Decoupling of bird migration from the changing phenology of spring green-up.

The green-up of vegetation in spring brings a pulse of food resources that many animals track during migration. However, green-up phenology is changing with climate change, posing an immense challenge for species that time their migrations to coincide with these resource pulses. We evaluated changes in green-up phenology from 2002 to 2021 in relation to the migrations of 150 Western-Hemisphere bird species using eBird citizen science data. We found that green-up phenology has changed within bird migration routes, and yet the migrations of most species align more closely with long-term averages of green-up than with current conditions. Changing green-up strongly influenced phenological mismatches, especially for longer-distance migrants. These results reveal that bird migration may have limited flexibility to adjust to changing vegetation phenology and emphasize the mounting challenge migratory animals face in following en route resources in a changing climate.

Is the future female for turtles? Climate change and wetland configuration predict sex ratios of a freshwater species.

Climate change and land-use change are leading drivers of biodiversity decline, affecting demographic parameters that are important for population persistence. For example, scientists have speculated for decades that climate change may skew adult sex ratios in taxa that express temperature-dependent sex determination (TSD), but limited evidence exists that this phenomenon is occurring in natural settings. For species that are vulnerable to anthropogenic land-use practices, differential mortality among sexes may also skew sex ratios. We sampled the spotted turtle (Clemmys guttata), a freshwater species with TSD, across a large portion of its geographic range (Florida to Maine), to assess the environmental factors influencing adult sex ratios. We present evidence that suggests recent climate change has potentially skewed the adult sex ratio of spotted turtles, with samples following a pattern of increased proportions of females concomitant with warming trends, but only within the warmer areas sampled. At intermediate temperatures, there was no relationship with climate, while in the cooler areas we found the opposite pattern, with samples becoming more male biased with increasing temperatures. These patterns might be explained in part by variation in relative adaptive capacity via phenotypic plasticity in nest site selection. Our findings also suggest that spotted turtles have a context-dependent and multi-scale relationship with land use. We observed a negative relationship between male proportion and the amount of crop cover (within 300 m) when wetlands were less spatially aggregated. However, when wetlands were aggregated, sex ratios remained consistent. This pattern may reflect sex-specific patterns in movement that render males more vulnerable to mortality from agricultural machinery and other threats. Our findings highlight the complexity of species' responses to both climate change and land use, and emphasize the role that landscape structure can play in shaping wildlife population demographics.

Fire management alters the thermal landscape and provides multi-scale thermal options for a terrestrial turtle facing a changing climate.

As effects of climate change intensify, there is a growing need to understand the thermal properties of landscapes and their influence on wildlife. A key thermal property of landscapes is vegetation structure and composition. Management approaches can alter vegetation and consequently the thermal landscape, potentially resulting in underappreciated consequences for wildlife thermoregulation. Consideration of spatial scale can clarify how management overlaid onto existing vegetation patterns affects thermal properties of landscapes relevant to wildlife. We examined effects of temperature, fire management, and vegetation structure on multi-scale habitat selection of an ectothermic vertebrate (the turtle Terrapene carolina triunguis) in the Great Plains of the central United States by linking time-since-fire data from 18 experimental burn plots to turtle telemetry locations and thermal and vegetation height data. Within three 60-ha experimental landscapes, each containing six 10-ha sub-blocks that are periodically burned, we found that turtles select time-since-fire gradients differently depending on maximum daily ambient temperature. At moderate temperatures, turtles selected sub-blocks with recent (<1 year) time-since-fire, but during relatively hot and cool conditions, they selected sub-blocks with later (2-3 year) time-since-fire that provided thermal buffering compared with recently burned sub-blocks. Within 10-ha sub-blocks, turtles selected locations with taller vegetation during warmer conditions that provided thermal buffering. Thermal performance curves revealed that turtle activity declined as temperatures exceeded ~24-29°C, and on "heat days" (≥29°C) 73% of turtles were inactive compared with 37% on non-heat days, emphasizing that thermal extremes may lead to opportunity costs (i.e., foregone benefits turtles could otherwise accrue if active). Our results indicate that management approaches that promote a mosaic of vegetation heights, like spatiotemporally dynamic fire, can provide thermal refuges at multiple spatial scales and thus be an actionable way to provide wildlife with multiple thermal options in the context of ongoing and future climate change.