黑线仓鼠的食物与食量

作者从1983年至1989年,在河北省三个不同的气候区,对农田中的黑线仓鼠(Cricetulus,bara-bensis)的食物与食量进行了调查。结果表明,黑线仓鼠主要取食农作物种子。同时取食草籽和根、茎、叶、花、果实及动物性食物。不同地区、不同作物地、不同季节和年度、不同性别鼠的食物差异显著。食物差异与鼠的种群繁值及数量动态有关。月夹捕率与颊囊中食物的总检出率和种子检出率正相关非常显著。直线回归方程式分别为y=38.388+2.866x n=60 r=0.343>r_(0.01)=0.325和y=29.734+2.669x r=0.394>r_(0.01360)=0.325。黑线仓鼠对食物的选择,主要受到食物质量的影响,同时也受到食物频度、作物的物候变化、动物的群落结构、种群密度、种内与种间竞争等多种因素的综合影响。在不同的时间和栖息地影响它食物选择的主要因素不同。日食量4-5g。     

野生藏酋猴冬季食物组成及营养成分

觅食是获取营养物质和能量的重要途经。对于栖息在四季分明地区的灵长类动物而言,低温以及食物资源相对匮乏的冬季是其生存和生长发育的瓶颈期。本研究以安徽黄山的野生藏酋猴(Macaca thibetana)天湖山群为对象,于2019年11月至2020年1月采用瞬时扫描取样法(Instantaneous scan sampling)采集猴群觅食行为数据,并分析其冬季食物组成及食物中各化学成分含量对取食的影响。结果显示,野生藏酋猴在冬季共取食23科31属34种植物,主要包括壳斗科(Fagaceae, 21.62%)、樟科(Lauraceae, 17.57%)、蔷薇科(Rosaceae, 8.11%)的植物,取食部位以叶片(66.22%)和果实(种子)(24.32%)为主。不同取食部位的水分、总糖、淀粉、脂肪、单宁等成分存在显著差异。其中,叶片的水分含量高于果实(种子)、茎和芽,茎和果实(种子)含有较高的总糖,果实(种子)的淀粉和脂肪含量最高,芽的单宁含量最高。此外,取食植物中的总糖含量高于非取食植物。结果表明,野生藏酋猴适应寒冷冬季与食物匮乏的觅食策略是对植物种类、植物部位及其主要营养成分的综合结...     

实验检验东方田鼠学习能力的性别差异

东方田鼠选择从禾本科植物叶片的不同部位采食会引起食物摄入率的巨大差异,这项具有明显的认知和学习行为的觅食活动是否存在性别差异。在由带两片叶的新鲜马唐茎秆配置的密集食物斑块上,测定东方田鼠觅食马唐叶片的行为序列、过程及参数,检验其在学习能力上的性别差异。结果表明,雌鼠和雄鼠的觅食决定时间尽管均随觅食学习天数的增加而减小,但雌鼠的觅食决定时间显著地高于雄鼠的;雌鼠和雄鼠均由从对叶片部位无差别选择和采食转向偏爱从叶片基部采食。学会这项采食技能后,雌鼠从叶片基部采食的选择指数显著地高于雄鼠的;二者的摄入率均随觅食学习天数的增加极显著地增大,但雌鼠的摄入率却极显著地高于雄鼠的。研究结果充分验证了提出的假设:雄鼠较雌鼠能更快地习得从禾本科植物叶片的基部采食和收获食物;但当二者习得这项采食技艺后,雌鼠较雄鼠能获得更高的食物摄入率;同时也说明,新建立的评价小型植食性哺乳动物认知和学习能力的实验方法,具有可靠的有效性和实用性。     

Girdling-induced nutrient accumulation in above ground tissue of peanuts and subsequent feeding by Spissistilus festinus, the three-cornered alfalfa hopper

Changes in nutrient partitioning in stems and leaves of peanut (Arachis hypogaea L.) were examined after girdling of stems by Spissistilus festinus (Say) (Homoptera:Membracidae), the three-cornered alfalfa hopper. Under field conditions amino acids increased more than 12-fold in concentration in the 2 cm stem section above the girdle compared to below the girdle or control stems for newly formed girdles (less than 7–11 days). Asparagine and proline were the predominant amino acids, and increased 40- and 60-fold, respectively, above the girdle compared to below the girdle. There was no buildup of nutrient assimilates for the older girdled stems that had callused (and presumably recovered from feeding injury). A time course from 1–11 days was followed under greenhouse conditions, and girdled regions remained enriched in sugars for one day and amino acids for four days after girdle formation. After girdle formation most S. festinus responded to nutrient sinks by feeding within 5 mm above the girdle. This behavior was most pronounced one day after girdle formation, but persisted for seven days after girdle formation. During this period a new girdle was often formed within 10 mm above the original girdle. Under field conditions, stems and leaves derived from stems that had sustained an early or late season girdle generally had a reduced dry weight, total nitrogen content, and total carbon content; however, significant differences did not always occur. Thus, although temporary changes occurred in nutrient partitioning in girdled stems, there appears to be longer term negative growth effects on leaves and stems.     

