In the 1820s Waterton returned to Walton Hall and built a nine-foot-high wall around three miles (5 km) of the estate, turning it into the world's first wildfowl and nature reserve, making him one of the world's first environmentalists. He also invented the bird nesting box. The Waterton Collection, on display at Stonyhurst College until 1966, is now in the Wakefield Museum. Waterton owned a dog who was prominent in the foundation of the modern English Mastiff and may be traced back to in the pedigrees of all living dogs of this breed.