What You See Is What You Get? Exclusion Performances in Ravens and Keas

BackgroundAmong birds, corvids and parrots are prime candidates for advanced cognitive abilities. Still, hardly anything is known about cognitive similarities and dissimilarities between them. Recently, exclusion has gained increasing interest in comparative cognition. To select the correct option in an exclusion task, one option has to be rejected (or excluded) and the correct option may be inferred, which raises the possibility that causal understanding is involved. However, little is yet known about its evolutionary history, as only few species, and mainly mammals, have been studied.
Methodology/Principal FindingsWe tested ravens and keas in a choice task requiring the search for food in two differently shaped tubes. We provided the birds with partial information about the content of one of the two tubes and asked whether they could use this information to infer the location of the hidden food and adjust their searching behaviour accordingly. Additionally, this setup allowed us to investigate whether the birds would appreciate the impact of the shape of the tubes on the visibility of food. The keas chose the baited tube more often than the ravens. However, the ravens applied the more efficient strategy, choosing by exclusion more frequently than the keas. An additional experiment confirmed this, indicating that ravens and keas either differ in their cognitive skills or that they apply them differently.
ConclusionTo our knowledge, this is the first study to demonstrate that corvids and parrots may perform differently in cognitive tasks, highlighting the potential impact of different selection pressures on the cognitive evolution of these large-brained birds.

研究背景
在鸟类类群中，鸦科鸟类（corvids）与鹦鹉（parrots）是展现高级认知能力的核心候选类群。然而，目前学界对二者之间的认知异同仍知之甚少。近年来，排除推理在比较认知学（comparative cognition）研究中受到越来越多的关注。在排除任务（exclusion task）中，受试者需先排除某一选项，进而推断出正确选项的位置，这一过程可能涉及因果理解。但由于目前仅对少数物种（且多为哺乳类）开展过相关研究，人们对排除能力的演化历程仍知之甚少。

研究方法与主要结果
我们以渡鸦（ravens）与啄羊鹦鹉（keas）为受试对象，开展了一项选择任务实验：受试鸟类需在两根不同形状的管道中搜寻隐藏的食物。我们为受试鸟类提供了两根管道中其中一根的部分线索，以考察它们能否利用该线索推断食物的藏匿位置，并据此调整搜寻行为。此外，该实验设置还可用于探究鸟类是否能够理解管道形状对食物可见性的影响。
实验结果显示，啄羊鹦鹉选择置饵管道的频率高于渡鸦，但渡鸦采用了更高效的排除推理策略，其通过排除法进行选择的频率显著高于啄羊鹦鹉。后续补充实验验证了这一结果，表明渡鸦与啄羊鹦鹉要么在认知能力上存在差异，要么对认知策略的运用方式有所不同。

结论
据我们所知，本研究首次证实鸦科鸟类与鹦鹉在认知任务中的表现可能存在差异，凸显了不同选择压力对这类脑容量较大的鸟类认知演化的潜在影响。