kleptoparasites

Kleptoparasitism is a feeding strategy in which one animal steals food that another has captured or gathered. The thief, a kleptoparasite, relies on the food obtained by another animal rather than hunting or scavenging for itself. Kleptoparasitism can be obligate, meaning the parasite depends on theft for survival, or facultative, where theft is opportunistic and not essential.

The mechanism typically involves chasing, harassing, or intercepting a forager to force it to drop its prey, following feeding aggregations to scavenge leftovers, or stealing prey mid-air or at the moment of capture. Victims can be individuals of the same species or different species, and kleptoparasitism can occur in both solitary and social foragers.

In birds, kleptoparasitism is especially common among seabirds and shorebirds. Frigatebirds, jaegers, and many skuas aggressively steal catches from other birds, while gulls and terns frequently rob fish from rivals at feeding sites. This behavior can influence foraging efficiency, predator–prey dynamics, and interspecific interactions.

Beyond birds, kleptoparasitism occurs in other animal groups. Some insects, including certain brood-parasitic bees and wasps, exploit the provisioning of nests laid by hosts. Instances also appear in various mammalian and other animal systems, often as opportunistic behavior rather than a fixed life strategy.

Ecological and evolutionary considerations include the energy costs and benefits to both thief and victim, selection pressures that shape defensive behaviors (guarding, vigilance), and the potential for dynamic interactions among competing species. Kleptoparasitism illustrates diverse resource-acquisition strategies across taxa.