日本研究人员3日说，通过喂食试验，他们首次发现乌鸦可以仅依据记号辨别数量，能够识数。
日本宇都宫大学动物形态学教授杉田昭荣和同事以8只巨嘴鸦为研究对象，在一个笼子里放置两个相同容器，盖子上分别描绘图案相同的2个记号和5个记号。
研究人员最初让这些乌鸦在这两个容器之间作选择，乌鸦需要啄破盖子取食，只有绘有5个记号的容器内装有鸟食。经过训练，这些乌鸦取食成功率达到70%。
研究小组随后按照组合方式、形状和总面积等类别分成20种组合类型，记号数量从2个至8个不等，并逐一试验。结果发现，乌鸦并不按照记号形状、位置、面积等进行判断，而是根据记号的数量作出选择。
这20种组合类型中，只有1种组合没有达到试验预期效果。其余19种类型中，乌鸦选择装有鸟食且记号数量较多的容器成功率达到70%至90%。
日本共同社报道，杉田和其他研究人员去年公布的研究结果显示，乌鸦能够识别男性和女性面部。“我们想揭示乌鸦更多不为人知的聪明，”山田说。
研究报告发表于本月出版的《动物行为》（Animal Behaviour）期刊。
相关英文论文摘要：
Quantity discrimination in jungle crows, Corvus macrorhynchos
We investigated whether jungle crows can select a given quantity of items (printouts of shapes and symbols) when simultaneously presented with smaller or larger quantities. We presented jungle crows with the choice between two sets of discrete homogeneous quantities (two versus five) in a fixed configural pattern during training. When crows could discriminate five items (15 out of 20 correct choices in two blocks of 10 trials each), they received control tests for non-numerical cues such as element configuration, shape, and total filled area and novel quantity (3 versus 5, 4 versus 5, 5 versus 6, 5 versus 7 and 5 versus 8) tests. During training, jungle crows learned the discrimination task relatively quickly. Additionally, the selections were generally not controlled by the non-numerical cues, indicating that the crows were responding to quantity. Jungle crows selected the familiar larger quantity in smaller sets (3 versus 5 and 4 versus 5) and the novel larger in larger comparisons (5 versus 7 and 5 versus 8) except that of 5 versus 6 quantities. These results suggest that jungle crows have a natural tendency to select the larger quantities and that decisions were affected by the numerical ratio and stimuli magnitude, indicating the use of analogue magnitude mechanism for numerical judgement, as is observed in other animals.
英文论文链接：https://www.sciencedirect.com/science/article/pii/S0003347211002338
