Factors inFluencing the abundance and distribution oF the snowy Plover at Mono lake , caliFornia

the Snowy Plover is a species at risk, yet surveys of its numbers at most interior nesting sites in california have been infrequent. We surveyed the nesting population at one of the state’s key sites at Mono lake at the edge of the Great Basin near yosemite National Park in 6 years from 1978 to 2014. Diversions of inflowing streams caused the lake level to decline steadily from 1941 to 1981, increasing the amount of exposed lakebed available for nesting and foraging plovers. Subsequently, the level has generally risen, despite periodic reversals, since diversions were curtailed in 1989. Numbers of adult plovers at Mono lake declined from 384 in 1978 to 71 in 2007, over a relatively narrow range of rising lake levels. in all years, plovers were distributed around the lake unevenly, with most on the northern and eastern shoreline. We found a positive relationship between the amount of exposed lakebed and the number of plovers detected on surveys. Plover numbers at Mono lake may be limited by the amount and quality of alkali playa for nesting and foraging, low population density as an adaptation to high rates of nest predation, and perhaps by birds shifting to improved habitat at nearby owens lake. in coming years, provided the lake rises to the target elevation of 6392 feet (1948.3 m), the extent of the plover’s habitat will shrink, calling for more frequent monitoring. the Snowy Plover (Charadrius nivosus) is one of the rarer shorebirds in North america, numbering about 26,000 birds (thomas et al. 2012). Within this region the species has a broad but discontinuous distribution, occurring along the Pacific coasts of the united States and Mexico; along the coast of the Gulf of Mexico; and in the interior deserts, plains, and highlands of the western and central united States and central Mexico. in california, the distinct population segment on the coast is listed as threatened by the u.S. fish and Wildlife Service, whereas the interior population is designated a species of special concern by the california Department of fish and Wildlife. the Snowy Plover continues to be at risk from habitat loss, water diversions, human disturbance, expanding populations of predators, and contaminants (Page et al. 1995, Shuford et al. 2008). Prior to the first statewide surveys in the late 1970s little was known about the size of the Snowy Plover population in the interior of california and the sites important to it. henderson and Page (1981) estimated california’s inland population at 1843 adults in 1978; Page et al. (1991) estimated it at 1745 in 1988. Mono lake ranked second among sites in numbers breeding and accounted for about 20% of the inland total in both years. Mono lake has attracted much attention because of court battles over environmental degradation of the lake from decades of water diversions that lowered the lake level by 45 feet (13.7 m) and reduced its volume by half (hart 1996). the fate of large numbers of nesting california Gulls (Larus