Hoarding of individual nuthatches Sitta europaea and march tits Parus palustris

The hoarding behaviour of one pair of nuthatches Sitta europaea L. and of four individual marsh tits Parus palustris L. was studied during autumn and winter in a deciduous grove in central Sweden. Sunflower seeds were offered at a feeding table. AM individuals studied stored seeds intensively throughout the whole study period. The two species showed very different hoarding patterns. The nuthatch pair aggressively defended the area around the feeding table, which was within their territory, from other nuthatches and also seemed to affect the hoarding behaviour of the coexisting marsh tits. Some significant differences were found also between con-specifics in some aspects of hoarding behaviour, which could in some cases be related to sex or dominance. These differences may make hoarding profitable for the individual birds if they also differ in their foraging patterns individually, and so will have a greater probability of finding their own stored items than other individuals. However, the evidence for individual segregation of hoarding patterns is not conclusive.     

围栏条件下社鼠的食物贮藏行为

在北京东灵山地区, 用活捕笼从野外捕获社鼠, 并在野外建造围栏, 以山杏种子和辽东栎坚果为备选食物, 对围栏条件下社鼠的食物贮藏行为进行了研究。数据的统计分析采用SPSS for Windows (version 1010) 进行。结果表明: 1) 社鼠主要表现出食物的集中贮藏方式; 2) 贮藏食物被模拟盗窃使社鼠的食物贮藏活动加强; 3)社鼠倾向于选择山杏种子进行贮藏, 而对辽东栎坚果则取食较多。文中还讨论了食物类型、模拟盗窃等因素对社鼠食物贮藏行为的影响。     

围栏条件下同域分布三种鼠对两种种子的贮藏行为差异

种子贮藏是啮齿动物利用食物资源的一种适应性行为。同域分布的啮齿动物可能进化出不同的贮藏方式和策略。为了解同域分布的啮齿动物的贮藏策略及种子特征在动物贮藏行为决策中的作用,于2014年10-12月,通过半自然围栏实验,在秦岭南坡的佛坪国家级自然保护区内调查了同域分布社鼠、中华姬鼠和甘肃仓鼠对板栗和锐齿槲栎种子的贮藏策略差异,并探讨了2种种子特征在鼠类贮藏行为决策中的作用。结果显示：1）社鼠主要集中贮藏板栗种子,未分散贮藏任何种子;中华姬鼠未贮藏板栗种子,对锐齿槲栎种子同时表现出集中和分散贮藏行为,以集中贮藏为主;甘肃仓鼠对2种种子均表现出集中贮藏行为,未表现分散贮藏行为。2）社鼠和甘肃仓鼠均倾向于集中贮藏有较高营养价值（高蛋白和脂肪）且单宁含量较低的板栗种子;中华姬鼠倾向于分散贮藏单宁含量高的锐齿槲栎种子。3）3种鼠均喜好取食有较高营养价值且单宁含量低的板栗种子,很少取食单宁含量高的锐齿槲栎种子。结果表明同域分布鼠类对不同种子的贮藏方式有所不同,种子特征影响鼠类的取食和贮藏策略。     

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.     

Fine-scale food hoarding decisions in New Zealand Robins ( Petroica australis ): is inter-sexual competition important?

