The breeding bird community is not known in detail but monitoring work to date indicates it is typical of what would be expected for the habitats represented at Cashel.
Breeding species, confirmed or probable, include kestrel, buzzard, red grouse, black grouse, cuckoo, tawny owl, skylark, meadow pipit, tree pipit, grasshopper warbler, whitethroat, willow warbler, whinchat, stoncchat, robin, blackbird, blue tit, wren, chaffinch, and carrion crow.
Other species recorded on the ground include hen harrier, peregrine, snipe, reed bunting, and raven. The oakwoods along the east side of Loch Lomond arc known to have important breeding populations of pied flycatcher, wood warbler and redstart, and these may breed occasionally at Cashel.
Capercaillie are resident on the wooded islands in Loch Lomond and may occasionally visit Cashel.
Black grouse is probably the bird species of greatest interest at Cashel - up to six females and seven males have been observed. These and capercaillie are very vulnerable to bird strike on deer fences and this must be taken into account in the management of the site.