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. . Area Manager DRAFT 28 subsequent nesting attempts; delayed fledging; and reduced survivorship of late-fledged young. Cowbirds have been documented at more than 90 percent of sites surveyed (Sogge and Tibbitts ',ccL..... 'ogge~[' .....~ ..nn..........._ - T'L....II_.L__ 'n.nA.....n.:_:~1~~...........1 lonA. C'............."'" ",...rI T-ihh-ittc TOQA.. -'/ , >J "" u..l. l'':f:J, LaJllp rCHU1Ii:a.uu 1 ::17"1', lVJ.U.lLlU,"-,l'tr..O) "'L UJ.. .l.//"T, uv66.... ............ ... ................... ..... ., Whitfield 1994; Griffith and Griffith 1995; Holmgren and Collins 1995; Kus 1995; Maynard 1995; McDonald et al. 1995; Sferra et al. 1995; Sogge I 995a,b; San Diego Natural History Museum 1995; Stransky 1995; Whitfield and Strong 1995; Griffith and Griffith 1996; Skaggs 1996; Spencer et al. 1996; Whitfield and Enos 1996; Sferra et al. 1997; McCarthey et al.1998). The probability of a flycatcher successfully fledging its own young from a cowbird parasitized nest is low (<5 percent). Also, nest loss due to predation appears consistent from year to year and across sites, generally in the range of 30 to 50 percent. Documented predators of flycatcher nests identified to date include common king snake (Lampropeltis getulus), gopher snake (Pituophis melanoleucos affinis), Cooper's hawk (Accipiter cooperii) and some corvid bird species (Paxton et al. 1997, McCarthey et al. 1998, Paradzick et al. 2000). Cowbird trapping has been demonstrated to be an effective management strategy for increasing reproductive success for the flycatcher, as well as for other endangered passerines (e.g., least Bell's vireo [Vireo bellii pusillus], black-capped vireo [V. atricapillus], golden-cheeked warbler [Dendroica chrysoparia]). It rnay also benefit juvenile survivorship by increasing the probability that parents fledge birds early in the season. Expansion of cowbird management programs has the potential to not only increase reproductive output and juvenile survivorship at source populations, but also to potentially convert small, sink populations into breeding groups that contribute to population growth and expansion. Status and Distribution Reasons for Listing and Current Threats. The flycatcher was listed as endangered because of a number of threats that caused extensive habitat loss, lack of adequate protective regulations, and other natural or manrnade factors, including brood parasitism by the brown-headed cowbird (U.S. Fish and Wildlife Service 1995). The reasons for decline of the flycatcher and its current threats are numerous, complex, and interrelated. The major factors are summarized below by categories, in approximate order of their significance (U.S. Fish and Wildlife Service 2002). Habitat Loss and Modification. The primary cause of the flycatcher's decline is loss and modification of habitat. Its riparian nesting habitat tends to be uncommon, isolated, and widely dispersed. Historically, these habitats have always been dynamic and unstable in place and time, due to natural disturbance and regeneration events, such as floods, fire, and drought. With increasing human populations and the related industrial, agricultural, and urban developments, these habitats have been modified, reduced, and destroyed by various mechanisms. Riparian ecosystems have declined due to reductions in water flow, interruptions in natural hydrological events and cycles, physical modifications to streams, modification of native plant communities by invasion of exotic species, and direct removal of riparian vegetation. Wintering habitat has also been lost and modified for this and other Neotropical migratory birds (Finch 1991, Sherry and Holmes 1993). The major mechanisms resulting in loss and modification of habitat involve water management and land use practices, as described below. 001436