I know it seems barbaric this displaying of dead animals, and its not something I personally like to see,
About 40 yrs ago I was at a boarding school in the countryside and at the time spent many hours over two years helping and learning from an estate gamekeeper,
The display of crows and other vermin was done all the time, I asked why and was told that the display would frighten away others of the species. The display of moles was as is stated above to demonstrate the competence of the keeper,
These sort of displays are not done out of the aim to shock the public or to gain gruesome enjoyment they are done as part of the keepers work and are part of their training and their folklore.
The poison for worms I think was strychnine and at 11 I remember using worms treated with it . I seem to remember that my health and safety induction was dont lick your fingers and remember to wash your hands back at school, Ah those were the days.......