Hoarding or caching in animal behavior is the storage of food in locations hidden from the sight of both conspecifics (animals of the same or closely related species) and members of other species. [1] Most commonly, the function of hoarding or caching is to store food in times of surplus for times when food is less plentiful. However, there is evidence that a certain amount of caching or hoarding is actually undertaken with the aim of ripening the food so stored, and this practice is thus referred to as ‘ripening caching’. [2] The term hoarding is most typically used for rodents, whereas caching is more commonly used in reference to birds, but the behaviors in both animal groups are quite similar.
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 rodents such as hamsters and squirrels, and many different bird species, such as rooks and woodpeckers. 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.
Caching behavior is typically a way to save excess edible food for later consumption—either soon to be eaten food, such as when a jaguar hangs partially eaten prey from a tree to be eaten within a few days, or long term, where the food is hidden and retrieved many months later. Caching is a common adaptation to seasonal changes in food availability. In regions where winters are harsh, food availability typically becomes low, and caching food during the times of high food availability in the warmer months provides a significant survival advantage. For species that hoard perishable food weather can significantly affect the accumulation, use and rotting of the stored food. [4] This phenomenon is referenced in the fable The Ant and the Grasshopper.
However, in ripening caching behavior, animals collect and cache food which is immediately inedible but will become "ripe" and edible after a short while. For instance, tayras (a Central American weasel) have been observed to harvest whole green plantains, hide them, and then come back to eat them after they have ripened. [2] Leafcutter ants 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. Contrary to popular belief, there is no scientific evidence that crocodilians such as the American Alligator cache large prey underwater to consume later. [5]
Scatter hoarding is the formation of a large number of small hoards. This behavior is present in both birds (especially the Canada jay) and small mammals, mainly squirrels and other rodents, such as the eastern gray squirrel, fox squirrel, and wood mouse. Specifically, those who do not migrate to warmer climates or hibernate for winter are most likely to scatter hoard. [6] [7] [8] 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 populations effectively. While it is clear why some animals scatter their food caches, there is still the question of why they would store the food outside of their bodies in the first place. The reason for this is that scatter hoarders must remain active during the caching period in order to hide the most food in the most places possible. Storing the food inside their body would reduce their mobility and be counterproductive to this objective. [9]
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, hoarders are still unable to eliminate the threat of pilferage. [10] However, having multiple cache sites is costly because it requires a good spatial memory. Scatter-hoarders generally have larger hippocampi [11] than animals that do not participate in scatter-hoarding behavior. Additionally, studies have shown that hippocampal volume in scatter-hoarders varies seasonally [12] and based on the harshness of the climate that the animal lives in. [13]
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. Hamsters are famous larder hoarders. Indeed, the German verb "hamstern" (to hoard) is derived from the noun "Hamster" which refers to the rodent; 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 hoard; 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. [14] [15] [16] Not all caches are concealed however, for example shrikes store prey items on thorns on branches in the open. [17]
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. [18]
There are only two species in which kin selection has resulted in a shared food store, i.e. beavers (Castor canadensis) and acorn woodpeckers (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. [19]
Wolves, foxes, and coyotes identify their food caches by scent-marking them, [20] [1] usually after they have been emptied. [3]
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. Models of scatter hoarding [21] [22] [23] suggested the value of cached food is equal to the hoarder's ability to retrieve it. [24]
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. [24]
Animals recache the food that they've pilfered from other animal's caches. For example, 75% percent of mildly radioactive (thus traceable) Jeffrey 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. [25] These results, and those from other studies, demonstrate the dynamic nature of the food supplies of scatter hoarding animals.
