Memory for the location of stored food in marsh tits

Marsh tits store several hundred food items per day, in separate locations within their territory, and recover most items within 24 h. Experiments in the laboratory determined that marsh tits return accurately to the sites of stored sunflower seeds 3 h and 24 h after storage. The proportion of returns exceeded chance encounter and initial preferences for those sites. The lack of interocular transfer in birds for some visual tasks provided a test for the hypothesis that memory is used to relocate stored food. After storing food with one eye covered, marsh tits did not return to storage sites when using only the ‘naive’ eye, but did so when using only the eye uncovered during storage. It seems likely that recovery of stored food by marsh tits and other birds occurs by memory of storage sites, not by chance encounter during foraging.     

Individual food-hoarding decisions in a nonterritorial coal tit population: the role of social context

Among the Paridae, food hoarding is thought to be strongly associated with the exclusive use of territories by winter groups, although it has also been described in populations with loose social systems. However, detailed data on such populations are scarce. To identify the mechanisms underlying individual storing decisions, I studied hoarding behaviour in a nonterritorial, high-density coal tit, Parus ater, population in a subalpine forest. The presence of close neighbours (within 5 m) had the strongest, negative influence on caching probability, whereas more distant neighbours foraging in the same flock did not affect the probability of caching. Adults concentrated their stores in the centre of their home ranges. Caching location, but not caching intensity, was affected by the time of day. Coal tits took longer, and travelled further, to cache food in the inner parts of trees than in the outer parts. Resident adults stored in inner, safer caching locations more often than juvenile residents and transients. Differences in hoarding effort according to the storing substrate, and the daily storing location pattern of juvenile residents and transients, suggest that stores have a different use depending on where they are located. Therefore, my results show that hoarding is compatible with a nonterritorial, nonbreeding social system; hoarding could thus have originated in an ancient, nonterritorial, but sedentary, tit species. Copyright 2000 The Association for the Study of Animal Behaviour.     

Mechanisms of cache retrieval in long-term hoarding birds

Food hoarding and memory have primarily been studied in two bird families, the Corvidae (crows, jays, nutcrackers, etc.) and the Paridae (tits, titmice and chickadees). In both families there are species that hoard large quantities of seeds and nuts in the autumn and depend on these stores during the winter. Caches are concealed or highly inconspicuous and the most efficient way to retrieve them is to remember the exact locations. However, a long-term memory for a large number of caches may be physiologically expensive, and especially after long retention intervals, an alternative strategy could be to retrieve caches by cheaper but less efficient methods. Very few studies have been designed to investigate the decay of the memory in birds, but both field observations and experiments point in the same direction: although long-term hoarding corvids seem to possess an accurate long-term memory, long-term hoarding parids do not appear to. I discuss possible reasons for this and suggest that differences between the families in their degree of dependence on stored food or/and size-related limitations of brain capacity may be important.     

Food storing by marsh tits

Wild marsh tits (Parus palustris) were allowed to hoard radioactively labelled sunflower seeds, which were subsequently found using a portable scintillation counter. Seeds were stored singly, in various sites close to the ground. Different birds favoured different types of site, although this preference was changeable. Seed density decreased with increasing distance from the feeder, and there was a negative correlation between seed sequence number and the distance it was carried. Hoarded seeds disappeared more rapidly than control seeds in identical sites 100 cm away, suggesting that the birds remember their exact location. Seeds also tended to be stored and recovered in the same sequence. The adaptive significance of these results is discussed.     

