Hoarding (animal behavior)

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Western scrub jays cache food such as acorns and insects. Western Scrub Jay.jpg
Western scrub jays cache food such as acorns and insects.

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.

Contents

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.

Function

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. [3] 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. [4]

Hoard distribution and size

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. [5] [6] [7] 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. [8]

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. [9] However, having multiple cache sites is costly because it requires a good spatial memory. Scatter-hoarders generally have larger hippocampi [10] than animals that do not participate in scatter-hoarding behavior. Additionally, studies have shown that hippocampal volume in scatter-hoarders varies seasonally [11] and based on the harshness of the climate that the animal lives in. [12]

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.

Guarding

Most species are particularly wary of onlooking individuals during caching and ensure that the cache locations are secret. [13] [14] [15] Not all caches are concealed however, for example shrikes store prey items on thorns on branches in the open. [16]

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. [17]

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. [18]

Pilfering

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 [19] [20] [21] suggested the value of cached food is equal to the hoarder's ability to retrieve it. [22]

Reciprocal pilfering

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. [22]

Recaching

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. [23] These results, and those from other studies, demonstrate the dynamic nature of the food supplies of scatter hoarding animals.

Deception

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. [24]

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. [25]

See also

Related Research Articles

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Hamsters are rodents belonging to the subfamily Cricetinae, which contains 19 species classified in seven genera. They have become established as popular small pets. The best-known species of hamster is the golden or Syrian hamster, which is the type most commonly kept as a pet. Other hamster species commonly kept as pets are the three species of dwarf hamster, Campbell's dwarf hamster, the winter white dwarf hamster and the Roborovski hamster.

<span class="mw-page-title-main">Squirrel</span> Family of rodents

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<span class="mw-page-title-main">Kangaroo rat</span> Genus of mammals belonging to the kangaroo rats, kangaroo mice, and pocket mice family of rodents

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.

<span class="mw-page-title-main">Canada jay</span> Passerine bird of the family Corvidae

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.

<span class="mw-page-title-main">Eastern gray squirrel</span> Tree squirrel native to eastern and central North America

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<span class="mw-page-title-main">Acorn</span> Nut of the oak tree

The acorn, or oaknut, is the nut of the oaks and their close relatives. It usually contains one seed, enclosed in a tough, leathery shell, 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.

<span class="mw-page-title-main">Douglas squirrel</span> Species of rodent

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<span class="mw-page-title-main">California scrub jay</span> Species of bird in the crow family

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<span class="mw-page-title-main">American red squirrel</span> Species of pine squirrel found in North America

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.

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<span class="mw-page-title-main">Woodhouse's scrub jay</span> Species of bird

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References

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  23. ↑ Vander Wall, S.B.; Joyner, J.W. (1998). "Recaching of Jeffrey pine (Pinus jeffreyi) seeds by yellow pine chipmunks (Tamias amoenus): potential effects on plant reproductive success". Can. J. Zool. 76: 154–162. doi:10.1139/cjz-76-1-154.
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  25. ↑ Legg, E.W.; Clayton, N.S. (2014). "Eurasian jays (Garrulus glandarius) conceal caches from onlookers". Animal Cognition. 17 (5): 1223–1226. doi:10.1007/s10071-014-0743-2. PMC   4138428 . PMID   24638877.

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