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Egg predation is a feeding strategy in many groups of
animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...
s (ovivores) in which they consume
egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...
s. Since an egg represents a complete
organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fung ...
at one stage of its
life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring *Life-cycle hypothesis, ...
, eating an egg is a form of
predation Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
, the killing of another organism for food. Egg predation is found widely across the animal kingdom, including in
fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
, birds,
snake Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joints ...
s,
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s, and
arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, o ...
s. 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
raven A raven is any of several larger-bodied bird species of the genus ''Corvus''. These species do not form a single taxonomic group within the genus. There is no consistent distinction between "crows" and "ravens", common names which are assigned t ...
s and
gull Gulls, or colloquially seagulls, are seabirds of the family Laridae in the suborder Lari. They are most closely related to the terns and skimmers and only distantly related to auks, and even more distantly to waders. Until the 21st century, ...
s have spread, threatening ground-nesting birds such as
sage grouse Sage-grouse are grouse belonging to the bird genus ''Centrocercus.'' The genus includes two species: the Gunnison grouse (''Centrocercus minimus'') and the greater sage-grouse (''Centrocercus urophasianus''). These birds are distributed through ...
and
tern Terns are seabirds in the family Laridae that have a worldwide distribution and are normally found near the sea, rivers, or wetlands. Terns are treated as a subgroup of the family Laridae which includes gulls and skimmers and consists of ...
s. 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 Parasitoid wasps are a large group of hymenopteran superfamilies, with all but the wood wasps (Orussoidea) being in the wasp-waisted Apocrita. As parasitoids, they lay their eggs on or in the bodies of other arthropods, sooner or later causin ...
which grows inside the egg of another insect.


Ecological relationship

Egg predation is an ecological relationship in which an animal (a
predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...
) hunts for and eats the eggs of another (prey) species. This reduces the
evolutionary fitness Fitness (often denoted w or ω in population genetics models) is the quantitative representation of individual reproductive success. It is also equal to the average contribution to the gene pool of the next generation, made by the same individua ...
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 The European golden plover (''Pluvialis apricaria''), also known as the European golden-plover, Eurasian golden plover, or just the golden plover within Europe, is a largish plover. This species is similar to two other golden plovers: the Ameri ...
, ''Pluvialis apricaria'': in Norway 78.2% of nests of this species were preyed on. Experimental removal of two nest and egg predators,
red fox The red fox (''Vulpes vulpes'') is the largest of the true foxes and one of the most widely distributed members of the order Carnivora, being present across the entire Northern Hemisphere including most of North America, Europe and Asia, plus ...
and
carrion crow The carrion crow (''Corvus corone'') is a passerine bird of the family Corvidae and the genus ''Corvus'' which is native to western Europe and the eastern Palearctic. Taxonomy and systematics The carrion crow was one of the many species orig ...
, raised the percentage of pairs that fledged young from c. 18% to c. 75%. Population increases among many generalist predators such as buzzard,
badger Badgers are short-legged omnivores in the family Mustelidae (which also includes the otters, wolverines, martens, minks, polecats, weasels, and ferrets). Badgers are a polyphyletic rather than a natural taxonomic grouping, being united by ...
, carrion crow,
pine marten The European pine marten (''Martes martes''), also known as the pine marten, is a mustelid native to and widespread in most of Europe, Asia Minor, the Caucasus and parts of Iran, Iraq and Syria. It is listed as Least Concern on the IUCN Red List ...
,
raven A raven is any of several larger-bodied bird species of the genus ''Corvus''. These species do not form a single taxonomic group within the genus. There is no consistent distinction between "crows" and "ravens", common names which are assigned t ...
, 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 Corvidae is a cosmopolitan family of oscine passerine birds that contains the crows, ravens, rooks, jackdaws, jays, magpies, treepies, choughs, and nutcrackers. In colloquial English, they are known as the crow family or corvids. Currently, ...
such as ravens are intelligent and able to develop novel foraging behaviours. Within the 21st century,
little raven The little raven (''Corvus mellori'') is a species of the family Corvidae that is native to southeastern Australia. An adult individual is about in length, with completely black plumage, beak, and legs; as with all Australian species of ''Cor ...
s have learnt to depredate
little penguin The little penguin (''Eudyptula minor'') is a species of penguin from New Zealand. They are commonly known as little blue penguins or blue penguins owing to their slate-blue plumage and are also known by their Māori name . The Australian l ...
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 Dame Jane Morris Goodall (; born Valerie Jane Morris-Goodall on 3 April 1934), formerly Baroness Jane van Lawick-Goodall, is an English primatologist and anthropologist. Seen as the world's foremost expert on chimpanzees, Goodall is best know ...
noted that some birds and mammals used tools to break eggs.
Egyptian vulture The Egyptian vulture (''Neophron percnopterus''), also called the white scavenger vulture or pharaoh's chicken, is a small Old World vulture and the only member of the genus ''Neophron''. It is widely distributed from the Iberian Peninsula an ...
s both drop small eggs to break them, and throw stones at
ostrich egg The egg of the ostrich (genus ''Struthio'') is the largest of any living bird. The shell has a long history of use by humans as a container and for decorative artwork. The eggs are not commonly eaten. Biology The female common ostrich lays her f ...
s which are too large to pick up. Several species of
mongoose A mongoose is a small terrestrial carnivorous mammal belonging to the family Herpestidae. This family is currently split into two subfamilies, the Herpestinae and the Mungotinae. The Herpestinae comprises 23 living species that are native to s ...
s throw eggs at rocks, or pick eggs up and drop them on rocks.


