兽类学报 ,2007,27 (3):209 - 214 Acta Theriologica Sinica

Hoarding of walnuts by David s rock squirrels Sciurotamias ’ ( davidianus within enclosure )

1 ,2 2  LU Jiqi ,ZHANG Zhibin

Department of Bioengineering Zhengzhou University Zhengzhou China (1 , , 450001, ) State Key Laboratory of Integrated Management of Pest Insects and Rodents Institute of Zoology the Chinese Academy of Sciences Beijing (2 , , , China 100080 , )

Abstract :A variety of animals store food to cope with temporally variable or unpredictable food supplies. We have little Sciurotamias davidianus knowledge of the food hoarding behavior of David’s rock squirrels ( ),a species endemic to China and mainly distributed in the hilly temperate zone in northern China. We constructed semi-natural enclosures in the Donglingshan mountains area in which we investigated the squirrels’food hoarding behavior by providing them with tagged Juglans regia walnuts ( ). The results showed that David’s rock squirrels exhibited both larder and scatter hoarding,and the latter seemed to be their preferred choice. Artificial pilferage of hoarded food items had no significant effect on the hoarding behavior of squirrels. Within the enclosures,squirrels tended to select certain sites to scatter hoard walnuts,and no walnuts were consumed at the location where they were provisioned. The possible factors affecting food hoarding of Da- vid’s rock squirrels were discussed. Key words Sciurotamias davidianus :Donglingshan Mountains; ;Larder hoarding;Scatter hoarding;Walnuts 围栏条件下岩松鼠对核桃的贮藏

路纪琪1 ,2 张知彬 2 

郑 州大 学生物 工程系 郑 州 中国科 学院 动物研 究所 农业虫鼠害综合治理国家重点实验室 北京 (1 , 450001)(2 , , 100080)

摘要 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 断 食 于 左右 随机 选择 只岩 松鼠 将其 放入 围 栏中 适应 。 6 h , 13 ∶ 00 , 1 , 随后 在给食处放置 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 2 ～ 3 h。 , 20 。 , 理情况 将埋藏 取食和剩余的核桃全部移出 另 置 枚新 的核 桃 继续 实验 第 三天 重 复上 述 检查 和记 , 、 , 20 , 。 , 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 。 关键词 岩松鼠 集中贮藏 分散贮藏 核桃 东灵山 : ; ; ; ; 中图分类号 文献标识码 文章编号 :Q958 1 :A :1000 - 1050 (2007) 03 - 0209 - 06

A wide variety of animals hoard food for later con- large concentrations of stored food (larders)are com- sumption during periods of food scarcity. Stored food pelled to space food items widely and hide them care- items are distributed in a variety of ways,from highly fully (i e ,scatter hoarding ),so they cannot easily clumped to highly dispersed. The extremes of this be found by other animals (Vander Wall and Jenkins, spectrum of cache-dispersion patterns have been 2002). Food hoarding has an advantage of increasing termed larder hoarding and scatter hoarding (Smith food availability during winter and early spring (Wau- et al and Reichman, 1984; reviewed by Vander Wall, ters  ,1995),it also decreases the likelihood that 1990 ). Food hoarding animals that cannot defend other foragers will find the food (Anderson and Krebs,

Foundation item :The key project (G2000046802) of the Ministry of Science and Technology of China; the key project (KSCX2 - SW - 103 ) of the Chinese Acadeny of Sciences Biography :LU Jiqi (1964 - ),male, doctor,professor, is engaged in animal ecdogy . E - mail:lujq@ zzu edu cn Received date Accepted date :2007 - 01 - 31; :2007 - 05 - 24  correspondence author,E - mail:zhangzb@ ioz ac cn 兽 类 学 报 卷 210 27

