Data from: Seed perishability determines the caching behaviour of a food-hoarding bird

1. Many animals hoard seeds for later consumption and establish seed caches that are often located at sites with specific environmental characteristics. One explanation for the selection of non-random caching locations is the avoidance of pilferage by other animals. Another possible hypothesis is that animals choose locations that hamper the perishability of stored food, allowing the consumption of unspoiled food items over long time periods. 2. We examined seed perishability and pilferage-avoidance as potential drivers for caching behaviour of Spotted nutcrackers (Nucifraga caryocatactes) in the Swiss Alps where the birds are specialized on caching seeds of Swiss stone pine (Pinus cembra). 3. We used seedling establishment as an inverse measure of seed perishability, as established seedlings cannot longer be consumed by nutcrackers. We recorded the environmental conditions (i.e., canopy openness and soil moisture) of seed caching, seedling establishment and pilferage sites. 4. Our results show that sites of seed caching and seedling establishment had opposed micro-environmental conditions. Canopy openness and soil moisture were negatively related to seed caching but positively related to seedling establishment, i.e., nutcrackers cached seeds preferentially at sites where seed perishability was low. We found no effects of environmental factors on cache pilferage, i.e. neither canopy openness nor soil moisture had significant effects on pilferage rates. We thus could not relate caching behaviour to pilferage-avoidance. 5. Our study highlights the importance of seed perishability as a mechanism for seed caching behaviour, which should be considered in future studies. Our findings could have important implications for the regeneration of plants whose seeds are dispersed by seed-caching animals, as the potential of seedlings to establish may strongly decrease if animals cache seeds at sites that favour seed perishability rather than seedling establishment.

1. 诸多动物会贮藏种子以备日后取食，并会将种子缓存点设置在具备特定环境特征的区域。关于动物为何选择非随机的缓存位点，一种主流解释是为了规避其他动物对缓存种子的盗食。另有一项可能的假说认为，动物会挑选能够降低贮藏食物易腐性的位点，从而使其能够在较长时段内取食未变质的食物。
2. 我们以瑞士阿尔卑斯山区的星鸦（Spotted nutcracker，Nucifraga caryocatactes）为研究对象，探讨了种子易腐性与盗食规避这两个潜在驱动因素对其缓存行为的影响——该区域的星鸦专门贮藏瑞士石松（Pinus cembra）的种子。
3. 我们以幼苗定植情况作为种子易腐性的反向衡量指标，因为一旦种子萌发为定植幼苗，便无法再被星鸦取食。我们记录了种子缓存位点、幼苗定植位点以及盗食位点的环境条件，即林冠开度与土壤湿度。
4. 研究结果显示，种子缓存位点与幼苗定植位点的微环境条件恰好相反。林冠开度与土壤湿度与种子缓存呈负相关，但与幼苗定植呈正相关，也就是说星鸦会优先将种子缓存于种子易腐性较低的位点。我们未发现环境因素对缓存盗食率存在显著影响，即林冠开度与土壤湿度均未对盗食率产生显著作用，因此我们无法将星鸦的缓存行为归因于盗食规避。
5. 本研究凸显了种子易腐性作为驱动种子缓存行为的机制的重要性，该因素应在未来的相关研究中得到重视。我们的研究结果对于以种子缓存动物传播种子的植物的种群更新具有重要意义：若动物将种子缓存于易促进种子腐坏而非利于幼苗定植的位点，则幼苗的定植潜力会大幅下降。