If you take a trip along the north coast you can usually get some good places. Causeway coast, Carric a rede rope bridge etc.
The majesty of the Causeway Coast vies for the birdwatchers attention with fulmar, eider, turnstone, black guillemot, buzzard, raven, chough and wheatear. Offshore are the seabird colonies of Rathlin Island. In the middle is the Antrim plateau - red gousemoor, bog and forest. To the east are the mudflats of Belfast and Larne Loughs, with the Bann, Lough Beg and Lough Neagh to the south.
One must if you have time is Rathlin Island. The west side has a bird sanctury with some stunning views of birds. I dont know to much about times of the year for best viewing etc. Can just remember going as a kid and viewing the birds. Quite a sight and good viewing platform. There is a ferry leaves ballycastle daily http://www.discovernorthernireland.com …rry-Ltd-Ballycastle-P2057
Some useful info here: http://www.rspb.org.uk …guide/r/rathlin/index.asp
Also slieve league in Donegal has some impressive sea cliffs. Here is a photo I took from the cliffs (Sorry No Birds) http://photography-on-the.net/forum/showthread.php?t=208712
Hope this helps enjoy your visit.