What is food exchange?  In bird photography, it is being referred to an act of transferring food from one bird to another for instance during feeding the young but more specifically focusing the mating ritual that takes place among raptors like the White-tailed Kite, Peregrine Falcon, and the Northern Harrier where the act takes place in mid-air.  Basically, the male would bring the fresh catch and pass on to the female in mid-air and the act continues throughout the season with the parents passing to food to their youngs in mid-air.

As its other common names suggest, the osprey’s diet consists almost exclusively of fish. It possesses specialized physical characteristics and exhibits unique behaviour to assist in hunting and catching prey. As a result of these unique characteristics, it has been given its own taxonomic genus, Pandion and family, Pandionidae. Four subspecies are usually recognized, one of which has recently been given full species status (see below). Despite its propensity to nest near water, the osprey is not classed as a sea eagle. Source: Wikipedia  

As its other common names suggest, the osprey’s diet consists almost exclusively of fish. It possesses specialized physical characteristics and exhibits unique behaviour to assist in hunting and catching prey. As a result of these unique characteristics, it has been given its own taxonomic genus, Pandion and family, Pandionidae. Four subspecies are usually recognized, one of which has recently been given full species status (see below). Despite its propensity to nest near water, the osprey is not classed as a sea eagle. Source: Wikipedia