Reproductive failure of endangered southwestern willow flycatchers on the Rio Grande, New Mexico

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The authors monitored nesting efforts and success in two small populations of southwestern willow flycatchers in two areas of the Rio Grande River (San Marcial, Socorro Co., and Velarde, Rio Arriba Co.), New Mexico, from May to August, 1996, and also make comparisons with findings of other years (1994-1997). Both within-year comparison of Velarde and San Marcial results for 1996, and between-year comparison of sites at San Marcial suggest that presence of water in the river channel could be a minimal requirement for nesting. Over-bank inundation of willow flycatcher territories may also be important to encourage nesting. Flow rates are typically lower during the months of July and August than in May and June, even in good nesting years. Thus, presence of water in the river during May and June may be most crucial. This study suggests that in a year of winter drought such as 1996, water management practices could have significant impacts on reproductive success of the endangered southwestern willow flycatcher. The authors conclude that southwestern willow flycatchers on the Rio Grande, NM, experience multiple threats to successful reproduction, including cowbird parasitism, predation, and the inability of paired males to acquire mates. They also suggest that weather patterns, along with water management practices, may also impact southwestern willow flycatcher reproduction. The number of different potential impacts, variation in their importance between locations and among years, and land ownership issues all present a complex and challenging conservation problem.

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ELECTRONIC FILE - Zoology