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Wednesday, September 11, 2013
hurricanes and their affect on birds
Major storms such as hurricanes are undeniably harmful, and have been occurring for ages – and will certainly occur again. Since we're in the middle of hurricane season, let's learn about birds and migration during a hurricane, while leaving news of the impact on humankind to those who know better than I.
As you might imagine, many birds fly rapidly from the area as a hurricane approaches. They’re alerted by the sudden drop in barometric pressure which they instinctively know means “leave fast” – after all, their species has been dealing with storms for ages. However, some will choose to stay put if they can find shelter, and ride it out.
In addition to the drastic pressure change, hurricanes generally approach from the south. They’re huge storms, with counterclockwise winds, carrying lots of water. This means that ahead of the core of the storm, winds will be blowing essentially from east to west inland from the upper gulf coast. (The same principles apply when a hurricane approaches any other land mass).
At the same time, our fall-migrating birds are heading from north to south, many flying down the Central Flyway (centered on the Mississippi River), and will be driven west toward Texas ahead of the hurricane's landfall. This will obviously increase the number of migrating birds coming through Texas, and decrease the number significantly that are moving through places to the east of the storm. As the storm approaches and makes landfall, winds will be strong, and birds would probably not brave headwinds in excess of 100mph just to get to the gulf coast. The beaches in Texas are better anyway!
The east side of the storm, with winds out of the south, is the "dirty" side of the storm, as these winds carry more wet debris and are far more destructive than east-to-west winds. So, for example, east Texas should be spared from much wind damage by a hurricane that hits Louisiana. A hurricane loses strength over land also. These counterclockwise winds discourage birds from flying into the nasty east side of incoming storms.
The non-migrating birds in the path of a hurricane just hunker down in a hole in a tree, under the eave of a house or in the center of a large tree. Some, unfortunately, will be killed. Others may get blown far away by a big storm (Katrina blew many birds as far away as Tennessee).
While watching migrating birds may be good in Texas and slow in Florida during a hurricane hitting Louisiana, another group of birds may visit. These are the water/shore birds (“pelagic” species) that live along coastlines. Many of them get "trapped" in the relatively calm eye of the hurricane and carried well inland, to places and habitats they haven't a clue about. Naturally, they turn around and head back to the coast as soon as they can. But it’s not out of the question that someone will see, for instance, a Shearwater or Avocet in north Texas as the remnants of a hurricane pass through. Birds trapped in the eye of an active storm have very little natural food around, since the preceding east-west winds scoured the area via high winds. Pelagic birds normally drop from what’s remaining of the hurricane’s “eye”, into large lakes. (Many pelicans were spotted in and over Lake Lewisville during hurricanes Katrina and Ike).
Of course, the biggest threat to all kinds of birds is the loss of their habitat and natural food. A Cardinal who lived in a Mississippi forest, for example, may have his forest blown down. Or a Meadowlark may suddenly have his meadow underwater. Or a Woodpecker in a Louisiana swamp may have his habitat inundated by salt water from the gulf. This affects both the birds’ homes and their food supply.
So let’s keep both people and birds in our thoughts as hurricanes develop, which they certainly will.
Posted by Owen Yost at 9/11/2013 02:43:00 PM