eWestern Birds

Recent Purple Martin Declines in the Sacramento Region of California: Recovery Implications

Daniel A. Airola and Dan Kop

ABSTRACT: We monitored the Purple Martins (Progne subis) breeding in the Sacramento region, California, in 2008 and 2009, following similar monitoring from 2002 to 2007. This bridge-nesting population is the last remnant of the formerly widespread Central Valley population. All 11 colonies occupied in 2007 remained active in 2008, but the number of occupied colonies declined to 9 in 2009. From 2007 to 2009 the number of breeding pairs declined by 34%, from 106 to 70. Since 2004, the population has declined by 60% (103 pairs), and the annual rate of decline has increased. Probability calculations suggest the decline has been caused by factors other than chance fluctuation. If the decline continues at its current rate, the population will be extirpated within 22 years. Causes of the decline are unknown, but our previous studies have implicated mortality during the breeding season from vehicle collisions. Sacramento-area populations also are threatened by disturbance from a variety of construction projects and land-use changes that may affect habitat suitability. Recent losses in Sacramento represent a 6–11% decline in California’s estimated Purple Martin population. Increased effort is needed to stabilize the Sacramento population, which would serve as the likely source for any future recovery within the Central Valley.

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