Kleptoparasitism or cleptoparasitism (literally, parasitism by theft) is a form of feeding in which one animal takes prey or other food from another that has caught, collected, or otherwise prepared the food, including stored food (as in the case of cuckoo bees, which lay their eggs on the pollen masses made by other bees). The term is also used to describe the stealing of nest material or other inanimate objects from one animal by another.
The kleptoparasite gains either by obtaining prey or other objects that it could not obtain itself, or by saving the time and effort required to obtain it. However, the kleptoparasite may run the risk of injury from the victim if the latter is able to defend its property.
Kleptoparasitism may be intraspecific (the parasite is the same species as the victim) or interspecific (the parasite is a different species). In the latter case, the parasites are commonly close relatives of the organisms they parasitize ("Emery's Rule").
Animals that have extraordinarily specialized feeding methods are often targets of kleptoparasitism. For example, oystercatchers are unusual in being able to break through the shells of mussels; adult oystercatchers suffer intraspecific kleptoparasitism from juveniles that are not yet strong or skillful enough to open mussels easily. Diving birds that bring their prey to the surface suffer interspecific kleptoparasitism from gulls, which are unable to fetch fish from the sea floor themselves. Chinstrap penguins also actively engage in kleptoparasitism, being known to steal rocks and other nest materials from members of their colony for use in their own nest.