"I hope you love birds too. It is economical. It saves going to heaven."
Emily Dickinson

Sunday, September 10, 2017

Where do birds go in a hurricane?

Wood stork in the Florida Everglades -- Photo by J.J. Meyer
This post is reprinted from Forbes. com. 

As the southern United States faces a second record-breaking hurricane in less than two weeks, I’ve been asked many times: “What happens to birds in hurricanes? Where do they go?”

Basically, birds have a variety of strategies for dealing with large storms, such as hurricanes, including: leaving the area; flying ahead of, or into the storm; or sheltering in place.

Birds may leave in advance of an approaching storm

Research has shown that birds can hear infrasound (ref) and are sensitive to barometric pressure (ref and ref), so they know when a storm is on its way -- especially when the storm is as large and as powerful as a hurricane. When a large storm approaches, birds in its path may adjust their behaviors within the parameters of their own life histories and according to season. For example, white-throated sparrows, Zonotrichia albicollis, are migratory songbirds, so if a large storm is approaching during their annual spring or autumnal migration period, they may migrate sooner than they might otherwise do (ref). Interestingly, research has found that sparrows speed up their autumnal migratory departure date in response to falling barometric pressures (but not temperature), whereas they delay their spring migratory departure in response to falling temperature (but not barometric pressure).

Birds may fly ahead of, into, or through, a storm
Some migratory birds may intentionally fly into a large storm. For example, a whimbrel, Numenius phaeopus, named Chinquapin, flew into Hurricane Irene’s dangerous northeast quadrant in 2011. This medium-sized shorebird was part of an ongoing research project and was carrying a satellite tracker, allowing scientists to watch this intrepid bird’s progress in real time as she migrated from Hudson Bay, Canada, to her wintering grounds in South America.

Chinquapin was lucky. Although this same bird successfully flew around the edge of Tropical Storm Colin in the previous year, a second satellite tagged bird flew into that storm and was killed.
But storms are not the worst of what whimbrels and other migratory birds encounter. Several other satellite tagged whimbrels, named Machi and Goshen, survived their flights through hurricanes in 2011. (Like Chinquapin, Goshen also tangled with Hurricane Irene, although she flew through the outer edge instead.) But both Machi and Goshen paused on the Caribbean island of Guadeloupe and tragically, both were shot dead within hours of their arrival. (This is a common fate for hurricane survivors landing on Guadeloupe.)
In the same year, another satellite tagged whimbrel, named Hope, flew into Tropical Storm Gert off the coast of Nova Scotia, Canada. Incredibly, she endured strong headwinds for 27 hours straight, but was able to fly at an average speed of only 7 miles per hour (11kph). In contrast, after she successfully emerged from the middle of that storm, she then was pushed by strong tailwinds at an average speed of 90 miles per hour (145kph) and safely returned to her staging grounds on Cape Cod -- after expending a huge amount of effort for no gain.

But migrating ahead of, or during, a hurricane is a strategy that is fraught with dangers and can have unexpected consequences, especially for small birds. For example, in 2005, a large flock of migrating chimney swifts, Chaetura pelagica, was swept up by Hurricane Wilma, and the lucky survivors relocated to Western Europe -- to the delight of bird watchers there.
Other small migratory bird species may become trapped inside a hurricane, as probably was the situation for those migrating chimney swifts. For example, radar images of Hurricane Matthew as it raged across Florida in 2016 showed it had a huge flock of birds trapped in its eye.

These birds were relocated by many hundreds or thousands of kilometers away from where they were, or wanted to be -- again, to the delight of local birders.

Birds may shelter in place and hang on for dear life
Many non-migratory birds seek shelter inside thick bushes or on the leeward side of trees. Trees and shrubs can dramatically reduce wind speeds and can keep birds dry even during a torrential downpour. And since birds adapted to sleeping whilst perched, their feet automatically close when they are relaxed, thereby making it easier for birds to hang on to something solid for dear life.
Birds may also find cover where ever it exists. For example, an injured Cooper’s hawk, Accipiter cooperii, now known as Harvey, took refuge in Willam Bruso’s taxi in Houston during Hurricane Harvey just a few days ago.

Harvey (the bird, not the hurricane) was given to the TWRC Wildlife Center the following day, where it was discovered that she had suffered a broken wing (and was probably in shock from the pain), thereby preventing the terrified bird from flying. Harvey is expected to make a full recovery.
In addition to taxis, other birds, such as woodpeckers and parrots, may seek shelter in their nest-holes or in other cavities. This works well unless the tree they are sheltering in is uprooted or snapped off at the cavity, or if these birds become trapped by floodwaters — just as people become trapped in their attics and drown.

Birds may die
Remember that flock of chimney swifts that I mentioned? Most of them met a horrible end: at least 727 of these tiny birds’ bodies were found later (ref) -- but how many thousands more died and were never found? Indeed, Hurricane Wilma’s effects on chimney swift numbers were so severe and widespread that, in the province of Québec, Canada, where these birds lived, chimney swifts became quite rare as the direct result of this one tragic event. In the following year, roost counts declined by an average of 62% and the total chimney swift population is estimated to have decreased by half.
Surprisingly, we don’t really have much robust data for how storms affect bird populations -- until they become vanishingly small. But researchers studying sooty terns, Onychoprion fuscatus, which are plentiful in the Atlantic, report a strong positive correlation between “wrecked” individuals found throughout the Caribbean and the number of tropical storms, particularly hurricanes (ref). These data are being used to build computer models that may help to more precisely predict storm-caused mortality for seabirds.

Read the complete story at Forbes.

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