1978; Smith and Reichman, 1984; Stapanian and verely disturbed due to extensive artificial cutting and Smith,1984;Brodin and Ekman,1994). Under nat- grazing by livestock for almost a century. Since the ural conditions,larder hoarding and scatter hoarding 1990’s,all villagers were relocated to allow for resto- may exert different roles in plant regeneration,the lat- ration and conservation of the local ecosystem. Lia- Quercus liaotungensis ter will playing an important role in this aspect odong oak ( ), wild apricot P armeniaca Vitex negundo Prunus davidiana (Vander Wall, 1990; Forget and Vander Wall, (  ), and Elymus excel 2001). Rodents in Family Sciuridae are among the are common shrubs. Under the shrubs, - sus Poa Elsholtzia stauntoni most studied food hoarders. Hoarding behaviour of red , spp , are commonly seen Sciurus vulgaris Larix principis rupprechtii squirrels ( )(Rice-Oxley 1993;Jiang, grass species. Larch ( - ),and P tabulaeformis 1995;Wauters and Casale,1996;Lee,2002;Wau- Chinese pine (  )have been planted in et al Sciurus carolinen ters  ,2002 );grey squirrels ( - small areas by a local reforestation farm. Wild apricot sis )(Thompson and Thompson, 1980; Kraus, typically set fruits from June to August,while walnuts Sciurus niger et al J regia 1983);fox squirrels ( )(Nixon  , ( ) are available from September to October. 1968; Stapanian and Smith, 1984 ) and Japanese The area is considered within the natural distribution Sciurus lis et al S davidianus squirrels ( )(Tamura  ,1999 ) have region of David’s rock squirrels (  ) et al been studied. (Shou,1962,Chen  ,2002)  Sciurotamias davidianus David’s rock squirrel ( ), 1 2 Enclosure design an endemic species in China,occurs widely in moun- Four enclosures (9 m × 9 m × 1 m ) were con- tainous and hilly areas throughout northern China. structed on abandoned cultivated land. The tops were They usually inhabit relativly open habitats such as covered with strips of wire mesh (2 5 cm × 2 5 cm) broad-l afed ores s,co ifer oress,fr it foests nd to prevent experimental animals from crawling out. s rubs andae con ider dtobesemi-arboreal (Shou, The floor within each enclosure was cemented to pre- et al 1962;Chen  ,2002). Similar to other Holarctic vent animals escaping by burrowing. We then spread a tree squirrels,David ’s rock squirrels do not hiber- layer (about 20 cm)of mixed soil and sand (1 ∶ 1)to nate. They exhibit a diurnal activity pattern,with ac- allow a matrix in which food could be cached. A tivity peaks in the early morning and late afternoon. wooden nest box (30 cm × 20 cm × 20 cm)was placed David’s rock squirrels preferred to eat oleaginous seeds in a corner of each enclosure. All food items were pro- Pinus tabulaeformis and nuts of Chinese pine ( ),wal- vided in a wooden feeder located at the enclosure cen- Juglans regia Prunus armenia nuts ( ),wild apricot ( - ter. The central feeder location forced animals to cross ca et al )(Shou,1962,Chen  ,2002). We expected open ground to acquire food items and then again to them to scatter hoard food as a behavioural strategy to potential hoarding sites. A water bottle was placed survive over the period of food shortage, that is, next to the nest box. Enclosures were divided in four through the long winter and early spring,and to pre- equal quadrants with the feeder as the origin to ease vent their hoarded food from being pilfered by intra-and mapping the cache locations inter-species individuals. It has been suggested that 1 3 Experimental animals David’s rock squirrel stores some nuts in tree holes Adult experimental animals were live captured et al (Chen  ,2002 ). However,the detail of food from the study area. The mean (± SD)body mass of n hoarding behaviour in this species remains unknown David ’s rock squirrels ( = 14 ) was 274 24 ± We conducted a series of tests to develop an un- 18 31 g. Their previous dietary experience was pre- derstanding of hoarding behaviour of David’s rock sumed to have consisted primarily of the predominate squirrels,The main goals of this study were:1)to de- vegetation. Following capture animals were weighed, termine the hoarding strategy of David’s rock squirrels examined to ensure they were healthy and to determine on walnuts (larder vs scatter hoarding);and 2)to test gender, and tagged for subsequent identification. how squirrels respond to perceived pilferage on hoarded Then, all David’s rock squirrels were individually food. housed in cages made of steel mesh (45 cm × 30 cm × Material and Methods 1 20 cm). Animals were given free access to rabbit pel- 1 1 Study area lets or peanuts and water throughout the holding peri- The study area,Liyuanling village (40° 00′ N, od. Lighting reflected natural day lengths during the 115°30′E)in Mentougou