It may well have been a Caspian Tern, Dave, as 4 were seen off Calaburras this last week and another at the Guadalhorce. They are very big, Lesser Black-backed Gull size, and dwarf Black-headed Gulls and yes, they will dip the huge bill into the water as they fly into the wind. White-winged Blacks are smaller than Black Terns and they look very white on the upper wing surfaces in comparison with Black and Whiskered Terns.
Reports of strong winds didn't seem to be correct as Colin, Sandra, Val, Chris, Gilly and I parked at the first causeway at Las Norias. The water level was still high. Colin and Chris spotted some overflying Avocets before I could get out of the car. The only other waders seen were 3 Common Sandpipers, a Green Sandpiper and some Black-winged Stilts. Waterbirds consisted of Gadwall, Red Crested Pochards, Mallard and ducklings, Great Crested Grebe, Coot and Moorhen. More interestingly were the terns. Saw a large one flying away from us, skimming the water, occasionally dipping its bill in to pick up, presumably, insects. Is this Caspian Tern behaviour? Also seen were Whiskered Tern together with either a Black Tern or possibly the reported White-Winged (Black) Tern. Unfortunately it fled to the far end of the lake, never to be seen again! Sandra then spotted movement in the reeds quite close to us - a Purple Swamphen. Also seen were a Yellow Wagtail, large flocks of Cattle Egrets and both Black-headed and Yellow Legged Gulls.
At the second causeway, we saw another Squacco, White-headed Duck, Shoveler, Pochard and Little Egret. A Marsh Harrier put a huge flock of Cattle Egrets to flight. The Booted Eagle high above us was a bonus. Thank you, Gilly.