Over the course of the next two weeks, more than 70,000 people are expected to visit Northwest Ohio to search for birds. They're not hunting or looking for pets. They are bird watchers from all over the country, and across the globe. Each May, hundreds of thousands of songbirds funnel north from their wintering grounds in South and Central America, headed for their nesting areas in Canada and beyond. The birds gather in the marshes along Lake Erie before crossing the lake. This phenomenon offers the best opportunity to observe many species of birds that are seldom seen the rest of the year. Black Swamp Bird Observatory stages "The Biggest Week in American Birding" from May 4-13 with events, lectures and special birding tours, and local hotels and restaurants do a booming business. A story on the birding extravaganza runs in Tuesday's Blade.