District,lies at an altitude of study period from September to October,2003 about 1 100 m,about 120 km northwest of Beijing, 1 4 Walnuts collection and marking China. This area belongs to the Donlingshan Food items offered squirrels during the study were Mountains region and has a warm temperate continental walnuts. During fruiting periods (September), ma- monsoon climate. The local ecosystem has been se- tured intact walnuts were collected,and kept hermeti- 期 et al Sciurotamias davidianus 3 LU Jiqi .:Hoarding of walnuts by David’s rock squirrels ( ) within enclosure 211 cally until experimental use. We selected walnuts for After checking and recording,all food items were use because they are wildly available, and are impor- removed from enclosure. The procedures were then re- tant in the diet of David ’s rock squirrels at the study peated with new walnuts (20). Subjects were removed area ,and are relatively large and easy to experimental- at the end of each trial and the nest box,feeder,and ly manipulate. Squirrels caught in the area were pre- the enclosure were thoroughly cleaned. An additional sumed to have had prior experience with walnuts. 4 squirrels were then randomly assigned to the enclo- n Fresh mass of walnut averaged 10 74 ± 1 42 g ( = sures and the test repeated. Subjects were tested only 50). Individual walnuts were marked following Zhang once. During every experimental day,a total 280 wal- and Wang (2001 ). A tiny hole was drilled at the nuts were provided. spine of each nut,and a small,light tin-tag (3 cm We defined those food items transported into nest- long and 1 cm wide) was connected with a fine wire boxes as larder hoarding,while any food items buried 3 cm long. The tags were coded using a sharp metal- in soil within the enclosures were scored as scatter pen. Tags were easily seen after the nuts were buried hoarding (Smith and Reichman 1984; Vander Wall by squirrels,because the tags were left on the ground 1990;Jenkins and Breck,1998). surface. Weight of the metal tags (0 1 g)was negli- 1 6 Statistical analyses gible relative to the weight of the food item. Former SPSS for Windows (version 10 0)was employed studies indicated that attaching these tags did not sig- for statistical analyses. Wilcoxon test was used to com- nificantly influence the transport and burial of tagged pare differences:1 ) of walnuts between larder and nuts by rodents (Li and Zhang 2003). scatter hording on both day 1 and day 2 ;2 )of con- 1 5 Experimental procedure sumed walnuts between out and inside nest box on day The study was carried out during September-Octo- 1 and day 2 ;3)of the transportation distances of bur- ber,2003. A subject was randomly assigned to each ied food items between day 1 and day 2 . 1-sample of the 4 enclosures. Animals were food deprived for 6 Kolmogorov-Smirnov test was used to examine whether hours prior to being placed in their respective enclosure the distribution pattern of transportation distance of and allowed 2 - 3 hours to adapt to their new environ- buried walnuts was normal. Results ment. To avoid potential conflict with the daily activity 2 peak,squirrels were put in their respective enclosures 2 1 Hoarding forms at 13 ∶ 00 on the first day (day 0 ). Twenty marked The results showed that David’s rock squirrels ex- walnuts were then placed in each centrally located hibited two forms of food hoarding (i e ,larder and feeder. At the same time the next day (day 1 ),all scatter hoarding ) under semi-natural conditions. It food items were examined and their location - inclu- seemed that David’s rock squirrels preferred to scatter ding where they were cached and the distance they hoard food items (seeds or nuts)(Table 1 ),though were carried-was identified. Food items were recorded there was no significant difference between larder and Z as fitting one of 5 categories as follows: scatter hoarded walnuts (Wilcoxon test, = - 1 099, in situ P EI-eaten :the tagged walnuts were eaten on = 0 272 ). When scatter hoarding,David ’s rock the spot of the point of provision. squirrels carried walnuts away from the feeder and bur- ER-eaten after removal:the tagged walnuts were ied one walnut in the soil at each cache site;many of eaten on the ground surface after removal. the buried walnuts were along the wall of enclosure B-buried:the tagged walnuts were buried in soil (Fig. 1). The average (± SD)transport distance of inside the enclosure. buried walnuts was 435 30 ± 114 82 cm, and the EN-entered nest:the tagged walnuts were trans- transport distance was distributed in a normal pattern Z P ported into nest-box. (1 - sample Kolmogorov-Smirnor test, = 1 275, = AS-abandoned on the surface:the tagged walnuts 0 079)(Fig. 2). were abandoned on ground surface after removal.

