Jim Steele/What’s Natural
In 2019, bird researchers published “Decline of the North American Avifauna,” reporting a decline in 57 percent of the bird species. They estimated a net loss of nearly 2.9 billion birds since 1970, and urged us to remedy the threats, claiming all were “exacerbated by climate change”, so we can stave off the “potential collapse of the continental avifauna.” Having professionally studied bird populations for over 20 years and restored their habitat, looking at their data suggests a far more optimistic perspective.
First, consider since 1970 many species previously considered endangered such as pelicans, bald eagle, peregrine falcon, trumpeter swan, and whooping crane have been increasing due to enlightened management. Despite being hunted, ducks and geese increased by 54 percent. Secondly, just 12 of the 303 declining species account for the loss of 1.4 billion birds, and counterintuitively their decline is not worrisome.
Three introduced species – house sparrows, starlings and pigeons – account for nearly one half billion lost birds. These birds were pre-adapted to human habitat and are considered pests that carry disease and tarnish buildings and cars with their droppings. Across America, companies like Bird-B-Gone are hired to remove these foreign bird pests. Furthermore, starlings compete with native birds like bluebirds and flickers for nesting cavities, contributing to native bird declines. The removal of starlings is not an omen of an “avifauna collapse”, but good news for native birds.
When European colonists cleared forests to create pastures and farmland or provide wood for heating, open-habitat species “unnaturally” increased. Previously confined to the Great Plains, brownheaded cowbirds quickly invaded the newly opened habitat. Unfortunately, cowbirds parasitize other species by laying their eggs in their nests. A cowbird hatchling then pushes out all other nestlings, killing the parasitized species’ next generation. The loss of 40 million cowbirds only benefits our “continental avifauna”.
Several bird species had evolved to colonize forest openings naturally produced by fire, or floods or high winds. Those species “unnaturally” boomed when 50 percent to 80 percent of northeastern United States became de-forested by 1900. Still, eastern trees will reclaim a forest opening within 20 years, so open habitat species require a constant supply of forest openings. However as marginal farms and pastures were abandoned, fires were suppressed and logging reduced, forests increasingly reclaimed those openings. With a 50 percent decline in forest openings, their bird species also declined; now approaching pre-colonial numbers. Accordingly, birds of the expanding forest interior like woodpeckers are now increasing.
White-throated Sparrows and Dark-eyed Juncos quickly colonize forest openings but then disappear within a few years as the forest recovers. Those 2 species alone accounted for the loss of another quarter of a billion birds; not because of an ecosystem collapse, but because forests were reclaiming human altered habitat. Nonetheless those species are still 400 million strong, and juncos remain abundant in the open habitat maintained by suburban backyards. If environmentalists want to reclaim the abundance of their boom years, they must manage forest openings with logging or prescribed burns.
Insect outbreaks also create forest openings. For hundreds of years forests across Canada and northeastern US have been decimated every few decades by spruce bud worm eruptions. So, forest managers now spray to limit further outbreaks. Today there are an estimated 111 million living Tennessee Warblers that have specialized to feed on spruce bud worms. But the warbler’s numbers have declined by 80 million because insect outbreaks are more controlled. Still they have never been threatened with extinction. Conservationists must determine what is a reasonable warbler abundance while still protecting forests from devastating insect infestations.
The grassland biome accounted for the greatest declines, about 700 million birds. Indeed, natural grasslands had been greatly reduced by centuries of expanding agriculture and grazing. But in recent times more efficient agriculture has allowed more land to revert to “natural” states. However fossil fuel fears reversed that trend. In 2005 federal fuel policies began instituting subsidies to encourage biofuel production. As a result, 17 million more acres of grassland have been converted to corn fields for ethanol since 2006.
Although still very abundant, just 3 species account for the loss of 400 million grassland birds: Horned Larks, Savannah Sparrows and Grasshopper Sparrows. Horned Larks alone accounted for 182 million fewer birds due to a loss of very short grass habitats with some bare ground. To increase their numbers, studies show more grazing, mowing or burning will increase their preferred habitat.
It must be emphasized that the reported cumulative loss of 2.9 billion birds since 1970, does not signify ecosystem collapses. But there are some legitimate concerns such as maintaining wetlands. And there are some serious human-caused problems we need to remedy to increase struggling bird populations. It is estimated that cats kill between 1 to 3 billion birds each year. Up to 1 billion birds each year die by crashing into the illusions created by window reflections. Instead of fearmongering ecosystem collapse, our avifauna would best be served addressing those problems.
(Jim Steele is director emeritus of the Sierra Nevada Field Campus, SFSU and authored Landscapes and Cycles: An Environmentalist’s Journey to Climate Skepticism. He writes a periodical column for Battle Born Media newspapers. You may contact him at email@example.com.)