DISSERTATION RESEARCH: Phenological shifts in seed-dispersal networks of the Sierra Nevada, California

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Many recreational and cultural events are based on the seasonal timing of natural events. For example, visitors flock to New England to enjoy fall leaf colors and birdwatchers congregate in May to welcome migrating birds. Seasonal timing also matters to plants and animals. To fuel their fall migrations, birds rely on calorie-rich wild fruits. Likewise, the plants that make those fruits rely on migrating birds to carry their seeds to places where they can grow into new plants. This mutually beneficial interaction works because the timing of wild fruit production matches the timing of bird migration. In many places, however, the seasonal timing of bird migration and fruit production has become misaligned. With not enough fruit to fuel their migratory flights, birds may suffer during migration. And, without birds to disperse their seeds, some plants could fail to produce the next generation. This research will measure how much fruit production and bird migration are misaligned. Investigators will study the environmental cues for fall migration and fruit production as well as the factors that control how many fruits are produced by wild plants. Members of the public will participate by providing observations on bird-fruit interactions and will learn about scientific research through field trips led by the investigators. The relationships between environmental cues and fall seasonal events in birds and plants remain largely unexplored. This project will use multi-year, multi-species, publicly available datasets to estimate year-to-year differences in the timing of fall migration in birds and fruiting in fleshy-fruited shrubs. Two methods will be employed to determine relationships. First, researchers will use Bayesian survival models to regress data on yearly timing of migration and fruiting from the National Phenology Network and eBird, respectively, with data on environmental drivers. Second, a common garden experiment with five genera of shrubs will be set up to mechanistically determine for the first time how increased temperature, drought, and the interaction between the temperature and drought affect the timing and abundance of fruits. Results will be useful in predicting the ability of birds to migrate and fruiting-plants to disperse their seeds.