1. Gruppo Ornitologico Maremmano, Grosseto, Italy
2. Dipartimento di Biologia, Università di Pisa, Pisa, Italy
3. Servicio de Biodiversidad, Gobierno de Canarias, Edf. Servicios Múltiples II, Las Palmas de Gran Canaria, Canary Islands, Spain
4. C/. Eduardo Zamacois, 13-3°A, Santa Cruz de Tenerife, Canary Islands, Spain
5. Canary Islands' Ornithology and Natural History Group (GOHNIC), La Malecita, Buenavista del Norte, Tenerife, Canary Islands, Spain