Competition for cache retrieval is hypothesised to influence food hoarding intensity. Previous work has tested this hypothesis by evaluating food hoarding rates during foraging bouts when animals are exposed to different levels of competition for cache retrieval. Little is known about how competition might influence fine-scale food hoarding decisions within foraging bouts. I evaluated fine-scale food hoarding decisions of New Zealand Robins (Petroica australis) by offering mealworms to competitively dominant males and subordinate females, both when they were alone and when they foraged together. I then compared food hoarding rates of sequentially handled prey between sexes and social conditions by assessing how the total number of prey cached increased with the total number of prey handled. Relationships for solitary females, solitary males and paired males were non-linear, indicating that they were more likely to consume initially handled prey, and increasingly likely to cache subsequently handled prey items. Non-linear rates of food hoarding may result from declines in the energetic value of prey that are consumed and stored internally as birds become satiated. Somewhat differently, the relationship for paired females was linear, indicating that paired females make a single food hoarding decision based on bout-level foraging conditions, which results in constant fine-scale food hoarding rates. Constant food hoarding rates in paired females, which experience the strongest competitive effects of any treatment, suggest that food consumption is consistently more advantageous than food hoarding under these conditions, regardless of satiation level. Overall results from this study indicate that New Zealand Robins continuously update food hoarding decisions according to their competitive environment and satiation levels, resulting in scale-dependent patterns in food hoarding intensity.     

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     

秦岭南北坡森林鼠类对板栗和锐齿栎种子扩散的影响

森林鼠类的种子贮藏行为对植物的扩散及更新会产生积极的影响。2012和2013年秋季,分别在秦岭北坡的周至国家级自然保护区和南坡的佛坪国家级自然保护区内,调查了森林鼠类对板栗(Castanea mollissima)和锐齿栎(Quercus aliena)种子的取食和扩散差异。结果显示:1)秦岭南北坡的环境因素,特别是植被因素,对鼠类扩散板栗和锐齿栎种子具有重要的影响。南坡较为丰富的壳斗科植被种类,导致2种种子在南坡存留时间均长于北坡,而北坡的扩散取食和丢失率均高于南坡。2)种子特征影响鼠类的取食或贮藏偏好。由于较高的蛋白、脂肪等营养含量,鼠类更喜好取食或搬运贮藏板栗种子。然而,低营养但高丹宁含量的锐齿栎种子仍然被鼠类大量贮藏。3)2种种子在南北坡的扩散历程在两个年份间有很大差异,在食物相对匮乏的年份(2012年),种子被扩散的速度更快且丢失的比率更高。这种差异反映了种子大小年现象对森林鼠类取食和贮藏策略的影响。4)无论在秦岭南坡还是北坡,营养价值含量(如蛋白和脂肪)较高的板栗种子的取食和贮藏距离都明显大于营养价值含量较低的锐齿栎种子,这与最优贮藏空间分布模型的预测一致。     

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。     

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.     

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     

Sensitivity to Seed Germination Schedule by Scatter‐Hoarding Pére David's Rock Squirrels During Mast and Non‐Mast Years

Mast seeding by oaks (Quercus) and other seed species has fundamental impacts on the behavior of individual scatter‐hoarding animals as well as their population and community dynamics. Scatter‐hoarding squirrels are highly sensitive to acorn germination schedule and stop germination by removing the embryo of non‐dormant acorns to prevent losses of energy and nutrients by rapid germination. However, we know little about how this behavior is affected by mast seeding. We investigated foraging decisions made by free‐ranging Pére David's rock squirrel (Sciurotamias davidianus) with three species that produce non‐dormant seeds and two species that produce dormant seeds (Fagaceae) during mast and non‐mast years in Central China from 2007–2010. Consistent with the food perishability hypothesis that squirrels make decisions to minimize the perishability of their caches, non‐dormant seeds were hoarded at a lower rate, but had a higher probability of embryo removal than dormant seeds. Compared with non‐mast years, a lower proportion of seeds were harvested during mast years, but a higher proportion of the harvested seeds were hoarded. In addition, the probability of embryo removal in the hoarded seeds was higher during mast years. Squirrels also dispersed seeds at shorter distances during mast years. Moreover, the interactions between mast seeding and seed germination schedule had significant effects on squirrel foraging decisions, including embryo removal. This study is the first to demonstrate that squirrels show greater sensitivity to seed germination potential when seeds are abundant.     

