Any help in finding this species and other nice birds and birding places in the area would be appreciated.
To be very honest you would do best to purchase a copy of 'A Birdwatching Guide to Donana' by John Butler published by Trafford Publishing ISBN: 978-1-4251-2192-1 (Alternatively visit their website www.trafford.com to purchase).
I think the above is your best option and will give you all the information you need, plus some ideas of where else to look in the area.
I second Peter's excellent advice. I was there four weeks ago and even though I know the Northern marshes quite well, used the book extensively. The area around El Rocio is incredibly dry at the moment and the rice fields in the northern marshes were the only areas containing water.
Incidentally, many of the firmer roads in the Northern marshes have been "streetviewed" on Google Earth, so you can see such sights as el Cortijo de los Madrigales (site North 12 in John's book) as wrap around 360º photos!
Also, if visiting Rio Tinto concentrate on the fabulous museum. No point in going on the mine excursion; it is not what you would expect. Train ride was very enjoyable so make sure you arrive in time for 1 o'clock departure (if going).
Hope you enjoy your visit to Andalucia and welcome to the "Club".