THE ADAPTIVE RADIATION AND FEEDING ECOLOGY OF SOME BRITISH FINCHES

The habitats and foods of ten species of finches studied near Oxford, England, are described in detail, and differences in feeding habits between them are related to differences in bill- and leg-structure, body-weight and behaviour. The Hawfinch, Siskin, Redpoll and Crossbill live primarily in woodland, the Greenfinch, Linnet and Goldfinch primarily in farmland, while the Bullfinch and Chaffinch breed, and occur throughout the year, in both these habitats. Habitat differences between species were probably more marked in primeval England than now, and the problems of studying animals in man-modified environments are discussed in this context. Diet was studied by observation and by gut-analyses of live and dead finches. Before roosting, finches usually accumulate food in their gullet, which is expandable but otherwise undifferentiated (the term “crop” is thus inappropriate). The Lesser Redpoll, the smallest species studied, can store up to about 0.8 c.c. of food in its gullet, but the Greenfinch, one of the largest finches, up to 2.5 c.c. Among the Carduelis finches, the Greenfinch lives mainly on the large seeds of various trees, cereal crops and agricultural weeds; the Goldfinch on the seeds of Compositae; the Siskin on alder and conifer seeds; the Lesser Redpoll on birch and other small seeds; and the Linnet on the seeds of various weeds of farmland. The Hawfinch and Bullfinch eat a greater proportion of buds and seeds from fleshy fruits than do other finches; but the Hawfinch prefers larger ones than does the Bullfinch. The three European crossbills feed almost entirely on conifer seeds; specializing on different tree species. In summer, the Chaffinch and Brambling live largely on invertebrates but in winter on beechmast or small seeds taken from the ground. In winter, Chaffinches reaching Britain from northern Europe tend to feed in large flocks in open areas and to roost communally, while residents tend to remain near their breeding places and roost singly. The migrations and distribution of finches in Europe are described briefly. At any time of winter, closely related species with similar feeding habits are often concentrated in different parts of a common wintering range. Furthermore, in some species, such as the Goldfinch and Chaffinch, the sexes winter mainly in different areas. In Oxford, food was least readily available during hard (winter) weather and there was then complete segregation in diet between different species, but at other times their diets often overlapped considerably. The overlap was much more pronounced in the species living in farmland (which is an artificial habitat) than in those living in natural or seminatural woodland; some tentative explanations for this are offered. The fringilline finches, the Chaffinch and Brambling, feed their young entirely on invertebrates, are territorial in the breeding season and collect food mostly within their territories. The cardueline finches, on the other hand, feed their young mainly, or entirely, on seeds, often nest in “loose colonies” and usually gather food communally at some distance from their nests. The fringilline finches carry food in their bills to the young, which therefore receive small, but frequent, meals; whereas the carduelines feed their young by regurgitation and at longer intervals. Among the carduelines, the Hawfinch is exceptional in that seeds are first swallowed and regurgitated to the nestlings, whereas insects are carried in the bill. The Bullfinch develops in the breeding season special buccal pouches in which food is carried to the young. In general, most finches select diets for their young which differ from their own diets in the breeding season. The Crossbill and Linnet often feed their young on seeds alone, and some other species may do so occasionally. The breeding of these carduelines is therefore independent of a supply of invertebrates, but always coincides with an abundance of seeds. They breed at seasons when other birds do not; the most extreme cases are the three crossbills, which, given an abundance of suitable seeds, will nest at any time of year. The process of seed-husking is described; the strength of the jaws, the extent of the gape and the width of the palatal grooves limit the size and hardness of seeds which a given species can take. No two species have bills of the same shape and size, and differences in diet between species are connected with differences in the structure of their bills and the way the bill is used. In general, the deeper the bill of a finch, the more numerous the types of seeds in its diet. The Greenfinch, Linnet and Redpoll have relatively short broad bills and feed more than do other Carduelis finches from plants whose seeds are relatively exposed (e.g. grasses) or enclosed within pods or capsules; they also pick up many fallen seeds from the ground, but each species concentrates on different sizes of seeds. The Goldfinch and Siskin have reIatively long, narrow bills and obtain much of their food by probing into cones and into the seed-heads of Com-positae; unlike other finches, they also use a gaping movement while feeding. The Goldfinch has a longer bill and eats more Compositae seeds than the Siskin, while tlie latter eats more tree seeds than the Goldfinch. Further, male Goldfinches have slightly longer beaks than females, and hence can obtain teasel seeds more efficiently; females feed only rarely from these plants. The Bullfinch and Hawfinch obtain much of their food by crushing fruits, seed-heads, etc. in their bills and peeling off the outer layer to get the seeds. The methods used by the crossbill species to open cones of varying degrees of hardness are described in detail. The Chaffinch and Brambling obtain almost all their food by rapid pecks; they show none of the behaviour patterns used by carduelines to open various types of seed-heads. Species also differ in the proportion of food obtained from the ground, from vegetation, or on the wing. These differences are related to the various positions in which each species is able to feed. Those species (Goldfinch, Siskin, Redpoll and Crossbills) which are most adept at clinging and hanging feed mainly from trees and herbaceous plants, while those that are least adept at this (Chaffinch and Brambling) obtain almost all their food from the ground or from firm horizontal twigs. The remaining species are intermediate in the proportion of time spent feeding from the ground or from vegetation; and only the Chaffinch, Brambling and Bullfinch obtain an appreciable amount of food on the wing. Differences between species in the frequency with which various positions are adopted during feeding can be related to differences in their average body weights, and (to a lesser extent) in their leg-structure; the most agile species are either light in weight or have relatively short strong legs. Body-weight, leg-proportions and bill-size (and hence feeding habits) may vary considerably between different populations of the same species. In Appendix 2, the leg-proportions of certain English finches are compared with those of their German and Russian counterparts. Some finch species use their feet in coordination with their bill to obtain food. The extent to which various species do this in the wild is discussed in relation to the ease with which they can be taught experimentally to pull up food suspended on the end of a long thread. The ecology, structure and behaviour of finches is discussed in relation to some current ideas on speciation and the ontogeny of feeding behaviour. The young of several species of finches respond initially to a similar range of potential food-items (both in size and appearance) and all attempt to deal with them in similar ways. However, each individual soon learns to concentrate on those foods it can obtain most efficiently with its own particular structures and behaviour patterns. It is thus the structural and behavioural differences between closely-related species which lead the individuals of each to prefer different foods. Further, some of the behaviour patterns themselves probably develop mainly as a result of learning conditioned by structure, so that some of the behavioural differences between species that affect food-choice are in turn dependent on structural differences. This implies that, from an evolutionary viewpoint, two forms need diverge only in structure (and not necessarily “psychologically”) for some ecological segregation to be achieved. There are, however, certain differences in feeding behaviour between the fringillines and carduelines that cannot be attributed merely to structural differences between the two groups, so presumably some “psychological factor” is also important in the development of these particular behaviour patterns. A close relationship between the structure, feeding behaviour and food of an animal is usually taken for granted, but it is often difficult to decide which of these came first in evolution. Among finches, however, there are sometimes indications that a structural change was necessary before a new behaviour pattern or feeding habit could evolve, though further modification of structure may then occur through adaptation to the new foods thereby made available. Some evolutionary trends among finches are described, and the role of competition in the evolution and maintenance of ecological differences between species is discussed. The effect of social experience on feeding behaviour is also discussed, and some examples are given of the spread of novel food-habits among finches, and of presumed traditional differences in feeding behaviour between different populations of the same species. Finally, some recent changes in food, and habitat-selection by finches are discussed in relation to problems of conservation.     

