大鵟对长爪沙鼠秋季的集群捕食策略

2003年9月10日—15日,在内蒙古东乌珠穆沁旗嘎达布其口岸附近的典型草原区鼠害草场研究了大鵟(Buteo hemilasius)对长爪沙鼠的捕食策略。鉴于秋季是长爪沙鼠的活跃期,直接采用鼠丘核心区的沙鼠洞口数作为衡量长爪沙鼠集群大小的指标,分析了大鵟对不同大小集群的长爪沙鼠家族集群的捕食选择偏好。实验涉及了3hm2的实验样地,样地中具有符合实验统计的长爪沙鼠洞群为87个。5d内作者观察到大鵟蹲守在样地中的长爪沙鼠29只次,共涉及23个沙鼠洞群。通过分析大鵟蹲守和没有蹲守过的沙鼠洞群的洞口数量,利用非参数的Mann-Whitney U检验法分析,结果表明:大鵟蹲守的洞群的洞口数量总秩和为2569.5,大鵟没有蹲守的沙鼠洞群的洞口数量秩和统计量为1258.5,统计量U值为489.5。校正之后的Z值为-2.37459,两组差异达到显著的水平(P=0.017574)。此外,分析还显示:沙鼠洞群洞口数量(S)与大鵟蹲守次数(F)呈显著的正相关关系,相关式为:F=-0.0559+0.023×S,(r=0.2707,P﹤0.05)。结果表明,大鵟会首先在洞口数量多的长爪沙鼠集群蹲守捕食,因此在越冬期间,长爪沙鼠的集群数量会被限制,进而可能形成一种最优化集群数量的模式。本文的研究结果从一定角度支持了鼠类通过形成最优集群以降低天敌捕食概率的理论。长爪沙鼠可能借助扩散行为,以及秋季的分群行为来降低集群密度从而降低被捕食风险。

The strategy adopted by Upland buzzard (Buteo hemilasius) to Prey on Meriones unguiculatus family group, in Autumn

Between september 10-15 of 2003, we focused on the grasslands in Inner Mongolia that are heavily populated with rodents, to understand the strategy adopted by the upland buzzard (Buteo hemilasius) to prey on the Mongolian gerbil (Meriones unguiculatus) in a typical steppe environment. Autumn is the season when M. unguiculatus are most active, therefore, the number of rodent holes in this season was used as a measure to determine the abundance of M. unguiculatus. Based on a previous study on M. unguiculatus community behavior, we found that when the rodents cluster in autumn, on an average, there is only 1 M. unguiculatus per 6.3 rat holes. Therefore, to reduce the interference of the temporary M. unguiculatus holes in autumn, we defined the groups that had fewer than five rodent holes as temporary, ineffective groups. This study only analyzed the groups with more than five rodent holes as a base group to assess the predation risk. The predation preference of B. hemilasius on different-sized M. unguiculatus clusters was analyzed. This study focused on 3 square meter of grassland, and the number of M. unguiculatus groups, based on the statistics, was 87. To determine the predation strategy of B. hemilasius, two researchers recorded the location and frequency of B. hemilasius within the sample area at different locations using telescopes. For 5 d B. hemilasius was observed swooping down 29 times within the sample area, which was inhabited 23 M. unguiculatus groups. The number of holes that B. hemilasius visited, and the frequency of B. hemilasius visits to each of the groups, was analyzed using the Mann-Whitney test for nonparametric data. From the results, we determined that B. hemilasius visited 2,569.5 holes, while 1,258.5 holes were not visited by B. hemilasius (U value=489.5, Adjusted Z Value=-2.37459), indicating a significant difference between the two (P=0.017574). This indicated that B. hemilasius was obviously biased towards the survey groups with more rodent holes, possibly for increased predation success rate. From the analysis that the correlation between the number of B. hemilasius visits (F) and the group size of another rodent, Brandt''s vole (Lasiopodomys brandtii, (S)), was also determined as follows:F=-0.0559+0.023S (r=0.2707, P < 0.05). From these results, we concluded that the upland buzzard first chose the M. unguiculatus groups that have a higher number of rodent holes as potential prey before it chose the L. brandtii groups. During the winter, the number of M. unguiculatus individuals in clusters will become restricted, and may form an optimal number in the cluster model. The results of the present study may support the theory that prey species form an optimal cluster to reduce predation risk. M. unguiculatus may use rodent holes to escape predation, or autumn swarming behavior to reduce the density of individuals in clusters, to reduce predation risk.