Transmission of maternal aggression in canaries requires direct mother- daughter interaction
This study on domestic canaries reveals that the transgenerational transmission of maternal aggression depends specifically on direct mother-daughter interactions during rearing, rather than on genetic inheritance, prenatal effects, or the postnatal environment alone.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
In the animal kingdom, the bond between a mother and her young is often the first lesson in survival. We tend to assume that a mother's behavior, whether it is gentle care or harsh discipline, is passed down to her daughters through a mix of inherited genes and the environment she creates. Sometimes, a mother might be aggressive toward her own offspring, a phenomenon observed in various birds and mammals that seems counterintuitive to the instinct of nurturing. Scientists have long wondered how such a difficult behavior persists from one generation to the next. Does a daughter learn to be aggressive because she inherited the genes for it, because she was exposed to high levels of stress hormones before hatching, or simply because she was raised by an aggressive mother? In nature, these factors are usually tangled together, making it nearly impossible to tell which one is doing the heavy lifting. To untangle this knot, researchers needed a way to separate the biological mother from the mother who actually raises the chick, allowing them to see which path truly carries the behavior forward.
A team of scientists at the University of Antwerp and Ghent University in Belgium set out to solve this puzzle using domestic canaries. For four consecutive years, from 2022 to 2025, they worked with a captive population of these birds, observing how mothers interacted with their chicks. In this species, maternal aggression manifests in a specific and observable way: the mother begins to pluck the feathers of her own nestlings, typically starting when the chicks are about two to three weeks old. The researchers classified a mother as aggressive if she performed this feather-plucking behavior on even a single chick in her brood. This behavior is not a constant state but a distinct switch that some mothers flip and others do not. The team wanted to know if a daughter would grow up to pluck her own chicks if her mother had done so, and if so, whether that was because of her DNA, the environment inside the egg, or the way she was treated after hatching.
To answer this, the researchers designed a multi-year experiment that involved a technique called cross-fostering. In the first phase, they observed a group of birds where the biological mother also raised her own young, just as happens in the wild. In these natural conditions, they found a clear pattern: daughters of aggressive mothers were more than twice as likely to become aggressive mothers themselves compared to daughters of non-aggressive mothers. This confirmed that the behavior does run in families, but it did not reveal the mechanism. Was it the genes, the prenatal environment, or the upbringing? To find out, the team moved to the next phase, where they took entire clutches of eggs from one mother and gave them to a different, unrelated mother to raise. This allowed them to separate the biological mother, who provided the genes and the egg environment, from the foster mother, who provided the post-hatching care and environment.
The results of this separation were surprising. When the researchers looked at the daughters raised by foster mothers, neither the behavior of the biological mother nor the behavior of the foster mother could predict whether the daughter would become aggressive. A daughter born to an aggressive biological mother but raised by a calm foster mother did not become aggressive. Conversely, a daughter born to a calm biological mother but raised by an aggressive foster mother also did not become aggressive. Even when a daughter was exposed to aggression from both her biological and foster mothers, she did not show maternal aggression as a mother. This suggests that neither genetics nor postnatal upbringing alone is sufficient to transmit this specific type of aggression.
The study points to a more complex requirement for the behavior to be passed down. The transmission of maternal aggression only appeared to work when the biological mother and the rearing mother were the same individual. It seems that the behavior is not a fixed trait carried by genes or learned solely through observation, but rather something that emerges from the specific, direct interaction between a mother and the particular offspring she is raising. The researchers propose that the behavior might depend on a dynamic relationship where the mother's traits and the chick's responses align in a way that is broken when the pair is separated. In other words, the "aggression" is not just a property of the mother or the daughter, but a product of their specific partnership.
This finding challenges the simple idea that aggressive mothers simply pass on a "bad gene" or a "bad habit." Instead, it suggests that the behavior is context-dependent, arising only when the prenatal signals and the postnatal care come from the same source. The study also noted that individual female canaries were not consistent in their behavior; a mother who was aggressive in one breeding season might be calm in the next, especially if the conditions of her breeding attempt changed. This variability further supports the idea that the behavior is a flexible response to the immediate situation rather than a rigid, unchangeable instinct. By showing that the behavior disappears when the mother-daughter link is broken, the research highlights that some traits are not just inherited or learned, but are created through the unique, unrepeatable connection between a parent and their child.
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