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Sex allocation theory predicts that females should bias their offspring sex ratios when the fitness benefits of producing sons or daughters differ depending on rearing environment. The Trivers-Willard hypothesis proposes that whether females produce more sons or daughters depends on food availability via both intrinsic maternal condition and differing reproductive potential (typically from mating system structure) for sons versus daughters. However, tests of its key predictions are often based on untested, implicit assumptions that are difficult to quantify, especially in migratory animals. In a 5-year study, we manipulated food availability in low- and high-elevation forest to test the Trivers-Willard hypothesis in the migratory black-throated blue warbler (Setophaga caerulescens). We found that the population-wide offspring sex ratio was significantly male-biased (population mean: 0.58), which was driven by an overproduction of sons in high-elevation forest (high-quality habitat mean: 0.59). Yet, we found no effect of food availability on offspring sex ratio from either natural variation or supplemental feeding. Sex-specific developmental costs did not differ for sons and daughters reared under low and high food availability. These results suggest that female black-throated blue warblers do not manipulate offspring sex ratios in response to food availability and are not consistent with the predictions of the Trivers-Willard hypothesis. This study highlights challenges of examining mechanisms driving patterns in offspring sex allocation in migratory species for which both the costs of rearing and relative fitness benefits of sons and daughters cannot be tracked into adulthood. 

Artificial light at night (ALAN) is a globally widespread and expanding form of anthropogenic change that impacts arthropod biodiversity. ALAN alters interspecific interactions between arthropods, including predation and parasitism. Despite their ecological importance as prey and hosts, the impact of ALAN on larval arthropod stages, such as caterpillars, is poorly understood. We examined the hypothesis that ALAN increases top-down pressure on caterpillars from arthropod predators and parasitoids. We experimentally illuminated study plots with moderate levels (10–15 lux) of LED lighting at light-naive Hubbard Brook Experimental Forest, New Hampshire. We measured and compared between experimental and control plots: (i) predation on clay caterpillars, and (ii) abundance of arthropod predators and parasitoids. We found that predation rates on clay caterpillars and abundance of arthropod predators and parasitoids were significantly higher on ALAN treatment plots relative to control plots. These results suggest that moderate levels of ALAN increase top-down pressure on caterpillars. We did not test mechanisms, but sampling data indicates that increased abundance of predators near lights may play a role. This study highlights the importance of examining the effects of ALAN on both adult and larval life stages and suggests potential consequences of ALAN on arthropod populations and communities.

 

This dataset has been prepared in support of a paper to be published in Proceedings of the Royal Society B: Biological Sciences. It includes both data files and R scripts used for the analysis in this publication: Deitch, J.F. and S.A. Kaiser. 2023. Artificial light at night increases top-down pressure on caterpillars: experimental evidence from a light-naive forest. Proceedings of the Royal Society B: Biological Sciences. (https://doi.org/10.1098/rspb.2023.0153) Artificial light at night (ALAN) is a globally widespread and expanding form of anthropogenic change that impacts arthropod biodiversity. ALAN alters interspecific interactions between arthropods, including predation and parasitism. Despite their ecological importance as prey and hosts, the impact of ALAN on larval arthropod stages, such as caterpillars, is poorly understood. We examined the hypothesis that ALAN increases top-down pressure on caterpillars from arthropod predators and parasitoids. We experimentally illuminated study plots with moderate levels (10-15 lux) of LED lighting at light-naive Hubbard Brook Experimental Forest, New Hampshire. We measured and compared between experimental and control plots: 1) predation on clay caterpillars and 2) abundance of arthropod predators and parasitoids. We found that predation rates on clay caterpillars and abundance of arthropod predators and parasitoids were significantly higher on ALAN treatment plots relative to control plots. These results suggest that moderate levels of ALAN increases top-down pressure on caterpillars. We did not test mechanisms, but sampling data indicates that increased abundance of predators near lights may play a role. This study highlights the importance of examining the effects of ALAN on both adult and larval life stages and suggests potential consequences of ALAN on arthropod populations and communities. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. 

