Montagu had an interest in marine and freshwater natural history, and in 1803 published his Testacea Britannica, a History of British Marine, Land and Freshwater Shells.
Montagu oli kiinnostunut merien ja järvien luonnonhistoriasta ja julkaisi vuonna 1803 teoksen Testacea Britannica, a History of British Marine, Land and Freshwater Shells.