The birds were especially common above the older buildings on campus, because they built nests in the chimney-like ventilation shafts. Dr. Dexter spent many nights marking animals with bands and painting identification patches on the wings. He was thus able to chronicle the lives of many individual birds. The data made an important contribution to bird population ecology. Swifts are normally territorial about their nesting places, so tolerance of visitors is inexplicable.
Swifts are indeed very fast flyers.
When they are not feeding, pairs or groups may fly in formation, air-show style. Seeing two birds flying side by side in exactly the same pose, is not unusual.