Egg predation is a feeding strategy in many groups of animals (ovivores) in which they consume eggs. Since an egg represents a complete organism at one stage of its life cycle, eating an egg is a form of predation, the killing of another organism for food.
Egg predation is found widely across the animal kingdom, including in fish, birds, snakes, mammals, and arthropods. Some species are specialist egg predators, but many more are generalists which take eggs when the opportunity arises.
Humans have accidentally or intentionally introduced egg predators such as rats to places that had been free of them, causing damage to native species such as ground-nesting seabirds. Predatory birds such as ravens and gulls have spread, threatening ground-nesting birds such as sage grouse and terns. Measure to control such predators include the use of poisoned bait eggs.
Definitions
An ovivore or ovivorous animal is one that eats eggs, from Latin , egg, and , to devour. An obligate ovivore or egg predator is an animal that feeds exclusively on eggs. This is different from an egg parasite, an animal such as a parasitic wasp which grows inside the egg of another insect.
Ecological relationship
Egg predation is an ecological relationship in which an animal (a predator) hunts for and eats the eggs of another (prey) species. This reduces the evolutionary fitness of the parents whose eggs are preyed on.
Generalist egg predators
Generalist predators can have a substantial effect on ground-nesting birds such as the European golden plover, Pluvialis apricaria: in Norway 78.2% of nests of this species were preyed on. Experimental removal of two nest and egg predators, red fox and carrion crow, raised the percentage of pairs that fledged young from c. 18% to c. 75%. Population increases among many generalist predators such as buzzard, badger, carrion crow, pine marten, raven, and red fox in Scotland have contributed to the decline in several ground-nesting bird species by taking eggs, young, and sitting hen (female) birds.
Learnt behaviours for egg predation
Corvids such as ravens are intelligent and able to develop novel foraging behaviours. Within the 21st century, little ravens have learnt to depredate little penguin burrows to access the eggs on Phillip Island off southeastern Australia. About a quarter of the attacks were down the entrance hole (for short burrows only); the remainder were by digging a hole through the roof of the burrow. Ravens depredated 61% of monitored burrows.
The primatologist Jane Goodall noted that some birds and mammals used tools to break eggs. Egyptian vultures both drop small eggs to break them, and throw stones at ostrich eggs which are too large to pick up. Several species of mongooses throw eggs at rocks, or pick eggs up and drop them on rocks.
Specialist egg predators
Some colubrid snakes such as the Formosa kukri snake Oligodon formosanus and the marbled sea snake Aipysurus eydouxii specialise in egg predation. These snakes have atrophied venom glands and their fangs are ineffective. The marbled sea snake also has a deletion mutation in its three-finger toxin gene, reducing its venom toxicity by between 50- and 100-fold. These changes have been explained as an evolutionary adaptation to their diet, since venom is not required to subdue their prey, unlike in their venomous and conventionally predatory ancestors.
Among invertebrates, the aquatic piscicolid leech Cystobranchus virginicus is an egg predator. It may be an obligate egg-feeder, as it has not been seen feeding on an adult, but has been found in the nests of a variety of species of North American freshwater fish of the genera Campostoma and Moxostoma. A species of thrips, Mirothrips arbiter, from Brazil is an obligate egg predator; it breeds in colonies of paper wasps (Polistinae); both its larvae and its adults feed on the eggs of the wasp.
Strategies against egg predation
r/K selection theory implies two broad strategies for surviving predation: to reproduce so rapidly (r-strategists) that predators are unable to eliminate the prey; or to provide sufficient care (K-strategists) for a smaller number of offspring that enough of them survive to adulthood. In the case of eggs, this means that r-strategists lay large numbers of eggs, while K-strategists take care to protect a smaller number of eggs. Lacebugs of the genus Corythucha are subject to egg predation by obligate egg predators like mirid bugs, pirate bugs, and thrips, and respond to it in varying ways. C. solani mothers defend their eggs from predators, while C. marmorata buries its eggs inside leaves and distributes them in space and time.