Changes in the Content of Indole-3-Acetic Acid and Cytokinins in Spruce, Fir and Oak Trees after Herbicide Treatment

Treatment of spruce, fir and oak trees with herbicides, which may be one of the forest damage inducing agents, caused pronounced changes in the contents and distribution of indole-3-acetic acid (IAA) and cytokinins (CKs) one year after treatment, i.e. at the time of the first microscopically visible damage in treated trees. In Picea pungens IAA content increased in the terminal buds by about 105 % and in the apical buds of the first order branches by 220 %. The same was true for young sprouts of Abies nordmanniana, while in leaves of oak trees IAA content was decreased by 15 % after glyphosate treatment and by 30 % after 2,4-dichlorophenoxyacetic acid (2,4-D) treatment. Another striking feature was a significantly decreased content of IAA in the lower parts of roots in Picea pungens (50 % of the control), which is accompanied by an increase in IAA content in the middle part of the roots (130 %). On the other hand, the IAA content of both sprouts and roots of A. nordmanniana was significantly increased after herbicide treatment.In P. pungens, the content of free cytokinins (sum of zeatin, zeatin riboside, isopentenyladenine and isopentenyladenosine) decreased due to herbicide treatment. The strongest decrease was seen in roots, especially in their upper and middle parts (the average reduction of cytokinin content in roots was 63 %). In the above-ground organs the reduction was seen namely for isopentenyladenine and isopentenyladenosine, while the abundance of zeatin riboside was, on the other hand, higher in treated plants. In Quercus robur leaves, the total content of cytokinins also decreased, namely after glyphosate treatment. In consequence of these changes, CK/IAA ratio decreased pronouncedly in all organs of herbicide-treated trees, with the exception of oak leaves treated by 2,4-D.     

Diet and feeding behavior of Rhinopithecus bieti at Xiaochangdu, Tibet: adaptations to a marginal environment

The diet and feeding ecology of a wild subpopulation of black-and-white snub-nosed monkeys (Rhinopithecus bieti) were studied at Xiaochangdu in Honglaxueshan Nature Reserve, Tibet. This region is climatologically harsher than any other inhabited by non-human primates. Black-and-white snub-nosed monkeys fed on 48 parts of 25 plant species, at least three species of lichens and seven species of invertebrates. The number of food items exploited varied markedly among seasons, with dietary diversity being greatest in spring and summer. In winter, black-and-white snub-nosed monkeys had to subsist on fallback foods such as dried grass and bark. Ubiquitous lichens formed a major dietary constituent throughout the year, contributing about 75% of feeding records. Even though lichens act as a staple, our findings signify that the monkeys at Xiaochangdu prefer feeding on foliage, which is higher in protein content than the former. We provide evidence that black-and-white snub-nosed monkeys are able to cope with an array of food items other than lichens and hence can be regarded as feeding generalists. We discuss the results with reference to previous studies on other subpopulations living in habitats that are floristically more diverse and offer more plant food items than the marginal habitat at Xiaochangdu.     

Food Habits of Formosan Rock Macaques (Macaca cyclopis) in Jentse,Northeastern Taiwan,Assessed by Fecal Analysis and Behavioral Observation

We studied the food habits of the Formosan rock macaques (Macaca cyclopis) in Jentse via fecal analysis and direct field observation from October 1991 to September 1992, and recorded macaques eating 51 plant species and insects of 5 orders. Macaques in Jentse spent more time feeding on fruits than on other plant parts or insects. However, there was seasonal variation in their food habits, i.e., they spent a higher proportion of time feeding on fruits and insects in summer, and on leaves and stems in winter. The major plant species consumed and the patterns of seasonal variation in the macaque diets identified by fecal analysis and field observation are similar. However, there are discrepancies between results from the two methods in some of the finer details of estimated dietary composition.     

