The following piece on the Oxford Swift Research Project is taken from the OUMNH website:
“The colony of swifts which nest in the Museum has been the subject of a research study since May 1948. It is one of the longest continuous studies of a single bird species in the world, and has contributed much to our knowledge of the swift.
Swifts had been nesting inside the ventilator shafts of the Museum tower for many years when David Lack, the head of the Edward Grey Institute at the Department of Zoology, began the swift research project. Swifts use nesting sites which are inaccessible to predators to safeguard the eggs and chicks. The parents are also quite vulnerable when nesting. Swifts had proved a difficult species to study as they spend most of their lives in the air, but Lack realised that the swift colony in the Museum would be ideal for long term research.
The book Swifts in a Tower was first published in 1956 and details David and Elizabeth Lack's work on the colony of swifts in the Museum. It describes the setting up of the project and reviews other swift species.”
The ventilator shafts in question are those on the central tower of the roof in the photo below.