After the first Arctic expedition, he noticed on returning to Avery Island, a great decline in the number of egrets. This led him to conduct experiments in captive breeding. McIlhenny founded the
Bird City wildfowl refuge on Avery Island around 1895, which helped to save the
snowy egret from extinction. In 1910, McIlhenny and
Charles Willis Ward bought of marshland and later an additional ; on November 4, 1911, they dedicated the marsh to the state of Louisiana as a wildlife refuge. McIlhenny persuaded Mrs
Russell Sage to purchase of Marsh Island on July 22, 1912, and the
Rockefeller Foundation to acquire an additional nearby. This created a bird reserve of about . McIlhenny was keen to study the birds on his estate and began bird ringing in 1912, initially using his own bands made of tin and lead on ducks, but he received few recoveries. In February 1916, he began to use bands issued by the American Bird Banding Association. Between 1912 and 1942, he
banded 286,743 birds. Based on his ringing studies he came to the conclusion that sex-ratios in ducks were skewed in the wild with males surviving to a greater age than females. Later studies based on McIlhenny's ringing data have yielded considerable information on the movements of
black vultures. In 1941, he wrote on the potential extinction of the
ivory-billed woodpecker, noting its presence in his estate on Avery Island and suggesting that the destruction of old growth forests was key to its demise. The subspecies of
white-tailed deer on Avery Island was named after McIlhenny as
Odocoileus virginianus mcilhennyi by Frederic W. Miller in 1928. McIlhenny used his personal estate, known as
Jungle Gardens, to propagate both Louisiana-native and imported plant varieties, including
azaleas,
irises,
camellias,
papyrus, and
bamboo. He wrote numerous academic articles, mainly about
birds and
reptiles, oversaw the publication in English of two European botanical treatises, and edited Charles L. Jordan's unfinished manuscript
The Wild Turkey and Its Hunting (a book often mistakenly attributed to McIlhenny). He supported the equality of women but suggested that there were evolutionary handicaps standing in the way. He also wrote books about
alligators (in which he claimed to have shot the longest American alligator 19 feet long),
egrets, and African-American
gospel music, including: temple in
Avery Island's
Jungle Gardens, the former personal estate of Edward Avery McIlhenny. • ''Befo' De War Spirituals: Words and Melodies'' (1933). •
Bird City (1934). • ''The Alligator's Life History'' (1935). •
The Autobiography of an Egret (1940). ==Death and legacy==