The following organisations all have Scottish wildlife as their raison d'etre
My local patch includes the Montrose Basin Local Nature Reserve - well worth a visit.
Other birdwatching information...
The County of Angus has a wealth of birdwatching opportunities and here is some useful information about locations and the facilities offered (Hides, toilets, cafe etc).
Mention should also be made of two other reserves that are nearby (but in Kincardineshire) - St. Cyrus and Fowlsheugh.
Bird behaviour is a fascinating study and this a collection of sightings and stories.