Nitrogen mineralization ofSesbania sesban used as green manure for lowland rice in Sri Lanka

Sesbania sesban was evaluated as green manure crop for lowland rice in the Dry Zone of Sri Lanka. The legume was grown during a fallow period before lowland rice (Oryza sativa) and ploughed under just before transplanting. Weight loss and nitrogen content in litterbags containing leaves, stems and roots of the legume were monitored. Comparisons were made between rice yields from 20 m² plots after green manuring in combination with different nitrogen fertilizer levels (0, 2.4, 4.8 and 7.2 gm⁻²) and nitrogen fertilizer (9.6 gm⁻²) alone. Above-ground biomass ofS. sesban was 440 gm⁻² (dry wt) when ploughed under after 84 days growth. N-content in leaves, stems and roots was 3.76%, 0.41% and 0.73%, respectively. This gave a N-input fromS. sesban of 9.2 gm⁻² (8.3 g from above-ground parts and 0.9 g from roots). The corresponding K and P inputs were 7.3 and 0.6 gm⁻² respectively. The nitrogen rich leaves, which contained 88% of the nitrogen in the above-ground parts, decomposed and released its nitrogen much more rapidly than the stems and roots. After only four days the leaves had released 5.3 g Nm⁻² and after 14 days they had released 6.4 g Nm⁻². The highest rice yield (505 gm⁻²) was obtained usingS. sesban and 4.8 gm⁻² of N-fertilizer. The yields with only N-fertilizer or onlyS. sesban were 442 gm⁻² and 396 gm⁻², respectively. Due to the rapid decomposition of the nitrogen rich leaves,S. sesban did not behave as a slow release fertilizer. Thus, it is not necessary to apply nitrogen fertilizers as a basal dose.     

The diet and feeding behavior of the silver leaf monkey (Trachypithecus auratus sondaicus) in Indonesia

I describe the diet and feeding behavior of silver leaf monkeys (Trachypithecus auratus sondaicus) in the Pangandaran Nature Reserve, West Java, Indonesia, and compare a group living in old secondary rain forest with a group living in mixed plantation/secondary forest to determine intraspecific variation in feeding behavior and the importance of the plantation species in the diet of the monkeys. Young leaves and leaf buds made up slightly less than half of their diets, with both groups showing a preference for a few species when seasonally available. Fruits and flowers of a few species were also preferentially selected when available. These included sweet, fleshy fruits, which most other colobines tend to avoid. Young leaf intake was greatest in months when fruit intake was low. Mature leaves were rarely eaten. Both groups spent approximately 20% of feeding time foraging on Moraceae species. Differences in the diet of the two groups were related largely to differences in vegetational composition and the availability and abundance of food items for the species common to both sites. Teak (Tectona grandis) was the top food species of the group living in mixed plantation/secondary forest, with the midribs of young leaves preferentially selected. Young leaves ofT. grandis, available throughout the study, provided a staple food and were eaten when preferred foods were scarce. More favored food items were available to the group living in old secondary forest, though none was a staple food.     

Calystegine distribution in potato (Solanum tuberosum) tubers and plants

Potato plants contain calystegines in leaves, stems, flowers, fruits and roots. Calystegines A₃ and B₂ are the main constituents. Highest concentrations were measured in sprouts emerging from the tubers. In 3 mm long sprouts, 3.3 mg total calystegines per g fresh mass were detected. Dormant tubers directly after harvest contain less calystegines in all parts than sprouting tubers. Flowers and young leaves are the aerial plant tissues with the highest calystegine concentration, i.e. 150 μg total calystegines per g fresh mass. Calystegine levels did not rise when sprouts were wounded. Tropinone application to sprouts and aerial tissues lead to an accumulation of pseudotropine and not to tropine. That indicates that stereospecific tropinone reduction is active in potato.     

喜马拉雅灰叶猴栖息地利用和食性生物学

2006年4月至2007年4月在巴基斯坦克什米尔地区马希亚拉国家公园(Machiara National Park)对喜马拉雅灰叶猴(Semnopithecus entellus ajex)的栖息地利用和食性生物学进行研究。结果表明,冬天,叶猴首选的栖息地多为温暖湿润的针叶林和落叶林混交地区;夏天,它们则迁移至高海拔的亚高山灌木丛林里。喜马拉雅灰叶猴主要以植物的叶子为食,研究期间在该地区共发现49种被采食过的植物(夏季27种,冬季22种)。通过观察它们的所有食物,发现老叶(36.12%)比嫩叶(27.27%)更受欢迎,随后依次为果实17.00%、树根9.45%、树皮6.69%、花2.19%和根茎1.28%。     

