Approximately two thirds of migratory songbirds in eastern North America negotiate the Gulf of Mexico (GOM), where inclement weather coupled with no refueling or resting opportunities can be lethal. However, decisions made when navigating such features and their consequences remain largely unknown due to technological limitations of tracking small animals over large areas. We used automated radio telemetry to track three songbird species (Red-eyed Vireo, Swainson's Thrush, Wood Thrush) from coastal Alabama to the northern Yucatan Peninsula (YP) during fall migration. Detecting songbirds after crossing ∼1,000 km of open water allowed us to examine intrinsic (age, wing length, fat) and extrinsic (weather, date) variables shaping departure decisions, arrival at the YP, and crossing times. Large fat reserves and low humidity, indicative of beneficial synoptic weather patterns, favored southward departure across the Gulf. Individuals detected in the YP departed with large fat reserves and later in the fall with profitable winds, and flight durations (mean = 22.4 h) were positively related to wind profit. Age was not related to departure behavior, arrival, or travel time. However, vireos negotiated the GOM differently than thrushes, including different departure decisions, lower probability of detection in the YP, and longer crossing times. Defense of winter territories by thrushes but not vireos and species-specific foraging habits may explain the divergent migratory behaviors. Fat reserves appear extremely important to departure decisions and arrival in the YP. As habitat along the GOM is degraded, birds may be limited in their ability to acquire fat to cross the Gulf. migration | ecological barrier | Gulf of Mexico | songbirds | weather D uring migration, animals encounter ecological barriers, inhospitable environmental features that prevent or impede movement due to increased risk of mortality from starvation, predation, collision, and severe environmental conditions (e.g., weather for aerial migrants, aquatic temperature or chemical gradients for aquatic migrants) (1-5). Because barriers can have important consequences on survival and future reproductive success (6), animals have evolved behavioral, morphological, and/or physiological means to safely negotiate them (7-9). Barriers can include large geographic features (e.g., large water bodies, deserts, mountains), inhospitable land cover types (e.g., agricultural "deserts"), anthropogenic structures (e.g., tall buildings, towers, dams, weirs), and unfavorable weather and aquatic conditions (e.g., droughts, storms, strong temperature gradients), although the extent to which any of these functions as a barrier to migration varies (4,5,(10)(11)(12).Approximately two thirds of all songbird species and millions of individuals breeding in eastern Canada and the United States encounter the Gulf of Mexico (GOM) while migrating to tropical or subtropical wintering grounds in the Caribbean, Mexico, and Central and South America (13). Unfavorable weather conditions combine...

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Knowledge of species' ecological requirements is key for designing effective conservation management. In butterflies, the needs of larval stages are often the most specialised part of 2 the life cycle, but for many species information on this is lacking. The Mountain Ringlet Erebia epiphron is a cold-adapted butterfly found in alpine grasslands in mountainous regions of Europe. Efforts to devise conservation strategies for this climate changethreatened species are hampered due to its basic ecology being poorly understood. Here, we describe a study on the autecology of Mountain Ringlets across its British distribution, focusing on the habitat preferences of egg-laying females as a proxy for larval preferences.Female Mountain Ringlets placed their eggs predominantly on Nardus stricta and Festuca ovina, but also on several other host plant species, suggesting larvae may be more broadly polyphagous than previously realised. Sites chosen for eggs had higher abundance of larval host plants, intermediate leaf litter cover, and lower cover of grass tussocks than random locations, as well as a shorter and sparser grass sward. Although the main host plant is ubiquitous in upland areas of Britain, our findings suggest that this butterfly's egg and larval stages have specialised ecological requirements, requiring specific microhabitat features characterised by a narrow range of vegetation composition and structural characteristics.Many habitat associations are liable to be explicable as adaptations to ensure placement of eggs and larvae in sites within optimal (warm or buffered) microclimates. We tentatively suggest that the distribution of Mountain Ringlets in the landscape is thermally-constrained.

