岩松鼠的食物贮藏行为

食物贮藏是许多动物对不可预见的食物供应变化的一种重要适应.岩松鼠(Sciurotamias davidianus)为中国特有物种,广泛分布于华北地区的山地和丘陵地带.作者在北京市东灵山地区建造半自然围栏(4 m×3 m× 1 m),以核桃(Juglans regia)和山杏(Prunus armeniaca)种子为备选食物,对岩松鼠(12只)的食物贮藏行为进行了研究.数据的统计分析采用SPSS for Windows进行.研究结果表明1)岩松鼠表现出集中和分散两种食物贮藏方式,而分散贮藏是其偏好的贮藏方式;2) 当遇到贮藏食物被盗窃时,岩松鼠倾向于搬运更多的食物进行集中和分散贮藏;3)岩松鼠没有在食盘就地取食任何一种食物;把食物搬离后,岩松鼠所取食的山杏种子数量明显多于所取食的核桃数量;4)岩松鼠只选择核桃进行分散贮藏;5)岩松鼠对核桃的搬运距离大于山杏种子.本研究结果提示,在自然条件下,岩松鼠对核桃和山杏的天然更新起着不同的作用[动物学报 51(3)376-382,2005].     

Spatial patterns of food storage by Merriam's kangaroo rats

We investigated scatter-hoarding behavior by Merriam's kangaroorats (Dipodomys merriami) in a complex arena in the laboratory.Animals cached seeds in four sand-filled boxes connected byrunways, with an artificial burrow at one end of the systemand a food source at the other. Animals initially cached moreseeds in boxes close to the food source, but amounts cachedbecame more evenly distributed among boxes as sessions progressed.The results were consistent with the hypothesis that scatterhoarding by kangaroo rats may represent a compromise betweenrapidly sequestering seeds, hence making them unavailable tonondigging competitors, and spacing-out caches, making themless vulnerable to pilferage by other rodents.     

Food hoarding behaviour of large field mouseApodemus peninsulae

An important behavioural adaptation for animal species with variable or unpredictable food availability is storing food. Food availability for large field mouseApodemus peninsulae (Thomas, 1907) is not reliable. We conducted a series of tests with the large field mouse to determine food hoarding behaviour, response when their hoarded food was removed, and whether perishable foods were treated different than non perishable foods. The study was conducted in four semi-natural enclosures (4 × 3 × 1 m), established on the Donglingshan Mountain near Beijing, China. Thirteen large field mice were placed in enclosures and offered wild apricotPrunus armeniaca seeds and Liaodong oakQuercus liaotungensis acorns. Our results indicated that although large field mice hoarded seeds in larder and scatter patterns, they more frequently exhibited larder hoarding. Liadong oak acorns were generally consumed near the feeder, whereas apricot seeds were more frequently transported to the nest box. Only apricot seeds were scattered among hoard sites. When seeds were removed from hoarding sites the mice responded by taking increased amounts of seeds to their nest for larder and scatter hoarding. Hoarding sites were not randomly distributed throughout the enclosure.     

Kangaroo Rats Remodel Burrows in Response to Seasonal Changes in Environmental Conditions

Burrow architecture enhances important animal functions such as food storage, predator avoidance, and thermoregulation. Occupants may be able to maximize fitness by remodeling burrows in response to seasonal changes in climate and predation risk. My objective was to examine how banner‐tailed kangaroo rats (Dipodomys spectabilis) modify the number of burrow entrances in response to seasonal conditions. For 3 yr, I monitored fluctuations in number of burrow entrances in kangaroo rat mounds. Individual kangaroo rats continually remodeled mounds in response to seasonal conditions. Compared to summer, mounds in winter had approximately 50% fewer entrances and plugged entrances were common. Monthly differences in number of entrances were closely linked with seasonal changes in soil temperature and precipitation. Number of entrances decreased as soil temperature and precipitation declined. Changes in burrow entrances likely reflect seasonal differences in the relative importance of burrow functions. Fewer burrow entrances during winter would create a warmer microclimate by reducing convective heat loss in mounds, resulting in thermoregulatory savings for occupants. During the summer, thermoregulatory costs of kangaroo rats are low, but risk of seed cache spoilage and predation from snakes increases. Adding burrow entrances after large summer rainfall events would increase the evaporation rate within mounds, reducing spoilage of seed caches. More burrow entrances would also reduce predation risk in the summer by providing additional escape routes.     

