As recently as 60 years ago, Western Bluebirds (Sialia mexicana) were common in Garry oak meadows and savannahs throughout the Pacific Northwest of Canada and the USA. The western subspecies (S. m. orientalis), known as the Georgia Depression population, breeds across western North America from southwestern Canada to Baja California. But they are listed as extirpated (locally extinct) in British Columbia, vulnerable in Washington, and secure in Oregon.
Why have Western Bluebird numbers been decreasing at the northern part of their range? Their rapid decline both on Vancouver Island and in areas of Washington and Oregon was due to a combination of habitat loss, removal of standing dead trees that provided nesting cavities, and competition with exotic bird species such as European Starlings and English House Sparrows.
Having suffered the most critical losses in the northern parts of their range, a joint Canada-US project to reintroduce Western Bluebirds began in 2012. Birds were translocated from a healthy population in southern Washington to the San Juan Islands and Vancouver Island. Sometimes individual birds were translocated, but the most success was found by moving mated pairs of birds.
Birds that successfully raise a brood of young are very likely to return to the same nesting area each breeding season, and many of the translocated birds were able to have 2 or even 3 clutches of eggs raised successfully over a breeding season. It has been a slow haul to re-establish a successful breeding population, as birds have a risk of mortality while on the nest and feeding their young, and due to unknown dangers over the migration and overwintering period. But by the end of the 2015 season, the San Juan population rested at around 44 birds (9 adults, 15 translocated fledglings, and 20 young born on the island) and the Vancouver Island population rested at 96 birds (37 adults, 14 translocated fledgelings, 45 young born on the island).
We have yet to look at the success rates of the 2016 season (because the birds are still breeding), but on Vancouver Island, we had 3 birds show up at the start of the mating season that were neither translocated nor fledged here. It is a happy mystery that birds are showing up in these breeding grounds of their own accord.
There is still more work to do to get the Western Bluebird population well established in the Salish Sea area. We still need to keep translocating birds to both Vancouver Island and the San Juan Islands, we need to reduce mortality sources for those birds, and we need to protect and recover high quality habitat that provides nesting and food sources for the birds. But this is turning into a fantastic success story for the recovery of the Western Bluebird.
Bring Back the Bluebirds – Garry Oak Ecostyems Recovery Team project page
Western Bluebird Species at Risk listing, Garry Oak Ecosystems Recovery Team