Understanding the factors that lead to hen piling up is crucial to avoid them

Behaviors considered abnormal or out of the ordinary often arise as a response to stressful or inadequate environments. Chickens piling up, or crowding together, is one such behavior, which  can indicate that the animals’ welfare is compromised. Factors linked to stress include environmental temperature conditions or  a lack of environmental enrichments.

Poultry management systems are continuously evolving to meet the expectations of conscious consumers and to contribute to animal welfare. Despite this, these systems are not immune to causing stress to the birds and must always be reassessed, improved, and remodeled. The behavior of piling up has various causes that must be observed to minimize the risks of production inefficiency, animal death, and economic losses for the producer.

Caroline Mazzocco, a zootechnician and auditor for Certified Humane®, recently defended her master’s dissertation shedding light on aspects of this topic that are still poorly understood by poultry farmers and researchers. Continue reading to understand the factors that can trigger hen piling up.

Why hen piling up occurs

Laying hens have a gregarious nature, meaning a social tendency to gather in groups. This behavior occurs because moving in groups increases their chances of survival, for instance, in searching for food, escaping predators, and facing environmental challenges. Often, younger individuals imitate the behavior of more experienced birds when choosing places to lay their eggs, perch, and feed. Their instinct for protection leads them to pile up.

This natural expression can lead to recurring piling up, meaning that once the grouping occurs, its tendency is to repeat multiple times. This crowding often has no apparent cause or reason, so farmers must always remain vigilant.

In addition to this natural behavior, piling up can also occur due to hysteria. This is practically unpredictable and happens due to sudden scares caused by any abrupt change in the environment. Examples include unexpected visits, light spots, noises, and events that interfere with the birds’ routine.

The problem is that this grouping often leads to asphyxiation and death of the birds. According to Caroline’s research, hen piling up is the predominant cause of mortality in poultry farming systems, accounting for 26% of occurrences. Given this number, the study examines poultry farmers’ perceptions and understanding of this behavior, identifying its predisposing factors, from structural points in the environment, physiological aspects of the birds, and even daily management practices.

Challenges for farmers and contributing factors

As a multifactorial behavior, hen piling up requires constant attention, as it can be difficult to detect when this problem is about to occur. Causes can include insufficient space, ventilation problems, inadequate lighting, and limited availability of resources such as perches, nests, feeders, and drinkers.

In larger farms, physical access and visual monitoring can be more limited, and farmers often need the help of technology to observe behavior. This type of solution can be expensive and pose logistical difficulties for implementation.

Additionally, symptoms of piling up, such as bird stress and injuries, may resemble manifestations of other problems, making it difficult to identify.

Implementing management practices that prevent piling up requires time and effort, but changes in routine, such as feeding and cleaning schedules, can be beneficial in minimizing hen piling up.

Strategies to prevent and mitigate piling up

Nest Management 

Piling up in nests occurs when many birds seek the same spot in the barn, such as corners. This happens mainly during the early laying stages when younger birds are not yet confident enough to choose their own nest and cluster with others.

To avoid piling up in nests, it is necessary to provide 1 nest for 4 or 5 birds or a minimum of 0.80 m² of collective nest for 100 birds, helping to reduce piling up in this area. Additionally, it is necessary to remove eggs as they are laid to prevent piling up of both birds and eggs.

Thermal Comfort 

When birds pile up, it indicates that they are either cold or escaping from hot areas. This leads them to cluster in areas with a more comfortable temperature, such as near fans to try to cool off. Ideally, the temperature should be uniform. To achieve this, it is possible to use side curtains in the barn to maintain the internal temperature in case of wind or rain.

Uniform Lighting 

Homogeneous light distribution is also recommended, preferably natural. The recommended intensity should allow for bird inspection and ensure there are no darker or shadowed areas they may seek for laying in the litter, leading to piling up. If the lighting is artificial, the system should guarantee a minimum of 8 hours of continuous artificial light and/or daylight, as well as 6 hours of continuous darkness or the natural dark period. This system should use a program of gradual reduction and increase of luminosity, simulating natural light and allowing the hens to prepare for darkness or light.

Considering the concepts of welfare and circadian physiology of the birds, natural lighting favors a uniform routine for all and promotes perching behavior, preventing crowding.

Environmental Enrichment 

The lack of stimuli in the environment can lead to piling up behavior, as sudden and unexpected stimuli can trigger hysteria and behavioral disturbances.

Providing efficient resources, such as feeders, drinkers, and nest boxes, and even offering additional quantities of these resources can help reduce piling up behavior. This is because environmental enrichment can improve the degree of bird welfare through the expression of feelings of pleasure, interest, and a sense of control, as well as improve the use of resources and available space.

According to Caroline’s dissertation, materials such as sand, sawdust, rice husks, and long-cut straw can encourage dust bathing. In addition, the availability of stones or polystyrene blocks and devices with hanging ropes or beads can help in expressing pecking behavior. Perches and raised platforms are also used to offer the animals the possibility to explore the area and exercise during flight.

Animal welfare is productivity 

The research results indicate that laying hen piling up is a behavior triggered by factors related to the environment in which they are kept. The study concludes that there is a need for more rigorous and detailed research to clarify behaviors and assess the economic impacts of production systems and animal welfare.

It is clear that when talking about animal welfare, simply placing animals in a cage-free system is not enough. It is necessary to create conditions for laying hens to live in healthy environments, free from disturbances that can cause stress and compromise their quality of life, thus enabling production.

To learn more about how to identify and avoid piling up behavior in laying hens, zootechnician and researcher Caroline Mazzocco can answer specific questions about laying hen management via email: mazoccocc@gmail.com.

Download the standards for egg laying hens

Published on February 13, 2025