This is an inferior mirage, inferior not because of any want of quality but because the mirage image is below the original object and inverted.
The pelicans are mostly in the water but their lower parts are invisible because of the 'vanishing line' effect.
At left, two rays from the pelican's head (A) reach the eye. The upper one is slightly curved downwards towards the warmer air. The lower ray from (A) is sharply curved and appears to the eye to come from a the head reflected by a mirror. Rays from point (B), lower down, do the same. Position (C) is different. Only one ray reaches the eye. Rays from lower down the pelican's body cannot reach the eye at all and so it is invisible.
The level (C) is the level of the mirage vanishing-line. The 'real' view and inverted mirage view join at the vanishing line and the eye can see no details of the scene that are below it.
a 400mm lens and the camera was ~1m above the water.
Mirages can change dramatically with camera or eye height - try it.