Spacing Behavior of a Non‐Larder‐Hoarding Tamiasciurus: A Study of Mearns's Squirrels in Xeric Coniferous Forests

In ecosystems with seasonal fluctuations in food supply many species use two strategies to store food: larder hoarding and scatter hoarding. However, because species at different geographic locations may experience distinct environmental conditions, differences in hoarding behavior may occur. Tree squirrels in the genus Tamiasciurus display variation in hoarding behavior. Whereas red (Tamiasciurus hudsonicus) and Douglas's (Tamiasciurus douglasii) squirrels in mesic coniferous forests defend territories centered around larder hoards maintaining non‐overlapping home ranges, red squirrels in deciduous forests defend small scatter‐hoarded caches of cones maintaining overlapping home ranges. As in other rodent species, variation in hoarding behavior appears to influence the spacing behavior of red and Douglas's squirrels. In contrast, Mearns's squirrels (Tamiasciurus mearnsi) in xeric coniferous forests neither rely on larder hoards nor appear to display territorial behavior. Unfortunately, little is known about the ecology of this southernmost Tamiasciurus. Using radiotelemetry, we estimated home‐range size, overlap, and maximum distance traveled from nest to examine the spacing behavior of Mearns's squirrels. Similar to scatter‐hoarding rodents, maximum distance traveled from nest was greater for males during mating season, whereas those of females were similar year round. Although no seasonal differences were detected, male home ranges were three times larger during mating season, whereas those of females were smaller and displayed a minor variation between seasons. Home ranges were overlapped year round but contrary to our expectations, overlap was greater during mating season for both sexes, with no detectable relationship between male home‐range size and the number of females overlapped during mating season. Overall, the results appear to support our hypothesis that in the absence of larder hoards, the spacing behavior of Mearns's squirrels should be different from larder‐hoarding congeners and more similar to scatter‐hoarding rodents.     

Sexual differences in food re-caching by New Zealand robins Petroica australis

We presented monogamous pairs of New Zealand robins Petroica australis with a superabundant supply of artificial prey and then observed birds re-cache previously hoarded prey. Males and females frequently relocated and redistributed previously hoarded prey. Both sexes also re-cached prey that was originally hoarded by their mate. However, re-caching rates of retrieved and pilfered prey differed between sexes. Female-made caches were re-cached at the same rate by both females and pilfering males, while male-made caches were re-cached more frequently by pilfering females. The re-caching of previously hoarded prey is consistent with the hypothesis that re-caching reduces theft. However, re-caching pilfered prey suggests that it might also play a role in cache theft strategies. Higher rates of re-caching by pilfering females cannot be explained by current hypotheses used to account avian re-caching behaviours. We suggest two new hypotheses, sexual dimorphism in spatial memory and indirect mate provisioning, which may help to explain the evolution of re-caching in New Zealand robins.     

The placement, recovery, and loss of scatter hoards by eastern chipmunks,Tamias striatus

Although eastern chipmunks typically larder hoard food in theirburrows, some scatter hoarding occurs, especially by newly emergedjuveniles and by females with young. To examine patterns ofscatter hoard placement and their adaptive significance, weused standard food provisioning tests followed by continuousmonitoring to determine the longevity and fate of scatter hoards.Longevity of scatter hoards was low (median 74 min) and pilferagewas high (46%). Chipmunks placed scatter hoards away from thepatch, closer to their burrow and within the defended area ofprimary use. Scatter hoard placement was affected by the numberof competitors at the patch. However, juveniles and femaleswith young differed slightly in their responses. competitorsthat approached scatteihoards were sometimes chased away bythe scatter hoard's owner, and the scatter hoard was moved toanother location by the owner. Females with young recoveredtheir largest scatter hoards first, but there was little additionalpattern in scatter hoard recovery. An experiment using simulatedscatter hoards showed that scatter hoards farther from a patchof food lasted longer and that disturbing and marking scatterhoards reduced their longevity. These observations indicate:(1) that scatter hoard placement is more related to avoidingpilferage of completed caches than to rapidly sequestering fooditems from an ephemeral patch and (2) that optimal cache distributionmay be affected by the cache-defense ability of individuals,by the relationship between competitor density and cache securitynear the patch, and by the territorial behavior of neighboringconspecifics.     

