Colours are commonly used as visual cues when measuring animals’ cognitive abilities. However, animals can have innate biases towards certain colours that depend on ecological and evolutionary contexts, therefore potentially influencing their performance in experiments. For example, when foraging, the colour red can advertise profitable fruits or act as a warning signal about chemically defended prey, and an individual’s propensity to take food of that colour may depend on experience, age or physical condition. Here, we investigate how these contexts influence blue tits’ (Cyanistes caeruleus) and great tits’ (Parus major) responses to red-coloured almond flakes. We found that juvenile birds preferred red both when it was presented simultaneously with green, and when it was presented with three alternative colours (orange, purple, green). Adult birds, however, only preferred red after a positive experience with the colour, or when it was presented with the three alternative colours. We then tested whether colour influenced avoidance learning about food unpalatability. Despite the prediction that red is a more salient warning signal than green, we found only weak evidence that birds discriminated red unpalatable almonds from a green palatable alternative more quickly than when the colours were reversed. Our results suggest that biases towards red food may depend on birds’ age and previous experience, and this might influence their performance in experiments that use red stimuli. Considering the ecological relevance of colours is, therefore, important when designing experiments that involve colour cues.

中文翻译：

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看到红色？觅食鸟类的颜色偏倚取决于环境。

在测量动物的认知能力时，颜色通常用作视觉提示。但是，动物可能会对某些颜色具有先天性偏见，这些颜色取决于生态和进化环境，因此有可能影响其在实验中的表现。例如，在觅食时，红色可能会宣传可获利的水果或充当有关化学防御猎物的警告信号，并且个人食用该颜色食物的倾向可能取决于经验，年龄或身体状况。在这里，我们研究了这些环境如何影响蓝山雀（Cyanistes caeruleus）和大山雀（Parus major））对红色杏仁片的反应。我们发现，幼鸟在同时呈现绿色和绿色以及呈现三种替代颜色（橙色，紫色，绿色）时都偏爱红色。但是，成年鸟只在对颜色有积极的体验之后或在使用三种替代颜色时才偏爱红色。然后，我们测试了颜色是否会影响对避免食物不良性的了解。尽管预测到红色是比绿色更显着的警告信号，但我们仅发现了微弱的证据，与将颜色反转后相比，鸟类将红色难吃的杏仁与绿色可口的替代品区别开的速度更快。我们的结果表明，偏爱红色食品可能取决于鸟类的年龄和以前的经历，这可能会影响他们在使用红色刺激的实验中的表现。因此，在设计涉及颜色提示的实验时，考虑颜色的生态相关性很重要。