A prudent hoarder: effects of long-term hoarding in the European nuthatch, Sitta europaea

Although hoarding has been studied intensively for many decades,few studies have attempted to measure its actual fitness consequences.To fill this gap, we used ptilochronology, the growth of replacementfeathers as a measure of nutritional status, and thus a reflectionof starvation risk, of individual European nuthatches (Sittaeuropaea) during winter. We found that nuthatches are long-termhoarders, retrieving stored food up to at least 98 days afterstoring it. Long-term hoarding enhanced the nutritional statusof individual birds significantly because those individualsexperimentally given an opportunity to store seeds during autumnregrew plucked rectrices faster and larger than did controlbirds. Nuthatches used their stored seeds prudently by adjustingthe amounts they ate to meet their requirements, as determinedby ambient temperatures. Nuthatches refrained from using storedfood during periods of relatively benign conditions so theycould use the food during periods of more severe conditions.     

Individual variation in winter supplementary food consumption and its consequences for reproduction in wild birds

The provision of wild birds with supplementary food has increased substantially over recent decades. While it is assumed that provisioning birds is beneficial, supplementary feeding can have detrimental ‘carry‐over’ effects on reproductive traits. Due to difficulties in monitoring individual feeding behaviour, assessing how individuals within a population vary in their exploitation of supplementary food resources has been limited. Quantifying individual consumption of supplementary food is necessary to understand the operation of carry‐over effects at the individual level. We used Radio Frequency Identification (RFID) technology and automated feeders to estimate individual consumption of supplementary winter food in a large wild population of great tits Parus major and blue tits Cyanistes caeruleus. Using these data, we identified demographic factors that explained individual variation in levels of supplementary food consumption. We also tested for carry‐over effects of supplementary food consumption on recruitment, reproductive success and a measure of survival. Individual variation in consumption of supplementary food was explained by differences between species, ages, sexes and years. Individuals were consistent across time in their usage of supplementary resources. We found no strong evidence that the extent of supplementary food consumption directly influenced subsequent fitness parameters. Such effects may instead result from supplementary food influencing population demographics by enhancing the survival and subsequent breeding of less competitive individuals, which reduce average breeding parameters and increase density‐dependent competition. Carry‐over effects of supplementary feeding are not universal and may depend upon the temporal availability of the food provided. Our study demonstrates how RFID systems can be used to examine individual‐level behaviour with minimal effects on fitness.     

