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Ground effect... or why birds skim across the water surface.
The ground speed effect is when the the wing of bird (or plane or anything) is so close to the ground that the wingtip vortices are perturbed resulting in less drag and more lift. In short it is significantly more efficient. As such, it is not surprising that some birds fly close to the water when going up-wind significantly more than down-wind (Finn et al. 2012, Journal of Field Ornithology). It is also interesting to note the same "study indicates that several species exploit both wind shear and ground effect to minimize energy expenditure during commuting and foraging, but that others do not, because of either complexity of habitat morphology or the demands of their foraging ecology."
So next time you want to take a pic of a bird skimming the water... find out the wind direction, place yourself accordingly and hope your subject obeys this rule! :)
The spot-billed pelican or grey pelican, is a member of the pelican family. It breeds in southern Asia from southern Pakistan across India east to Indonesia. It is a bird of large inland and coastal waters, especially large lakes. At a distance they are difficult to differentiate from other pelicans in the region although it is smaller but at close range the spots on the upper mandible, the lack of bright colours and the greyer plumage are distinctive.
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