Fall's Journey South

Fall's Journey South Update: October 2, 1998

Today's Report Includes:

Hurricane Georges on Sept 27
WXP Weather Processor Server

How Do Hurricanes Affect Migration?
This has been a dramatic week for weather and birds alike! Hurricane Georges roared through the Caribbean on a rampage of destruction in places like Haiti, St. Martins, the Dominican Republic, Puerto Rico, Cuba, and the US Gulf Coast, dumping well over a foot of rain in areas of Florida, Alabama, and Louisiana. Even after it lost its power and simmered down to a tropical depression, it continued to downpour.

Despite the hurricane, hawks put on a record-breaking show in Corpus Christi, Texas at Hazel Bazemore County Park (27.30N, 97.60W). Broad-winged Hawks all move together on few days each fall, migrating in huge numbers along the Gulf coast. In the late 1980s birders noticed that they could see a lot of them over this tiny county park. During the years since then, they've had a few days when counters found about 100,000 hawks in a single day, but this year they had four days in a row with counts of over 100,000. On September 26 alone, they had 306,766 Broad-wings-over a quarter of a million! The thrilled and amazed birders have already broken their all-time record for the season total with 904,121 hawks by September 30. The hawks don't seem to have been affected by the hurricane at all,

Photo by Harlen and Altus Aschen

which did most of its damage east of Texas.

Homeless, Tempest-Tossed
Imagine the impact of such a storm on birds that were caught in it! High winds that rip roofs off buildings toss even huge birds like pelicans around like paper airplanes, whipping them about with the other flying debris. Woodpeckers and other cavity nesters ride out storms in tree holes, which works unless the tree snaps or is uprooted. Songbirds fly for dear life in advance of storms or try to ride them out, clinging for dear life onto sturdy, sheltered branches. Many survive. But many do not.

This week Journey South was going to report about the birds of Monterey Bay, but with this week's events we decided to move east, into hurricane territory, which leads us to this week's

Challenge Question #5: Why don't hurricanes hit the West Coast as they do the East and Gulf Coasts?

Don't Pressure Me!
Some strong-flying birds avoid the impact of hurricanes by flying in advance of the storm, carried by the winds at the outer reaches of the storm system. How do they know these winds come from storms rather than normal weather conditions? They can feel drops in barometric pressure.

We humans feel changes in pressure, too. Did you ever ride an elevator in a tall building? Our ears pop when air pressure changes. Birds have more sensitive inner ears, feeling much smaller changes in pressure. The drop in pressure from the ground to the top of the Sears Tower in Chicago is the same drop you'd feel in a hurricane (but without all that wind!)-1.7 inches of mercury. The normal air pressure at the top of the Sears Tower is about the same as the pressure in the eye of Hurricane Georges at its fiercest!

Letter from Florida
When birds detect an approaching storm, especially in fall when they don't have a nest or babies to protect, they sometimes hightail it out of there fast.

Some birds don't go too far. Phil Berry, a birder in Gulf Breeze, Florida, wrote to Journey North on September 30: "We are ending our 5th day of Georges here. I live on the intercoastal waterway, within sight of the Gulf. We have experienced fallouts of several species of migrating warblers. Shorebirds have left the beach and have been in my back yard (a golf course) since Sunday morning. Access to the beach has been curtailed for them, so they find it necessary to move to the golf course to find food. Other than the above, things appear normal. my hummer feeders were left up during the storm and were well-used."

Swept Away!
Other birds are picked up by the storm system and carried long distances-there are records of White-billed Tropicbirds from Bermuda being blown up to Vermont after one hurricane. Birders search for rare birds after hurricanes, and Journey South will report on interesting birds they find.

South Pelto platform

Evacuate!
Bob Russell is trying to spend this autumn watching migration from an oil platform on the Gulf, but many of this fall's storms, have forced him and the other scientists to be evacuated back to the mainland. A few oil company crew members remained during the storms, and told Bob that it looked like there were "large fallouts of migrants ?on some platforms in our absence following the passages of Hurricane Earl (Sept 2), Tropical Storm Frances (Sept 10-11), and Tropical Storm Hermione (Sept 19)." Because the workers had too many other responsibilities to keep records, Bob tells us that he can only guess "about the magnitude and composition of these fallouts."

More News from the Oil Platforms
Bob also said that the storms brought a big change in the numbers and kinds of seabirds they see on the platforms. The storm-tossed water became too cloudy and opaque, and the "vertical structure" of the water broke down, which means that the plants and animals that usually stay at particular levels were all mixed up. This made it hard for seabirds to feed. Royal Terns, Sandwich Terns, Black Terns, and Laughing Gulls became scarce, and true pelagic seabirds disappeared, with one exception. On Sept. 12, following Tropical Storm Frances, lots of Sooty and Bridled Terns and a Manx Shearwater (one of the few observations ever from the northern Gulf!) turned up at South Marsh Island.

For more details about the trans-Gulf migration August 29 - September 18
Bob did have one great night of songbird migration on September 15. Check out the details at the Trans-Gulf Migration WWW site

Click to see larger image
Map: Coutesy of the Weather Channel

Discussion of Challenge Question #4

Based on the weather map for September 25,1998, it might be a good idea to issue a traveler's alert in the large area of fog in all of western Michigan (including Lansing) southern Wisconsin (including Milwaukee and Madison), northern Illinois (including Chicago), just about all of Iowa, most of Nebraska, and the northeastern tip of Colorado. Rain and clouds would be expected in all the areas with green on the map, where high and low pressure areas are colliding, especially in the Florida Keys and Caribbean Islands--that system is Hurricane Georges!

How to Respond to Today's Challenge Question # 5:

Address an e-mail message to: jn-challenge-fall@learner.org
In the Subject Line of your message write: Challenge Question # 5
.In the body of the message, answer the Challenge Question.

The Next Journey South Update Will Be Posted on October 9, 1998

How You Can Help Track Fall's Journey South
How You Can Help Track Spring's Journey North