The Importance of the Northeastern Gulf of Mexico to Foraging Loggerhead Sea Turtles

Identification of high-use foraging sites where imperiled sea turtles are resident remains a globally-recognized conservation priority. In the biodiverse Gulf of Mexico (GoM), recent telemetry studies highlighted post-nesting foraging sites for federally threatened loggerhead turtles (Caretta caretta). Our aim here was to discern loggerhead use of additional northern GoM regions that may serve as high-use foraging sites. Thus, we used satellite tracking and switching state-space modeling to show that the Big Bend region off the northwest Florida coast is a coastal foraging area that supports imperiled adult female loggerhead turtles tracked from different nesting subpopulations. From 2011 to 2016, we satellite-tagged 15 loggerheads that nested on four distinct beaches around the GoM: Dry Tortugas National Park, FL; Everglades National Park, FL; St. Joseph Peninsula, FL; and Gulf Shores, AL. Turtles arrived at their foraging ground in the Big Bend region between June and September and remained resident in their respective foraging sites for an average of 198 tracking days, where they established mean home ranges (95% kernel density estimate) 232.7 km2. Larger home ranges were in deeper water; 50% kernel density estimate centroid values were a mean 26.4 m deep and 52.7 km from shore. The Big Bend region provides a wide area of suitable year-round foraging habitat for loggerheads from at least 3 different nesting subpopulations. Understanding where and when threatened loggerheads forage and remain resident is key for designing both surveys of foraging resources and additional protection strategies that can impact population recovery trajectories for this imperiled species

Marine Threats Overlap Key Foraging Habitat for Two Imperiled Sea Turtle Species in the Gulf of Mexico

Effective management of human activities affecting listed species requires understanding both threats and animal habitat-use patterns. However, the extent of spatial overlap between high-use foraging areas (where multiple marine species congregate) and anthropogenic threats is not well-known. Our modeling approach incorporates data on sea turtle spatial ecology and a suite of threats in the Gulf of Mexico to identify and map “hot spots” of threats to two imperiled turtle species. Of all 820 “high” threats grid cells, our tracked turtles foraged at least 1 day in 77% of them. Although threat data were not available outside the U.S. Exclusive Economic Zone, our map of turtle and threat “hot spots” can be incorporated in future more comprehensive threat analyses for the region. Knowledge of these shared foraging- and threat-areas can assist managers charged with designing effective conservation and population recovery strategies, in future habitat modeling efforts, and in designations of Gulf of Mexico habitat with high conservation value

Winter GPS tagging reveals home ranges during the breeding season for a borealnesting migrant songbird, the Goldencrowned Sparrow

Determining space use for species is fundamental to understanding their ecology, and tracking animals can reveal insights into their spatial ecology on home ranges and territories. Recent technological advances have led to GPS-tracking devices light enough for birds as small as ~30 g, creating novel opportunities to remotely monitor fine-scale movements and space use for these smaller species. We tested whether miniaturized GPS tags can allow us to understand space use of migratory birds away from their capture sites and sought to understand both pre-breeding space use as well as territory and habitat use on the breeding grounds. We used GPS tags to characterize home ranges on the breeding grounds for a migratory songbird with limited available breeding information, the Golden-crowned Sparrow (Zonotrichia atricapilla). Using GPS points from 23 individuals across 26 tags (three birds tagged twice), we found home ranges in Alaska and British Columbia were on average 44.1 ha (95% kernel density estimate). In addition, estimates of territory sizes based on field observations (mean 2.1 ha, 95% minimum convex polygon [MCP]) were three times smaller than 95% MCPs created using GPS tags (mean 6.5 ha). Home ranges included a variety of land cover classes, with shrubland particularly dominant (64–100% of home range cover for all but one bird). Three birds tracked twice returned to the same breeding area each year, supporting high breeding site fidelity for this species. We found reverse spring migration for five birds that flew up to 154 km past breeding destinations before returning. GPS-tracking technology allowed for critical ecological insights into this migratory species that breeds in very remote locations

Wildlife Movement and Connectivity across Large Scales: Migratory Ecology of Golden-crowned Sparrows (Zonotrichia atricapilla) and Evaluating Landscape Connectivity Designs for Terrestrial Wildlife in California

