1904: William F. and Anna M. Vilas - he, a former Army officer, lawyer and U.S. senator - donate a 63-acre tract for a park, with the stipulation that no admission be charged. It was named in memory of the couple's son, Henry, who died at a young age five years earlier due to complications from diabetes.
1911: The zoo officially opens as the first animal exhibits are installed in the park. The first animals exhibited were five whitetail deer donated by T.C. Richmond.
1913: The bear cage is built.
1914: The Madison Zoological and Aquarium Society, the first community group to support the zoo and the forebear of today's Friends of the Zoo, is formed.
1917: The zoo's first lion house is built.
1918: Annie, the zoo's first elephant, is donated by Alfred Ringling, one of the famous Ringling Brothers. Annie lives until 1948.
1919: The zoo becomes the first in the United States to build a "monkey island." It is replaced in 1934.
1929: The zoo's primate house is built. The building was remodeled in 1968 to accommodate the zoo's new orangutans.
1934: A 9-year-old boy is mauled by a zoo polar bear after climbing a tree near the polar bear cage and dangling his foot inside. He died several days later.
1937: The city assumes ownership of the zoo, Vilas Park and other parks from the Madison Park & Pleasure Drive Association.
1950: A female named Al Malaikah becomes the first dromedary camel born at the zoo. The zoo would add a building for its camels in 1961.
1952: Two new grizzly bears and a polar bear bring the zoo's bear menagerie to 22.
1960: A group of 38 Rhesus monkeys escape from the zoo during a feeding in August, taking refuge in the Vilas neighborhood and UW Arboretum. Most were recaptured days later, but efforts to recapture the final pair last into December.
1966: Winkie, the zoo's 7,500-pound elephant, kills a 3-year-old girl after pulling her into its cage. The girl had gotten around an outer gate to feed the elephant popcorn. Winkie was later traded to a breeding farm for a smaller elephant.
1968: The zoo spends a record $10,000 to bring in a young pair of giraffes.
1972: After nine years of planning and fundraising, the children's zoo opens, allowing kids to get up close and personal with a sea lion, baby elephant, fawns, bear cubs, toucans and other animals.
1973: The zoo unveils a new home for its big cats, replacing the original 1917 lion house.
1977: Zoo opens its otter exhibit. Elephant Winkie Too charges and knocks over a zookeeper during a feeding, seriously injuring her before she could crawl to safety. She sued the city for $1 million and settled in 1983 for $25,000.
1983: Ownership of the zoo is transferred from the city of Madison to Dane County, a process that takes a decade to complete.
1988: The zoo's polar bear Chief is shot by police while mauling a mentally ill man who had entered the bear's habitat. The man survived. Two young polar bears are brought to the zoo from Alaska to replace Chief. Though the bears were obtained for free, the community raised in a short time to buy the bears.
1991: The zoological society announces a decade-long $11 million Rezoovenation capital fundraising campaign.
1993: The Discovery Center and herpetarium, home to slithery reptiles and amphibians, opens.
1995: The primate house opens, offering a new roof over the heads of the zoo's orangutans, colobus monkeys and gibbons.
1998: The UW-Madison Primate Center discontinues its monkey exhibit at the zoo after the loss of federal funding and controversy over the use of some of the animals for invasive research.
2000: A new visitors center opens after a $1.25 million renovation of the former aviary. The center houses a permanent zoo history exhibit and temporary exhibits. The zoo loses its two elephants after the Association of Zoos and Aquariums determines they should be housed in more open areas.
2003: The zoo opens its new $4.2 million tropical rain forest aviary and completes a concept plan for the $27 million Zoo Century capital campaign.
2006: North American Prairie exhibit with bison, prairie dogs and a badger opens. The Conservation Carousel begins offering rides for $1.
2008: Year-round flamingo exhibit opens. Children's Zoo train begins to offer rides.
2009: To help Dane County through a difficult economic time, the zoological society agrees to contribute more than $500,000 more to zoo operations than originally planned.
SOURCES: State Journal archives, Vilas Zoo and Friends of the Zoo staff, author Anne Vandenburgh