Group-foraging common ravens, (Corvus corax), scatter hoard their food and also raid the caches made by others. Cachers withdraw from conspecifics when hiding their food and most often place their caches behind structures, obstructing the view of potential observers. Raiders watch inconspicuously and keep at a distance to cachers close to their cache sites. In response to the presence of potential raiders or because of their initial movements towards caches, the cachers frequently interrupt caching, change cache sites, or recover their food items. These behaviors suggest that ravens are capable of withholding information about their intentions, which may qualify as tactical deception. [26]
Similarly, Eurasian jays (Garrulus glandarius) when being watched by another jay, prefer to cache food behind an opaque barrier rather than a transparent barrier, suggesting they may opt to cache in out-of-view locations to reduce the likelihood of other jays pilfering their caches. [27]
Squirrels are members of the family Sciuridae, a family that includes small or medium-sized rodents. The squirrel family includes tree squirrels, ground squirrels, and flying squirrels. Squirrels are indigenous to the Americas, Eurasia, and Africa, and were introduced by humans to Australia. The earliest known fossilized squirrels date from the Eocene epoch, and among other living rodent families, the squirrels are most closely related to the mountain beaver and dormice.
Hibernation is a state of minimal activity and metabolic depression undergone by some animal species. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate. It is most commonly used to pass through winter months – called overwintering.
Corvidae is a cosmopolitan family of oscine passerine birds that contains the crows, ravens, rooks, magpies, jackdaws, jays, treepies, choughs, and nutcrackers. In colloquial English, they are known as the crow family or corvids. Currently, 135 species are included in this family. The genus Corvus containing 50 species makes up over a third of the entire family. Corvids (ravens) are the largest passerines.
Kangaroo rats, small mostly nocturnal rodents of genus Dipodomys, are native to arid areas of western North America. The common name derives from their bipedal form. They hop in a manner similar to the much larger kangaroo, but developed this mode of locomotion independently, like several other clades of rodents.
The Canada jay, also known as the gray jay, grey jay, camp robber, or whisky jack, is a passerine bird of the family Corvidae. It is found in boreal forests of North America north to the tree line, and in the Rocky Mountains subalpine zone south to New Mexico and Arizona. A fairly large songbird, the Canada jay has pale grey underparts, darker grey upperparts, and a grey-white head with a darker grey nape. It is one of three members of the genus Perisoreus, a genus more closely related to the magpie genus Cyanopica than to other birds known as jays. The Canada jay itself has nine recognized subspecies.
The eastern gray squirrel, also known, particularly outside of North America, as simply the grey squirrel, is a tree squirrel in the genus Sciurus. It is native to eastern North America, where it is the most prodigious and ecologically essential natural forest regenerator. Widely introduced to certain places around the world, the eastern gray squirrel in Europe, in particular, is regarded as an invasive species.
The acorn, or oaknut, is the nut of the oaks and their close relatives. It usually contains a seedling surrounded by two cotyledons, enclosed in a tough shell known as the pericarp, and borne in a cup-shaped cupule. Acorns are 1–6 cm long and 0.8–4 cm on the fat side. Acorns take between 5 and 24 months to mature; see the list of Quercus species for details of oak classification, in which acorn morphology and phenology are important factors.
The Douglas squirrel is a pine squirrel found in western North America, from the Pacific Northwest to central California, with an isolated subspecies in northern Baja California, Mexico. It is sometimes known as the chickaree or pine squirrel, although these names are also used for the American red squirrel. Variant spellings of the common name are Douglas' squirrel and Douglas's squirrel. The Native Americans of Kings River called it the "Pillillooeet", in imitation of its characteristic alarm call.
The least chipmunk is the smallest species of chipmunk and the most widespread in North America.
The California scrub jay is a species of scrub jay native to western North America. It ranges from southern British Columbia throughout California and western Nevada near Reno to west of the Sierra Nevada. The California scrub jay was once lumped with Woodhouse's scrub jay and collectively called the western scrub jay. The group was also lumped with the island scrub jay and the Florida scrub jay; the taxon was then called simply scrub jay. The California scrub jay is nonmigratory and can be found in urban areas, where it can become tame and will come to bird feeders. While many refer to scrub jays as "blue jays", the blue jay is a different species of bird entirely.