Resource allocation in different parts of juvenile mountain birch plants: effect of nitrogen supply on seedling phenolics and growth

The composition and concentrations of phenolic compounds were studied in the first true leaves, cotyledons, stems and roots of 2.5-week-old seedlings of mountain birch ( Betula pubescens ssp. czerepanovii ). The differences in secondary compounds among these plant parts were both qualitative and quantitative. In all parts, condensed tannins accounted for more than 50% of the phenolics. In the first true leaves and cotyledons, chlorogenic acid was the most abundant of the HPLC phenolics. The main components in stems were (+)-catechins and rhododendrins whereas in roots, the main components were ellagitannins. The seedlings were grown at three levels of nitrogen supply (very low-N, low-N, moderate-N), and the effect of nitrogen on concentrations of phenolic compounds was studied in all plant parts. The dry weight of all plant parts, except the roots, increased with increased nitrogen. In all parts, the concentration of condensed tannins was higher at lower levels of nitrogen than at moderate-N. The concentrations of total HPLC phenolics and also those of the compound groups of HPLC phenolics were, however, affected only in the first true leaves and roots. The concentrations in the first true leaves were generally higher in seedlings grown at very low-N and low-N than in seedlings grown at moderate-N. The concentrations in roots were highest at low-N. Not all compounds responded to nitrogen supply in the same manner. The changes in concentrations cannot be exclusively interpreted as changes in the accumulation of phenolic compounds, due to dilution caused by the increase in biomass in better nitrogen availability. There were differences in carbon allocation between condensed tannins and HPLC phenolics in seedlings grown at different nitrogen levels.     

克里雅绿洲旱生芦苇根茎叶C、N、P化学计量特征的季节变化

旱生芦苇在水分限制、元素匮乏的环境条件下,经长期进化适应形成了自身独特的生理生态特征,研究其C、N、P化学计量特征随生长季节的变化规律有助于深入了解该植物生存和适应策略。系统分析了克里雅绿洲旱生芦苇根、茎、叶的C、N、P化学计量特征及其季节动态,深入探讨了不同生长季、不同器官以及两因素的交互作用对以上特征的影响。结果表明:旱生芦苇C、N、P含量均值分别为393.36、12.43、1.25 mg/g,C∶N、N∶P、C∶P均值分别为54.55、9.96、441.27。整个生长季内芦苇各器官间C、N、P平均含量的变化规律一致,为叶茎根,C、N、P化学计量比的变化规律不一致;芦苇C含量随生长季节的变化不断增加,N、P随季节的变化逐渐减少,C、N、P化学计量比随季节的变化规律也不尽相同。对芦苇C、N、P含量及其化学计量比整体变异来源分析显示,生长季节的变化对芦苇C、P、C∶N、C∶P变化的贡献大于器官间差异,器官间差异对芦苇N、N∶P变化的贡献大于生长季节的变化;说明芦苇生长发育过程中各生长季各器官对元素的吸收利用具有特异性。结合N、P元素含量及N∶P值的大小可知,研究区芦苇生长受到N、P共同限制,且更易受N元素的限制。     

Distribution of hydraulic resistance in seedlings,sprouts and an adult tree ofPasania edulis Makino

Hydraulic resistance is an important factor in predicting water status. Hydraulic resistance of petiols, stems and branches, and roots was measured inPasania edulis Makino in order to compare the distribution of resistance between current seedlings, current stump sprouts and a 16 year old adult tree. Total resistance showed only minor variations despite large variations in plant size. This result is thought to be consistent with allometry between leaf mass and supportive organ mass, and with changes in permeability of conductive organs. Root resistance was low in sprouts and the adult tree due to their mature root systems. Current seedlings with undeveloped root systems had high root resistance. The proportion of petiol resistance in total resistance was high compared to the proportion of their conductive distance, and was thought to be a limiting factor of tree water status. The petiol resistance of the adult tree leaves was higher than for seedling and sprout leaves. From a comparison with the leaf water relation characteristics, the petiol resistance was thought to be provided as low values for intolerant leaves against water stress in order to compensate water inflow, and high values for tolerant leaves to regulate water inflow.     

