Abstract: To understand the characteristics of retrieval in squirrels’ (Sciurus vulgaris) food-hoarding behaviors in the field and what intensities in different stages of winter the squirrels retrieve the food resources that they hoarded, we surveyed their retrieved-caches in a snowy field by means of stratified random sampling in the periods of early-winter (Nov. 6 - 14 in 2004), mid-winter (Jan. 16-24 in 2005) and late-winter (Mar.22 - 31) in Liangshui National Nature Reserve, Heilongjiang Province, Northeastern China. The results showed:1)There was a significant difference (x² = 30.734,df = 2, P < 0. 05) in the retrieving intensities among three stages of winter, early-winter showing the most activity and mid-winter the least. Regression in the frequencies of samples indicated that the populations of data in all of three stages complied with Exponential Distribution (early-winter: Z = 0.749,df = 17, P = 0.682; mid-winter: Z = 0.948, df = 9, P = 0.330; late-winter: Z = 1. 039, df = 13, P = 0.230). 2) The number of retrieved-caches which seeds had been eaten in situ (namely hulls can be found)contributed to 83 percent of the total caches; the remaining caches examined lacked seed hulls. Presumably, these caches may have been re-cached elsewhere by squirrels in order to prevent pilferage or other risk of loss. Because of low yield and seed over-harvest by humans in recent years, we found that retrieved-caches with only one or two seed hulls were very common (up to 92% of total retrieved-caches that seeds had been eaten in situ). 3) The ANOVA by weather factor (temperature and snow depth) showed that, there was a significant difference among the three stages of winter concerning the scales of retrieved-caches (caliber: F _{(2 , 285 )} = 51.26, P < 0. 05; depth: F _{(2 , 285 )} =519.21, P < 0.05). A certain snow depth, perhaps, is beneficial to retrieval by squirrels.So, we concluded that these different performances of squirrels on retrieving intensities indicated a behavioral adaptation to changes of surroundings (especially food supply), in terms of ethology, it is in accord with one of the economic laws of animal foraging behaviors, namely, the minimization of starvation risk. And, optimized seed-retrieval behavior still can be found in the characteristicsof retrieving caches which we surveyed.

Key words: Food-hoarding, Liangshui Nature Reserve, Retrieval, Retrieved-caches, Sciurus vulgaris

摘要： 为了解松鼠贮食行为中的重取食物行为特征,以及在冬季不同生存环境条件下,重取贮藏的红松种子的状况,于2004年初冬(11月中旬),仲冬(2005年1月下旬)和晚冬(3月下旬)采用随机抽样法对凉水自然保护区内雪地上的松鼠重取食物后遗留的贮藏点(称为重取贮点)进行了调查和分析。结果表明:1)冬季不同时期松鼠的重取贮点强度存在明显差异,初冬最大,晚冬次之,仲冬最小,3 个时期的样本数据频率分布检验表明其总体皆服从指数分布;2)当场取食的贮藏点占到83%,17% 的贮藏点未发现籽壳遗留。受松籽低产量及人为过量收获的影响,单个贮藏点贮藏1 粒和2 粒种子的占92.9% ;3)受气温和雪被厚度因素的影响,3 个时期重取贮藏点的口径与深度存在显著差异,一定深度的雪被可能有助于松鼠的重取,但过深的雪被也许会使松鼠无法重取。本研究表明,本地区松鼠在冬季不同时期重取红松种子的强度分配符合将饥饿风险降至最小的觅食经济学原则;松鼠重取行为的优化在贮藏点的被取食状况、口径与深度等特征上得到体现。

关键词: 贮食, 重取, 重取贮点, 松鼠, 凉水自然保护区