Many species need to move across landscapes for a variety of reasons central to their survival and reproduction. Landscape connectivity allows gene flow among populations, provides opportunities for demographic rescue, facilitates necessary range shifts due to climate change, and can bolster a species’ ability to respond to other threats such as habitat loss. In western North America, species face many challenges that affect their ability to move and survive across different landscapes, including habitat loss and fragmentation, climate change, transportation infrastructure, and land use changes. Landscape connectivity has therefore become a key conservation target. To address potential losses of landscape connectivity, many habitat linkage designs have been created for the state of California. These designs were created with the intent to preserve important natural spaces between wilderness areas and ultimately allow the movement and connectivity of species. However, many linkage designs are created based on remote sensing of land cover types – with the assumption that natural areas are better for wildlife connectivity – and few are based on actual observations of wildlife occurrence or movement. In Chapter 1, we used ~180,000 terrestrial mammal, reptile and amphibian detections collected opportunistically throughout California over the past 20 years to assess whether species were more likely to be found within areas designated as linkages from five different linkage designs. We had a two-step approach and investigated 1) whether the linkages predicted wildlife distribution during residence periods (using occupancy modeling) and/or 2) whether animals were preferentially using linkages for movement or migration (using wildlife-vehicle collision data). We found that the linkage areas were not important predictors for the probability of landscape occupancy or movement for most species, with the exception of a few large-bodied mammals. These results demonstrated that landscape linkage designs are not a one-size fits all conservation strategy and using data from wildlife movements, instead of only habitat quality and disturbance metrics, is important. In urban environments, linkage designs may accurately reflect the critical last places for wildlife to move and should be reserved. However, in agricultural, forested, rangeland, and other mixed-use landscapes where wildlife may move more easily, connectivity as a gradient across the landscape should be the target of conservation. The species in Chapter 1 were all terrestrial and therefore limited to movement on the ground. However, some species can fly over roads and habitats that are not ideal for them, some even migrating across multiple large-scale management boundaries and into different biomes. Connectivity for these species is on a larger scale and conservation actions are reliant on detailed information across different seasons and life stages. For migratory birds in particular, studying migration has been a difficult challenge, especially for smaller birds that are difficult to track. Recently though, technological advances have led to miniaturized GPS tags that small songbirds can carry. In Chapter 2 and 3, we used these tiny tags in addition to stable isotope analysis fill knowledge gaps about the migration ecology and breeding grounds for Golden-crowned Sparrows (Zonotrichia atricapilla). In Chapter 2, we investigated habitat selection along migration routes for the Golden-crowned Sparrow, which migrates from wintering grounds in California to northern breeding grounds in Canada and Alaska. We tagged birds with GPS on two California wintering grounds. We put out 50 GPS tags and used a resource selection function combined with conditional logistic regression to determine how land cover class, vegetation greenness and climate variables influenced habitat selection during migration. We also reported on general migration descriptions for this understudied species. We acquired 22 tracks across 19 individuals, with a total of 541 valid spring and fall migration locations. We found that birds selected for shrubland and higher vegetation greenness in both migration seasons as well as grasslands during fall migration. Birds also selected for locations with higher daily maximum temperature during spring migration. Routes during spring migration were lower in elevation on average, shorter in duration, and had fewer long stopovers than in fall migration. For two birds, we found repeated use of the same stopover areas in spring and fall migration. This study provided new insights into habitat selection along migration routes for a common temperate-zone migrating songbird. We found important habitat associations along migration routes and previously unknown behaviors for this species, such as repeated use of stopover areas by individuals in different migratory seasons. GPS tags are useful tools for studying migration, as demonstrated in Chapter 2, but their cost and the necessity to retrieve them from returning birds presents limitations for sample sizes. Therefore, it is useful to combine GPS data with other methods to get a better understanding of migratory ecology. In Chapter 3, we demonstrate that the techniques of GPS and stable isotopes can be used to complement each other and fill knowledge gaps for understudied species by providing data on remote breeding territories, and migratory connectivity and strategy. We used feather isotope values from 170 samples across five wintering grounds for the Golden-crowned Sparrow and GPS tracks from 22 tags to calibrate predictive isoscapes with known origins based on GPS. We found evidence for regional connectivity for Golden-crowned Sparrows partitioned by wintering groups, with differentiation especially between southern and northern wintering birds. We also found that breeding home range sizes for this species were larger than reported for other Zonotrichia species, with shrubland cover common at breeding sites. Using stable isotope information, we also found Nitrogen isotope values that suggested females were eating at a higher trophic level at the breeding grounds than males. With three birds tracked twice with GPS data, we were able to determine that birds returned to the same breeding location each year, supporting high breeding and wintering site fidelity for this species. Using GPS in conjunction with stable isotopes proved a useful method, as we refined predictive isoscapes and identified patterns of migratory connectivity. We also uncovered new natural history information for this understudied species that breeds in very remote areas. Determining what species need in terms of connectivity is vital for species persistence as we make important conservation decisions that allow or restrict movements. There are many tools available for assessing both what species need and how well we design strategies to allow for connectivity. Combining GPS and stable isotope analysis can uncover patterns and habitat requirements for long-distance migrants, and spatial data analysis can help us determine how to improve conservation efforts. With an increasing human population, climate change and more frequent fires in western North America, it will continue to be increasingly important to gather data on species connectivity and how to design effective conservation strategies

