Hoarding (animal behavior)
Encyclopedia
Hoarding or caching is a type of animal behavior where an animal will store its food in times of surplus for times when food is less plentiful. The term hoarding is most typically used for rodent
s, whereas caching is more commonly used in reference to bird
s, but the behaviors in both animals groups are quite similar.
The place where the food is stored is called a cache or hoard. They are usually hidden from the sight of competing individuals of the same species as well as others.
Hoarding is done either on a long-term basis – cached on a seasonal cycle, with food to be consumed months down the line – or on a short term basis, in which case the food will be consumed over a period of one or several days.
Some common animals that cache their food are rodent
s such as hamster
s and squirrel
s, and many different bird
species, such as rook
s and woodpecker
s. The Western Scrub Jay
is noted for its particular skill at caching.
There are two types of caching behavior: larder-hoarding, where a species creates a few large caches which it often defends, and scatter-hoarding, where a species will create multiple caches, often with each individual food item stored in a unique place. Both types of caching have their advantage.
In "ripening caching" behavior, animals collect and cache food which is immediately inedible but will become "ripe" and edible after a short while. Following are some examples.
Tayra
s (a Central American weasel) have been observed to harvest whole green plantain
s, hide them, and then come back to eat them after they have ripened. This behavior gives rise to debates about whether it is entirely instinctive or if Tayras really have some concept of time where they know that fruit takes a time to ripen and that they will be hungry in the near future.
Crocodilians such as the Alligator
are predators with ineffective teeth action - they can bite prey to kill it but can't tear flesh or chew. Small enough prey are swallowed whole while for larger prey, such as a deer, the carcass is cached underwater and left to rot (or "ripen") until it is easy to eat.
Leafcutter ant
s harvest pieces of inedible leaves and then cache them in underground chambers to ripen with a fungus which is the main food for the colony.
and other seed
s. Many species of squirrel
, including the eastern gray squirrel
and the fox squirrel
, are well known for scatter hoarding. This behavior plays an important part in seed dispersal
, as those seeds that are left uneaten will have a chance to germinate
, thus enabling plants to spread their population
s effectively.
Cache spacing is the primary technique that scatter hoarders use to protect food from pilferers. By spreading the food supply around geographically, hoarders discourage competitors who happen upon a cache from conducting area-restricted searching for more of the supply. Despite cache spacing, however, hoarders are still unable to completely eliminate the threat of pilferage. However, having multiply cache sites is costly because it requires a good memory. Scatter-hoarders generally have a large hippocampus
.
Many animals are scatter hoarders, including squirrel
s, chipmunk
s, and the wood mouse
.
In larder hoarding, the hoard is large and is found in a single place termed (a larder
), which usually also serves as the nest where the animal lives. Hamster
s are famous larder hoarders. Indeed, the word "hamster" is derived from the German verb "hamstern" which means "to hoard"; similar verbs are found in various related languages (Dutch hamsteren, and Swedish hamstra). Other languages also draw a clear connection between hamsters and hoarding: Polish
chomikować, from chomik – hamster; Hebrew
hamster; oger (אוגר) comes from to hoarde; le'egor (לאגור).
A disadvantage of larder hoarding is that if a cache is raided, this is far more problematic for the animal than if it were a scatter hoarder. While the hoard is much easier to remember the location of, these larger hoards must also be more staunchly defended.
Most species are particularly wary of onlooking individuals during caching and ensure that the cache locations are secret. Not all caches are concealed however, for example shrike
s store prey items on thorns on branches in the open.
Shared or individual hoarding
Although a small handful of species share food stores, food hoarding is a solo endeavor for most species, including almost all rodents and birds. For example, a number of jays live in large family groups, but they don't demonstrate sharing of cached food. Rather, they hoard their food supply selfishly, caching and retrieving the supply in secret. (Waite, 1992) There are only two species in which kin selection has resulted in a shared food store: Beavers (Castor canadensis) and Acorn Woodpecker
s (Melanerpes formicivorous); the former live in family groups and construct winter larders of submerged branches, while the latter are unusual in that they construct a conspicuous communal larder (Koenig and Mumme, 1987).
Pilferage occurs when one animal takes food from another animal's larder.
Some species experience high levels of cache pilferage, up to 30% of the supply per day. Previous models of scatter hoarding developed by Stapanian and Smith (1978, 1984), Clarkson et al. (1986), and others, suggested the value of cached food is equal to the hoarders ability to retrieve it. (cited from Vander Wall, 2003)
Reciprocal Pilferage
It has been observed that members of certain species, such as rodents and chickadees, act as both hoarder and pilferer. In other words, pilfering can be reciprocal and, thus, tolerable. Although this kind of food caching system seems cooperative, it has been suggested that it is actually driven by the selfish interests of the individual. (Vander Wall and Jenkins, 2003)
Recaching
Animals recache the food that they've pilfered from other animal's caches.
