who invented the modern zoo concept and by Heini Hediger, a pioneer of ethology. At Chester, Mottershead took Hagenbeck's idea for moats and ditches as an alternative to cage bars, and extended their use throughout the zoo, often with species that Hagenbeck had not considered. For example, when chimpanzees were released into their new enclosure at Chester in 1956, a group of grassy islands, they were separated from visitors by no more than a strip of water. Nobody knew then if chimps could swim. It turned out that they could not, and today the chimp islands are a centrepiece of Chester Zoo. In 1986 the zoo was enclosed with a fence, in line with the Zoo Licensing Act 1981. 21st century Realm of the Red Ape, an Indonesian-forest-themed exhibit, featuring threatened Sumatran and Bornean orangutan, opened in May 2007. In January 2009, Chester Zoo unveiled Natural Vision, a £225 million plan to transform itself into the largest conservation attraction in Europe. The first phase of the plan was to be a £90 million, enclosed African-rainforest-themed sanctuary containing a band of gorillas and a troop of chimpanzees, as well as okapi and a variety of tropical birds, amphibians, reptiles, fishes, and invertebrates, moving freely among lush vegetation. It included a water ride to take visitors through the exhibit. Natural Vision was to eventually include a 90-room hotel, a Conservation College, and a revamped main entrance that would link the zoo to a marina to be developed on zoo land, all to be completed by 2018. Plans went before the public for comment in June 2009. The projected Heart of Africa bio-dome, along with plans for the hotel, were shelved in 2011 due to the loss of £40m potential funding when the North West Regional Development Agency was abolished. In December 2012 planning permission was gained for a later phase of the Natural Vision masterplan. One of the largest zoo developments in Europe, Islands at Chester Zoo is a £40 million redevelopment project to extend the zoo's footprint and recreate six island habitats of Southeast Asia. As of 2017 it is now open. A 600,000 square foot nature reserve was opened in April 2018. The reserve sits outside the boundary of the main zoo and is free for people to enter. In October 2018, two Indian elephant calves (Nandita Hi Way, age 3 years, and Aayu Hi Way, age 18 months), died