Marine Threats Overlap Key Foraging Habitat for Two Imperiled Sea Turtle Species in the Gulf of Mexico

Effective management of human activities affecting listed species requires understanding both threats and animal habitat-use patterns. However, the extent of spatial overlap between high-use foraging areas (where multiple marine species congregate) and anthropogenic threats is not well-known. Our modeling approach incorporates data on sea turtle spatial ecology and a suite of threats in the Gulf of Mexico to identify and map “hot spots” of threats to two imperiled turtle species. Of all 820 “high” threats grid cells, our tracked turtles foraged at least 1 day in 77% of them. Although threat data were not available outside the U.S. Exclusive Economic Zone, our map of turtle and threat “hot spots” can be incorporated in future more comprehensive threat analyses for the region. Knowledge of these shared foraging- and threat-areas can assist managers charged with designing effective conservation and population recovery strategies, in future habitat modeling efforts, and in designations of Gulf of Mexico habitat with high conservation value

Loggerhead sea turtle (Caretta caretta) diving changes with productivity, behavioral mode, and sea surface temperature.

The relationship between dive behavior and oceanographic conditions is not well understood for marine predators, especially sea turtles. We tagged loggerhead turtles (Caretta caretta) with satellite-linked depth loggers in the Gulf of Mexico, where there is a minimal amount of dive data for this species. We tested for associations between four measurements of dive behavior (total daily dive frequency, frequency of dives to the bottom, frequency of long dives and time-at-depth) and both oceanographic conditions (sea surface temperature [SST], net primary productivity [NPP]) and behavioral mode (inter-nesting, migration, or foraging). From 2011-2013 we obtained 26 tracks from 25 adult female loggerheads tagged after nesting in the Gulf of Mexico. All turtles remained in the Gulf of Mexico and spent about 10% of their time at the surface (10% during inter-nesting, 14% during migration, 9% during foraging). Mean total dive frequency was 41.9 times per day. Most dives were ≤ 25 m and between 30-40 min. During inter-nesting and foraging, turtles dived to the bottom 95% of days. SST was an important explanatory variable for all dive patterns; higher SST was associated with more dives per day, more long dives and more dives to the seafloor. Increases in NPP were associated with more long dives and more dives to the bottom, while lower NPP resulted in an increased frequency of overall diving. Longer dives occurred more frequently during migration and a higher proportion of dives reached the seafloor during foraging when SST and NPP were higher. Our study stresses the importance of the interplay between SST and foraging resources for influencing dive behavior

Land cover and NDVI are important predictors in habitat selection along migration for the Golden-crowned Sparrow, a temperate-zone migrating songbird