ABSTRACT. Willow Flycatcher (Empidonax traillii) populations have been in decline across the western United States for decades. California populations are especially vulnerable with fewer than 500 pairs remaining in the state. Declines and local extirpations continue despite extensive habitat restoration and improved management designed to help conserve Willow Flycatchers. Such efforts may have failed to help reverse these trends in part because Willow Flycatchers rarely recolonize habitat after extirpation, regardless of present habitat suitability. Failure to recolonize habitat may be because prospecting Willow Flycatchers, like many other songbird species, assess habitat suitability based on the presence of conspecifics, making them unlikely to consider unoccupied habitat as potential breeding grounds. If true, broadcasting conspecific vocalizations in suitable but unoccupied habitat could help facilitate recolonization. During the 2016 and 2017 breeding seasons, we assessed the effectiveness of providing artificial social cues as a means of restoring Willow Flycatchers to suitable but unoccupied restored meadows in the Sierra Nevada mountains of California. We selected 14 experimental meadows where conspecific songs were broadcast during the settlement and breeding periods and 19 control meadows where no broadcasts took place. All the meadows were recently restored, contain high-quality habitat with hydrological characteristics and vegetation similar to meadows where Sierra Willow Flycatchers successfully breed, and were confirmed to be unoccupied in the year prior to their inclusion in the study. We observed Willow Flycatchers at five of 14 experimental meadows (35.75%) during the breeding season and at one of 19 control meadows (5.3%). We found that habitat characteristics also play a role in the efficacy of this technique, as Willow Flycatcher presence was highly significantly related to the combination of both the experimental treatment and meadow size. These results demonstrate that within large, restored meadows, conspecific broadcasts may be an effective strategy for restoring Willow Flycatchers. Utilisation de la diffusion de chants de conspécifiques pour le rétablissement du Moucherolle des saulesRÉSUMÉ. Les populations de Moucherolles des saules (Empidonax traillii) sont à la baisse dans tout l'ouest des États-Unis depuis des décennies. Les populations californiennes sont particulièrement vulnérables, comptant moins de 500 couples. Les baisses et les disparitions locales se produisent toujours malgré les efforts importants de restauration d'habitat et d'aménagement ciblant la conservation de ces moucherolles. Ces efforts pourraient avoir failli à renverser les tendances, en partie en raison du fait que le Moucherolle des saules recolonise rarement un habitat qu'il a abandonné, sans égard aux conditions actuelles propices. L'échec de la recolonisation d'habitat est peut-être attribuable au fait que les moucherolles qui prospectent, tout comme de nombreuses autres espèces d'oiseaux chanteurs, évaluen...

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River regulation can modify natural flow regimes with deleterious effects on aquatic communities. While the effects of flow manipulation on the physical environment and populations and assemblages of aquatic organisms have been described thoroughly, how and to what extent river regulation influences ecosystem processes like food web architecture is less studied. Emergent aquatic insect prey can provide an important food resource to riparian consumers like birds and bats with concomitant consequences for nutrient cycling through aquatic-terrestrial food webs, thus potentially increasing the spatial influence of river regulation into the riparian zone and beyond. We used naturally abundant stable isotopes of carbon and nitrogen to compare food web architecture (trophic position and reliance on an aquatic nutritional pathway) leading to birds and bats between a regulated river, the Tuolumne River downstream of Hetch Hetchy Reservoir, and an adjacent unregulated river, the Merced River, located in Yosemite National Park on the west slope of the Sierra Nevada, California, USA. We found that both birds and bats derived >50% of their nutrition from food webs originating in photosynthesis by algae. In addition, birds and bats occupied a similar trophic position to predatory fish in other systems. Both birds and bats seemed to rely more strongly on an aquatic nutritional pathway during the dryer year of our study period, underscoring the potential importance of emergent aquatic prey as a water subsidy in dry systems and in dry years. In the Tuolumne River, reservoir managers strive to simulate characteristics of the natural flow regime, including seasonal scouring flows and prolonged floodplain inundation. Although we found no conclusive evidence of an effect of river regulation on food web responses, our study suggests that nutrient cycling through aquatic-terrestrial food webs expands the potential influence of river regulation to organisms and ecosystems typically characterized as terrestrial.

Ranges of species around the world are expected to contract in response to climate change. Species distribution models (SDMs) are a powerful tool for predicting changes in habitat availability, but the variables selected to create SDMs influence their performance. In addition to climate, habitat characteristics and species traits can play a role in predicting species distribution. In this paper, we consider how variable selection influences the accuracy of SDMs when applied to isolated subpopulations of two widely distributed bird species: great gray owl (Strix nebulosa) and willow flycatcher (Empidonax traillii). In the Sierra Nevada of California, these species are restricted largely to discrete patches of meadow habitat within a forest matrix, providing the potential to identify specific locations to target conservation efforts. We contrast predictions made by SDMs that consider climatic variables alone with those that incorporate both climate and geophysical variables. Adding geophysical variables resulted in differing model predictions. For willow flycatchers, adding geophysical variables improved predictive performance. In the case of great gray owls, models with and without geophysical variables had nearly identical performance under historical conditions but differed starkly in their predictions. The full model (climatic and geophysical variables) predicted habitat availability to decrease moderately, whereas the climate-only model predicted nearly complete loss of favorable habitat by 2099. The climate-only model is consistent with expectations based on previous SDMs of birds across North America, but previous studies also assumed homogeneity in species traits and range-wide habitat requirements. The full model appears more consistent with recent trends in great gray owl numbers in the Sierra Nevada specifically, where the population has remained relatively stable over recent decades. Given contradictions in our model predictions, care should be taken when trying to apply similar SDMs to other systems.