[4] He was breveted as a colonel in the regular Army with seniority from that date, retaining the rank until his regiment was disembodied,[5] which occurred at the end of 1799.

In 1834 he succeeded his father as 13th Earl of Derby and withdrew from politics, instead concentrating on his natural history collection at Knowsley Hall, near Liverpool.

He had a large collection of living animals:[6] at his death, there were 1,272 birds and 345 mammals at Knowsley, shipped to England by explorers such as Joseph Burke.

Several species were named after him, for example the Derbyan parakeet, Psittacula derbiana and an Australian species of parrot named firstly by Nicholas Vigors as Platycercus stanleyii, in 1830 when he was Lord Stanley, and referred to in the vernacular as "The Earl of Derby’s Parrakeet" by the author John Gould in the sixth volume of his magnum opus Birds of Australia.

[7] From the Earl of Derby's Collection, the State Library of NSW purchased six volumes of exquisite Australian natural history drawings dating from the early days of British settlement in NSW and this Library publishes talks and exhibitions of its research on this collection.