Handa's seabird colonies are the reason most visitors make the crossing from Tarbet. The north and west cliffs hold guillemots, razorbills, kittiwakes, fulmars, and shags in vast numbers, while a healthy puffin population burrows into the turf along the clifftop margins. The island is particularly important for razorbills, which use it as one of their major UK breeding sites. All species arrive from around April, reach peak activity through June and July, and are mostly gone by early August.
Away from the cliffs, the heather moorland supports great skuas and great black-backed gulls. The skuas patrol aggressively, and the Scottish Wildlife Trust wardens advise carrying a stick above your head when crossing the moorland — the birds target the highest point. It sounds alarming but the experience of being shadowed by a bonxie on full attack is one of the more memorable wildlife encounters in Scotland.