NATURE WALK: Elizabeth Davidson, left, leads Deb Sewall, Andy McEvoy and Bryan Prelgovisk on path skirting the woods on the edge of a blueberry field on a recent morning walk at the Davidson Nature Preserve in Vassalboro. The 97-acre Davidson Nature Preserve was donated to the Kennebec Land Trust in 2005. There are blueberry fields open for picking, mixed woodlands, and a heron rookery situated above a beaver bog. In addition to the many songbirds nesting here, the preserve is an important stop-over point for spring and fall long distance migrants, especially warblers.