In spermatophyte plants, seed dispersal is the movement, spread or transport of seeds away from the parent plant. Plants have limited mobility and rely upon a variety of dispersal vectors to transport their seeds, including both abiotic vectors, such as the wind, and living (biotic) vectors such as birds. Seeds can be dispersed away from the parent plant individually or collectively, as well as dispersed in both space and time. The patterns of seed dispersal are determined in large part by the dispersal mechanism and this has important implications for the demographic and genetic structure of plant populations, as well as migration patterns and species interactions. There are five main modes of seed dispersal: gravity, wind, ballistic, water, and by animals. Some plants are serotinous and only disperse their seeds in response to an environmental stimulus. These modes are typically inferred based on adaptations, such as wings or fleshy fruit. However, this simplified view may ignore complexity in dispersal. Plants can disperse via modes without possessing the typical associated adaptations and plant traits may be multifunctional.
The Siberian jay is a small jay with a widespread distribution within the coniferous forests in North Eurasia. It has grey-brown plumage with a darker brown crown and a paler throat. It is rusty-red in a panel near the wing-bend, on the undertail coverts and on the sides of the tail. The sexes are similar. Although its habitat is being fragmented, it is a common bird with a very wide range so the International Union for Conservation of Nature has assessed its conservation status as being of "least concern".
The American red squirrel is one of three species of tree squirrels currently classified in the genus Tamiasciurus, known as the pine squirrels. The American red squirrel is variously known as the pine squirrel or piney squirrel, North American red squirrel, chickaree, boomer, or simply red squirrel. The squirrel is a small, 200–250 g (7.1–8.8 oz), diurnal mammal that defends a year-round exclusive territory. It feeds primarily on the seeds of conifer cones, and is widely distributed across much of the United States and Canada wherever conifers are common, except in the southwestern United States, where it is replaced by the formerly conspecific southwestern red squirrel, and along the Pacific coast of the United States, where its cousin the Douglas squirrel is found instead.
The Panamint kangaroo rat is a species of rodent in the family Heteromyidae. It is endemic to the Mojave Desert in eastern California and western Nevada, in the United States.
The banner-tailed kangaroo rat is a species of rodent in the family Heteromyidae. It is found in arid environments in the southwestern United States and Mexico where it lives in a burrow by day and forages for seeds and plant matter by night.
The yellow-pine chipmunk is a species of order Rodentia in the family Sciuridae. It is found in parts of Canada and the United States.
Rodents are mammals of the order Rodentia, which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are native to all major land masses except for Antarctica, and several oceanic islands, though they have subsequently been introduced to most of these land masses by human activity.
Woodhouse's scrub jay is a species of scrub jay native to western North America, ranging from southeastern Oregon and southern Idaho to central Mexico. Woodhouse's scrub jay was until recently considered the same species as the California scrub jay, and collectively called the western scrub jay. Prior to that both of them were also considered the same species as the island scrub jay and the Florida scrub jay; the taxon was then called simply the scrub jay. Woodhouse's scrub jay is nonmigratory and can be found in urban areas, where it can become tame and will come to bird feeders. While many refer to scrub jays as "blue jays", the blue jay is a different species of bird entirely. Woodhouse's scrub jay is named for the American naturalist and explorer Samuel Washington Woodhouse.
Astrocaryum standleyanum is a species of palm known by many common names, including chumba wumba, black palm, chonta, chontadura, coquillo, palma negra, pejibaye de montaña, güerre, güérregue, güinul, mocora, pucaishchi (Chachi), and chunga (Emberá). It is native to Central and South America, where its distribution extends from Nicaragua to Ecuador. It is most common in central Panama, even becoming abundant in the tropical forests around the Panama Canal, but in general it is not a common plant.
Diplochory, also known as “secondary dispersal”, “indirect dispersal” or "two-phase dispersal", is a seed dispersal mechanism in which a plant's seed is moved sequentially by more than one dispersal mechanism or vector. The significance of the multiple dispersal steps on the plant fitness and population dynamics depends on the type of dispersers involved. In many cases, secondary seed dispersal by invertebrates or rodents moves seeds over a relatively short distance and a large proportion of the seeds may be lost to seed predation within this step. Longer dispersal distances and potentially larger ecological consequences follow from sequential endochory by two different animals, i.e. diploendozoochory: a primary disperser that initially consumes the seed, and a secondary, carnivorous animal that kills and eats the primary consumer along with the seeds in the prey's digestive tract, and then transports the seed further in its own digestive tract.