啮齿动物的分散贮食行为

食物贮藏是许多动物重要的适应性行为,分散贮藏的食物以植物种子为主。每个贮藏点贮藏数量不等的食物项目。啮齿动物分散贮藏食物之后,可降低食物被其他个体获取的机率,提高对食物资源的控制能力,最终有利于自身的生存和繁殖成功。植物种子被贮藏之后,可减少非贮食鼠类对种子的取食。同时,合适的微生境和埋藏有利于种子萌发、幼苗建成和植物的更新;使植物的分布区得以扩展。探讨啮齿动物的分散贮食行为,能够更好地理解食物贮藏在啮齿动物生活史中的作用,进一步认识鼠类和植物的相互关系以及不同啮齿动物在群落形成中的潜在作用。本综述了啮齿动物分散贮食的研究进展,并提出今后工作中的几点建议。     

Foraging Behaviour of Subordinate Great Tits (Parus major). Can Morphology Reduce the Cost of Subordination?

This paper studies the magnitude of the behavioural shift, from forage standing to forage hanging, of subordinate great tits ( Parus major ) in two different social contexts: feeding solitarily vs. feeding with a dominant conspecific. The aim is to test the hypothesis that differences in morphological design provide subordinates with varying abilities to reduce the presumed costs of subordination. We find that different subordinate individuals change the foraging behaviour, occupying a different niche when an intra-specific competitor is present. Morphology linked to sexual dimorphism, specifically body mass, is the factor responsible for the different magnitudes of change. Lighter subordinates can remain longer than heavier ones at the feeding patch without interrupting their foraging. Thereby, the former reduce the costs of being subordinate more than the latter. Among subordinates, females are lighter than males; they also spend more time feeding in the presence of a dominant conspecific than males do. No differences are found between age categories. We find no relationship between tarsus length and individual ecological plasticity. Our results support the idea that the ecological plasticity due to morphological differences is a mechanism that allows subordinate individuals to overcome costs associated with subordination.     

Singing Activity Reveals Personality Traits in Great Tits

In animal communication, sexually selected signals have been shown to often signal individual attributes such as motivation or quality. Birdsong is among the best studied signalling systems, and song traits vary substantially among individuals. The question remains if variation in signalling also reflects more general and consistent individual characteristics. Such consistent individual differences in behaviour that are relatively stable over time and contexts are referred to as personality or behavioural syndromes. Here, we studied the relation between singing and explorative behaviour, a well‐studied personality trait, using great tits (Parus major) under standardized aviary conditions. The results show that singing activity measured as the number of songs sung in spring prior to breeding correlated with male but not with female explorative behaviour. In contrast, song repertoire was not related to explorative behaviour but varied over the day. The link between explorative and singing behaviour suggests that sexually selected signals are more than signals of quality but can also reflect other intrinsic behavioural characteristics such as personality traits.     

Individual differences in the use of social information in foraging by captive great tits

We investigated individual differences in copying behaviour of captive great tits, Parus major, by analysing their response to a tutor indicating a new feeding site. We used two groups, each of seven male birds, labelled 'fast' and 'slow' explorers based on previous studies in which consistent individual differences in the speed of exploring were found. The birds were trained to search for food hidden in a number of differently coloured and shaped feeders, and later to search in only one type of feeder. During the tests, food was absent and the birds were observed in two different situations: alone or in the presence of a tutor, a bird that had been trained to feed in a different kind of feeder. When alone, slow birds readily extended their search to other feeders while fast birds did not change their routine of visiting the previously rewarded ones. In the presence of the tutor, the opposite occurred: slow birds did not change their behaviour while fast birds significantly increased their visits to the feeders indicated by the tutor. Fast and slow individuals thus differ in their foraging and copying behaviour, consistent with the producer-scrounger model. Copyright 2000 The Association for the Study of Animal Behaviour.     

