Every day brings a change as the weather warms in the springtime: new migrating birds arrive, new flowers open; frog mating calls dominate and then subside; trees are suddenly in leaf. Don't miss this dynamic time of the year cooped up inside: join us for two-hour hikes with trained naturalists, every Tuesday in April and May 4. Please register by the previous Monday morning to guarantee that the hike will run. Cost: $5 per person; $12 maximum per family.