Emily Carter
Kidnapping is a peculiar behaviour exhibited by some female emperor penguins that have lost their biological offspring. This behaviour has puzzled scientists for a long time, as there seems to be no clear evolutionary advantage to this practice. However, recent studies indicate that hormones, specifically high levels of the hormone prolactin (PRL), may play a crucial role in influencing the penguins' parenting urges and driving them to steal chicks to satisfy their parental instincts.
| Characteristics | Values |
|---|---|
| Reason for kidnapping | Unknown, but possibly due to high levels of the hormone prolactin (PRL) |
| Species that exhibit this behaviour | Emperor penguins |
| Prolactin's role | PRL is involved in parental behaviour and is poorly influenced by chick stimuli; it may have evolved to maintain a willingness to return to the colony after a long absence |
| Study results | Penguins with artificially decreased PRL levels kidnapped chicks less often than those with normal levels |
| Duration of kidnapping | A few hours to a week at most |
| Outcome for kidnapped chicks | They usually die from the cold or predation |
| Other factors | Kidnapping may be a way for females to make themselves more attractive to males for the next season |
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What You'll Learn
High prolactin levels
The behaviour of female emperor penguins that have lost their chicks kidnapping the chicks of other penguins has puzzled scientists for a long time. One hypothesis that has been put forward is that this behaviour is the result of high residual levels of the hormone prolactin (PRL). Prolactin is involved in parental behaviour, and high prolactin concentrations are necessary in emperor penguins to ensure that they will return to their egg/chick and mate after long stints out on the ocean.
Penguins with artificially decreased PRL levels kidnapped chicks less often than control penguins, and within the group with decreased PRL levels, the probability of kidnapping a chick was positively correlated to PRL levels measured before treatment. This suggests that high prolactin levels may be a factor in chick-kidnapping behaviour.
In emperor penguins, increased prolactin secretion appears to be triggered around the time of egg-laying and continues through incubation and brooding until rearing is completed. Prolactin secretion independent of external stimuli may have evolved in pelagic seabirds to maintain parental care despite long absences from the breeding colony. For example, during breeding, emperor penguins have to forage in remote ice-free areas.
In Adélie penguins, plasma prolactin and corticosterone concentrations measured under continuous daylight in early January did not show any daily rhythm components. However, prolactin levels did differ significantly among individuals, and it is possible that some individuals have circadian rhythms in hormone levels that are out of synchrony with other animals in the population. Prolactin levels were also found to be significantly higher in females than in males.
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No evolutionary advantage
The kidnapping of chicks by female emperor penguins has puzzled scientists for a long time. While penguin behaviour is largely determined by their genes, there is no clear evolutionary advantage to kidnapping. The mother's genes do not benefit from the kidnapping as the chick is not genetically related to the mother that kidnaps it. The kidnapped chick is abandoned after a short while, leaving it to die from the cold or predation.
A 2006 study found that when scientists reduced prolactin (PRL) levels in penguins, they were less likely to kidnap chicks. PRL is a hormone involved in parental behaviour and is also referred to as the "parenting hormone". Emperor penguins that had their PRL levels artificially decreased by the administration of bromocriptine kidnapped chicks less often than those that maintained higher levels of PRL.
It has been speculated that other factors may favour the kidnapping behaviour. For example, it could be a way for females to manipulate males and make themselves more attractive to males for the next season by suggesting they are able to bear and care for a chick. However, there is no evidence to support this hypothesis.
Overall, the kidnapping behaviour of female emperor penguins remains a mystery. While it may be influenced by hormones, there does not seem to be any evolutionary advantage to the practice, as the kidnapped chicks do not survive and therefore do not pass on their genes to the next generation.
In summary, the kidnapping of chicks by female emperor penguins is a fascinating but puzzling behaviour. While it may be influenced by hormones, there is no clear evolutionary advantage to the practice, and the ultimate reasons for it remain unknown.
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Hormonal byproduct
The phenomenon of female emperor penguins kidnapping chicks that are not their own has puzzled scientists for a long time. While penguin behaviour is largely determined by their genes, the mother's genes do not benefit from the kidnapping as the chick is not genetically related to the mother that kidnaps it. Moreover, the mother usually abandons the kidnapped chick after a short while, leaving it to die from the cold or predation. This behaviour appears to offer no clear evolutionary advantage.
