Modeling the effects of sea level rise on Long-billed Curlews at Humboldt Bay

Thesis (M.S.)--Humboldt State University, Environmental Systems: Mathematical Modeling, 2015Sea level rise is predicted to have a negative effect on shorebird populations living in coastal environments. At Humboldt Bay, the availability of tidal flats that serve as habitat to many shorebirds throughout the year may become increasingly limited as higher sea levels permanently inundate lower elevation tidal flats. The Long-billed Curlew (Numenius americanus) is amongst the shorebird species at Humboldt Bay that may face reductions in population as feeding habitat becomes less available. I estimate how curlews will react to habitat change by developing a model that simulates the dynamics between the curlews, their prey, and their environment at Humboldt Bay. To understand how curlews are affected by habitat change due to sea level rise, I introduce predicted changes in habitat to the model. To predict how the habitat changes, I use the Sea Level Affecting Marshes Model, SLAMM, to estimate how different extents of sea level rise change intertidal habitat area. Based on the observed local sea level rise at Humboldt County, SLAMM predicts that mean sea level will increase 0.2-0.9 m over the next hundred years. This corresponds to a loss of 17-64% of current intertidal habitat area. Less dominant curlews are predicted to be strongly affected by the changes in the habitat and will have significant decreases in foraging time, overall weight, and overwinter success. In contrast, higher dominant curlews are more resistant to changes in the habitat and will be less affected by moderate changes in habitat. Given the maximum sea level rise scenario, overwinter success of higher dominant curlews may drop to 50% of the present value. In the same conditions, only 5% of low dominance curlews are expected to be successful. The model predicts that the maximum carrying capacity of Humboldt Bay will stay above 90% given moderate increases in sea level, while maximum \ud carrying capacity will drop below 40% given the maximum sea level rise scenario. The loss of intertidal habitat at Humboldt Bay will not only affect the Long-billed Curlew population, but will also limit other shorebird species. Modeling the effects of habitat change on Long-billed Curlew is a first step in understanding how shorebirds will respond to sea level rise. My methods can be extended to other shorebird species in the future to predict how overall abundance and diversity at Humboldt Bay will change in response to sea level rise