Bird watchers use them on certain days at the end of March (5)
I believe the answer is:
hides
'bird watchers use them' is the definition.
I can't tell whether this definition defines the answer.
'certain days at the end of march' is the wordplay.
'certain days' becomes 'ides' (I can't explain this - if you can you should believe this answer much more).
'at' means one lot of letters go next to another (I've seen this in other clues).
'the end of' suggests the final letters.
The last letter of 'march' is 'h'.
'ides' after 'h' is 'HIDES'.
'on' is the link.
Can you help me to learn more?
(Other definitions for hides that I've seen before include "Conceals - animal skins" , "Cloaks" , "lies low" , "coats" , "Dressed skins of animals" .)