The Aran Islands is an amazing place for wildlife.
The Cooku can be heard from the end of April onwards through to May and June. You not only have a good chance of seeing the cooku but hearing them together in unison. You will also witness Swallows at the start of summer, the House-Martins, Curlus, plenty of Pheasants, along with different types of Seabirds along the cliff edges, including Gannets. There are also Lapwings which are also called Plubbers, including golden Plubbers which are in an area of the Inis Mor island all of their own. You will also find the smaller Plubbers, ringed Plubbers, Herrons and a Herron league where they all nest in one place on the island. You might occasionally see a Perawinged Falcon whom breed on the cliffs on Inis Meain, and you might see other types of bird of prey as well. It is an amazing place for wildlife in itself.
There are other types of living beings on the island, The butterflies are various here and there are some experts who may be able to help you if you require more information . If you are lucky you might also see a Stote. Otters who live along the coastline are hard to see as they come out at night. You will find pleanty of rabbits (no Hairs or foxes) . You will also come across lizards sunning themselves on the rocks in summer whom are a very ancient species of animal.
We have the most amazing wild flowers because the landscape is similar to the Burren. The beautiful Gentian comes out in April, as well as not only the primroses but the cowslips and even the oxalic , the bloody cranes-ville, birds for trefoil, and beautiful examples of fuchsia growing all over the island. If you are into flowers the Aran Islands is a mecca especially if you come in May. So all in all the wildlife is wonderful especially if you get the fine weather and have a good look around. Bring your binoculars with you or your magnifying glass or camera and make the most of it.