Comments: Threats are largely unknown. Research on both breeding and wintering grounds needed. PREDATION: Was the only cause of nest mortality in Arizona; 69 percent of observed nests (n=26) fledged at least one young (Martin 1993). Documented predators include Cooper's hawk (Accipiter cooperii), red squirrel (Tamiasciurus hudsonicus), and grey-collared chipmunk (EUTAMIAS CINEREICOLLIS). Potential predators include other accipiters, long-tailed weasel (Mustela frenata), vagrant shrew (Sorex vagrans), Steller's jay (CYANOSITTA STELLERI), and house wren (Troglodytes aedon) (Martin and Li 1992, Martin 1993). BROOD PARASITISM: An occasional cowbird host, but little information on parasitism rates, behavioral adaptations to parasitism, or affects on reproductive success or populations. Apparent rarity of occurrences possibly due to this warbler's preference for higher elevations (Harrison 1984, cited in USDA 1994). In Arizona, of 167 nests only 3 documented with cowbird young or eggs (Martin and Olsen, in press). Within city limits of Flagstaff, one of three observed nests was parasitized (Fischer 1978, cited in Martin and Olson in press). No other information on nests near agriculture or human habitations.
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