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Turkey vultures crossing the strait

Diann MacRae, of Bothell, is an independent researcher who has been studying turkey vulture migration since 1984. She studied biological sciences as an undergraduate at Oregon State University and as a graduate student at the University of Washington. MacRae will be leading an Audubon field trip to Salt Creek on Sunday, Sept 28, to look for turkey vultures crossing the Strait of Juan de Fuca. I caught up with her recently to ask about her project.



Ed: What makes TV migration special?

DM: At its peak, southbound migration of TVs crossing the strait from Vancouver Island to the Olympic Peninsula is visually one of the most impressive bird migration events in North America.

Ed: Please amplify.

DM: Most birds migrate at night and we never see them. TVs, however, migrate in the heat of the day. They will sometimes cross the strait in flocks of several hundred, albeit stretched out by several minutes in arrival times.



Ed: When does this happen?

DM: This time of year, from mid-September into early October.



Ed: These are birds that moved north in the spring to breed?

DM: Yes, they have been nesting on Vancouver Island, the Gulf Islands and the Sunshine Coast. By early September, they have begun moving south along the east coast of the island. Ultimately they bunch up in the hundreds around Rocky Point, the southernmost tip of the island, awaiting optimal conditions for crossing the strait.



Ed: It's only 12 miles or so across the strait, and some birds can fly more than 1,000 miles nonstop. What's the big deal?

DM: Vultures are soaring birds, lacking the muscle power for flights requiring lots of flapping. They thrive in hot weather, soaring on thermals generated by solar heating. Water in the strait is cold, not generating many thermals, making this relatively short distance a major barrier for TVs.



Ed: So when and how do they cross the strait?

DM: TVs need a warm sunny day, with solar heating generating significant thermals over land. TVs spiral in the thermals, climbing several thousand feet. Then, often around midday, they glide southward across the strait, losing altitude as they go. I've seen them flapping to avoid landing on the water. Last year we counted about 1,500 TVs, almost all of them crossing on just two days. In some years the crossings are spread out over many days.



Ed: Is there a best place to look for migrating TVs?

DM: TVs preferred path across the strait seems to be from Rocky Point to the Salt Creek Recreation Area. Some years I've camped there for several weeks, counting TVs every day, but not this year. Unfortunately in some years, many TVs cross the strait to points other than Salt Creek, so I have missed seeing them and have been largely de-pendent on getting reports from other observers.



Ed: Does a tailwind help, as it would for an airplane?

DM: A north wind, from the Arctic, would be cold. Our observations show that the TVs prefer warmer winds from the east or southeast for their crossings. We routinely keep track of weather, wind speed and barometric pressure. They definitely avoid flying in rain.



Ed: Do all the TVs make it across?

DM: I've never seen a TV land in the water, but most years a half dozen or so TVs winter over on Vancouver Is-land.



Ed: Would those be young TVs or adults?

DM: We don't know, for the most part. TVs are easy to recognize by their two-tone, dark and light wing pattern while soaring. Observers, however, may not realize that young TVs have dark heads rather than the familiar red heads of adults.



Ed: As an independent researcher, who supports your project?

DM: In the past I've gotten grants from various scientific organizations. Lately my financial support has been rather modest, coming from your Audubon chapter and a few private citizens. Support in the form of reports of TV migration from independent observers, however, continues to be a very valuable part of the project.



Dave Jackson is "Our Birds" series editor and Web master. Send comments to him at editor@olybird.org or 683-1355. Diann MacRae's contact information is on the home page of the local Audubon Society Web site (www.olybird.org) for reporting migrating TVs. The Web site also has details of the upcoming trip to Salt Creek. The next introductory bird class starts Tuesday, Sept. 23. Class details, as well as previous articles in this series, also are available on the Web site.



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