Thaler, E, . J. T. R, Sharrock, I. J. F. &, Vernon, J. D. R, Thaler, E, . J. T. R, Vernon, J. D. R & Sharrock, I. J. F. & / February 1971 – vol. 64, issue 2–87 Elusive species and the B.T.O. Ornithological Atlas project Some species are proving to be difficult to locate in fieldwork for the Ornithological Atlas. In order to prepare full maps for these species, we cannot rely solely on fieldwork carried out purely for the Atlas, but need to collect data from all sources. All breeding season records during 1968-72 (even casual observations of just one bird... This article is only available to registered users.To read more, please log in or purchase a subscription.