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

没有一个蛋农愿意走进鸡舍，发现一堆死鸟，只知道同样的事件明天和后天可能再次发生，而无法阻止它。这是窒息的影响，这是一种奇怪的行为，母鸡相互摞在一起，导致堆在下面的鸡死亡。没有人真正理解为什么鸡会这样做，它们通常表现得缓慢而平静，导致窒息。当然，产蛋的农民希望减少这种行为，但当他们在农场观察鸟类时，这种情况就不会发生。它断断续续地发生，很难预测。因此，迫切需要新的方法来理解这种行为。在这些令人窒息的事件中，鸟类的行为和动机引起了科学家们的极大兴趣，因为动物通常不会以如此平静的方式造成同一物种其他动物的死亡。这项研究旨在调查窒息发生的时间、地点和方式，以及窒息对存活下来的鸡的影响。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。与一家产蛋公司合作，我们将能接触到110群鸟。这些都有一个监测系统，Birdbox，记录有关母鸡的环境信息（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。我们还将进一步收集这些鸡在雏鸡时期是否受到压力的信息，它们生活的鸡舍的细节，窒息事件发生的时间以及发生在鸡舍的哪个地方。所有这些信息都将用于发现窒息的潜在原因，并在发生之前查看是否有早期预警信号。虽然有助于理解窒息行为的发展，但这些分析本身并不能确定导致鸡以窒息他人的方式移动的直接线索，或者确切地说，是什么动作导致了窒息。为了解决这个问题，我们将在鸡身上放置心率监测器，并使用热成像和标准摄像机拍摄窒息事件。热成像摄像机将允许我们自动测量鸡的运动，以便能够创建一个真实的模拟窒息。窒息的模拟可以让我们了解母鸡的动作，这意味着其他母鸡不会让路，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，或者鸟类在开始互相窒息时是否真的像它们看起来那样平静。我们还将测量压力大的鸡群和母鸡福利的其他指标：对人类和新事物的恐惧，鸡蛋中的压力激素，蛋壳缺陷和骨骼损伤。了解窒息行为是很重要的，因为它损害了鸡的福利，导致一个鸡群中1.4%的鸡死于窒息（这相当于所有死亡率的21%），并可能导致受严重影响的鸡群中20%以上的母鸡死亡。虽然1.4%听起来很小，但这相当于英国鸡蛋农场有超过30万只母鸡死亡，8600万只鸡蛋损失。窒息的实际影响可能比这要大得多，因为通常被窒息杀死的母鸡不会被承认。此外，那些幸存下来的人受伤和压力的可能性从未被调查过。我们的研究结果将用于了解导致这种行为的原因，这将有助于农民了解如何进行干预以防止窒息。我们的结果将能够揭示鸟箱中的信息是否可以提供即将窒息的警告，或者母鸡的特定动作是否可能对窒息的早期预警有用。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.