Located at the historical confluence of the San Joaquin and the Kings rivers, this IBA includes the 12,425-acre Wildlife Area as well as the Producer's Dairy, which covers an area east of the refuge and the Alkali Sink Ecological Reserve at the north boundary of the IBA. Primarily managed for winter waterfowl, Mendota is characterized by large, marshy impoundments with 3000 acres of agricultural lands planted in silage for cattle (esp. Trefoil). Small riparian restoration projects have been attempted that involve setting back levees, but the aridity of the environment and the high cost of water has hampered these efforts (B. Huddleston, pers. comm.). Due to diversions of the San Joaquin before it reaches Mendota, all of the water on the refuge is piped down from the Sacramento Valley. Still, a modest amount of riparian vegetation has developed along Fresno Slough in what is referred to as the Mendota Pool, and a narrow band of riparian woodland persists within levees along the San Joaquin River to the north (now pumped dry except during wet winters). Unfortunately, the riparian habitat along the San Joaquin has been routinely cleared for flood control and only scattered large trees remain (TNC 1998).

Edited March 2010

Ornithological Summary

Though the avifauna at Mendota is poorly-known within California birding circles, it is one of the key sites for birds in the San Joaquin Valley, and the only significant natural habitat within a vast industrial-agricultural landscape (mainly cotton) between the Grasslands Ecological Area and the Tulare Lake Bed, over 50 miles to the south. Mendota has emerged as hosting the largest nesting aggregation of White-faced Ibis in the state (over 2000 pr. in the late 1990s, Ivey et al. 2002), with an estimated 7000 birds observed in late May 2001. These birds leave the refuge in the morning to feed in pastures of the adjacent Producer's Dairy, returning at dusk. Tricolored Blackbirds have bred in extremely large numbers at the dairy (25,000 birds estimated in 2001), as previous colonies within the wildlife area were predated upon by another colonial breeder, Black-crowned Night-Heron. Winter and spring shorebird use is high, with over 10,000 birds present on peak spring days. Because some water is available during the summer, the wetlands on the refuge are also utilized by breeding Northern Harrier, and both Black and Forster's terns have summered and may eventually breed (S. Brueggeman, pers. comm.). During the late fall, water spread on the refuge attracts up to 200,000 ducks and geese, as well as hundreds of Sandhill Crane that later move north to spend the rest of the winter after the water levels are lowered. In spring, thousands of shorebirds utilize the mudflats left behind in the draining impoundments. Riparian species such as White-tailed Kite and Blue Grosbeak, essentially eliminated from most of the farmed San Joaquin Valley floor, maintain sizable populations here, particularly at the Mendota Pool. The Alkali Sink Ecological Reserve area is regularly used by Greater and Lesser Sandhill Cranes, Northern Harriers, Swainson?s Hawks, Mountain Plovers, Burrowing Owls, and Tricolored Blackbirds (J. Davis pers. comm.).

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Conservation Issues

Because the refuge devotes its scarce water allotments to providing wintering habitat for waterfowl (duck-hunting essentially supports this refuge), other groups of birds, particularly riparian obligates, make do with only limited habitat and attention. Efforts to allow some riparian vegetation along the San Joaquin River could be explored, as could cooperative agreements with neighboring landowners (especially Producer's Dairy), as has been done at Grasslands Ecological Area to the north. According to The Nature Conservancy (1998), "excessive grazing" and "widespread use of rodenticides" remain a threat to the habitat here.

Ownership

This IBA includes the 12,425-acre Wildlife Area as well as the Producer?s Dairy, which covers almost as large an area immediately north of the refuge.

Habitat

Mendota is characterized by large, marshy impoundments with 3000 acres of agricultural lands planted in silage for cattle (esp. Trefoil). A modest amount of riparian vegetation has developed along Fresno Slough in what is referred to as the Mendota Pools, and a narrow band of riparian woodland persists within levees along the San Joaquin River.

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