Specialist egg predators

Some colubrid
snake Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joints ...
s such as the Formosa kukri snake '' Oligodon formosanus'' and the marbled sea snake '' Aipysurus eydouxii'' specialise in egg predation. These snakes have atrophied
venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...
glands and their fangs are ineffective. The marbled sea snake also has a deletion mutation in its
three-finger toxin Three-finger toxins (abbreviated 3FTx) are a protein superfamily of small toxin proteins found in the venom of snakes. Three-finger toxins are in turn members of a larger superfamily of three-finger protein domains which includes non-toxic prot ...
gene, reducing its venom toxicity by between 50- and 100-fold. These changes have been explained as an evolutionary
adaptation In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
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 Thrips ( order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Different thrips species feed mostly on plants by puncturing and sucking up the contents, although a few are ...
, ''Mirothrips arbiter'', from Brazil is an obligate egg predator; it breeds in colonies of paper wasps (
Polistinae The Polistinae is a subfamily of eusocial wasps belonging to the family Vespidae. They are closely related to the more familiar wasps (“yellowjackets” as they are called in North America) and true hornets of the subfamily Vespinae, containi ...
); both its larvae and its adults feed on the eggs of the wasp.


Strategies against egg predation

r/K selection theory In ecology, ''r''/''K'' selection theory relates to the selection of combinations of traits in an organism that trade off between quantity and quality of offspring. The focus on either an increased quantity of offspring at the expense of indivi ...
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 The Miridae are a large and diverse insect family at one time known by the taxonomic synonym Capsidae. Species in the family may be referred to as capsid bugs or "mirid bugs". Common names include plant bugs, leaf bugs, and grass bugs. It is th ...
, pirate bugs, and
thrips Thrips ( order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Different thrips species feed mostly on plants by puncturing and sucking up the contents, although a few are ...
, 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. Bird nests are vulnerable to egg predation, especially for those such as eider ducks which nest on the ground. In response to the robbing of eggs from eider duck nests, half the individuals started a fresh clutch of eggs in a new nest; they always avoided the area around the robbed nest. Tree-nesting birds, too, are depredated by snakes, mammals, and birds, particularly in tropical forests. In Costa Rica, the rate of nest predation on artificial nests was greatest at intermediate altitudes (between 500 and 650 metres), with a decline in predation at higher altitudes to 2,740 metres. This may explain why many bird species migrate uphill to breed. Egg predation by snakes is rarely directly opposed, but the Asian long-tailed skink '' Eutropis longicaudata'' aggressively protects its eggs from the Formosa kukri snake, '' Oligodon formosanus''. Bird eggs are coloured and patterned, seemingly primarily for
camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
to deceive the eyes of egg predators; for example,
Eurasian curlew The Eurasian curlew or common curlew (''Numenius arquata'') is a very large wader in the family Scolopacidae. It is one of the most widespread of the curlews, breeding across temperate Europe and Asia. In Europe, this species is often referred t ...
s nest among tall grasses and have eggs that are green and spotted like their background, as well as being defended by the adults; in contrast, the eggs of
little ringed plover The little ringed plover (''Charadrius dubius'') is a small plover. The genus name ''Charadrius'' is a Late Latin word for a yellowish bird mentioned in the fourth-century Vulgate. It derives from Ancient Greek ''kharadrios'' a bird found in river ...
s, laid on pebbly beaches, are pale and speckled, hard to see among small stones.


