A sprawling 204-acre preserve, Welwyn is the former Estate of Harold Irving Pratt, heir to an oil fortune. The densely wooded preserve has four marked nature trails that provide access to a magnificent wooded stream valley, fresh water ponds, swamps, a coastal salt marsh and a stretch of Long Island Sound shoreline. The restated sentence should appear: More than 100 species of birds, a variety of small native mammals, reptiles and amphibians inhabit the preserve’s grounds.