Re-introduction of the western bluebird to oak- prairie habitats in Pacific Northwest, USA

Summary

The western bluebird (Sialia mexicana), extirpated from Washington's San Juan Island by the 1970s primarily through loss of nesting cavities, was reintroduced there over a six-year project (2007-2012) by the Ecostudies Institute and American Bird Conservancy, motivated by evidence that a 165-kilometre gap of unsuitable urban habitat had prevented natural recolonization from the nearest source population, and supported by local partners who installed over 500 nest boxes across the island. From 2007 to 2011, 102 adults and 35 juveniles were captured, mostly as breeding pairs, from source populations up to 450 km away and held briefly in outdoor aviaries before release; an initial small-aviary, short-holding protocol in 2007 produced poor results (only one pair established, 45% dispersed back to source), prompting a shift to larger aviaries and one-to-three-week holding periods that raised territory establishment to 42% for adult pairs, alongside successful use of released single females to correct a male-biased sex ratio (60% establishment). Monitoring found successful breeding every year, with the population growing to an estimated 38 individuals across 14 breeding territories by the end of 2011, and 87 monitored nests fledging 274 juveniles overall, with fecundity and survival statistically comparable to reference Pacific Northwest populations. Difficulties included nest predation by house sparrows and mammals, a persistently male-biased sex ratio, and unusually cold, wet breeding seasons in 2011-2012 that reduced reproduction. The project rates itself successful, crediting a dedicated multi-organization partnership and the team's willingness to adapt translocation methods as results came in.