A Miocene rodent nut cache in coastal dunes of the Lower Rhine Embayment, Germany

A fossil burrow system containing a food cache was discovered in coastal facies in the Lower Rhine Embayment near Cologne, Germany, in the lignite sequences of the Garzweiler open-pit mine. Because these sediments are of Burdigalian age (late Early Miocene), this cache appears to be the geologically oldest food cache to date. The burrow occurs in the Morken Sand beds (horizon 5D), and it is hypothesized here that it was excavated by a Miocene burrowing animal from the surface of a palaeosol into the underlying dune sand in an interdune area. Based on the morphology of the burrow system and the size of the galleries, the burrow was made by a rodent, most likely a large hamster (e.g. Lartetomys or Karydomys ) or, conceivably, a large ground squirrel. The chambers, and sometimes the galleries, of the burrow were filled with a monospecific cache of considerable size, estimated here as a minimum of 1800 nuts, although it was probably much larger. This food cache, a larder hoard, consisted of the three-dimensionally preserved nuts of Castanopsis pyramidata (Fagaceae). Because many extant rodents are long-term larder hoarders in regions experiencing seasonal food shortages (e.g. those with cold winter conditions or a dry season), the occurrence of this type of food cache in the Early Miocene implies an acute or chronic scarcity of food resources which, in turn, may be linked to either seasonal cycles in food availability in the backbeach environment or, plausibly, may possibly foretell the onset of climatic seasonality in the entire region.     

围栏条件下中华姬鼠和北社鼠对完好和虫蛀锐齿槲栎种子的取食和贮藏行为差异

正种子贮藏是啮齿动物利用食物资源的一种适应性行为(Vander Wall,1990)。经过长期的进化,啮齿动物形成了两种主要的贮藏食物行为:一是集中贮藏,即把收集的大量食物集中在其洞穴或临时栖息场所贮藏,通常有少量贮藏点,每个贮藏点有大量种子;二是分散贮藏,即把收集的种子分散贮藏在相对较大范围或其巢域周围,通常有大量贮藏点,但每个贮藏点仅贮藏约1～3粒种子。与集中贮藏相比,分散贮藏扩展了植物种子的分布范围,降低了种子被动物取食的概率。由于被分散贮藏的     

Memory for food caches: not just for retrieval

Many animals use hoarding as a long-term strategy to ensurea food supply at times of shortage. Hoarders employ strategiesthat enhance their ability to relocate caches such as rememberingwhere caches are located. Long-term scatterhoarders, whose cacheshave potentially high pilferage rates, should also hoard ina way to reduce potential cache pilferers' ability to find caches.Previous studies have demonstrated that this could be achievedby hyperdispersing caches to reduce the foraging efficiencyof pilferers. This study investigates whether coal tits (Parusater) indeed place their caches away from existing ones. Inour experiment, birds hoarded food in 3 conditions: when cachesfrom a previous storage session were still present, when cachesfrom a previous storage session were not present anymore becausethe bird had retrieved them, and when caches from a previousstorage session had been removed by the experimenter. We showthat coal tits hoard away from existing caches and that theydo not use cues from extant caches to do this. This evidenceis consistent with the use of memory for the locations of previouscaches when deciding where to place new caches. This findinghas important implications for our understanding of the selectivepressures that have shaped spatial memory in food-hoarding birds.     

Effects of burrow condition and seed handling time on hoarding strategies of Edward's long-tailed rat (Leopoldamys edwardsi)

Many hoarding rodents use burrows not only for dwelling and protection from natural enemies, but also for food storage. However, little is known how burrows used by scatter-hoarding animals influence their foraging behaviors. In addition, handling time for a given food item has a fundamental impact on hoarding strategies of these hoarding animals: food items with longer handling time are more likely to be hoarded due to increasing predation risk because the animals spend more time outside their burrows if they consumed such food. By providing with two types of artificial burrows (aboveground vs. underground) and two types of food items (i.e. seeds) with contrasting handling times, we investigated how burrow condition and handling time co-influence hoarding strategies of a key scatter-hoarding rodent, Edward's long-tailed rat (Leopoldamys edwardsi) in large enclosures in southwest China. We found that only a few animals larder-hoarded fewer seeds when only aboveground burrows were available, while over 80% of the animals preferred to use the underground burrows and hoard significantly more seeds in the burrows when both aboveground and underground burrows were provided simultaneously. We also found that seed handling time significantly affected hoarding strategies of the animals: they consumed and/or scatter-hoarded more Camellia oleifera seeds with shorter handling time outside the burrow, but consumed and larder-hoarded more Lithocarpus harlandii seeds with longer handling time in underground burrows. Our study indicates that both burrow types and seed handling time have important impacts on hoarding strategies of scatter-hoarding animals.     

