Population Trends of Ferruginous Pygmy-owls in Northern Mexico and Implications for Tumacácori and other Arizona National Park Units


Flesch, A. D. and R. J. Steidl

Recovery and persistence of cactus ferruginous pygmy-owls (Glaucidium brasilianum cactorum) in Arizona likely will depend on owls from northern Sonora, Mexico, where they are more abundant. Because pygmy-owls have declined to near extinction in Arizona yet have been proposed for removal from the federal list of endangered species for reasons unrelated to recovery (USFWS 2005), knowledge of populations in neighboring Sonora, Mexico and on lands in Arizona managed by the U.S. National Park Service will prove important. In 2005, we continued to monitor pygmy-owls in northern Sonora within 75 km of Arizona where we had observed a 37% decline in abundance between 2000 and 2004 (Flesch and Steidl 2006). We also determined territory occupancy at 94 sites and nest success and productivity at 47 nests within 120 km of Arizona where abundance remained relatively stable between 2001 and 2004 (Flesch and Steidl 2005a). We then surveyed potential habitat in Tumacácori National Historical Park (NHP) where pygmy-owls had not been previously surveyed. Although abundance of pygmy-owls in Sonora increased somewhat in 2005 relative to previous years, the trend in abundance is still negative, averaging -6.0 ± 1.9% (± SE) per year (P = 0.0021) since 2000, a 30% decline over 6 years. We detected no annual trends in territory occupancy between 2002 and 2005 and little evidence of trends in nest success and nest productivity between 2001 and 2005. We found no pygmy-owls during surveys at Tumacácori NHP in 2005 and 2006, yet vegetation structure is suitable and could be improved to enhance potential nesting opportunities for pygmy-owls. Continued declines of pygmy-owls in northern Sonora may reduce recovery options in Arizona.

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Technical Reports