Join Peter Alden as he guides you on a walk to the "secret Great Blue Heron Colony." There were 70 pairs last summer, along with Great Horned Owl nest (March-April) and a Pileated Woodpecker nest (May-June). Incubation by adults April-May; babies growing late April-early July. Meet at Verrill Farm on Wheeler Road in south Concord and carpool.  Allow two hours; walk is easy; need time to watch activity at tip of dry peninsula in heart of a new beaver swamp. Tour includes up to 12 people. Guided by Peter Alden, author of 15 books including National Audubon Field Guide to New England. Peter is a veteran bird and eco-tourism guide to 100 countries and the seven seas. He is founder of Biodiversity Days with Edward O. Wilson where 2700 species have been noted in two days of events in Thoreau Country.