the decision of when to breed determines what food resources will be abundant during each stage of reproduction (e.g., mink, Ben‐David 1997; sea ducks, Love et al 2010), the types and variety of nest sites available for breeding (e.g., house martins, Piersma 2013), the prevalence of parasites and predators that may harm the adult or its offspring (e.g., squirrels and hares, O’Donoghue and Boutin 1995; cliff swallows, Brown and Brown 1999), and the energy budget available for investment into other life history traits (e.g., wheatears, Low et al 2015). Previous researchers have documented the many costs associated with breeding at suboptimal times (blue tits, Nilsson 1994; sandpipers, McKinnon et al 2012; owls, Toyama et al 2015), and the importance of proper timing has become especially clear in circumstances in which environmental conditions have recently deviated from historical norms (e.g., flycatchers, Both and Visser 2001; swallows, Brown and Brown 2000; grouse, Ludwig et al 2006; deer, Plard et al 2014).…”