Dietary cognition in educated predators: implications for the evolution of prey defence strategies

许多昆虫用有毒的化学物质来保护自己免遭捕食。它们经常用明显的警告颜色向潜在的攻击者（通常是试图吃掉它们的鸟）宣传它们的化学防御，如瓢虫、黄蜂和色彩鲜艳的蝴蝶。通常，科学家们认为鸟类学会了将警告颜色与毒素的影响联系起来，因此在未来完全避开具有相似颜色图案的个体。然而，这一假设最近被证明是错误的。鸟类实际上会继续吃少量的有毒昆虫，即使它们知道自己已经被保护起来了。它们小心翼翼地控制它们所吃的有毒昆虫的数量，以获得有毒猎物中所含的营养，但要确保它们不会吃太多的昆虫，从而导致任何严重的健康问题。拟议中的实验旨在调查影响鸟类选择食用有毒猎物的因素。我们认为，当鸟类可以从其他来源获得所需的营养时，即当环境中有更多可选择的无毒猎物时，或者当无毒猎物的营养水平更高时，它们会少吃有毒昆虫。我们还预计其他有毒物种的存在会影响鸟类的觅食决定。然而，我们目前还不知道捕食者对猎物有什么了解，也不知道它们是如何决定有毒猎物作为食物来源的“价值”。我们将通过给野外捕获的椋鸟（饲养在实验室里）有毒和无毒昆虫的序列，并测量它们选择吃哪些昆虫来研究这个问题。通过注射奎宁溶液（一种温和的毒素）来控制昆虫的毒性，通过注射蛋白质溶液来控制它们的营养成分。研究结果将使我们了解鸟类对它们所吃的食物的了解，它们在决定吃什么时如何使用这些信息，以及猎物的营养如何影响它有毒的好处。我们还将进行数学模拟，研究捕食者应该使用什么觅食策略来最大限度地增加营养摄入量，同时尽可能降低毒素摄入量。然后，这些模拟将被扩展到研究捕食者的觅食策略如何决定在什么情况下猎物会从有毒中受益，以及这些猎物何时会从用明亮的警告色来宣传它们的毒性中受益。这些模拟还将用于帮助我们了解喷洒有毒化学物质（以阻止鸟类食用它们）如何影响鸟类食用有毒昆虫（如瓢虫和蜜蜂）的决定。这也可能让我们决定如何最好地阻止这些昆虫物种的数量下降。

Many insects defend themselves against predation with toxic chemicals. They often advertise their chemical defences to potential attackers (generally birds attempting to eat them) using conspicuous warning colouration, as seen in ladybirds, wasps and brightly-coloured butterflies. Typically, scientists have assumed that birds learn to associate the warning colouration with the effects of the toxins, and as a result totally avoid individuals with similar colour patterns in the future. However, this assumption has recently been shown to be wrong. Birds actually continue to eat toxic insects at low levels, even when they know that they are defended. They carefully control the number of toxic insects that they eat in order to gain the nutrients contained in the toxic prey, but ensuring they do not eat enough insects to cause them any serious health problems. The proposed experiments aim to investigate what factors influence birds' choices to eat toxic prey. We would expect that birds will eat fewer toxic insects when they can gain the nutrients they need from other sources i.e. when there are more alternative non-toxic prey in the environment, or when non-toxic prey have higher levels of nutrients. We would also expect the presence of other toxic species to influence birds' foraging decisions. However, we do not currently know what predators learn about their prey, or how they decide how 'valuable' toxic prey are as a food source. We will investigate this by giving wild-caught starlings, which are housed in a laboratory, sequences of toxic and non-toxic insects, and measuring which insects they choose to eat. The toxicity of the insects will be manipulated by injecting them with quinine solution (a mild toxin), and their nutrient content can be manipulated by injecting them with a protein solution. The results will allow us to understand what birds learn about the food they eat, how they use this information when deciding what to eat, and how the nutrition of a prey species influences the benefit of it being toxic. We will also produce mathematical simulations that investigate what foraging strategies predators' should use to maximize their nutrient intake whilst keeping their toxin intake as low as possible. These simulations will then be extended to investigate how predators' foraging strategies determine under what circumstances prey will benefit from being toxic, and when such prey will benefit from advertising their toxicity with bright warning colouration. These simulations will also be used to help us to understand how spraying crops with toxic chemicals (to stop birds eating them) influences birds decisions to eat toxic insects like ladybirds and bees. This might also allow us to decide how best to stop these insect species declining in numbers.