For example, Vander Wall and Joyner (1998) found that 75% percent of radioactive Jeffery pine seeds cached by yellow pine chipmunks were found in two cache sites, 29% of the seeds were found in three sites, 9.4% were found in four sites and 1.3% were found in five sites over a 3-month period. These results, and those from other studies, demonstrate the dynamic nature of the food supplies of scatter hoarding animals.
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s, whereas caching is more commonly used in reference to bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s, but the behaviors in both animals groups are quite similar.
The place where the food is stored is called a cache or hoard. They are usually hidden from the sight of competing individuals of the same species as well as others.
Hoarding is done either on a long-term basis – cached on a seasonal cycle, with food to be consumed months down the line – or on a short term basis, in which case the food will be consumed over a period of one or several days.
Some common animals that cache their food are rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s such as hamster
Hamster
Hamsters are rodents belonging to the subfamily Cricetinae. The subfamily contains about 25 species, classified in six or seven genera....
s and squirrel
Squirrel
Squirrels belong to a large family of small or medium-sized rodents called the Sciuridae. The family includes tree squirrels, ground squirrels, chipmunks, marmots , flying squirrels, and prairie dogs. Squirrels are indigenous to the Americas, Eurasia, and Africa and have been introduced to Australia...
s, and many different bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
species, such as rook
Rook (bird)
The Rook is a member of the Corvidae family in the passerine order of birds. Named by Carl Linnaeus in 1758, the species name frugilegus is Latin for "food-gathering"....
s and woodpecker
Woodpecker
Woodpeckers are near passerine birds of the order Piciformes. They are one subfamily in the family Picidae, which also includes the piculets and wrynecks. They are found worldwide and include about 180 species....
s. The Western Scrub Jay
Western Scrub Jay
The Western Scrub-Jay , is a species of scrub-jay native to western North America. It ranges from southern Washington to central Texas and central Mexico. It comprises three distinct subspecies groups, all of which may be separate species...
is noted for its particular skill at caching.
There are two types of caching behavior: larder-hoarding, where a species creates a few large caches which it often defends, and scatter-hoarding, where a species will create multiple caches, often with each individual food item stored in a unique place. Both types of caching have their advantage.
Edible Caching vs. Ripening Caching
Sometimes caching behavior is just thought of a way to save excess edible food for later consumption - either soon to be eaten food, such as when a jaguar hangs a partially eaten prey in a tree to be eaten within a few days, or long term seasonal situations where excess food collected in a time of abundance will be eaten during scarcity times.In "ripening caching" behavior, animals collect and cache food which is immediately inedible but will become "ripe" and edible after a short while. Following are some examples.
Tayra
Tayra
The tayra , also known as the Tolomuco or Perico ligero in Central America, and San Hol or viejo de monte in the Yucatan Peninsula is an omnivorous animal from the weasel family Mustelidae. It is the only species in the genus Eira...
s (a Central American weasel) have been observed to harvest whole green plantain
Plantain
Plantain is the common name for herbaceous plants of the genus Musa. The fruit they produce is generally used for cooking, in contrast to the soft, sweet banana...
s, hide them, and then come back to eat them after they have ripened. This behavior gives rise to debates about whether it is entirely instinctive or if Tayras really have some concept of time where they know that fruit takes a time to ripen and that they will be hungry in the near future.
Crocodilians such as the Alligator
Alligator
An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. There are two extant alligator species: the American alligator and the Chinese alligator ....
are predators with ineffective teeth action - they can bite prey to kill it but can't tear flesh or chew. Small enough prey are swallowed whole while for larger prey, such as a deer, the carcass is cached underwater and left to rot (or "ripen") until it is easy to eat.
Leafcutter ant
Leafcutter ant
Leafcutter ants, a non-generic name, are any of 47 species of leaf-chewing ants belonging to the two genera Atta and Acromyrmex.These species of tropical, fungus-growing ants are all endemic to South, Central America, Mexico and parts of the southern United States.The Acromyrmex and Atta ants have...
s harvest pieces of inedible leaves and then cache them in underground chambers to ripen with a fungus which is the main food for the colony.
Hoard distribution and size
Scatter hoarding is the formation of a large number of small hoards or caches of nutsNut (fruit)
A nut is a hard-shelled fruit of some plants having an indehiscent seed. While a wide variety of dried seeds and fruits are called nuts in English, only a certain number of them are considered by biologists to be true nuts...
and other seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
s. Many species of squirrel
Squirrel
Squirrels belong to a large family of small or medium-sized rodents called the Sciuridae. The family includes tree squirrels, ground squirrels, chipmunks, marmots , flying squirrels, and prairie dogs. Squirrels are indigenous to the Americas, Eurasia, and Africa and have been introduced to Australia...
, including the eastern gray squirrel
Eastern Gray Squirrel
The eastern gray squirrel is a tree squirrel in the genus Sciurus native to the eastern and midwestern United States, and to the southerly portions of the eastern provinces of Canada...
and the fox squirrel
Fox Squirrel
The fox squirrel is the largest species of tree squirrel native to North America...
, are well known for scatter hoarding. This behavior plays an important part in seed dispersal
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
, as those seeds that are left uneaten will have a chance to germinate
Germination
Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...
, thus enabling plants to spread their population
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
s effectively.
