Bluebirds are small, colorful songbirds found throughout North America. There are three main species: the Eastern Bluebird, the Mountain Bluebird, and the Western Bluebird. Bluebirds are cavity nesters, meaning they build their nests in holes in trees, nest boxes, or other cavities. Over the past several decades, bluebird populations declined significantly, mostly due to loss of nesting habitat and competition from non-native species like House Sparrows and European Starlings. However, in recent years, bluebird populations appear to be recovering in many areas thanks to nest box programs and other conservation efforts. But are bluebird numbers continuing to increase across their range? Let’s take a closer look at the population trends for each bluebird species.
Eastern Bluebird
The Eastern Bluebird breeds in open country across eastern North America. Its range stretches from southern Canada down through the eastern and central United States. The Eastern Bluebird declined steeply between the 1920s and 1970s as modern agricultural practices and development eliminated pastures, orchards, and open woodlands that provided nesting cavities. The widespread use of pesticides also reduced the bluebirds’ insect food supply. However, the installation of nest boxes, removal of non-native competitors, and promotion of bluebird-friendly habitat has helped Eastern Bluebird numbers rebound significantly since the 1970s. According to the North American Breeding Bird Survey, Eastern Bluebirds increased at a rate of about 2% per year between 1966 and 2015. Christmas Bird Counts also show a substantial increase in Eastern Bluebirds over the past 50 years. While Eastern Bluebird populations still face threats from habitat loss and intensified agriculture, active management and monitoring programs across its range suggest this species has made a strong recovery and continues to increase.
Mountain Bluebird
The Mountain Bluebird is found in open country across western North America. Its breeding range extends from Alaska down through western Canada to the western United States. Like other bluebird species, the Mountain Bluebird underwent significant declines in the early 1900s due to changes in land use and competition from invasive species. Nest box programs have also helped Mountain Bluebird numbers rebound. Breeding Bird Survey data shows Mountain Bluebirds increased at an average rate of 0.5% per year from 1966-2015. Christmas Bird Counts also indicate increasing winter numbers over the past several decades. While Mountain Bluebird populations appear to be stable or slightly increasing overall, there is some regional variation. Numbers seem to be declining in parts of the southern range but increasing farther north. More monitoring is needed to better understand the localized trends. With continued conservation efforts, prospects look good for the Mountain Bluebird’s future.
Western Bluebird
The Western Bluebird’s range overlaps with the Mountain Bluebird along the Pacific Coast, from southern Alaska to northern Mexico. Like its relatives, this species declined during the mid-1900s but has rebounded thanks to nest box programs and removal of competitors. Breeding Bird Surveys show Western Bluebirds increased at an average annual rate of 1.2% from 1966-2015. Winter numbers have also risen over the past 50 years according to Christmas Bird Counts. However, the Western Bluebird’s population trajectory varies across different parts of its range. For example, numbers are declining in California but increasing in other areas like Oregon and Washington. While Western Bluebird populations appear stable or slightly increasing overall, continued monitoring and habitat management will be important to ensure the species’ long-term survival, especially in parts of its range where numbers are declining.
Summary of bluebird population trends
Species | Population Trend 1966-2015 (Breeding Bird Survey) | Winter Population Trend (Christmas Bird Count) |
---|---|---|
Eastern Bluebird | Increasing ~2% per year | Increasing |
Mountain Bluebird | Increasing ~0.5% per year | Increasing |
Western Bluebird | Increasing ~1.2% per year | Increasing |
Reasons for increasing bluebird populations
The installation of nest boxes across North America has been a major driver behind the recovery of bluebird populations over the past several decades. Nest boxes provide crucial cavities for breeding, allowing bluebirds to establish nesting territories in areas where natural nest sites are scarce. Nest box programs have been hugely successful at boosting bluebird numbers.
Removal and control of non-native competitors has also helped bluebirds thrive. Non-native species like House Sparrows and European Starlings often take over natural cavities preferred by bluebirds. Eliminating these invasive species from bluebird nesting areas reduces competition for nest sites.
Promotion of bluebird-friendly habitat is another important factor. Pasturelands, open woodlands, golf courses, and parks provide the open, grassy areas bluebirds need to forage for insects. Conservation incentives that protect open habitat benefit bluebirds.
Milder winters in recent decades due to climate change may also be contributing to higher overwinter survival and increasing populations. Bluebirds are vulnerable to harsh weather. Warmer winters likely improve survival rates.
Threats to bluebirds
While bluebird populations are increasing overall, a number of threats remain:
– Loss of open, grassy breeding habitat due to development, reforestation, and intensive agriculture.
– Declining insect populations due to pesticides, loss of habitat, and climate change effects. Insects are a vital food source.
– Competition with non-native cavity nesters like House Sparrows and European Starlings. Ongoing management is needed.
– Extreme weather events like storms, drought, and prolonged cold snaps which can lead to starvation and reduced reproductive success.
– Predation from cats, snakes, and other predators around nest boxes. Proper placement and monitoring of nest boxes can help.
– Nest parasitism from Brown-headed Cowbirds that lay eggs in bluebird nests. Controlling cowbird populations may help.
– Vehicle collisions during the breeding season. Roads near nesting areas take a toll.
Conclusion
After steep declines in the 1900s, bluebird populations in North America have largely rebounded over the past 50 years thanks to dedicated conservation efforts. Nest box programs, removal of competitors, protection of breeding habitat, and climate effects have all likely contributed to increasing numbers. However, bluebirds still face threats from habitat loss, extreme weather, predation, cowbirds, and vehicle collisions. Ongoing management and monitoring will be needed to ensure their populations remain stable into the future. While the increasing trends are encouraging, bluebirds are sensitive indicators of environmental conditions. Tracking bluebird numbers provides insight into the overall health of open country ecosystems. With continued efforts to provide nesting habitat and reduce threats, these colorful songbirds will hopefully continue to brighten our fields and gardens for generations to come.