干旱胁迫下红砂幼苗非结构性碳水化合物动态变化特征

该试验以荒漠区主要建群种红砂幼苗为研究对象,设置适宜水分(CK)、轻度干旱(MD)、中度干旱(SD)和重度干旱(VSD)4个胁迫处理(即田间持水量的80%、60%、40%和20%),采用盆栽控水试验,分别测定干旱胁迫15、30、45和60 d时红砂幼苗的叶、茎、粗根和细根中非结构碳水化合物(NSC)及其组分的含量,分析不同胁迫强度下不同干旱持续时间红砂幼苗NSC的动态变化及各组分差异,以揭示红砂NSC对干旱胁迫的响应机制。结果表明:(1)干旱胁迫强度和胁迫持续时间对红砂幼苗不同器官NSC及其组分均有显著影响,其中胁迫持续时间对NSC动态变化的影响尤为显著。(2)干旱胁迫初期,红砂叶中的NSC含量呈下降趋势,而茎中的NSC含量呈上升趋势,粗根和细根中NSC含量在各胁迫处理下基本保持稳定。(3)干旱胁迫后期,红砂叶和茎中的可溶性糖、淀粉和NSC含量逐渐增加,而粗根和细根中的淀粉和NSC含量呈下降趋势(中度干旱除外),且这一时期重度干旱处理下各器官可溶性糖和NSC的含量明显高于CK。研究发现,重度干旱胁迫能显著诱导提高红砂幼苗不同器官中的NSC含量,并通过分解根中淀粉和增加叶片中可溶性糖含量的方式来调节细胞渗透势平衡,以维持细胞活力,进而保持红砂在干旱胁迫后期的存活。     

Economy of Symbiotically Fixed Nitrogen in Red Clover (Trifolium pratenseL.)

The seasonal dynamics of symbiotic fixation, distribution andfate of nitrogen (N) were studied on two successive crops ofred clover (Trifolium pratenseL.) grown outdoors in soil containersunder the Mediterranean climate of southern France. Nitrogenaseactivity was followed throughout the growing season using acetylene(C₂H₂) reduction assays. The distribution and transfer of symbioticallyfixed N were followed by periodic measurements of¹⁵N distributionin plants after exposure of the root systems to labelled dinitrogen(¹⁵N₂). In both years there were two peaks of nitrogenase activity,one in spring and one in late summer, separated by a sharp decreaseduring the flowering period. Over the entire growth cycle, symbioticallyfixed N accounted for 61 to 96% of the total plant N. Once weekafter incorporation, 60 to 90% of N derived from the atmospherewas recovered in the aerial parts of the plants. More than 50%of this was in the leaves, but there were differences in distributionaccording to the stage of development. The maximum percentage(20–28%) recovered from nodulated roots occurred in May–June,during maximum growth of the vegetative organs, and in September.Above-ground symbiotically fixed N was highly mobile with time,moving from the rosette leaves to the leaves attached to theelongated stems and then to the seeds, where 25 to 50% of Nfixed in May and June was recovered in September. Because of:(1) the high turnover rate of leaves; and (2) the relativelyhigh N content of dead leaves, as much as 50% of the symbioticallyfixed N in a year was potentially available to the soil micro-organismsas litter. The maximum transfer was in spring and winter. Ofthe remainder, 20 to 35% was recovered in living plant partsduring regrowth in March of the second year. Transfers to andfrom the root system were less pronounced, but significant decreasesin N content of the roots occurred early in the second yearjust after foliage regrowth was initiated. It is concluded that,because of its high foliage productivity and turnover rate,and high yield of symbiotically fixed N, red clover is a goodcandidate to provide substantial amounts of N to the soil throughoutthe year and therefore restore N fertility. Red clover; Trifolium pratenseL.; forage legumes; labelled dinitrogen (¹⁵N₂) reduction; acetylene reduction; nitrogen fixation; nitrogen distribution; nitrogen transfer     

The effects of nutrients and secondary compounds of Coffea arabica on the behavior and development of Coccus viridis