However, scientists have recently hypothesized that the kidnapping behaviour may be a result of high residual levels of prolactin (PRL), a hormone involved in parental behaviour. Emperor penguins that have lost their chicks during a foraging trip still maintain high residual PRL levels, which, combined with colonial breeding, probably facilitates kidnapping. In a study, penguins with artificially decreased PRL levels by bromocriptine administration kidnapped chicks less often than control penguins. Within the bromocriptine-treated group, the probability of kidnapping a chick was positively correlated to PRL levels measured before treatment.
PRL secretion in penguins is poorly influenced by chick stimuli and has likely evolved to maintain a willingness to return to the colony after a long absence at sea. Penguins that have lost their chicks maintain high residual PRL levels throughout the entire breeding season. This high level of PRL, combined with the loss of their own chick, may drive penguins to kidnap unrelated chicks to satisfy their parental instincts.
It is important to note that the function and causes of kidnapping juveniles are not yet fully understood. While the high PRL levels may explain the proximal causes of kidnapping behaviour, there may be other ultimate factors at play that are yet to be discovered. Additionally, the phenomenon of penguin chick kidnapping is primarily observed in non-cooperative breeding systems, and more research is needed to understand how this behaviour fits into the broader context of penguin social dynamics.
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Manipulating males
A possible explanation for the kidnapping behaviour of female penguins is that it is a way for them to manipulate males and make themselves more attractive to males for the next mating season. This is because, by kidnapping a chick, the female penguin is suggesting that she is able to bear a chick and care for it, making her a more attractive prospect for males. This theory was proposed by biologist Olivier Chastel of the French National Center for Scientific Research.
Chastel's theory is supported by the observation that female penguins that have lost their own chicks are the most likely to kidnap another chick. By kidnapping a chick, these females may be attempting to compensate for the loss of their own offspring and maintain their maternal instincts. This behaviour could also be driven by the high levels of the hormone prolactin, which is involved in parental behaviour and bonding in penguins.
The idea that female penguins kidnap chicks to manipulate males is further supported by the fact that kidnapping is often followed by abandonment. The female penguin may only need to demonstrate her parental abilities for a short time to attract a male, and so she may lose interest in the kidnapped chick after a few hours or a week. This behaviour suggests that the primary motivation for the kidnapping is not to care for the chick, but rather to signal the female's parental abilities to potential mates.
While this theory provides a possible explanation for the kidnapping behaviour of female penguins, it is important to consider other factors as well. For example, the extreme conditions of the Antarctic environment may also play a role, as penguins that have lost their chicks during a foraging trip may still have high levels of prolactin, influencing their parenting urges. Additionally, the social dynamics of colonial breeding in penguins could also contribute to the complexity of this behaviour.
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Lack of understanding
The behaviour of female emperor penguins kidnapping chicks that are not their own has puzzled scientists for a long time. While penguin behaviour is largely determined by their genes, there is no clear evolutionary advantage to kidnapping another chick. The mother's genes do not benefit from the kidnapping, as the chick is not genetically related to the mother that kidnaps it.
Scientists have speculated that the kidnapping behaviour might be a way for females to manipulate males and make themselves more attractive to males for the next season by suggesting they are able to bear and care for a chick. However, this does not explain why the mother penguin would abandon the kidnapped chick after a short while, leaving it to die from the cold or predation.
Another theory is that the behaviour is influenced by hormones. Specifically, it has been suggested that high levels of the hormone prolactin (PRL), which is involved in parental behaviour, may drive the kidnapping behaviour. Emperor penguins that have lost their chicks maintain high levels of PRL, which could facilitate the kidnapping of another chick. However, it is not clear why they would then neglect and abandon the kidnapped chick.
Overall, the function and causes of kidnapping behaviour in emperor penguins are not well understood. While hormones may play a role, there are likely other factors at play as well. More research is needed to fully understand this puzzling behaviour.
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Frequently asked questions
It is believed that the high residual levels of the hormone prolactin (PRL) in penguins that have lost their chicks may drive them to kidnap other chicks.
PRL is a hormone involved in parental behaviour. Penguins with high levels of PRL are more likely to become kidnappers.
The kidnapping usually lasts for a few hours or a week at most, after which the kidnapper penguin abandons the stolen chick. The abandoned chicks usually die from the cold or predation.
No obvious advantages have been observed for the kidnappers. The only benefit seems to be satisfying their parental instincts.
