The Wildfowl and Wetlands Trust is a wonderfully friendly and informational organisation specifically aimed at waterbirds. On a par with the BTO, if you join any Birding associations these are the two to go for.
Birding in Portugal
Quinta do Barranco da Estrada 7665-880 Santa Clara a Velha Portugal
Email : Phone : (+351) 283 933 065 Chamada para rede fixa
Whatsapp : (+351) 938 386 326 Chamada para rede movél nacional