Every summer weekend, in communities large and small, a familiar scene plays out. Farmers, awake since before dawn, unload their trucks, set up tables and tents, and arrange piles of fresh produce, jars of colorful flowers, and coolers of meats and cheeses. Soon, swarms of customers clutching string bags and wallets are making their rounds, picking up an organically grown melon at one stand, a free-range chicken at the next, and bags of fresh herbs across the aisle.

 The bird walk has started inauspiciously. As guide Cynthia Fox leads a group of binocular-toting birders through the back trails of the Sarah P. Duke Gardens, the birds seem to be sleeping in.