Gentle L K, Gosler A G
Edward Grey Institute of Field Ornithology, Department of Zoology, University of Oxford, UK.
Proc Biol Sci. 2001 Mar 7;268(1466):487-91. doi: 10.1098/rspb.2000.1405.
The fat reserves of small birds are built up daily as insurance against starvation. They are believed to reflect a trade-off between the risks of starvation and predation such that in situations of high predation risk birds are expected either to reduce their fat reserves in response to mass-dependent predation risk or to increase them in response to foraging interruptions. We assessed the effect on fat reserves of experimentally altering the perceived (but not the actual) risk of predation of wild great tits at a winter feeding site. The perceived predation risk was alternated between 'safe' and 'risky'. Increasing the perceived risk of predation involved 'swooping' a model sparrowhawk over the feeder at four unpredictable times each day using a remote mechanism We produce evidence that the experiment was suceessfull in altering the perceived risk of predation. As predicted from the hypothesis of mass-dependent predation risk, great tits (Parus major) carried significantly reduced fat reserves during the 'risky' treatment. Furthermore, dominant individuals were able to reduce their reserves more than subordinates. As birds returned to feeders within seconds after a predator 'attack', the reduction in fat reserves cannot be attributed to an interruption in feeding.
小型鸟类的脂肪储备每天都会积累，作为抵御饥饿的保障。人们认为这反映了饥饿风险和被捕食风险之间的权衡，即在高捕食风险的情况下，鸟类要么会因体重相关的捕食风险而减少脂肪储备，要么会因觅食中断而增加脂肪储备。我们评估了在冬季喂食地点通过实验改变野生大山雀感知到的（而非实际的）捕食风险对其脂肪储备的影响。感知到的捕食风险在“安全”和“危险”之间交替。增加感知到的捕食风险包括每天使用遥控装置在四个不可预测的时间让一只模拟雀鹰在喂食器上方“俯冲”。我们提供的证据表明，该实验成功改变了感知到的捕食风险。正如从体重相关捕食风险假说所预测的那样，大山雀在“危险”处理期间脂肪储备显著减少。此外，优势个体比从属个体能够更多地减少其储备。由于鸟类在捕食者“攻击”后几秒钟内就回到了喂食器，脂肪储备的减少不能归因于觅食中断。