Phytochemicals may modify the food quality, reduce a plant's palatability to insects, or defend against pests. This work aimed to study 1) relationships between the nitrogen and potassium levels given to plants in nutritive solutions and the foliar phytochemical concentrations, 2) the effect of nutrients and secondary compounds of Coffea arabica on the behavior of Coccus viridis, and 3) tolerance of C. arabica to losses. Deficient, normal, and excessive nitrogen and potassium fertilization treatments were used. Each treatment had two plants (one infested and one noninfested plant). The contents of phytochemicals in the infested plants' leaves and their dry matter of roots, stems, and leaves as well as the total contents in noninfested plants, were determined. The adults and nymphs of C. viridis were counted for 60 d in all treatments. It was verified that elevated nitrogen and potassium levels in the nutritional solutions led to increased of nymphs and adults of C. viridis to the coffee plants over time. Potassium and nitrogen had both direct and indirect effects on C. viridis. The direct effect was because of the increase of the nitrogen content in the leaves. The indirect effect instead was because of reductions in the caffeine and chlorogenic acid contents in the leaves. This is the first study to show relationship nutrient levels of coffee phytochemicals in response to herbivory by scale insects. Caffeine and chlorogenic acid applied on coffee leaves stimulated the locomotory activity of the green scale, thus reducing their feeding compared with untreated leaves. The elevation of caffeine and chlorogenic acid levels in coffee leaves affect this generalist insect by stimulating the locomotion of crawlers.     

喜马拉雅灰叶猴栖息地利用和食性生物学研究(英文）

2006年4月至2007年4月在巴基斯坦克什米尔地区马希亚拉国家公园（Machiara National Park）对喜马拉雅灰叶猴(Semnopithecus entellus ajex)的栖息地利用和食性生物学进行研究。结果表明,冬天,叶猴首选的栖息地多为温暖湿润的针叶林和落叶林混交地区;夏天,它们则迁移至高海拔的亚高山灌木丛林里。喜马拉雅灰叶猴主要以植物的叶子为食,研究期间在该地区共发现49种被采食过的植物（夏季27种,冬季22种）。通过观察它们的所有食物,发现老叶(36.12%)比嫩叶(27.27%)更受欢迎,随后依次为果实17.00%、树根9.45%、树皮6.69%、花2.19%和根茎1.28%。     

Effects of habitat disturbance on the behavioral ecology and demographics of the Tana river red colobus (Colobus badius rufomitratus)

Annual surveys in 1985–1987 revealed that, since 1975, the total population of the Tana River red colobus (Colobus badius rufomitratus)declined by approximately 80%. An intensive study in 1986–1988 of two groups of colobus in the Tana River Primate National Reserve indicated that habitat disturbance from the changing river course and shifting agricultural practices were primarily responsible for the decline. Clearcutting around Mchelelo forest in the late 1960s compressed colobus populations to levels probably above the carrying capacity. Between 1975 and 1986 primate population density declined dramatically, the number of red colobus groups in Mchelelo forest decreased by half, and the size of the remaining group was greatly reduced. In 1986, there were fewer solitary colobus and small parties in the forest, harem male takeovers did not occur, infant survivorship increased, and demographic parameters generally had improved. The colobus groups in Mchelelo in 1973–1975, living at higher densities, showed different feeding and ranging behaviors than 1986–1988 groups. Range size was smaller in 1975, range overlap occurred, and a greater portion of the forest was used per day and per month. Mature leaves accounted for a much higher proportion of the diet. Time spent feeding and resting was the same in both studies. Social organization in predominantly one- male groups was maintained and adult and subadult females transferred between groups.     

Partial feeding preferences and the profitability of winter-feeding sites for brent geese

The suitability of depletion theory for predicting the distribution and movements of wintering brent geese feeding in habitat patches containing foods differing qualitatively as well as quantitatively is evaluated. By monitoring both digestibility and nutrient content of potential foods throughout the season, we assess profitability of habitat patches using assimilation rates.

We argue that these geese do not conform to the predictions of an ideal free distribution because they are constrained both by nitrogen limitation and perceived mortality risks. Instead, for most of the season they exhibited partial feeding preferences by feeding on two or more types of food each day. They fed on salt marsh plants throughout the entire wintering season. In addition, from October until March they fed for part of each day on supplementary sites that were more profitable for nitrogen. In October they fed first on intertidal algae, the most profitable source of nitrogen. When this became depleted in late autumn, they moved inland to feed initially on winter wheat, where they were subject to control shooting, then onto pastures. By mid-March the pastures were no longer a significantly more profitable source of nitrogen. The geese then switched to feeding only on the salt marshes at a cost of a 39% decrease in their overall assimilation rates.

The nitrogen limitation hypothesis was supported by results of experimentally altering the nitrogen content of pasture swards. Feeding preferences correlated positively with changes in nitrogen content, but not water-soluble carbohydrate content of experimental swards.

We conclude that predictions of simple depletion models are unlikely to explain the movements of herbivores between patches that differ in digestibility and nutrient content as well as in the quantity of foods available and that multi-currency models are a more appropriate means of predicting foraging behaviour of herbivores exhibiting partial feeding preferences.