In 1920, while in solitary confinement at Leavenworth, Stroud discovered a nest with three injured sparrows in the prison yard. He cared for them and within a few years had acquired a collection of about 300 canaries. He began extensive research into birds after being granted equipment by a prison-reforming warden. Stroud wrote "Diseases of Canaries", which was smuggled out of Leavenworth and published in 1933, as well as a later edition (1943). He made important contributions to avian pathology, most notably a cure for the hemorrhagic septicemia family of diseases, gaining much respect and some level of sympathy among ornithologists and farmers. Stroud ran a successful business from inside prison, but his activities infuriated the prison staff, and he was eventually transferred to Alcatraz in 1942 after it was discovered that Stroud had been secretly making alcohol using some of the equipment in his cell.