Why do hens smother? An investigation into the causes and consequences of smothering

没有哪个蛋农会想走进鸡舍，发现一堆死鸡，却知道同样的事情明天和第二天可能会再次发生，而无法阻止。这就是窒息的影响，一种奇怪的行为，母鸡互相堆叠，导致堆底的鸡死亡。没有人真正理解为什么鸡会这样做，而且在窒息之前，它们通常会缓慢而平静地移动。自然，生产鸡蛋的农民希望减少这种行为，但当他们在农场观看鸟类时，这种情况不会发生。它间歇性地发生，很难预测。因此，迫切需要新的方法来理解这种行为。鸟类在这些窒息事件中的行为和动机引起了科学家的极大兴趣，因为动物通常不会以如此明显的平静方式导致同一物种的其他动物死亡。本研究旨在调查窒息发生的时间、地点和方式，以及窒息对存活鸡的影响。窒息是不可预测的，这意味着需要大量的农场来研究这种行为。与一家鸡蛋生产公司合作，我们将有机会获得110群鸟类。所有这些都有一个监测系统，Birdbox，记录有关母鸡环境的信息（例如通风和温度），食物和水的摄入量，产蛋量以及母鸡死亡的数量和原因。我们还将收集进一步的信息，了解这些鸡在还是小鸡的时候是否受到了压力，它们生活的谷仓的细节，窒息事件发生的时间以及它们发生在谷仓的哪里。所有这些信息都将用于寻找窒息的潜在原因，并在发生之前查看是否有早期预警信号。虽然这些分析有助于理解窒息行为的发展，但它们本身并不能识别导致鸡以窒息其他鸡的方式移动的直接线索，或者确实是什么运动导致窒息。为了解决这个问题，我们将把心率监测器的鸡和电影窒息事件使用热和标准相机。热感摄像机将使我们能够自动测量鸡的运动，以便能够创建一个逼真的窒息模拟。窒息的模拟将使我们了解母鸡的运动是什么意思，这意味着其他母鸡不会让开，最终被杀死。心率监测器将使我们能够看到压力是否会引发窒息，或者鸟类是否真的像它们开始窒息时表现出的那样平静。我们还将测量应激鸡群和母鸡福利的其他指标：对人类和新物体的恐惧，鸡蛋中的应激激素，蛋壳中的缺陷和骨骼损伤。了解窒息行为很重要，因为它损害鸡的福利，导致鸡群中1.4%的鸡死于窒息（这相当于所有死亡率的21%），并且可以杀死严重受影响鸡群中20%以上的母鸡。虽然1.4%听起来很小，但这相当于英国鸡蛋农场超过30万只母鸡死亡和8600万枚鸡蛋损失。闷死的真实的影响可能比这大得多，因为闷死的母鸡通常不会被承认。此外，幸存者受伤和压力的可能性以前从未被调查过。我们的研究结果将用于了解导致这种行为的原因，这将有助于农民知道如何进行干预以防止窒息。我们的研究结果将能够揭示鸟箱中的信息是否可以提供窒息即将发生的警告，或者母鸡的特定动作是否可能对窒息的早期警告有用。通过这个项目，我们将受益于了解窒息对蛋鸡福利的真正影响。

There can be no egg farmer who wants to walk into a chicken house and find a pile of dead birds, only to know the same event could happen again tomorrow and the next day, without being able to prevent it. This is the impact of smothering, a strange behaviour whereby hens pile on top of each other causing deaths of chickens at the bottom of the pile. No-one really understands why chickens do this and often they appear to move slowly and calmly in the lead up to smothering. Naturally, farmers who produce eggs would like to reduce this behaviour, but it doesn't happen when they are present in the farm watching the birds. It happens intermittently and is hard to predict. New approaches are therefore urgently needed to understand this behaviour. The behaviour and motivations of birds during these smothering events is of great interest to scientists because animals don't often cause the death of other animals of the same species in such an apparently calm manner. This research aims to investigate when, where and how smothering happens, and the effect smothering has on the chickens that survive. The fact that smothering is unpredictable means that a large number of farms are needed in order to study this behaviour. Working with an egg producing company we will have access to 110 flocks of birds. These all have a monitoring system, Birdbox, which records information about the environment of the hens (e.g. ventilation and temperature), food and water intake, egg production, and numbers and causes of hen deaths. We will also gather further information on whether these chickens were stressed when they were still chicks, details of the barns where they live, at what time smothering events occur and where in the barn they happen. All this information will be used find the potential causes of smothering and to see if there could be early warning signs before it happens. Whilst useful for understanding the development of smothering behaviour, these analyses by themselves won't identify the immediate cues that cause chickens to move in ways which smother others, or indeed what movements cause smothering. To address this we will place heart rate monitors on chickens and film smothering events using thermal and standard cameras. The thermal cameras will allow us to automatically measure movements of chickens to be able to create a realistic simulation of smothering. The simulation of smothering will allow us to understand what it is about hen's movements which means other hens don't move out the way and end up getting killed. Heart rate monitors will enable us to see whether stress might trigger smothering, or whether birds really are as calm as they appear when starting to smother one another. We will also measure other indications of a stressed flock and hen welfare: fearfulness toward humans and novel objects, stress hormones in the egg, faults in eggshells and bone injuries. It is important to understand smothering behaviour because it harms chickens welfare and causes deaths of 1.4% of birds in a flock die from smothering (this equates to 21% of all mortalities) and can kill more than 20% of hens in badly affected flocks. Whilst 1.4% overall may sound small, this equates to over 300,000 hens deaths and 86 million eggs lost across the UK egg farms. The real impact of smothering is probably much greater than this because often hens killed by smothering will not be recognised as such. In addition, the potential for injuries and stress in those that survive have never before been investigated. Our results will be used to understand what causes this behaviour which will help farmers know how to intervene to prevent smothering. Our results will be able to reveal if information in the BirdBox could provide a warning that smothering is imminent, or whether particular movements made by hens might be useful for early warnings of smothering. Through this project we will benefit by understanding the true impact of smothering for laying hen welfare.