Abstract
Biological impacts of climate change are exemplified by shifts in phenology. As the timing of breeding advances, the within‐season relationships between timing of breeding and reproductive traits may change and cause long‐term changes in the population mean value of reproductive traits. We investigated long‐term changes in the timing of breeding and within‐season patterns of clutch size, egg volume, incubation duration, and daily nest survival of three shorebird species between two decades. Based on previously known within‐season patterns and assuming a warming trend, we hypothesized that the timing of clutch initiation would advance between decades and would be coupled with increases in mean clutch size, egg volume, and daily nest survival rate. We monitored 1,378 nests of western sandpipers, semipalmated sandpipers, and red‐necked phalaropes at a subarctic site during 1993–1996 and 2010–2014. Sandpipers have biparental incubation, whereas phalaropes have uniparental incubation. We found an unexpected long‐term cooling trend during the early part of the breeding season. Three species delayed clutch initiation by 5 days in the 2010s relative to the 1990s. Clutch size and daily nest survival showed strong within‐season declines in sandpipers, but not in phalaropes. Egg volume showed strong within‐season declines in one species of sandpiper, but increased in phalaropes. Despite the within‐season patterns in traits and shifts in phenology, clutch size, egg volume, and daily nest survival were similar between decades. In contrast, incubation duration did not show within‐season variation, but decreased by 2 days in sandpipers and increased by 2 days in phalaropes. Shorebirds demonstrated variable breeding phenology and incubation duration in relation to climate cooling, but little change in nonphenological components of traits. Our results indicate that the breeding phenology of shorebirds is closely associated with the temperature conditions on breeding ground, the effects of which can vary among reproductive traits and among sympatric species.
Highlights
Effects of contemporary climate change have been found across all biomes as organisms shift their seasonal phenologies and geographic distributions (Parmesan & Yohe, 2003)
Despite overall warming trends for the Arctic, a long-term cooling trend occurred during the early part of the breeding season at Nome, Alaska
Changes in breeding phenology between decades did not lead to changes in mean clutch size, egg volume, or daily nest survival rate of the population
Summary
Effects of contemporary climate change have been found across all biomes as organisms shift their seasonal phenologies and geographic distributions (Parmesan & Yohe, 2003). Few studies have tested for additional impacts of long- term changes in climatic conditions on reproductive traits beyond the timing of egg-laying (Both & Visser, 2005; Dickey, Gauthier, & Cadieux, 2008; Skagen & Adams, 2012), and most have considered northern temperate species of birds with flexible reproductive traits, such as a variable clutch size or multiple breeding attempts per season (but see Skinner, Jefferies, Carleton, & Abraham, 1998). Given the known links between the timing of breeding and reproductive performance, we predicted that (3) advances in clutch initiation in response to warmer temperatures would be coupled with increases in mean clutch size, egg volume, and nesting success (Figure 1b). We tested whether (4) the relationships between clutch initiation date and subsequent reproductive traits have changed between decades
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