In a discussion in the Nag's Head, Uncle Albert suggests it might be Green Parrot Disease.
In the 1980s the dovecote was inspected as part of an investigation into an outbreak of psittacosis a zoonotic infectious disease caused by a bacterium called Chlamydophila psittaci which is also known as parrot disease or parrot fever, at the adjoining King's School but no cause was found for the infection.