围栏条件下岩松鼠对核桃的贮藏

许多动物都能够贮藏食物以应对一定时期的食物短缺。岩松鼠是中国特有的一种啮齿动物,主要分布于华北山地和丘陵地区,对于其食物贮藏行为还了解不多。我们在北京东灵山地区建立了半自然围栏,在围栏一角设置一木质巢箱供其休息,在围栏中心设一食盘(给食处),就岩松鼠对核桃(已预先标记)的贮藏特征进行了观察。每只受试动物在实验开始前6 h断食,于13∶ 00 左右,随机选择1 只岩松鼠,将其放入围栏中适应2 ～ 3 h。随后,在给食处放置20 枚已标记的核桃。于第二天同一时间进入围栏,检查并记录岩松鼠对核桃的处理情况,将埋藏、取食和剩余的核桃全部移出,另置20 枚新的核桃,继续实验。第三天,重复上述检查和记录,将岩松鼠及被其处理的核桃全部移出,清理巢箱、整理围栏。随后放入第二只岩松鼠,重复上述实验过程,如遇恶劣气候,则实验顺延,直至实验结束。结果表明:岩松鼠兼具集中贮藏和分散贮藏两种食物贮藏方式,并且分散方式是其主要的食物贮藏方式;岩松鼠在围栏中选择一定的位置贮藏食物;文中还讨论了可能影响岩松鼠食物贮藏的因素。     

Food hoarding behaviour of black-capped chickadees (Poecile atricapillus ) in relation to forest edges

In temperate forests, small birds avoid the use of forest edges in adverse winter weather suggesting high foraging costs in terms of energetic requirements. Since hoarding species will often retrieve caches during adverse winter weather, they may perceive forest edges, especially exposed ones, as low quality hoarding sites. We tested whether black-capped chickadees ( Poecile atricapillus) inhabiting fragmented forests modify and reduce hoarding activity near forest edges. We also tested whether hoarding behaviour will be most affected in sites with forest edges more exposed to extreme weather. Black-capped chickadees taking food from a feeder 30 m from the nearest forest edges hoarded items mostly towards the forest interior, whereas no preference in hoarding location was observed with birds taking food from a feeder placed >100 m from the edge. Furthermore, birds avoided direct flights towards forest edges and, at sites exposed to prevailing winds, hoarding trips were shorter than at other locations. These results suggest that individuals avoid hoarding near forest edges and there, they lower their investment in terms of hoarding effort. The observed difference in hoarding behaviour was more evident near forest edges delimiting wide unforested areas than in edges delimiting narrower unforested areas. Edge exposure to prevailing winds influenced hoarding behaviour much less. We suggest that hoarding birds may partially overcome the ecological costs of habitat loss and fragmentation due to abiotic edge effects. By hoarding food away from forest edges in good weather, they may use forest interiors as low-cost retrieval sites under adverse weather.     

Effects of habitat and season on removal and hoarding of seeds of wild apricot (Prunus armeniaca) by small rodents

The wild apricot (Prunus armeniaca) is widely distributed in the Donglingshan Mountains of Mentougou District of Beijing, China, where its seeds may be an important food resource for rodents. Predation, removal and hoarding of seeds by rodents will inevitably affect the spatio-temporal pattern of seed fate of wild apricot in this area. By marking and releasing tagged seeds of wild apricot, we investigated seeds survival, scatter-hoarding, cache size and seedling establishment, and the preference of micro-habitats used by rodents to store seeds. The results showed that: (1) rodents in this area hoarded food intensively in autumn, as well as in spring and summer. (2) There were significant effects of habitat and season on removal rate of tagged seeds at releasing plots. In both two types of habitats, Low and High shrub, tagged seeds were removed most rapidly by rodents in autumn, at intermediate rates in spring and least rapidly in summer. (3) During three seasons, mean dispersal distance of scatter-hoarded seeds in Low shrub habitat was greater than that in High shrub. Most removed seeds were buried within 21.0 m of the releasing plots. (4) In both two types of habitats, Low and High shrub, rodents tended to carry seeds to US (Under shrub) and SE (Shrub edge) microhabitats for scatter-hoarding or predation. (5) Among the caches made by rodents, most caches contained only one seed, but up to three seeds were observed; caches of 2–3 seeds were common in autumn. (6) By comparing dental marks, we determined that large field mice (Apodemus peninsulae) and David’s rock squirrels (Sciurotamias davidianus) contributed to removal and predation of released tagged seeds. However, only the large field mice exerted a pivotal and positive role on the burial of dispersed seeds. (7) Establishment of three seedlings originated from seeds buried by rodents was documented in High shrub habitat.     

