How Do Tornadoes Affect Birds?
After the initial destruction, twisters can benefit some avian species.
In the wake of Oklahoma's tornado tragedy, it's only natural that the people affected will be on everyone's minds. Any natural disaster calls for prolonged introspection, especially facing the loss of life. Eventually curiosity turns us onto other consequences--the wildlife and surrounding habitats that the storm also left in its path. How do plants, birds, and other wildlife fare after a tornado tears through an area?
The general consensus seems to be that we don't really know. As weather systems go, the impact of hurricanes is easier to study because their broad spread and brooding nature makes them easier to predict. But tornadoes, which typically rip through a region called 'Tornado Alley'--between Iowa, Colorado, and Texas--from late springinto summer, are coiled tightly like forceful weather springs, and they move fast--making them harder to detect in advance. Despite the many mysterious surrounding twisters, we do have some knowledge about how they affect nature.
Sensing the storm
Birds are lucky in that they can detect minute pressure shifts before unusual weather arrives. However, Kenn Kaufman, Audubon field editor and author, believes that our feathered friends are worse at predicting tornadoes than we are because the twisters move so fast and are so localized. "Humans have more advanced warning than birds do because we have the nightly news," he says. There is one thing that birds can do more effectively than us, though, he says--escape. The assumption is that "a lot birds get out of the way," he says; "they have enough sense" to leave.
In the tornado's path
Like hurricanes--which can actually spawn twisters--tornadoes are hugely destructive and can flatten things in their paths even more severely. "The intense concentration of habitat destruction that occurs undoubtedly makes a difference in bird habitat," Kaufman says. Trees where birds nest are ripped from the ground, and debris from shredded structures and vegetation obscures underground burrows. Any birds caught up in the storm are presumably killed--although there is no real way of measuring wildlife deaths after a storm. Bodies are hard to find amid the debris, and over long distances in the rural areas where tornadoes often strike. Furthermore, to gain a real grasp of the mortality, experts would require pre-tornado wildlife census against which to compare the numbers of surviving individuals after the storm--a rarity.
David King, a research wildlife biologist with the USDA Forest Service in Amherst, Massachusetts, adds that when it comes to the effect that tornadoes have on wildlife, direct mortality is less of a concern to conservationists. "I think principally the effects on wildlife are through changes in habitat," he says, since habitat so strongly influences wildlife survival after a storm.
After a tornado has blown a hole through a forest, for instance, "You'd see a lot of logs lying down, and brush and snags standing where trees have been snapped off," says King, who has studied forests hit by twisters. "The principal changes are to the removal of forest canopy." That allows a lot of light to hit the ground, which in turn results in smaller saplings colonizing the former wooded areas, forming a dense thicket over time. The habitat shifts from forest to shrub, making way for different species to move in to the area. "The golden-winged warbler is a shrubland species that has been the subject of a lot of conservation concern, and would use tornado-damaged sites," says King. He adds to that list the chestnut-sided and prairie warblers, as well brown thrashers.
A return to (a different kind of) normalcy
As illustrated by birds, as a forest undergoes transitions between destruction, regrowth, and maturity, the species that inhabit it may change, King explains.
When it comes to birds, the timing of tornadoes--stormy late spring and early summer--often coincides with nesting season. After the storm passes, birds are often drawn back to their established territories. "There's such a powerful instinct for them to return to their nesting habitat," Kaufman explains, "they can go back and figure out, oh well this is the spot." Unfortunately for them, 'the spot' might be a downed tree or an obliterated building.
Kaufman offers a purely anecdotal account. He recalls that after a tornado passed through Kansas in the late 1960s, he noticed a posse of barn swallows repeatedly circling one area. Afterward, he realized a barn had stood there before the tornado struck, and was likely where the birds had built their nests. (The birds could not have rebuilt in the area, since everything was gone.)
While much remains unknown, King loosely compares the tornado-stricken habitats is to those devastated by fire: Some landscapes--especially forests--actually thrive after disaster strikes. In these ecosystems, upheaval brings revival that can be key to some species' survival. Fallen branches provide more cover, nooks, and crannies where animals can take cover. Rotting wood also spurs new growth as it fertilizes the soil. The benefits are significant enough that ecologists suggest authorities refrain from clearing forests of damaged vegetation after severe weather events. Believe it or not the U.S. Forest Service still refers to this as woody "debris" and often burns it.
For some birds, change is salvation. King offers a hopeful anecdote in the form of the whip-poor-will, a forest-dwelling bird that faces habitat loss. In forests, fallen trees give a photosynthetic boost to the lower, shrubby level--an ecosystem that birds like the whip-poor-will need more than deep, shadowy forest. "They won't actually use mature forest," King says. "They require shrubland."
Once, after a tornado passed through Broomfield, Massachusetts, King recalls that whip-poor-wills populated the area where new shrubland opened up to the sky. Sometimes, new life can spring from nature's worst destruction.