A message from Philip Sullivan:

Since May in particular, the parasite trichomoniasis has been infecting birds, especially finches, and the infection rate in 2020 is unusually high!
The main source of food in the autumn and winter months is bird tables and feeders in our gardens.  The remedy is simple :
Clean your tables and feeders regularly but at least fortnightly and keep bird food as dry as possible as the parasite thrives in wet conditions.