啮齿动物分散贮食的影响因素

分散贮藏食物是许多啮齿动物所采取的一种重要的觅食策略。分散贮藏方式对于植物的幼苗建成、更新、群落演替和生态系统功能的维持有着积极的意义。多种因素影响啮齿动物对食物分散贮藏。内部因素有性别、年龄、社群关系、饥饿状态等;外部因素包括食物特征、竞争与盗食环境条件等。这些因素并非独立地发挥作用,内部因素受外部刺激的综合影响,而且外部因素只能通过改变动物的内部状态才能发挥作用。特别是在一些室内的或围栏实验中,实验设计的差异不仅影响动物的食物贮藏及其管理,也会造成实验结果的不同。     

贮食动物的盗食与反盗食行为策略

食物贮藏是许多动物应对食物短缺、保障其生存和繁衍的一种适应性行为。保护好贮藏食物以供食物短缺期利用,是食物贮藏成功的标志和进化动力。同种或异种动物盗食是贮藏食物损失的重要原因。嗅觉、视觉与空间记忆、随机搜寻等是动物搜寻和盗取食物的重要手段;避免盗食、阻止盗食和容忍盗食是动物反盗食的重要策略。动物通常采用多种行为策略进行盗食和反盗食,分配食物资源,形成相对稳定的种内、种间关系。盗食与反盗食互作及其对贮食行为进化的意义已成为行为生态学的研究热点和前沿之一,针对鸟类和哺乳类动物的研究尤为丰富。本文总结了贮食动物常见的盗食和反盗食行为策略及其相互作用的研究进展,主要内容涉及贮食动物利用嗅觉、视觉与空间记忆、随机搜寻等盗取其他个体食物的盗食策略,以及通过隐藏、转移、保卫、容忍等方式减少被盗食,保护贮藏食物的行为策略。针对现有研究状况,从种间盗食与反盗食及其与物种共存的关系,种间非对称盗食关系及其适应意义,盗食与反盗食最适行为策略及其与贮食动物适合度的关系等方面对今后研究提出了建议。     

Rodent handling of Araucaria araucana seeds

In an intermast year of very low seed production, we studied seed handling in an Araucaria araucana (Araucariaceae) forest in Neuquén Province, Argentina. Rodents identified in 844 photographs from automatic cameras removed 589 seeds marked with small embedded magnets. Within 12 days of removal, 460 were recovered using a magnetic field locator; 79% of recoveries were from burrows and caches in litter or soil. Rodents exhibited a diversity of seed‐handling strategies and differed in their potential as dispersal agents. Seed removal was most likely between 15.00 hours and 21.00 hours, but diurnal and nocturnal visits were recorded for all species. Oligoryzomys longicaudatus (Cricetidae) was a seed predator that took 8% of marked seeds and left none whole. Chelemys macronyx (Cricetidae) and Rattus norvegicus (Muridae) removed 25% and 19% of marked seeds respectively. These two species deposited the majority of seeds in groups of 10 or more in burrow larders that were unfavourable seedling establishment sites far from daylight. Abrothrix longipilis (Cricetidae) removed 43% of seeds, scatter‐hoarded the largest percentage of whole seeds (37%), moved some seeds farther than 40 m, and left them in favourable seedling establishment sites near daylight. For all species, the number and proportion of seeds cached whole increased as more seeds were removed. Rodents, especially A. longipilis, may play an important role in regeneration of A. araucana. Seed‐handling strategies and potentially effective dispersal are discussed in terms of masting seed production.     

