Hi Neil, the beginning of May has to be one of the best times to come. There is a great book "A Birding Tourist's Guide to Mallorca" which details all the major sites to visit. I am not sure where you can get a copy of it but others on this site I hope will let you know and will also help with information. It all depends where you are staying and if you will have transport. The main reserve at s'Albufera is a must, the number of species seen is excellent. Also Albufereta marsh, the watchtower at Albercutx is the best place for raptor migration, a walk down the Bóquer Valley is very productive and can turn up a few surprises, the Central Plain is often ignored by visiting birders but will probably have a few Lesser kestrels and Red-footed falcons staying for a while. You will have to know exactly where to go though, it is a big area! The list of birds to see is amazing and includes Eleanora's falcons, Scops owl, Woodchat shrike, Balearic warbler, Moustached warbler, Sardinian warbler, Hoopoe, Alpine swift, Pallid swift, both Griffon and Black vultures can be seen but mostly in the mountains. Cuber reservoir would be the best place to go with the added possibility of seeing Rock thrush and Subalpine warbler, well, the list goes on. If there is a specific bird you want to see let me know. Anything else also, just post here and I and others will help you. Good luck and do post your sightings when the time comes. All the best, Mike