Animal feeding behaviour

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Feeding is the process by which organisms, typically animals, obtain food. Terminology often uses either the suffix -vore from Latin vorare, meaning 'to devour', or phagy, from Greek φαγειν, meaning 'to eat'.

Evolutionary history[]

The evolution of different feeding strategies is varied with some feeding strategies evolving several times in independent lineages. In terrestrial vertebrates, the earliest forms were large amphibious piscivores 400 million years ago. While amphibians continued to feed on fish and later insects, reptiles began exploring two new food types, other tetrapods (carnivory), and later, plants (herbivory). Carnivory was a natural transition from insectivory for medium and large tetrapods, requiring minimal adaptation (in contrast, a complex set of adaptations was necessary for feeding on highly fibrous plant materials).^[1]

Evolutionary adaptations[]

The specialization of organisms towards specific food sources is one of the major causes of evolution of form and function, such as:

mouth parts and teeth, such as in whales, vampire bats, leeches, mosquitos, predatory animals such as felines and fishes, etc.
distinct forms of beaks in birds, such as in hawks, woodpeckers, pelicans, hummingbirds, parrots, kingfishers, etc.
specialized claws and other appendages, for apprehending or killing (including fingers in primates)
changes in body colour for facilitating camouflage, disguise, setting up traps for preys, etc.
changes in the digestive system, such as the system of stomachs of herbivores, commensalism and symbiosis

Classification[]

Method of feeding[]

By mode of ingestion[]

There are many modes of feeding that animals exhibit, including:

Filter feeding - obtaining nutrients from particles suspended in water
Deposit feeding - obtaining nutrients from particles suspended in soil
Fluid feeding - obtaining nutrients by consuming other organisms' fluids
Bulk feeding - obtaining nutrients by eating all of an organism
Ram feeding and suction feeding - ingesting prey via the fluids around it.

By mode of digestion[]

Extra-cellular digestion - excreting digesting enzymes and then reabsorbing the products
Myzocytosis - one cell pierces another using a feeding tube, and sucks out cytoplasm
Phagocytosis - engulfing food matter into living cells, where it is digested

By food type[]

Polyphagy is the ability of an animal to eat a variety of food, whereas monophagy is the intolerance of every food except of one specific type (see generalist and specialist species).

Another classification refers to the specific food animals specialize in eating, such as:

Carnivore - the eating of animals
- Haematophagy - eating blood
- Insectivore - eating insects
  - Myrmecophagy - eating ants and/or termites
- Keratophagy or Ceratophagy - eating horny material, such as wool by cloths moths, or snakes eating their own skin after ecdysis.
- Lepidophagy - eating fish scales
- Man-eater - eating humans
- Molluscivore - eating molluscs
- Mucophagy - eating mucus
- Ophiophagy - eating snakes
- Piscivore - eating fish
- Avivore - eating birds
- Spongivore - eating sponges
Herbivore - the eating of plants
- Folivore - eating leaves
- Frugivore - eating fruits
- Graminivore - eating grasses
- Granivore - eating seeds
- Nectarivore - eating nectar
- Palynivore - eating pollen
- Xylophagy - eating wood
Omnivore - the eating of both plants and animals
Fungivore - the eating of fungus
Bacterivore - the eating of bacteria

The eating of non-living or decaying matter:

Coprophagy - eating faeces
Detritivore - eating decomposing material
Geophagy - eating inorganic earth
Osteophagy - eating bones
Scavenger - eating carrion

There are also several unusual feeding behaviours, either normal, opportunistic, or pathological, such as:

Cannibalism - feeding on members of the same species
Self-cannibalism - feeding on parts of one's own body (see also autophagy)
Sexual cannibalism - cannibalism after mating
Kleptoparasitism - stealing food from another animal
Trophallaxis - eating food regurgitated by another animal
Oophagy - eating eggs
Ovophagy - eating embryos
Paedophagy - eating young animals
Pica - appetite for largely non-nutritive substances, eg clay or hair, sometimes in pregnancy or in pathological states, typically a medical or veterinary concern.
Placentophagy - eating placenta