The sense of olfaction has been traditionally considered of low relevance in bird biology. In particular, the location of cached seeds by scatter-hoarder corvids is assumed to depend on spatial memory, whereas no study has demonstrated the use of olfaction to detect these seeds. In this study we tested whether olfaction might play a role in the precise location of cached nuts by magpies, Pica pica, a scatter-hoarder corvid species. We conducted an experiment under natural conditions where nuts belonging to four treatments were buried, simulating natural caches, and we monitored the rate of nut detection by magpies. Three of the treatments included nuts with natural odour or odour of a strong-smelling substance (untreated nuts, nutshells filled with soil and nuts soaked in diesel), whereas the fourth treatment consisted of 3D-printed fake nuts made of polypropylene. The experiment was replicated in two sites and in several breeding territories, using a total of 624 nuts. Motion-activated cameras were installed to identify the animals foraging in the plots. The results show that magpies detected untreated nuts, nutshells or nuts soaked in diesel ca. three times more than 3D-printed fake nuts. Among detected and unburied nuts, the 3D-printed nuts were largely abandoned on site, followed by nutshells without a kernel, natural nuts and nuts soaked in diesel. All this strongly supports the hypothesis that magpies use olfaction to pinpoint cached nuts, either for nut recovery or pilfering, but once a nut is detected they may use other senses such as vision or touch for selection. Given the strong changes in landscape features that may occur under natural conditions between the time of nut caching and nut retrieval, we suggest that the use of olfaction might be crucial to help spatial memory in determining the location of cached nuts in corvids.

中文翻译：

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通过嗅觉精确检测散布囤积鸟的缓存

传统上，嗅觉在鸟类生物学中的相关性较低。特别是，散布囤积者鸦科动物缓存种子的位置被认为取决于空间记忆，而没有研究证明使用嗅觉来检测这些种子。在这项研究中，我们测试了嗅觉是否可能在喜鹊（Pica pica，一种散布囤积的鸦科动物）缓存坚果的精确位置中发挥作用。我们在自然条件下进行了一项实验，其中四种处理的坚果被埋葬，模拟天然藏匿处，我们监测了喜鹊对坚果的检测率。其中三种处理包括具有天然气味或强烈气味物质气味的坚果（未经处理的坚果、充满土壤的坚果壳和浸泡在柴油中的坚果），而第四种处理包括由聚丙烯制成的 3D 打印假坚果。该实验在两个地点和几个繁殖地区进行了重复，总共使用了 624 种坚果。安装了运动激活相机以识别在地块中觅食的动物。结果表明喜鹊检测到未经处理的坚果、坚果壳或浸泡在柴油中的坚果。比 3D 打印的假坚果多三倍。在检测到的和未掩埋的坚果中，3D 打印的坚果大部分被丢弃在现场，其次是无核的坚果壳、天然坚果和浸泡在柴油中的坚果。所有这些都有力地支持了这样一种假设，即喜鹊使用嗅觉来查明缓存的坚果，无论是为了坚果回收还是偷窃，但是一旦检测到坚果，它们可能会使用其他感官，例如视觉或触觉进行选择。