24-7 -- The soft, plaintive cries of the bluebird were eerily silent this past summer. Mountain bluebirds seem to have taken a population nose-dive all across Alberta. People monitoring bluebird nest boxes reported a marked reduction in nesting pairs. This is significant for a species that was once declared 'at risk' and has since made a great recovery. At this point in time, there are no definitive answers or explanations from the scientific community and no one can estimate how long it will take them to rebound.
Many wild species fluctuate from time to time, either in yearly or multi-year cycles. A look at any given set of population statistics generally shows increases and decreases in a random pattern and any number of environmental or human-caused factors can account for them.
So the question remains, is this year's decline in mountain bluebirds a natural occurrence? If so, how serious is it and will they soon recover? Ultimately, what factor or factors might account for it?
Other cavity nesters seem unaffected.
Like the mountain bluebird, tree swallows are cavity nesters, capitalizing on holes in trees created by the aging process, by woodpeckers, by insect damage, and so on. They also rely heavily on artificial bird houses constructed and placed by people. Sometimes those houses are single adornments erected in an urban yard, sometimes they are part of a 'bluebird trail', literally miles of nest boxes attached like lonely sentinels to fence posts in farmers' fields. In 2008, trail monitors reported normal tree swallow numbers, and for other cavity nesters, such as wrens and chickadees, the story seems to be the same, no significant difference from previous years. So what's happened to the bluebirds and should we be alarmed?
It's not news to anyone that wildlife is declining all over the world. Many of these trends can be directly attributed to human activity. Songbirds are susceptible to pesticides, outdoor cats, window strikes, and a myriad of other human factors that scientists say claim the lives of millions upon millions of wild birds each year. Birds are also threatened by natural causes such as weather anomalies and disease, though it should be noted the latter can also be exacerbated by human activities. For example, some studies link toxoplasmosis in perching birds to feral cats.
What makes the summer '08 picture so alarming is the historical demise of North American bluebirds that occurred in the last two centuries. Forest clearing across much of their range resulted in the loss of critical nesting sites but the biggest threat came from the invasion of two non-native songbirds: the house sparrow and the starling. Both species are cavity nesters - brought to North America from England and Europe - that compete aggressively for appropriate cavities. Starlings are very early migrants and take advantage of the best nest spots early in the breeding season. House sparrows, also known as English sparrows and English weaver finches, don't migrate at all so they are also able to dominate nesting spots early.
By the 1960's and 70's, bluebirds had reached all-time low numbers due to this invasion. Youth groups, birding societies, and naturalists, were among those who built huge numbers of nest boxes and placed them in rural locations to assist the bluebird's return. This program was hugely successful, bringing bluebirds 'back from the brink'. Decades later, people are still buying and building bluebird houses in great quantities and several species are making great use of them. Nest box plans can be very sophisticated as repeated trial and error studies have defined exactly what makes the best bird house in order to maximize survival of the young.
Is the '08 decline a one-time incident then? Will fewer bluebirds return next spring or will their numbers rebound in 2009 and 2010? Is there anything that can be done to help?
You bet there is. Bluebirds are insectivores so we can reduce or eliminate pesticide use and let birds take care of the insect control business. We can protect both bluebirds and pet cats by keeping the latter indoors. We can also erect ornithologically-correct bird houses and provide proper maintenance for existing bird houses.
One particular biologist in Alberta has been working hard for two decades, educating people about hazards for wildlife that are created by human activity. Long time director of the Alberta Institute for Wildlife Conservation, Dianne Wittner noticed an apparent shortage of bluebirds as early as March, the month they return from the south. As summer progressed, the nest boxes normally occupied by bluebirds remained vacant.
Wittner suspected the cold, snowy spring may have impacted bluebirds which nest earlier than swallows, though she also noted that unfavourable spring weather is the norm in Alberta. "Year after year, we see bluebirds forced to abandon nests when sudden cold weather affects food supply (insects). Inspection of bluebird houses during these events often reveals frozen eggs and starving adults." Furthermore, bluebirds are able to produce two clutches per season if conditions are right, which has not been the case in recent years. Wittner speculates several bad springs in a row may have caused gradual population reductions. However, she is quick to add no one really knows for sure what is going on. "It could be several factors working together, but whatever it is, I hope it's only temporary. Bluebirds are so incredibly beneficial, not to mention how beautiful they are. Like all songbirds, they battle a host of natural factors, let alone those imposed upon them by people."
It will be interesting to see if other species of bluebirds show a significant decline across the continent. All three species have suffered setbacks since the introduction of the house sparrow and the starling and all three have been assisted with the advent of artificial nest boxes. The true test will come next March when bluebirds return.
In the meantime, when Wittner is not saving wild lives, she is busy encouraging people to erect bird houses for a variety of species. Through a website called Northern Bird Houses, Wittner and her team offers information on proper placement of species-specific nest boxes and ledges to help offset habitat loss. "There is no substitute for habitat conservation," she says, "But everyone can help wildlife in their own yards with a few simple steps. One of those is the addition and maintenance of a good bird house. You will be rewarded year after year by this very simple act and who knows how many wild birds will benefit?"
Fayette Front Page
Georgia Front Page