His early inspiration to work on Bird conservation came from a talk by John Terborgh and his travels in the summer of 1974 Manú National Park in south-eastern Peru.

[3] His summer in Peru made him change his plans from pursuing graduate study in University of California, Berkeley.

[6] Along with other biologists, Fitzpatrick has described several species and sub-species new to science such as bar-winged wood wren,[7] cinnamon screech owl,[8] royal sunangel,[9] Manu antbird,[10] the cinnamon-breasted tody-tyrant,[11] and the cinnamon-faced tyrannulet.

In 1985, Fitzpatrick and Woolfenden earned a Brewster Medal for their long-term study, the highest research award given by the American Ornithologists' Union.

[16] He has served on many professional ornithological committees, two species recovery teams (for the Hawaiian crow and the ivory-billed woodpecker), and advisory boards right up to the present.

For his achievements in the study of Peruvian birds and his guidance to a new generation of ornithologists, the newly described Sira barbet of Peru was named in his honor in 2012.