This dataset is published in support of "No evidence of sex ratio manipulation by black-throated blue warblers in response to food availability" by Kaiser et al. 2023 in Behavioral Ecology and Sociobiology. Data and code to test the assumptions and key predictions of the Trivers-Willard hypothesis, which proposes that females produce more sons or daughters depending on food availability, in the black-throated blue warbler at the Hubbard Brook Experimental Forest, NH, 2007-2012. Datasets support analyses of sex ratio bias at both the nest and nestling levels. Data tables support the comparison of the ratio of variances in the scaled pre-fledging mass of male and female nestlings using an F test and reproduction of Figures 2a and 2b. Figures are those used in the published manuscript. Code supports the calculation of offspring sex ratio bias at the population level, and considering separately both low- and high-quality habitats, using the Neuhäuser test, statistical models testing the assumptions of the Trivers-Willard hypothesis, effects of food availability and parental provisioning on offspring sex ratio, and effects of food availability on pre-fledging nestling mass of sons and daughters, and a power analysis to determine the power to detect an effect of food supplementation on sex ratio. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the US Forest Service, Northern Research Station. 

Numbers and lengths of Lepidoptera larvae (caterpillars, all species) were censused on shrub level foliage at biweekly intervals from late May/early June through late July/early August each year. Measurements were conducted on the Main bird plot in the Hubbard Brook Experimental Forest and on three additional plots within the White Mountain National Forest from 1986-1997. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. 

This dataset provides body measurements and encounter histories for black-throated blue warblers. Birds were captured in mist nets, given unique combinations of colored leg bands and a numbered, aluminium USGS leg band, and aged as either yearlings or older breeders based on plumage characters. Standard body measurements were taken, following Pyle 1997 (Pyle, P. 1997. Identification guide to North American birds. Slate Creek Press, Bolinas, CA). All birds were released unharmed after banding and measurements were completed. Capture histories were generated from resightings of banded individuals on three gridded study plots at the HBEF: low elevation (250-350 m; 85 ha), middle elevation (450-600 m; 65 ha), and high elevation (750-850 m; 35 ha). See Rodenhouse et al. 2003 for plot details. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. Data have been described and published in: Rodenhouse, N. L., Sillett, T. S., Doran, P. J., & Holmes, R. T. (2003). Multiple density-dependence mechanisms regulate a migratory bird population during the breeding season. Proceedings. Biological sciences, 270(1529), 2105–2110. https://doi.org/10.1098/rspb.2003.2438 Sillett, T. S., & Holmes, R. T. (2002). Variation in Survivorship of a Migratory Songbird throughout Its Annual Cycle. Journal of Animal Ecology, 71(2), 296–308. http://www.jstor.org/stable/2693447 

This dataset provides counts of potential nest predators recorded on surveys conducted in black-throated blue warbler territories at the Hubbard Brook Experimental Forest. Surveys occurred on three gridded study plots at the HBEF: low elevation (250-350 m; 85 ha), middle elevation (450-600 m; 65 ha), and high elevation (750-850 m; 35 ha). See Rodenhouse et al. 2003 for plot details. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. 

Understanding the demographic drivers of range contractions is important for predicting species' responses to climate change; however, few studies have examined the effects of climate change on survival and recruitment across species' ranges. We show that climate change can drive trailing edge range contractions through the effects on apparent survival, and potentially recruitment, in a migratory songbird. We assessed the demographic drivers of trailing edge range contractions using a long‐term demography dataset for the black‐throated blue warbler (Setophaga caerulescens) collected across elevational climate gradients at the trailing edge and core of the breeding range. We used a Bayesian hierarchical model to estimate the effect of climate change on apparent survival and recruitment and to forecast population viability at study plots through 2040. The trailing edge population at the low‐elevation plot became locally extinct by 2017. The local population at the mid‐elevation plot at the trailing edge gradually declined and is predicted to become extirpated by 2040. Population declines were associated with warming temperatures at the mid‐elevation plot, although results were more equivocal at the low‐elevation plot where we had fewer years of data. Population density was stable or increasing at the range core, although warming temperatures are predicted to cause population declines by 2040 at the low‐elevation plot. This result suggests that even populations within the geographic core of the range are vulnerable to climate change. The demographic drivers of local population declines varied between study plots, but warming temperatures were frequently associated with declining rates of population growth and apparent survival. Declining apparent survival in our study system is likely to be associated with increased adult emigration away from poor‐quality habitats. Our results suggest that demographic responses to warming temperatures are complex and dependent on local conditions and geographic range position, but spatial variation in population declines is consistent with the climate‐mediated range shift hypothesis. Local populations of black‐throated blue warblers near the warm‐edge range boundary at low latitudes and low elevations are likely to be the most vulnerable to climate change, potentially leading to local extirpation and range contractions.