Impacts of nest predators and weather on reproductive success and population limitation in a long‐distance migratory songbird

Abstract

Although avian nesting success is much studied, little is known about the relative importance of the factors that contribute to annual reproductive success and population limitation, especially for long-distance migratory songbird species. We combined a fi eld experiment limiting access to nests by mammalian predators with modeling of long-term fi eld data of American redstarts (Parulidae: Setophaga ruticilla ) to assess the eff ects of multiple environmental variables on breeding success and population limitation. Experimental treatment (baffl es placed around tree boles beneath active nests; n ϭ 71) increased nesting success of this single-brooded species signifi cantly (77 vs 50% in controls; n ϭ 343), demonstrating that scansorial mammals, primarily red squirrels Tamiasciurus hudsonicus and eastern chipmunks Tamias striatus , reduced reproductive success. Based on unbaffl ed nests (n ϭ 466), daily nest survival varied annually, and was positively infl uenced by May temperature and negatively by sciurid nest predator abundance. Daily nest survival was also infl uenced positively by June rainfall, and declined with nest age but not with calendar date. Since nest failure was overwhelmingly caused by nest predation, these signifi cant climate and nest-age eff ects in our models are indirect, likely infl uencing nest predator and/or nesting bird behaviors that in turn infl uenced nest predation. Redstart population density had no eff ect on nesting success, after accounting for other factors. Annual reproductive success accounted for 34% of the variability in annual population change in redstarts in our study area. Our fi ndings document 1) breeding season population limitation in this species, 2) a link between tree masting and bird population dynamics via mammal population fl uctuations, 3) the independent contributions of summer versus winter population processes in a migratory species, and 4) the potential complexity of climate-biotic interactions.

Climatic conditions produce contrasting influences on demographic traits in a long‐distance Arctic migrant

“…For example, retrospective analyses have emphasised the importance of demographic rates related to breeding productivity or subadult return rate as drivers of population growth across a diverse range of species including seabirds (Ezard, Becker & Coulson ), songbirds (Sherry et al . ) and raptors (Carrete, Donázar & Margalida ). Previously, Harrison et al .…”

Density and nest survival of golden‐cheeked warblers: Spatial scale matters

“…These temporal patterns may result from changes in predator activity patterns or abundance. One factor that may cause annual variation in predator behavior is weather (Sperry and Weatherhead 2008, Cox et al 2013, Sherry et al 2015. Rat snakes increase activity as temperatures warm during the spring and early summer and this increased activity may be correlated with changes in seasonal nest success (Sperry et al 2008).…”

Biogeography of boreal passerine range dynamics in western North America: past, present, and future

“…Some evidence suggests that nest predation rates are relatively low (∼ 30%) in boreal forests relative to temperate forests (Darveau et al ), and predation pressure has been shown to decrease with latitude in other taxa (shorebirds, McKinnon et al ). Thus we considered it unlikely that predation pressure would limit population expansion into boreal Alaska, despite the strong role that predation plays in population dynamics of temperate forest birds (Sherry et al ).…”

“…Four of the species for which our model predicts current Alaskan boreal occupancy have not been detected there, which is not surprising given the plethora of factors that may contribute to successful range expansion and detection, and the large stochastic component (Pielou 1991). For example, the absence of American redstart Setophaga ruticilla and warbling vireo Vireo gilvus may be explained by their strong association with deciduous habitats, particularly along riparian corridors (Sherry andHolmes 1997, Gardali andBallard 2000), which are largely discontinuous across the northwestern cordillera into boreal Alaska -but do connect with southeastern Alaska, where these species are found. Indeed, several other species -e.g.…”