The avifauna of the island has recently been described in an authoritative text (Hope Jones & Whalley 2004) and will not be detailed here.
The island is a notable stronghold for a number of species.
Anglesey supports virtually all of the Welsh breeding tern colonies (with the exception of the little terns of Gronant (near Prestatyn) and the common terns of Shotton pools on the English border). These include arctic and common terns at The Skerries, Ynys Feurig, the Inland Sea and Cemlyn Bay, the latter site also supporting a huge sandwich tern colony. Roseate terns formerly used these areas regularly but are currently only occasional breeders here. Welsh roseate terns appear to be part of larger Irish Sea breeding population, which mostly occupy Rockabill island in Dublin Bay. Common and arctic tern colonies on Llyn Alaw reservoir and Ynys Gorad Goch (between the two bridges on the Menai Strait) have collapsed in the past decade, probably due to increased levels of disturbance.
The chough has a stronghold on the north and west coast of the island and especially on Holy Island where a Special Protection Area comprising Glannau Ynys Gybi and Glannau Rhoscolyn is designated for this species. This red-billed, red-legged member of the crow family is a familiar and popular sight over Holyhead Mountain and adjacent farmland.
Seabird breeding colonies include Puffin island (Ynys Seiriol), with cormorant (for which this is a Special Protection Area) shag, guillemot, razorbill, black guillemot, kittiwake, fulmar, herring gull, greater and lesser black-backed gulls, some suspiciously loitering eider duck and of course a few puffin. In the 18th century, the puffins here were compared to swarms of bees in their abundance, but the arrival of the brown rat in about 1816 coincided with their steady decline since then. Numbers today are rarely more than a score, though the birds are difficult to census, nesting deep in cracks at the top of the cliffs.
Guilemot and razorbill are prominent at South Stack, the RSPB reserve, along with a handfull of puffin, kittiwake, fulmar and gulls. Smaller seabird colonies are scattered elsewhere such as cormorants at Fedw Fawr (Penmon) and Ynys yr Adar (Newborough) puffins with the terns of The Skerries.Oystercatcher and shelduck are prominent and ubiqitous birds of the coast along with herring gull, greater and lesser black-bakced gulls. However, the large breeding gull colonies of Newborough Warren, Puffin Island and Bodorgan headland have collapsed, probably due to predation (fox) and disease (botulism).
Southwest Anglesey is a stronghold for the barn owl, the wet meadows associated with the sluggish drainage of this area providing abundance prey of water vole, bank vole and rats. The use of persistent rodenticides has been implicated it the decline of barn owl elsewhere, but the increased traffic speed of the A55 expressway is probably at least as critical here, with a dramatic increase in road casualties. Tawny owl is common where woodland occurs. Little owl and short eared owl also occur.
Peregrine are widespread around the coast and at other locations offering cliff nesting sites. Buzzards have recolonised the island in the last 2 decades and are now reasonably common. Hen harrier and occasional marsh harrier winter on the dunes and marshes but hopes that marsh harrier would breed here have so far proved unfounded.
Tree sparrow persist in a few locations near Brynsiencyn and south of Llyn Alaw reservoir.
Breeding populations of lapwing, curlew and other ground nesting birds have collapsed in recent decades. Partly this reflects the decline of these breeding species nationally, but also the arrival (or, more likely, return) of ground predators - foxes since the early 1970s and polecat sometime during the 1990s.
Jones P.H. & Whalley P. (2004) Birds of Anglesey / Adar Mon, Menter Mon, Llangefni.