Table Walnuts handled by David s rock squirrels within the experimental enclosures 1 ’ Time EN B AS EI ER ET Mean ± SD 2 29 ± 2 20 5 36 ± 6 78 5 00 ± 3 94 0 1 21 ± 1 48 0 29 ± 0 61 Day 1 Range 0 - 6 0 - 18 0 - 14 0 0 - 4 0 - 2 Total 32 75 70 0 17 4 Mean ± SD 1 36 ± 1 28 4 86 ± 6 38 3 93 ± 3 50 0 1 64 ± 1 28 0 36 ± 0 63 Day 2 Range 0 - 4 0 - 18 0 - 10 0 0 - 4 0 - 2 Total 19 68 55 0 23 4 兽 类 学 报 卷 212 27

2 2 Consumed and abandoned walnuts outside their nest box than inside (but the difference Z P On day 1,no walnuts were eaten at the spot of the was not significant,Wilcoxon test, = - 1 851, = feeder,while some walnuts were consumed by experi- 0 064 ). When consuming walnuts outside the nest mental animals out and inside their nest box (Table 1). box,squirrels usually carried walnuts far away from the On average,David’s rock squirrels ate more walnuts feeder and closer to their nest (Fig. 2,Fig. 3).

Fig 1 Scatter graphs of scatter hoarded walnuts inside the experimental enclosures,the nest box was placed at top left corner (- 450 , 450). a:Day 1; b:Day 2

Fig. 2 Proportional distribution of transport distance of different status of walnuts. a:Day 1; b:Day 2

Fig. 3 Scatter graphs of consumed walnuts outside the nest box. a :Day 1 ;b:D ay 2 期 et al Sciurotamias davidianus 3 LU Jiqi .:Hoarding of walnuts by David’s rock squirrels ( ) within enclosure 213

In addition to hoarding and eating,David’s rock other AS walnuts were carried to the second quadrant squirrels also abandoned some walnuts on the soil sur- where the nest box was located (Fig 2,Fig 4). Giv- face after removal (AS)(Table 1). A large portion of en enough time, these AS walnuts may either have AS walnuts was closer to the feeder,and many of the been larder or scatter hoarded,or consumed directly

F ig. 4 Scatter graphs of walnuts abandoned on the soil surface. a:D ay 1;b:Day 2

2 3 Response to perceived pilferage on hoarded wal- squirrels exhibited two forms of food hoarding,i e , nuts larder and scatter hoarding. Furthermore, David ’s Prior to day 2 we removed all walnuts that were rock squirrels preferred to hoard food in scatter form. larder and scatter hoarded,as well as the remains of Our results also confirmed previous observations on this et al consumed walnuts;this treatment has a similar effect of species (Chen  ,2002 ),and was accordant to pilferage on hoarded food by other individuals. Con- the result that tree squirrels are typical scatter-hoarders et al fronted with perceived pilferage,David’s rock squir- (Vander Wall,1990 ;Tamura  ,1999; Lee, rels adjusted their hoarding behavior accordingly. On 2002). On the other hand,scatter hoarding is a faster day 2 they removed fewer walnuts from the feeder com- means of sequestering a food source (Hart,1971 ) pared to day 1,in other words,more walnuts were left Among the potential factors influencing cache at feeder. The number of walnuts that were carried in- strategy,MacDonald (1976 )suggested that the likeli- to the nest,buried and abandoned on the surface de- hood of pilferage determine cache strategy,which is in creased on day 2,though the differences were not sig- turn affected by the age, sex, reproductive status nificant;while squirrels consumed more walnuts both (Clarke and Kramer,1994 )and dominance status of out and inside nest box (Table 1). On day 2,squir- the food hoarder (Jenkins and Breck,1998 ). The rels consumed significantly more walnuts outside nest threat of pilferage has led to various hoarding strate- Z P than inside (Wilcoxon test, = - 2 501 , = gies, generally involving either the concentration of 0 012). food in a central,easily defended larder or the scatter- Squirrels scatter hoarded more walnuts on day 2 ing of food widely enough so that the discovery of one than they larder hoarded,but the difference was not or a few caches is unlikely to lead the discovery of all Z P significant (Wilcoxon test, = - 1 154, = (Stelis,2000 ). It is generally believed that for food 0 249 ). The walnuts that were buried,consumed out- hoarding to evolve,food hoarders must keep pilferage side nest,and abandoned on the soil surface showed a to some acceptably low level. To achieve this,food similar distribution pattern within the enclosure hoarding animals must have evolved behavioral and (Fig 1,Fig 3,Fig 4 );between day 1 and day 2, spatial patterns of hoarding that minimized pilferage there were no significant differences between transport (Vander Wall and Jenkins, 2002 ). Hoarders that distance of buried walnuts,consumed walnuts,and AS cannot defend large concentrations of stored food (lard- walnuts (Fig. 2). ers)are compelled to store food items in a scatter pat- Discussion 3 tern (Vander Wall and Jenkins,2002 ). To survive o- Result of this study showed that David ’s rock ver the period of food scarcity,long winter and early 兽 类 学 报 卷 214 27

Behavioral Ecology 3 spring,David’s rock squirrels in northern China have riam ’s kangaroo rats. , :60 - 65. Jenkins S H,Breck S W. 1998. Differences in food hoarding among six Journal of Mammalogy 79 to store a large quantity of food. species of heteromyid rodents. , :1221 Our results indicated that artificial pilferage on - 1233 . stored food items had no significant influence on food Jiang Z G. 1995. Food hoarding behavior in Red squirrel. In:Zhang J hoarding behavior of experimental animals,this may be ed,Studies of Mammal Biology in China. Beijing:Chinese Forestry Press,185 - 190. because, for scatter hoarding animals, pilferage on Johnson T K,Jorgensen C D. 1981 . Ability of desert rodents to find bur- Journal of Range Management 34 stored food exists extensively (Stapanian and Smith, ied seeds. , :312 - 314. et al Kraus B. 1983. 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