The Value of a hoard: not just energy

We present a stochastic dynamic programming model of the contributionof stored food to winter survival. Using the acorn woodpecker(Melanerpes formtcivorus) as a model organism, we demonstratethat a hoard of small energetic value can impart considerableimprovement in the probability of surviving the winter and soimprove fitness. With this model we hope to resolve Koenig andMumme's paradox, that acorn woodpeckers expend much time andeffort to create and maintain hoards of acorns which provideno more that 16% of their energetic needs over the period inwhich they are used. We further demonstrate that the contributionof hoarded acorns to survival depends on the variability inforaging outcome, independently of the energetic value of thehoard in absolute terms. We point out that the results applyin principle to all hoarding animals and suggest a number offurther elaborations of the model.     

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.     

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.     

Social context affects risk taking by a satellite species in a mixed-species foraging group

Mixed-species flocks of birds form during winter in the easterndeciduous forests of North America. These flocks consist oftwo flock-leading nuclear species, tufted titmouse (Baeolophusbicolor) and Carolina chickadee (Poecile carolinensis), andseveral follower, or satellite, species, including downy woodpecker(Picoides pubescens) and white-breasted nuthatch (Sitta carolinensis).Hypotheses explaining the adaptiveness of participation in suchmixed-species foraging groups have focused on increased foragingsuccess and/or decreased predation risk. We tested the predictionthat if nuthatches join nuclear species to reduce predationrisk, they should be more reluctant to visit an exposed feederin the absence of titmice than in their presence. When the feederwas positioned 16 m from forest cover, latency to visit thefeeder was greater for both male and female nuthatches whentitmice were absent. Removal of titmice had no effect on latencyat 8 m. In the absence of titmice, nuthatches visited the feederless frequently at both distances. These results indicate thatreduced predation risk is a benefit that satellite species gainby flocking with nuclear species.     

Desiccation stress in recalcitrant Quercus robur L. seeds results in lipid peroxidation and increased synthesis of jasmonates and abscisic acid

In a series of experiments the desiccation-sensitive seeds ofQuercus robur were exposed to drying conditions both beforeand after a period of moist storage. Viability loss occurredat higher moisture contents in stored seed than in newly harvestedseeds. Measurements were made at intervals during desiccation.In both stored and unstored seeds viability loss was precededby an increase in the rate of ethane evolution, a commonly usedindicator of lipid peroxidation, and by an increase in electrolyteleakage indicative of membrane damage. Jasmonic acid (JA), itsmethyl ester (MeJA) and ABA were quantified in the same extractsfrom both cotyledonary and axis tissues. The concentration ofall three hormones was higher in the axis than in the cotyledonsof untreated seeds and were within the range of concentrationsquantified elsewhere in seed tissues from other species. Theconcentration of JA, MeJA and ABA progressively increased duringdrying in both cotyledons and axes of whole seeds and in excisedaxes prior to viability loss and then subsequently declined.The concentration of these hormones increased earlier duringdrying in stored seeds in line with their enhanced desiccationsensitivity. Exogenous JA, MeJA and ABA were shown to inhibit germination.However, none of these substances promoted ethylene evolution,which also inhibits germination of Q. robur seeds, or inducedsenescence-like deterioration. The results presented are discussed in relation to the natureof desiccation sensitivity and viability loss in Q. robur seeds. Key words: Quercus robur, seed, desiccation, jasmonates, abscisic acid     

Seasonal patterns of food limitation in Daphnia galeata: separating food quantity and food quality effects

