So, I decided reduce zoom when focus some gulls (medium of scale, around 600 mm), for better catching birds into frame. And worked!!
Another handicap was chosen shot speed. I understood that a faster speed was necesary, and went up until 1/500 sec first...
...and 1/1000 sec after. Then, gull became "freezed" enough.
Black headed Gull (Larus ridibundus)
Just in lagoon shore, a Lesser black-backed Gull, highly contrasted over dark waters, was a new oportunity for prove. On that sunny morning, light was really intense, and wanted to photograph it without "burn" the whites. Diaphragm don´t close more than F: 8 in SX50, so you must increase shot speed in those occasions when light is higher .
Lesser Black-backed Gull (Larus fuscus)
Well, as you can see, I keep on proving...