A couple of hours on the beach.
After getting information from Andy Patterson about two Red-breasted Mergansers (Serreta Mediana / Mergus serrator) on the sea from the sea watch point. I arrived at the sea front end of the urbanization and set up the scope on the rocks nearby. The first bird seen was a 1st winter Oystercatcher (Ostrero Euroasiático / Haematopus ostralegus) which was feeding on the Common Mussels (Mytilus edulis) on the rock. Also seen from here was a winter plumaged Sandwich Tern (Charrán Patinegro / Sterna sandvicensis) which sat on the rocks next to the Oystercatcher till a wave forced both of them up on to the beach. Out on the sea there was a group of 4 Common Scoters (Negrón Común / Melanitta nigra), a single Razorbill (Alca Común / Alca torda), Northern Gannets (Alcatraz Atlántico / Morus bassanus), Mediterranean (Gaviota Cabecinegra / Larus melanocephalus), Yellow-legged (Gaviota Patiamarilla / Larus Michahellis), Lesser-black backed (Gaviota Somria / Larus fuscus) and Black-headed Gulls (Gaviota Riedora / Larus ridibundus), along with more Sandwich Terns and 8+ Northern Pintail (Ánade Rabudo / Anas acuta). On the river a couple of Audouin's Gull (Gaviota de Audouin / Larus audouinii) were roosting and Grey Heron (Garza Real / Ardea cinerea) and Little Egret (Garceta Común / Egretta garzetta) were stalking fish from the reedy margins. On the sand bar a group of 20+ Sanderling (Correlimos Tridáctilo / Calidris alba) one of my favorite waders were roosting along with a couple of Common Sandpipers (Andarrios Chico / Actitis hypoleucos).I then scanned along the shore line and picked up the two Mergansers down by the far sea watch point so I got in the car and made my way down to the reserve entrance, on the walk down to the beach numerous Monk Parakeets (Cotorra Argentina / Myiopsitta monachus) flew over, also seen were Zitting Cisticola (Buitrón / Cisticola juncidis), White Wagtail (Lavandera Blanca / Montacilla alba), Spotless Starling (Estornino Negro / Sturnus unicolor), Skylark (Alondra Común / Alauda arvensis), Snipe (Agachadiza Común / Gallinago gallinago), Robin (Petirrrojo / Erithacus rubecula), Linnet (Pardillo Común / Carduelis cannabina), House Sparrow (Gorrión Común), Hoopoe (Abubilla / Upupa epops), Grey Wagtail (Lavandera Cascadena / Motacilla cinerea), Goldfinch (Jilguero / Carduelis carduelis), Great Cormorant (Cormorán Grande / Phalacrocorax carbo), Crested Lark (Cogujada Común / Galerida cristata) and Crag Martin (Avión Roquero / Ptyonoprogne rupestris). Whist passing the main pool a quick glance added Greenshank (Archibebe Claro / Tringa nebularia) x3, Spoonbill (Espátula Común / Platalea leucorodia) x3 and a couple of Northern Shoveler (Cuchara Común / Anas clypeata). Once on the beach, the two birds were soon picked up down near the river mouth, so I walked down to the sea watch point and had some nice views of them. I managed a couple of poor record shots and also picked up out on the sea another couple of Common Scoter. I then walked back via the raised ridge pasted the two hides to the car. On the way I picked up a couple of both Booted Eagle (Aguililla Calzada / Hieraaetus pennatus) and Marsh Harrier (Aguilucho Lagunero Occidental / Circus aeruginosus) but did not see the expected Osprey. On the pools to the left of the bank several more Sanderling were seen along with Black-winged Stilt (Ciguenuela Común / Himantopus himantopus), Dunlin (Correlimos Común / Calidris alpina), Ringed Plover (Chorlitejo Grande / Charadrius hiaticula), Common Pochard (Porrón Europeo / Aythya ferina), Mallard (Anade Azulón / Anas platyrhynchos), Eurasian Coot (Focha Común / Fulica atra) and Common Moorhen (Gallineta Común / Gallinula Chloropus). On the other drier side of the bank Black Redstart (Colirrojo Tizón / Phoenicurus ochruros), Cetti's Warbler (Ruisenor Bastardo / Cettia cetti), Common Chiffchaff (Mosquitero Común / Phylloscopus collybita), Common Stonechat (Tarabilla Común / Saxicola torquata), Greenfinch (Verderón Común / Carduelis chloris), Common Kestrel (Cernicalo Vulga / Falcotinnunculus), Meadow Pipit (Bistita Común / Anthus pratensis) and Serin (Verdecillo / Serinus serinus) were all recorded. Whilst I was wondering I also saw a single female Red-veined Dart (Sympetrum fonscolombii) and quite a few Painted Lady's (Vanessa cardui).
Photographs from the top: Oystercatcher (Ostrero Euroasiático / Haematopus ostralegus), Sandwich Tern (Charrán Patinegro / Sterna sandvicensis) and two record shots of the Red-breasted Mergansers (Serreta Mediana / Mergus serrator).