Fossil record

Egg predation may be an ancient feeding strategy. A fossil of the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
snake '' Sanajeh'' of western India, found coiled around an egg and a hatchling sauropod dinosaur, was most likely a predator of sauropod nest sites including of eggs. ''Sanajeh'' was about in length; its skull was long. ''
Oviraptor ''Oviraptor'' (; ) is a genus of oviraptorid dinosaur that lived in Asia during the Late Cretaceous period. The first remains were collected from the Djadokhta Formation of Mongolia in 1923 during a paleontological expedition led by Roy Chapman ...
'' was a late Cretaceous dinosaur; it was given its name, meaning "egg thief", as it was initially thought to be an egg predator; later, it was discovered to have been brooding its own eggs, and its toothless jaws have been reinterpreted as adapted to a different diet, perhaps of leaves. Sauropod dinosaurs, some of the largest animals that have ever lived, appear surprisingly to have followed an r-strategy, producing a large number of hard-shelled eggs. This contrasts with the K-strategy, in whales, which are marine
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s of comparable size. Whales produce few eggs which develop internally, receiving a high level of parental investment. A possible cause is that egg size is limited: extrapolating from the sizes of bird eggs relative to adult body weight, a 10 tonne sauropod would produce eggs weighing some 333 kilograms, far over the limit (around 10 kilograms) which an egg shell could support. If that is correct, then sauropods inevitably had to follow an r-strategy with many relatively small eggs, not specifically a response to egg predation.


Interaction with humans


Damage to commercial fisheries

Among fish, egg predation by species such as
haddock The haddock (''Melanogrammus aeglefinus'') is a saltwater ray-finned fish from the family Gadidae, the true cods. It is the only species in the monotypic genus ''Melanogrammus''. It is found in the North Atlantic Ocean and associated seas w ...
(''Melanogrammus aeglefinus'') can contribute to the decline in commercially-important fish populations such as of Atlantic herring (''Clupea harengus''). This effect can be important in attempts to restore fisheries damaged by
overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stock), resulting in the ...
.


Introduced and invasive species

Invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...
frequently prey on eggs and young of native species. The harlequin ladybird ''
Harmonia axyridis ''Harmonia axyridis'' is a large lady beetle or ladybug species that is most commonly known as the harlequin, multicoloured Asian, or Asian lady beetle. This is one of the most variable species in the world, with an exceptionally wide range of col ...
'' eats eggs of species including other ladybirds, such as the two-spot ladybird ''
Adalia bipunctata ''Adalia bipunctata'', the two-spot ladybird, two-spotted ladybug or two-spotted lady beetle, is a carnivorous beetle of the family Coccinellidae that is found throughout the holarctic region. It is very common in western and central Europe. It ...
''. Females of the prey species laid eggs with higher amounts of defensive alkaloids when egg predation was occurring. Egg predation is an especially severe threat to colonies of ground-nesting seabirds. These have often selected offshore islands as nest sites, as the islands historically had fewer predators than the mainland. Accidental introductions of predator species have upset seabird reproduction, as the predators have a concentrated supply of food in the form of eggs on the ground or in burrows, and can increase rapidly. Offshore island populations in Australasia have been widely affected by exotic species such as rats, arriving by ship from Eurasia. Native species, such as blotched blue-tongue lizards, '' Tiliqua nigrolutea'', and water-rats, '' Hydromys chrysogaster'', may also have an impact on seabirds like the short-tailed shearwater, '' Ardenna tenuirostris'' on islands off
Tasmania ) , nickname = , image_map = Tasmania in Australia.svg , map_caption = Location of Tasmania in AustraliaCoordinates: , subdivision_type = Country , subdi ...
, though predation rates were relatively low. Eggs were usually taken when burrows were unattended, implying that the parent birds were able to defend their eggs effectively against these predators.


Control of egg predators

Where populations of concern are threatened by egg predators, conservationists may attempt to control the predators so as to allow the prey species to recover. In the case of bird predators, one approach has been to put out bait eggs treated with the slow-acting avicide DRC-1339. This has for example controlled
raven A raven is any of several larger-bodied bird species of the genus ''Corvus''. These species do not form a single taxonomic group within the genus. There is no consistent distinction between "crows" and "ravens", common names which are assigned t ...
s which threatened ground-nesting
sage grouse Sage-grouse are grouse belonging to the bird genus ''Centrocercus.'' The genus includes two species: the Gunnison grouse (''Centrocercus minimus'') and the greater sage-grouse (''Centrocercus urophasianus''). These birds are distributed through ...
, and among seabirds,
gulls Gulls, or colloquially seagulls, are seabirds of the family Laridae in the suborder Lari. They are most closely related to the terns and skimmers and only distantly related to auks, and even more distantly to waders. Until the 21st centur ...
which threatened nesting
tern Terns are seabirds in the family Laridae that have a worldwide distribution and are normally found near the sea, rivers, or wetlands. Terns are treated as a subgroup of the family Laridae which includes gulls and skimmers and consists of ...
colonies.
Sea turtle Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerhead, ...
s breed by laying and burying their eggs on nesting beaches, so the control of egg predators at these sites may be effective in assisting the recovery of turtle populations.


See also

* Balut *
Seed predation Seed predation, often referred to as granivory, is a type of plant-animal interaction in which granivores (seed predators) feed on the seeds of plants as a main or exclusive food source,Hulme, P.E. and Benkman, C.W. (2002) "Granivory", pp. 132 ...


References

{{Feeding Predation