Abstract Background Migrating passerines in North America have shown sharp declines. Understanding habitat selection and threats along migration paths are critical research needs, but details about migrations have been limited due to the difficulty of tracking small birds. Recent technological advances of tiny GPS-tags provide new opportunities to delineate fine-scale movements in small passerines during a life stage that has previously been inherently difficult to study. Methods We investigated habitat selection along migration routes for a temperate-zone migratory passerine, the Golden-crowned Sparrow (Zonotrichia atricapilla), given GPS tags on California wintering grounds. We used a resource selection function combined with conditional logistic regression to compare matched sets of known stopover locations and available but unused locations to determine how land cover class, vegetation greenness and climate variables influence habitat selection during migration. We also provide general migration descriptions for this understudied species including migration distance, duration, and elevation, and repeated use of stopover areas. Results We acquired 22 tracks across 19 individuals, with a total of 541 valid spring and fall migration locations. Birds traveled to breeding grounds in Alaska and British Columbia along coastal routes, selecting for shrubland and higher vegetation greenness in both migration seasons as well as grasslands during fall migration. However, model interactions showed they selected sites with lower levels of greenness when in forest (both seasons) and shrubland (fall only), which may reflect their preference for more open habitats or represent a trade-off in selection between habitat type and productivity. Birds also selected for locations with higher daily maximum temperature during spring migration. Routes during spring migration were lower in elevation on average, shorter in duration, and had fewer long stopovers than in fall migration. For two birds, we found repeated use of the same stopover areas in spring and fall migration. Conclusions Using miniaturized GPS, this study provides new insight into habitat selection along migration routes for a common temperate-zone migrating songbird, contributing to a better understanding of full annual cycle models, and informing conservation efforts. Golden-crowned Sparrows selected for specific habitats along migration routes, and we found previously unknown behaviors such as repeated use of the same stopover areas by individuals across different migratory seasons

Land cover and NDVI are important predictors in habitat selection along migration for the Golden-crowned Sparrow, a temperate-zone migrating songbird

BackgroundMigrating passerines in North America have shown sharp declines. Understanding habitat selection and threats along migration paths are critical research needs, but details about migrations have been limited due to the difficulty of tracking small birds. Recent technological advances of tiny GPS-tags provide new opportunities to delineate fine-scale movements in small passerines during a life stage that has previously been inherently difficult to study.MethodsWe investigated habitat selection along migration routes for a temperate-zone migratory passerine, the Golden-crowned Sparrow (Zonotrichia atricapilla), given GPS tags on California wintering grounds. We used a resource selection function combined with conditional logistic regression to compare matched sets of known stopover locations and available but unused locations to determine how land cover class, vegetation greenness and climate variables influence habitat selection during migration. We also provide general migration descriptions for this understudied species including migration distance, duration, and elevation, and repeated use of stopover areas.ResultsWe acquired 22 tracks across 19 individuals, with a total of 541 valid spring and fall migration locations. Birds traveled to breeding grounds in Alaska and British Columbia along coastal routes, selecting for shrubland and higher vegetation greenness in both migration seasons as well as grasslands during fall migration. However, model interactions showed they selected sites with lower levels of greenness when in forest (both seasons) and shrubland (fall only), which may reflect their preference for more open habitats or represent a trade-off in selection between habitat type and productivity. Birds also selected for locations with higher daily maximum temperature during spring migration. Routes during spring migration were lower in elevation on average, shorter in duration, and had fewer long stopovers than in fall migration. For two birds, we found repeated use of the same stopover areas in spring and fall migration.ConclusionsUsing miniaturized GPS, this study provides new insight into habitat selection along migration routes for a common temperate-zone migrating songbird, contributing to a better understanding of full annual cycle models, and informing conservation efforts. Golden-crowned Sparrows selected for specific habitats along migration routes, and we found previously unknown behaviors such as repeated use of the same stopover areas by individuals across different migratory seasons

Marine Threats Overlap Key Foraging Habitat for Two Imperiled Sea Turtle Species in the Gulf of Mexico

Effective management of human activities affecting listed species requires understanding both threats and animal habitat-use patterns. However, the extent of spatial overlap between high-use foraging areas (where multiple marine species congregate) and anthropogenic threats is not well-known. Our modeling approach incorporates data on sea turtle spatial ecology and a suite of threats in the Gulf of Mexico to identify and map “hot spots” of threats to two imperiled turtle species. Of all 820 “high” threats grid cells, our tracked turtles foraged at least 1 day in 77% of them. Although threat data were not available outside the U.S. Exclusive Economic Zone, our map of turtle and threat “hot spots” can be incorporated in future more comprehensive threat analyses for the region. Knowledge of these shared foraging- and threat-areas can assist managers charged with designing effective conservation and population recovery strategies, in future habitat modeling efforts, and in designations of Gulf of Mexico habitat with high conservation value