Food limitation for the cladoceran Daphnia galeta was measuredgrowing them with natural lake seston for one growing seasonunder standardized conditions in the laboratory. Growth rateswere related to several measures of food quantity. Particulateorganic carbon (POC) <30 µm was the best predictorof total food availability measured. It was better than chlorophyll-a(Chl-a) of the same size fraction, algal volume calculated fromcell counts or total particle volume from Coulter Counter measurements.Daphnids were also grown with Scenedesmus acutus under the sameconditions and their growth rates were compared. Sestonic carbonconcentrations were related to Scenedesmus carbon concentrations,that provided equal growth rates. The ratio of the carbon concentrationsof both food types (seston, Scenedesmus) represented the foodquality of seston. Thus, the nutritional quality of naturallake seston relative to a standard alga was determined overone growing season. Growth rates of seston fed animals revealedthat they were food limited during long periods of the year.This was also ascertained by standard clutch sizes of fieldanimals. However, the causes of food limitation varied withinthe duration of the studied period. Whereas during the clear-waterphase the food quantity was limiting (while the quality washigh: 100% Scenedesmus), shortly after on 10 June and 17 Junefood conditions were close to threshold concentrations due tolow food quality. For the remainder of the summer, a POC of0.3–0.6 mg C I^–1 with a quality of     

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.     

动物分散贮食行为对植物种群更新的影响

分散贮食是许多动物取食行为策略的重要组成部分。对以植物种子为主要贮食对象的动物来说,种子内营养物质含量、种子大小以及种子内次生化合物的含量等因素都直接影响动物的贮食行为。动物偏爱贮藏个体较大的种子,大种子多被搬运并分散贮藏在远离种源的地方,而小种子则多被就地取食,以补充动物贮食过程中的能量消耗。贮食动物主要通过空间记忆、特殊路线以及贮藏点周围的直接线索等途径重新获取贮藏点内食物。在重取过程中,一些贮藏点被遗忘,其中的种子成为植物种群更新的潜在种子库。因此,分散贮食动物不仅是种子捕食者,还是种子传播者,它们对植物种子的捕食、搬运和贮藏,影响了植物种子的存活和幼苗的建成,从而在一定程度上影响植物种群的更新、分布。植物种群为了促进种子的传播,在进化过程中逐渐形成了形式多样的适应性策略,降低种子的直接被捕食率,提高种子的被贮藏率。研究动物分散贮食行为对植物种群更新的影响,将有助于理解贮食动物与植物之间的互惠关系,从而认识贮食动物种群在生态系统中的作用,为生物多样性的保护提供科学依据。     

Tropical rodents change rapidly germinating seeds into long-term food supplies

Seed‐hoarding vertebrates may survive yearly periods of food scarcity by storing seeds during the preceding fruiting season. It is poorly understood why rodents creating long‐term reserves, especially those in the tropics, incorporate seeds from plant species that germinate rapidly and hence seem unsuitable for long‐term storage. We carried out a series of experiments to understand why red acouchies (Myoprocta exilis) scatter‐hoard Carapa procera (Meliaceae) seeds, which lack dormancy and germinate rapidly. Hypotheses tested were: (1) even germinated seeds are still significant long‐term energy reserves for acouchies, (2) acouchies use the seeds only as short‐term supplies, and (3) acouchies manipulate the seeds to slow down germination. The first two hypotheses were not supported; seed reserves were rapidly depleted during experimental planting, and acouchies did use seeds for long‐term storage. We did find support for the third hypothesis. Acouchies intervened in germination by removing the protruding radicle and epicotyl after which they re‐cached seeds. Pruning stopped further seedling development, yet the pruned seeds did not decay. The cotyledons apparently stayed alive and physiologically active as “zombie seeds” that only formed undifferentiated calli. Pruned seeds were suitable for long‐term storage, with negligible loss of endosperm over time. Pruning was most effective after sprouting of the epicotyl, and germinating seeds were most susceptible to pruning during two weeks upon emergence. Acouchies actively managed their food supplies and must continuously survey for germinating seeds to timely intervene in seed reserve depletion, within the brief period of seedling emergence. We suggest that the trees use the rodents to achieve seed dispersal, and gain from imperfect intervention in germination by the rodents. Because scatter‐hoarding rodents and large‐seeded plant species with similar germination co‐occur in tropical forests world‐wide, it is plausible that the phenomenon of seed pruning to preserve seeds is more general than currently appreciated.