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

Abstract

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