The effect of dominance rank on fat deposition and food hoarding in the Willow Tit Parus montanus– an experimental test

We studied the effects of dominance rank on fat deposition and hoarding behaviour in Willow Tits Parus montanus . Dominant individuals can displace subordinates which gives them priority to new food sources; they can also pilfer stored food from subordinates. This gives subordinates less certain access than dominants both to their own caches and to new food sources. Theory predicts that subordinates should invest more than dominants both in body fat reserves and stored food. Empirical evidence is equivocal; some studies have shown that subordinates built up larger reserves than dominants, whereas others show the opposite. In an earlier indoor experiment, Pravosudov and Lucas found no effect of rank on either hoarding rate or fat reserves, but the experimental design was such that the results were ambiguous. This paper reports on a similar, but improved, experiment in outdoor aviaries. However, our results agree with the earlier experiment, since we found no effect of rank on either food storing or fat deposition. The reasons for this are explored.     

Individual variation in sleep behaviour in blue tits Cyanistes caeruleus: assortative mating and associations with fitness‐related traits

Sleep is ubiquitous in animals, but there is great inter‐ and intraspecific variation in the daily amount of sleep that is needed. Chronic sleep curtailment or experimental sleep deprivation are known to impair health and performance of individuals, but not much is known about the fitness consequences of naturally occurring variation in sleep behaviour. Here we test for assortative mating in sleep behaviour and for correlations between sleep phenotypes and reproductive success and survival in a free‐living blue tit population. We found that partners of a social breeding pair were mated assortatively in regard to standardized awakening time, i.e. awakening time relative to that of other birds of the same sex in the population. We found no evidence for assortative mating for other sleep parameters. In female blue tits no sleep parameter that we measured was significantly correlated with lay date or clutch size. Females that had extra‐pair young in their brood did not differ in awakening time, or in any other sleep parameter, compared to females without extra‐pair young. In males, the probability of siring extra‐pair young was related to sleep onset and sleep duration, but not as predicted. Males that began to sleep earlier and slept longer were more likely to sire extra‐pair offspring. None of the sleep parameters were significantly correlated with local survival of first‐year birds. Our results suggest that there is no strong effect of variation in sleep behaviour on fitness in blue tits, at least under natural conditions. Such a relationship might only become evident when natural sleep patterns are experimentally disturbed, or when sleep quality is affected by anthropogenic noise or light pollution.     

The effect of dominance on food hoarding: a game theoretical model

Many food hoarding animals live in small groups structured by rank. The presence of conspecifics in the hoarding area increases the risk of losing stored supplies. The possibility of stealing from others depends on a forager's rank in the group. Highly ranked individuals can steal from subordinates and also protect their own caches. Since storing incurs both costs and benefits, the optimal hoarding investment will differ between individuals of different rank. In a game theoretical model, we investigate how dominant and subordinate individuals should optimize their hoarding effort. Our model imagines animals that are large-scale hoarders in autumn and dependent on stored supplies for winter survival. Many examples can be found in the bird families Paridae and Corvidae, but the model can be used for any hoarding species that forage in groups. Predictions from the model are as follows: First, subordinates should store more than dominants, but in a predictable environment, this difference will decrease as the environment gets harsher. Under harsh conditions, dominants should store almost as much as subordinates and, later, spend almost as much time retrieving their own caches as subordinates. Second, if on the other hand, bad winter conditions were not expected when storing, dominants should spend more time pilfering caches from subordinates. Third, in populations that are highly dependent on stored supplies, dominants should store relatively more than in populations that are less dependent on stored supplies. Fourth, harsher environments will favor hoarding. And finally, if dominant individuals store, it implies that hoarders have a selfish recovery advantage over conspecific pilferers.     

Social influences on food caching in willow tits: a field experiment

We studied the food hoarding behavior of willow tits (Parusmontanus), a scatter-hoarding passerine wintering in dominance-structuredflocks. We examined social influences on microhabitat selectionand spatial cache distribution at temporary feeders. Dominantadult males stored food closer to die feeder and at a greaterrate than did subordinates. When alone, the birds stored foodcloser to the feeder than when accompanied by conspecifics.Conifers were preferred over deciduous trees as cache trees.The subordinates cached more in die outer parts of branchesthan dominants. There were no significant differences in dierelative or absolute heights of die caches, nor in the verticalor horizontal hoarding niche breadths between dominants andsubordinates. We experimentally removed die dominants from dieflock for 90 min and recorded the behavior of die remainingsubordinates immediately after die removal. The removal resultedin a decrease in die hoarding distance of die remaining birds,indicating that die presence of dominants directly affecteddie behavior of subordinates and suggesting that kleptopar-asitismby dominants may be prevented by rarhing farther away. Withdie dominants removed, die subordinates cached at a greaterrate than before die removal. The decrease in die hoarding distanceand increase in die hoarding rate were die only significanteffects of die experiment, perhaps suggesting that, during ashort absence of dominants, die subordinates do not benefitfrom changing dieir caching microhabitat They might be excludedfrom those new, possibly safer, microhabitats after die dominantbird rejoins die flock.     

