The answer: 640 miles. The question: what distance must a waterbird or shorebird travel across the arid Great Basin landscape during migration?
The human equivalent is a road trip between Salt Lake City and Phoenix or between New York City and Charlotte, North Carolina. Imagine how hard (or impossibly) those road trips would be without gas stations, restaurants, or rest stops at which we can rest, refuel, and refresh. Many of us wouldn’t attempt the trip. And those of us that do, might not make it to our destination.
Semiannually, migratory waterbirds and shorebirds face the prospect of a Great Basin crossing, a journey that is only made possible by a network of freshwater and saline (or salt) lakes and associated wetlands. The supply and quality of food and other resources across the network largely depends on the amount, timing, and location of water. A recent Audubon report and scientific paper by Susan Haig and colleagues describe stressors that affecting water supplies that birds like the Eared Grebe need to survive.
Water use by human communities and changing climate conditions will determine the future of waterbirds and shorebirds in the Great Basin. As summarized in the Audubon report and in a recent article from the Nevada Independent, water diversions and extraction for consumptive uses have negatively affected the inflow of water to saline lakes. This has led to a reduction of up to 39 percent of tributary inflows to Great Salt Lake and eliminated 84 percent of Lahontan Valley’s historic wetlands.
Climate change has and will continue to affect saline lake water supplies through increased temperatures, increasing drought frequency and severity, and changing precipitation (e.g., shifting from snow to rain and leading to earlier snowmelts). Haig and colleagues documented increasing minimum air temperatures in the Great Basin from 1900 to 2008 with a greater rate of increase from 1980 to 2008. From 1980 to 2015, Haig and colleagues also demonstrated that, on average, streamflow occurred earlier and persisted for a shorter duration, contributing to longer periods of relatively dry summer and autumn conditions. They found relationships between climate variables and waterbird abundance, such as a decline in Killdeer abundance associated with summer temperature increases.
Falling lake levels can directly affect habitat for waterbirds and shorebirds whose food resources and foraging activities are dependent on specific water levels. Effects of shrinking habitats on populations can be intensified in several ways. As water inflows decrease, salinity (salt content) and contaminant concentrations will increase. These increases can have direct physiological impacts on birds, but there are also indirect effects that need to be recognized. For instance, brine shrimp are an important invertebrate food resource for migrants, such as Eared Grebes, at several locations in the network, and while brine shrimp are salt tolerant, excessive salt levels can reduce their numbers and quality. Audubon studied this most recently at Lake Abert where the brine shrimp industry had to close due to reduced inflows and increased salinity.
For birds flying across the Great Basin, there may be bottlenecks, or areas where significant populations depend on one area—that increases their vulnerability to habitat loss due to a large fraction of the population being funneled through one area. Researcher Iwamura and colleagues demonstrate that sea-level rise may result in a loss of 23-42 percent of shoreline habitat for migrant shorebirds that use a network of Pacific coastal sites. However, they estimated population flows might be reduced up to 72 percent, especially for species that experience network bottlenecks. A similar assessment has not been conducted for the Great Basin network, but there are known bottlenecks. We know that large numbers of Eared Grebes pass through Great Salt Lake, Mono Lake, and the Salton Sea each year, and declining habitat conditions at these locations might have particularly important consequences.
While the road ahead appears bumpy for waterbirds and shorebirds in the Great Basin, existing scientific and planning foundations can be built upon to enable the conservation and management of these species. Planning documents, such as those of the Intermountain West Joint Venture, have identified priority species and set regional population goals. These goals need to be scaled to specific locations in order to guide local wildlife management. There is a need to develop a robust understanding of how future water use and climate change may affect individual lakes and wetlands across the Great Basin. This understanding should shape future policies and management of waterbird and shorebird habitat.
The National Audubon’s Saline Lakes Program, in partnership with management agencies and other conservation groups, seeks to build momentum for a coordinated regional assessment of future conditions for saline lakes and their associated wetlands—it’s an important next step toward securing Great Basin waterbird and shorebird populations.