Scatter-hoarder.html



Hoarding is type of animal behaviour where an animal will store its food within a cache, in times of surplus, for times when food is less plentiful. It will also scatter hoard when it can't defend a large concentration of stored food. In other words, it will spread out the food supply, perhaps throughout its home range, hiding it well to prevent other animals from finding and pilfering it. There are two types of caching behaviour, scatter-hoarding, where a species will create multiple caches, often with each individual food item stored in a unique place, and larder-hoarding, where a species creates a few larger caches which it often defends.

Some characteristics of hoarding

Long-term or short-term hoarding
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.

Shared or individual hoarding
Although there is a small handful of species who utilize shared food stores, for most species, including all rodents and birds, food hoarding is a solo endeavor. 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 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 (Koenig and Mumme, 1987).

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.

Recaching
Animals recache the food that they've pilfered from other animal's caches. For example, Vanderwall 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.

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 Vanderwall, 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. (Vanderwall and Jenkins, 2003)

Animals that are scatter-hoarders

• Squirrels
• Chipmunks
• Woodmouse

References

Clarkson K, Eden SF, Sutherland WJ, Houston AI, (1986) Density, dependence and magpie hoarding. J Anim Ecol 55:111-121.

Jenkins, Stewart H. and Breck, Stewart W. (1998) Differences in food hoarding among six species of heteromyid rodents. J Mammal. 79:1221-1233.

Koenig WD, Mumme RL. (1987) Population ecology of the cooperatively breeding acorn woodpecker. Princeton, New Jersey. Princeton University Press. 0691084645

Stapanian, MA, Smith CC. (1978) A model for seed scatterhoarding: coevolution of fox squirrels and black walnuts. Ecology 59:884-896.

Stapanian MA, Smith CC. (1984) Density-dependent survival of scatterhoarded nuts: an experimental approach. Ecology 65:1387-1396.

Vander Wall SB, Joyner JW. (1998) Recaching of Jeffery pine (pinus jefferyi) seeds by tallow pine chipmunks (Tamias amoenus): potential effects on plant reproductive success. Can J Zool 76:154-162.

Vanderwall, Stephen B. and Jenkins, Stephen H.(2003) Reciprocal pilferage and the evolution of food-hoarding behavior. Behavioral Ecology. Vol. 14, No. 5.

Waite TA. (1992) Gray jay scatterhoarding behavior, rate maximization and the effect of local cache density. Ornis Scand 23:175-182.