Cache spacing is the primary technique that scatter hoarders use to protect food from pilferers. By spreading the food supply around geographically, hoarders discourage competitors who happen upon a cache from conducting area-restricted searching for more of the supply. Despite cache spacing, however, hoarders are still unable to completely eliminate the threat of pilferage. However, having multiply cache sites is costly because it requires a good memory. Scatter-hoarders generally have a large hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
.
Many animals are scatter hoarders, including squirrel
Squirrel
Squirrels belong to a large family of small or medium-sized rodents called the Sciuridae. The family includes tree squirrels, ground squirrels, chipmunks, marmots , flying squirrels, and prairie dogs. Squirrels are indigenous to the Americas, Eurasia, and Africa and have been introduced to Australia...
s, chipmunk
Chipmunk
Chipmunks are small striped squirrels native to North America and Asia. They are usually classed either as a single genus with three subgenera, or as three genera.-Etymology and taxonomy:...
s, and the wood mouse
Wood mouse
The wood mouse is a common murid rodent from Europe and northwestern Africa. It is closely related to the yellow-necked mouse but differs in that it has no band of yellow fur around the neck, has slightly smaller ears, and is usually slightly smaller overall: around 90 mm in length...
.
In larder hoarding, the hoard is large and is found in a single place termed (a larder
Larder
A larder is a cool area for storing food prior to use.Larders were commonplace in houses before the widespread use of the refrigerator.Essential qualities of a larder are that it should be:*as cool as possible*close to food preparation areas...
), which usually also serves as the nest where the animal lives. Hamster
Hamster
Hamsters are rodents belonging to the subfamily Cricetinae. The subfamily contains about 25 species, classified in six or seven genera....
s are famous larder hoarders. Indeed, the word "hamster" is derived from the German verb "hamstern" which means "to hoard"; similar verbs are found in various related languages (Dutch hamsteren, and Swedish hamstra). Other languages also draw a clear connection between hamsters and hoarding: Polish
Polish language
Polish is a language of the Lechitic subgroup of West Slavic languages, used throughout Poland and by Polish minorities in other countries...
chomikować, from chomik – hamster; Hebrew
Hebrew language
Hebrew is a Semitic language of the Afroasiatic language family. Culturally, is it considered by Jews and other religious groups as the language of the Jewish people, though other Jewish languages had originated among diaspora Jews, and the Hebrew language is also used by non-Jewish groups, such...
hamster; oger (אוגר) comes from to hoarde; le'egor (לאגור).
A disadvantage of larder hoarding is that if a cache is raided, this is far more problematic for the animal than if it were a scatter hoarder. While the hoard is much easier to remember the location of, these larger hoards must also be more staunchly defended.
Behaviors related to hoarding
GuardingMost species are particularly wary of onlooking individuals during caching and ensure that the cache locations are secret. Not all caches are concealed however, for example shrike
Shrike
Shrikes are passerine birds of the family Laniidae. The family is composed of thirty-one species in three genera. The family name, and that of the largest genus, Lanius, is derived from the Latin word for "butcher", and some shrikes were also known as "butcher birds" because of their feeding habits...
s store prey items on thorns on branches in the open.
Shared or individual hoarding
Although a small handful of species share food stores, food hoarding is a solo endeavor for most species, including almost all rodents and birds. For example, a number of jays live in large family groups, but they don't demonstrate sharing of cached food. Rather, they hoard their food supply selfishly, caching and retrieving the supply in secret. (Waite, 1992) There are only two species in which kin selection has resulted in a shared food store: Beavers (Castor canadensis) and Acorn Woodpecker
Acorn Woodpecker
The Acorn woodpecker is a medium-sized woodpecker, 21 cm long with an average weight of 85 g.-Description:...
s (Melanerpes formicivorous); the former live in family groups and construct winter larders of submerged branches, while the latter are unusual in that they construct a conspicuous communal larder (Koenig and Mumme, 1987).
Pilferage occurs when one animal takes food from another animal's larder.
Some species experience high levels of cache pilferage, up to 30% of the supply per day. Previous models of scatter hoarding developed by Stapanian and Smith (1978, 1984), Clarkson et al. (1986), and others, suggested the value of cached food is equal to the hoarders ability to retrieve it. (cited from Vander Wall, 2003)
Reciprocal Pilferage
It has been observed that members of certain species, such as rodents and chickadees, act as both hoarder and pilferer. In other words, pilfering can be reciprocal and, thus, tolerable. Although this kind of food caching system seems cooperative, it has been suggested that it is actually driven by the selfish interests of the individual. (Vander Wall and Jenkins, 2003)
Recaching
Animals recache the food that they've pilfered from other animal's caches.
For example, Vander Wall and Joyner (1998) found that 75% percent of radioactive Jeffery pine seeds cached by yellow pine chipmunks were found in two cache sites, 29% of the seeds were found in three sites, 9.4% were found in four sites and 1.3% were found in five sites over a 3-month period. These results, and those from other studies, demonstrate the dynamic nature of the food supplies of scatter hoarding animals.