Multidimensional environmental influences on timing of breeding in a tree swallow population facing climate change

Abstract

Most phenological traits are extremely sensitive to current climate change, and advances in the timing of important life-history events have been observed in many species. In birds, phenotypic plasticity in response to temperature is thought to be the main mechanism underlying yearly adjustment in the timing of breeding. However, other factors could be important and interact to affect the levels of plastic responses between and/or within-individuals. Here, we use long-term individual-based data on tree swallow (Tachycineta bicolor) to identify the spatial and environmental drivers affecting plasticity in laying date and to assess their importance at both population and individual levels. We found that laying date has advanced by 4.2 days over 10 years, and that it was mainly influenced by latitude and an interaction between spring temperature and breeder density. Analyses of individual plasticity showed that increases in temperature, but not in breeder density, resulted in within-individual advances in laying date. Our results suggest that females can adjust their laying date as a function of temperature, but that this adjustment will be partly constrained in habitats with lower breeder densities. Such potential constraint is especially worrying for the broad array of species already declining as a result of climate change.

Male experience buffers female laying date plasticity in a winter-breeding, food-storing passerine

“…Although this pattern of laying date plasticity along a gradient of temperatures has been reported in a number of species, it has only been observed in temperate, spring-breeding birds (e.g. Bourret et al, 2015;Brommer et al, 2008;Husby et al, 2010). Our study is the first to examine laying date plasticity in a species that breeds during the late winter and also relies on stored food during the reproductive period.…”

“…Thus in our system, plasticity may be driven by necessity, rather than capacity, according to variation in the social environment, although females can also vary in plasticity due to developmental and genetic differences (see below). In contrast, Bourret et al (2015) provided evidence that low laying date plasticity in tree swallows was associated with suboptimal environmental conditions, whereas high plasticity was associated with better environmental conditions. Plasticity is therefore not synonymous with quality or condition, and can reflect constraints of the environment.…”

“…There is evidence that plasticity in reproductive timing is heritable (Brommer, Rattiste, & Wilson, 2008;Husby et al 2010;Nussey, Clutton-Brock, et al, 2005) and selection can act upon variation in plasticity (Nussey, Clutton-Brock, et al, 2005). Some studies have shown that individuals vary in their plasticity in reproductive timing within populations (Bourret, B elisle, Pelletier, & Garant, 2015;Brommer, Meril€ a, Sheldon, & Gustafsson, 2005;Brommer et al, 2008;Husby et al, 2010;Nussey, Clutton-Brock, et al, 2005;Nussey, Postma, et al, 2005;Porlier et al, 2012;Reed et al, 2009;Thorley & Lord, 2015), although other studies have provided evidence that individuals exhibit similar degrees of plasticity (Charmantier et al, 2008;Porlier et al, 2012;Reed et al, 2006). Despite the importance of understanding individual plasticity in the context of environmental change (Charmantier & Gienapp, 2014;Chevin, Lande, & Mace, 2010;Nussey, Wilson, & Brommer, 2007), the mechanisms driving differences in plasticity between individuals within a population are not fully understood.…”

“…For example, Bourret et al (2015) provided evidence that tree swallows, Tachycineta bicolor, in low-density populations altered their timing of breeding in response to changes in spring temperature less than individuals in high-density populations, for which the habitat was assumed to be of higher quality. In addition to local environmental conditions, one intriguing possibility is that the social environment of breeders may affect the relationship between the timing of breeding and climatic conditions.…”

The influence of iridescent coloration directionality on male tree swallows’ reproductive success at different breeding densities

“…We may therefore observe a female preference for extra-pair male back greenness and crown saturation, which would fade at high density given the lower amount of energy allocated to extra-pair mate choice. It is also possible that females benefit from mate choice only under certain environmental conditions (Maan and Seehausen 2011;Robinson et al 2012) and thus expressed a stronger mate choice only in low-density conditions in our study system (e.g., conditions that represent a poorer habitat quality; Bourret et al 2015). This could also explain why there would be color preferences at low density that are weakening at high density.…”