Western Gull movement and nutrient deposition on Channel Islands, CA

This data package includes data on the foraging-associated movement and nutrient deposition of large nesting colonies of Western Gulls (Larus occidentalis), a generalist carnivore known to forage on human refuse. The study took place on the Channel Islands of California. Specifically, we equipped gulls with GPS loggers to assess the frequency of urban foraging alongside bird density data to estimate wild and urban-derived guano deposition on the island sites. We also conducted nest counts and vegetation surveys to assess potential nutrient sources, in addition to collecting soil samples at different sites throughout the islands to measure nutrient differences in the soil between the early and late part of the Western Gull nesting season.Metadata for methods and datasets can be found in file "Guerra_WEGU_subsidies_metadata.rtf". Code for analysis can be found in file: wegu.subsidies.ms.code_f.RmdThis study was conducted on Anacapa Island (ANIS) and Santa Barbara Island (SBIS), the two smallest of the Channel Islands off the coast of California (USA), which are currently managed as part of the Channel Islands National Park. Currently, they currently host large breeding colonies of various seabird species, including L. occidentalis (Carter et al. 1992). Soil sampling We sampled soil on ANIS and SBIS in 2019 to test for concentrations of available nitrogen and phosphorus, as these soil characteristics are associated with nutrient deposition in seabird colonies (Ellis 2005; Young et al. 2010). Sampling locations throughout the two islands were selected based on nesting L. occidentalis densities from previous breeding seasons (personal communication with National Park Service) to approximate an equal distribution of high and low bird density sites at each island. Eight sites were sampled on East Anacapa Island and eleven sites were sampled throughout Santa Barbara Island. In order to assess the nutrient deposition throughout the nesting season, we collected soil at two separate time points: early in the nesting season when gulls are establishing territories and starting to build nests ("pre-nesting", April 2019) and once most chicks had hatched ("post-nesting", August 2019). At each site on each island (Fig S1), we collected four random samples of topsoil (10 cm) within a 5 m radius of site origin. We also conducted nest counts (five 10 m x 4 m belt transects covering a 200 m2 area around site origin) at each site in August 2019 to account for bird density in soil nutrient differences. Additionally, we conducted five vegetation survey quadrats at each site to assess presence and abundance of nitrogen-fixing plant species (family: Fabaceae) that could be driving nitrogen inputs to study site soil. Soil samples were dried at the field site, homogenized (by site), and sieved (