With no financial backing other than understanding parents, who would lend the money necessary to buy film, Hosking began to develop a market for his wildlife photographs. His working year was divided; he photographed during the spring and summer, where birds were mainly photographed at the nest because, as explained below, pre-focussing was necessary. In autumn and winter, articles could be written for magazines like "Picture Post" and "Country Life"; and book ideas were developed and then illustrated with high numbers of good quality images, some taken using the then new Kodachrome colour film, making these books very desirable. Some books like "Birds of the Day", published by Collins in 1944, sold more than 50,000 copies.