He had interests in the food of British birds and their geographical distribution and strongly encouraged detailed and accurate record keeping in local ornithology.

He was a founder of the British Oological Association, which changed its name after his death to the Jourdain Society in his memory.

From 1900 he went on an ornithological expedition abroad almost every year until his death, which resulted in a number of papers on the birds of the countries he visited.

While at Appleton he actively encouraged ornithological study at Oxford University, welcoming interested students to his home.

Jourdain produced several ornithological papers, although many were started but never finished, and authored or contributed to a number of books, notably the sections on Breeding-habits, Distribution Abroad and Food in the Handbook of British Birds (1938–41).

He led the first Oxford University Expedition to Spitzbergen and travelled extensively in Europe and North Africa.