Interactive effects of keystone rodents on the structure of desert grassland arthropod communities

Certain species play particularly large roles in ecosystems, and are often referred to as keystones. However, little is known about the interactive effects of these species where they co-occur. Prairie dogs ( Cynomys spp.) and banner-tailed kangaroo rats Dipodomys spectabilis are commonly considered keystone species of grassland ecosystems, creating a mosaic of unique habitats on the landscape through ecosystem engineering and herbivory. We examined the separate and interactive effects of these species on the structure of grassland arthropod communities. We conducted a cross-site study at two locations in the northern Chihuahuan Desert, and evaluated the impacts of these rodents on ground-dwelling arthropod and grasshopper communities in areas where prairie dogs and kangaroo rats co-occurred compared to areas where each rodent species occurred alone. Our results demonstrate that prairie dogs ( C. gunnisoni and C. ludovicianus ) and banner-tailed kangaroo rats had keystone-level impacts on arthropod communities both separately and interactively. Their burrow systems provided important habitats for multiple trophic and taxonomic groups of arthropods, and increased overall arthropod abundance and species richness. Many arthropods also were attracted to the aboveground habitats around the mounds and across the landscapes where the rodents occurred. Detritivores, predators, ants, grasshoppers, and rare rodent burrow inhabitants were especially associated with prairie dog and kangaroo rat activity. The impacts of prairie dogs and kangaroo rats were unique, and the habitats they created supported different assemblages of arthropods. Where both rodent species co-occurred, there was greater heterogeneity and arthropod diversity on the landscape. Our results suggest that the interaction of multiple keystones, especially those with engineering roles, results in unique and more diverse communities in time and space.     

Effects of food value, predation risk, and pilferage on the caching decisions of Dipodomys merriami

Animals that scatter cache their food face a trade-off betweenthe benefits of protecting caches from pilferers and the costsassociated with caching. Placing food into a large number ofwidely spaced caches helps to protect it from pilferage butalso involves costs such as greater exposure to predators. Ipredicted that animals would disperse food into a larger numberof more widely spaced caches when caching (1) a preferred foodversus a less preferred food and (2) under conditions of lowpredation risk versus high predation risk. To test these predictions,I examined the scatter-caching decisions of Merriam's kangaroorats (Dipodomys merriami). D. merriami distributed caches inclumped patterns, regardless of food preference, but they showeda tendency to invest more in a preferred food by distributingcaches more widely. Under the relative safety of the new moon,they did not disperse caches more widely, rather they partitionedthe same amount of food into a larger number of caches thanthey did under the full moon, when predation risk is higher.To examine whether their cache spacing decisions had a significantimpact on the success of cache pilferers, I measured discoveryby pilferers of artificial caches of two food types at differentcaching distances. Results indicate that the cache spacing behaviorof D. merriami functions to protect caches from pilferers, becauseincreased spacing of artificial caches decreased the probabilityof pilferage for both types of food.     

Inter-Population Variation in Hoarding Behaviour in Degus, Octodon degus

Although foraging comprises a set of behaviours that typically vary with resource availability and/or climatic conditions, few studies have analysed how foraging, particularly food hoarding, varies across populations inhabiting different habitats. We carried out an inter-population study on foraging behaviour with the caviomorph rodent Octodon degus collected from two geographically separated populations in central Chile, with contrasting climates. One population was located in a mountainous zone (at 2600 m elevation) characterized by a high-altitude climate. The other population was from a low-altitude Mediterranean climate zone (450 m elevation). Under laboratory conditions, we measured population-specific differences in food consumption and hoarding by recording food utilization. We also assessed whether acclimation played a role in behavioural differences, by using two different sets of animals that had been in captivity for (1) 2 wk or (2) 6 mo, under common conditions. The results showed variation in food hoarding between populations. Individuals from the low-altitude population exclusively displayed scatter hoarding behaviour. In contrast, high-altitude animals carried out larder hoarding combined with scatter hoarding (37.4% and 62.6% respectively). There was no intra-population variation between degus with different acclimation periods under captivity, thus inter-population differences in larder hoarding were maintained despite 6 mo of acclimation to a common environment. The geographic variation observed suggests that larder hoarding is favoured under harsher environmental conditions. We discuss some probable causes for this variation. The lack of effect of acclimation suggests that inter-population differences in larder hoarding might be the result of local adaptation or, less likely, it corresponds to an ontogenetically acquired irreversible behaviour.