Timing to temperature: Egg‐laying dates respond to temperature and are under stronger selection at northern latitudes

Abstract

Global climate change produces spatially variable patterns of environmental change. This could put migratory species at risk as the synchrony between migration timing and suitable breeding conditions could become mismatched. For migratory birds, whether the timing of egg laying is a plastic trait that can vary in response to environmental change has been sparsely studied across regions and systems and thus remains poorly known. We investigated the effects of temperature variability and climate warming on the breeding phenology of purple martins (Progne subis), a long‐distance migratory songbird, using a 20‐yr data set comprised of 28,165 records of nest timing and fledgling success spanning the entire breeding range (25–54° N). We discovered that purple martins lay eggs earlier in warmer springs and fledge more young when they lay earlier. After controlling for spatial patterns in the data with Moran's eigenvector maps, we found that selection favored earlier breeding in most years, particularly at more northern latitudes. However, selection pressure for earlier breeding did not increase over the 20‐yr period, perhaps owing to high variability in temperature across years. Our results therefore demonstrate plasticity in the timing of egg laying in response to temperature variation and climate change over 20 yr across the range of this widely distributed, long‐distance migrant. Whether these plastic responses are common or sufficiently matched to climate change among other declining migratory songbird species should be further investigated.

Warmer April Temperatures on Breeding Grounds Promote Earlier Nesting in a Long-Distance Migratory Bird, the Prothonotary Warbler

“…Prothonotary warblers do not belong to either of these categories of vulnerable species. Similarly, breeding earlier in warmer years with no apparent cost to reproduction has been documented in many other migratory bird species including reed warblers (Halupka et al, 2008), tree swallows (Dunn et al, 2011), purple martins Progne subis (Shave et al, 2019), and black-throated blue warblers (Townsend et al, 2013). In each of these study systems, authors suggested that earlier breeding was not costly, in part, because food resources (i.e., insects) were available enough to accommodate it.…”

“…To the contrary, a growing body of research is finding that warming in temperate latitudes associated with global climate change is advancing the timing of clutch initiation in several species of migratory birds (e.g., Winkler, 1999, 2010;Both et al, 2004;Mazerolle et al, 2011;Tomotani et al, 2018). Earlier nesting may be a byproduct of temperaturerelated advances in plant and insect phenologies experienced by birds upon arrival at breeding grounds (Townsend et al, 2013;Shave et al, 2019). However, earlier breeding can cause reductions in reproductive success if the timing of breeding creates a mismatch between seasonal pulses in critical resources (Both et al, 2010) (i.e., food) and peak demand for feeding young (Visser and Gienapp, 2019).…”

Integrating Causal and Evolutionary Analysis of Life-History Evolution: Arrival Date in a Long-Distant Migrant

“…On the other hand, the number of fledglings and probability of obtaining recruits are fitness components much more related to females and thus the fitness benefits of early arriving for males must be because for instance early arriving males pair with early laying females (Saino et al, 2004;Cooper et al, 2010;Tomotani et al, 2017) or occupy higher quality territories. Thus, the fitness consequences of male arrival time may (partly) arise through correlation with female timing, especially female breeding time, which is related to reproductive success and to local environmental conditions (Dunn and Winkler, 1999;Townsend et al, 2013;Visser et al, 2015;Tomotani et al, 2018;Shave et al, 2019).…”

The effects of four decades of climate change on the breeding ecology of an avian sentinel species across a 1,500‐km latitudinal gradient are stronger at high latitudes

“…Evidence of the impact of recent climate change on phenology of animals and plants is ample today (Both et al, 2006;Dunn & Winkler, 1999;Hällfors et al, 2020;Helm et al, 2019;Parmesan & Yohe, 2003;Root et al, 2003;Saino et al, 2011;Schwartz et al, 2006;Shave et al, 2019;Townsend et al, 2013), but the underlying mechanisms of the changing patterns are poorly understood (Knudsen et al, 2011), especially considering the variation of climate change with latitude (Parmesan, 2007). In birds, phenological shifts, like advancement of breeding time due to warmer and earlier springs, may facilitate larger clutches and the opportunity to rear more young (Dunn, 2004).…”

“…Still, some studies at northern sites experienced more stable spring and summer temperatures during the last decades (Ram et al, 2019) or even temperature decrease (Both et al, 2004;Both & Marvelde, 2007) finding nonsignificant trends on breeding time change in several bird species. Nevertheless, studies on the effect of climate change on breeding time and breeding success over a large latitudinal gradient are scarce (Parmesan, 2007; but see examples in Dunn & Winkler, 1999;Hällfors et al, 2020;Meller et al, 2018;Shave et al, 2019) and need further investigation.…”