Food supplementation and predation risk in harsh climate: interactive effects on abundance and body condition of tit species

Food availability and predation risk can have drastic impacts on animal behaviour and populations. The tradeoff between foraging and predator avoidance is crucial for animal survival and will strongly affect individual body mass, since large fat reserves are beneficial to reduce starvation but may increase predation risk. However, two-factor experiments simultaneously investigating the interactive effects of food and predation risk, are still rare. We studied the effects of food supplementation and natural predation risk imposed by pygmy owls Glaucidium passerinum on the abundance and fat reserves of tit species in boreal forests of north Europe, from January to March in 2012 and in 2013. Food supplementation increased the number of individuals present in a given forest patch, whereas the level of predation risk had no clear impact on the abundance of tit species. The stronger impact of food supply respect to predation risk could be the consequence of the harsh winter conditions in nort...

食物可获得性与捕食风险，会对动物的行为及种群产生剧烈影响。觅食与反捕食之间的权衡对动物生存至关重要，且会显著影响个体体重——充足的脂肪储备虽有助于降低饥饿风险，但同时可能提升被捕食概率。然而，同时探究食物与捕食风险交互效应的双因素实验仍较为少见。本研究于2012年与2013年的1-3月间，在北欧寒带针叶林（boreal forests）内开展野外实验，探究了食物补充投喂（food supplementation）以及花头鸺鹠（Glaucidium passerinum）带来的自然捕食风险，对山雀类（tit species）的种群丰度与个体脂肪储备的影响。结果表明，食物补充提升了指定林块内的山雀个体数量，而捕食风险强度对山雀类的种群丰度并无显著影响。相较于捕食风险，食物供应的影响更为显著，这或许与北欧东北部严酷的冬季环境有关……