Numerical and behavioural responses of migrant passerines to experimental manipulation of resident tits (Parus spp.): heterospecific attraction in northern breeding bird communites?

Summary We studied experimentally interspecific competition among foliage-gleaning passerine birds by manipulating the density of resident tits. In 1988 tit density was experimentally increased on three small islands in a central Finnish lake, and decreased on three other islands by tit removal. In order to avoid the effects of between-island differences in habitat quality, the role of the islands was reversed when the experiment was repeated in the following year. Censuses and observations on foraging and feeding behaviour were conducted to assess the numerical and behavioural responses of migrant conguilders (mainly chaffinches and willow warblers) with respect to the manipulated abundance of the tits. We also measured whether variation in food consumption of tits affected the frequency with which the migrants found food by calculating average intervals between successful prey captures, time lags to prey-capture and giving-up times. Our results indicate that interspecific competition is of minor importance in structuring breeding bird assemblages and species feeding ecologies on the study islands. No consistent difference in foraging or feeding niches of chaffinches and willow warblers was found between low and high tit density conditions. Niche overlap analysis showed no avoidance by chaffinches and willow warblers of the microhabitats which tits used. Tit abundance had no significant effect on feeding success or behaviour. Experimentally increased abundance of resident birds was associated with increased abundance of breeding migrants, however. This pattern was found not only in the foliage gleaning guild but also with all passerine birds, indicating that food was not an important contributor to this pattern. We elaborate a hypothesis suggesting heterospecific attraction in northern breeding bird assemblages. Habitat generalist migrants may use the presence of residents as an indicator of safe and/or productive breeding sites in northern unpredictable circumstances.     

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].     

Monitoring of rice weevil, Sitophilus oryzae, feeding behavior in maize seeds and the occurence of supernumerary molts in low humidity conditions

Rice weevils, Sitophilus oryzae (L.), complete their development from egg to early adulthood inside grains of wheat, rice or maize, but little is known about their feeding behavior within the seeds. An ultrasonic insect feeding monitor was used to characterize the feeding patterns of individual rice weevils as they developed in maize grains. Weevils reared in grains held at ca. 40% r.h. took longer to develop from egg to pupation than those reared in grains kept at ca. 70% r.h. Feeding patterns revealed that larvae developing in grains held at ca. 70% r.h. had only four instars, whereas supernumerary molts (five instars) occurred in certain individuals reared in grain held at ca. 40% r.h. The supernumerary molts may represent a response of the insect to stresses associated with low moisture levels in the seeds.     

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.     

Long-term hoarding in the Paridae: a dynamic model

Using stochastic dynamic programming we modeled the hoardingand foraging behavior of tits and chickadees, Pandas, that areresident in the boreal forest at high latitudes. Here autumnshave a rich supply of seeds and temperatures are relativelymild, while winters are cold with short days and a low foodsupply. We assumed that parids have a memory of limited durationand that forgotten seeds accumulate in a bank that adds to thegeneral food supply in the hoarder's territory. Our model predictsthat birds should start "high-intensity" hoarding in early autumn,but not before that. Because of mass-dependent costs the birdswill keep their fat levels low during the autumn. When winterarrives they will carry more body fat, both for the long winternights and to hedge against the large effects of weather variationsin winter. After increasing the fat level at the start of winter,fat should gradually increase even more, to compensate for thediminishing food supply. Most hoarding occurs in autumn as away of building up the supply of long-term stores. Remembered,or short-term caches, may hedge against stochastic events inthe environment. Even though conditions are not beneficial forhoarding in winter, the birds still stored in winter to maintainlarger short and long-term hoards if environmental variationincreased. Almost all time in winter that not was spent foragingwas spent perching, mainly to avoid predation