The Eastern Bluebird (Sialia sialis) is a beloved North American songbird known for its striking blue, russet, and white plumage. This species experienced a severe population crash across its range, leading many to believe it was destined for rarity or local extinction. Its history is characterized by this dramatic fall, followed by a remarkable and sustained recovery, demonstrating how coordinated conservation efforts can reverse long-term population declines.
The History of Decline
The decline of the Eastern Bluebird began in the late 19th century and accelerated dramatically through the mid-20th century. A primary cause was the widespread loss of suitable nesting sites, as bluebirds are secondary cavity nesters, relying on existing holes rather than excavating their own.
The shift from wooden fence posts to metal posts in agricultural settings eliminated many traditional nesting sites. Furthermore, the removal of dead trees, or “snags,” from orchards and woodlands as part of modern land management practices reduced the availability of their preferred nesting locations.
This habitat loss was compounded by intense competition from non-native, invasive bird species introduced to North America. Aggressive European Starlings and House Sparrows competed fiercely for the remaining natural cavities. These competitors often displaced bluebirds, destroyed their nests, and even killed adult birds.
By the 1960s, bluebird populations had plummeted by as much as 90% in their historic eastern range. Adding to these pressures was the widespread use of persistent chemical pesticides, such as DDT, in the mid-20th century. These chemicals reduced the insect populations bluebirds rely on for food, particularly during the breeding season, contributing to nesting failures.
Current Status: A Confirmed Comeback
The Eastern Bluebird is no longer considered rare and has achieved a significant population rebound across its range. Data from the North American Breeding Bird Survey (BBS) indicate that populations have increased consistently over the last several decades. Current population levels have returned to, or even surpassed, the numbers recorded when the survey began in 1966. For example, the Canadian population has shown a “Large Increase” relative to 1970.
This positive trend is attributed to a combination of factors, including broad environmental policy changes. The eventual ban on widespread, persistent organochloride pesticides allowed insect populations to recover, restoring a food source. However, the most direct cause of the comeback was the highly organized intervention of concerned citizens. The recovery culminated in the 1978 formation of the North American Bluebird Society (NABS), which formalized and amplified citizen-science efforts, providing structure for sustained conservation.
Public Involvement in Ongoing Conservation
The recovery of the Eastern Bluebird is a direct result of widespread public involvement, primarily through the creation of standardized nest boxes and the “Bluebird Trail” movement. These trails are networks of carefully placed and monitored nest boxes. They are designed to exclude larger competitors like European Starlings by featuring an entrance hole 1.5 inches in diameter, a size too small for starlings to enter.
Proper placement and management of these artificial cavities are mandatory for success. Boxes must be mounted on smooth metal poles, not on trees or wooden posts that predators can easily climb. To further protect the nests, monitors utilize specialized devices, such as stovepipe baffles. These are cylindrical metal guards placed on the pole to deter climbing predators like snakes, raccoons, and opossums.
Bluebird trails employ a strategy of pairing boxes, placing two boxes five to fifteen feet apart in open, grassy areas. This arrangement allows bluebirds to use one box while a native competitor, such as a Tree Swallow, uses the other, reducing territorial conflicts. The continued success of the population relies on the public’s commitment to maintaining and actively monitoring these trails.