Popular Essay

When we think about nursing and caring for newborn babies, there’s a specific image that comes to mind through our personal experiences. A tight, intimate relationship is formed between a mother and her nursing child, which serves as the foundation for their relationship moving forward. In the animal kingdom, however, different species have different ways in which they care for their young. For example, the northern elephant seal is often found in large, crowded colonies when mothers begin to take care of their newborn pups. These crowded conditions led to the need for unique behaviours in the mother seals, including methods for distinguishing their pups from others.

 

Juliette Linossier and her team investigated a population of northern elephant seals in California, and their results have been shared in an article in the Biology Letters journal, titled “Maternal responses to pup calls in a high-cost lactation species” (2021). Their study focused on observing the reactions of mother seals to their pups, and noting how these reactions affected their pups’ development. Through their research, they found that the mothers were able to distinguish the sound of their own pups from others, within 1-2 days after giving birth. They also found that the pups were healthier when their mothers were consistent with their responses to their pups’ calls.

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The reason this research is significant is that it is known that seal pups separated from their mothers are less likely to survive. The ability of the mother seals to identify their pups based solely on their call shows that this ability evolved in order for the pups to develop successfully into adulthood. It was noted that, should a mother nurse a pup that was not her own, she would run the risk of her pup not receiving enough nutrition for development. Interestingly, despite this risk, it was found that some mothers do still nurse pups that are not their own, a behaviour called ‘allonursing’. Through this study, the discovery that mother seals have the ability to recognize their pups’ calls raises the question: why do some mother seals knowingly nurse other pups?

The Experiment

Linossier and her team conducted their study by recording the calls of the seal pups, and playing them back for their mothers to, 1) observe their reactions, and, 2) observe the consistency of their reactions. This study took place at the Año Nuevo State Park in California, and was conducted in a way that did not cause harm to the seals. It was noted that the mother seals reacted more strongly to their own pup’s calls compared to those of another seal pup. Furthering the study, many of the mother seals demonstrated inconsistent reactions to the calls, specifically with varying levels of intensity. The pups of the mother seals that did react more consistently (that being, always highly reactive, or always weakly reactive) were found to be larger and healthier at the end of the nursing period. The scientists believe this could be a result of the pups adapting to their mother’s behaviour, knowing specifically what they need to do to get their mother’s attention to feed.

What This Means

In drawing the conclusion that mothers can clearly identify their young by sound, the importance of the mother-pup relationship during the nursing period is highlighted. To provide proper care and nutrition for their pups, it makes sense that evolution led to reliable methods through which mother seals can identify their young. The allonursing behaviour observed in the northern elephant seal, then, can no longer be explained by a mother confusing another pup for her own. Other scientists have investigated this behaviour across other species of mammals. Their predictions for why allonursing occurs range from relying on and supporting other mothers, to wanting to practice as a parent (Roulin, 2002). Linossier and her team also suggest it could also have to do with group benefits, or the many genetic and hormonal factors that can influence behaviour.

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Another piece of this research to highlight is the level of response from some of the mother seals. Specifically, even though the mother seals can identify their pups, their reactions to their calls were sometimes less spectacular than the team expected. The mothers that had lower reactivity to their pups, however, still produced healthier pups if their reactions remained consistent. Pups with less attentive mothers were able to adjust their behaviour, based on the behaviour of their mother, in order to remain as fit as those receiving more attention. Pups who had sometimes attentive mothers, and other times less attentive mothers, were worse off. It would be interesting to further understand these dynamics as they pertain to certain characteristics that have evolved in this animal species.
 

In Conclusion...

These new findings provide interesting insight into the dynamics of a seal species, and how their young are cared for. With the revelation that the mother seals can identify their pup’s unique calls, we’re left wondering why some seals then actively choose to nurse pups that aren’t their own. It would be interesting to see future research investigate why seals of this species engage in allonursing behaviour, and what factors specifically play a role. Additionally, further studies regarding the social outcomes of the pups as a result of the consistency of their maternal care could highlight key factors in this species’ survival. It is always interesting to think about the possibilities in terms of why animals behave the way they do, as it can provide insight into other species, maybe even our own.

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References

Linossier, J., Casey, C., Charrier, I., Mathevon, N., & Reichmuth, C. (2021). Maternal responses to pup calls in a high-cost lactation species. Biology Letters, 17(12), 20210469. https://doi.org/10.1098/rsbl.2021.0469

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Roulin, A. (2002). Why do lactating females nurse alien offspring? A review of hypotheses and empirical evidence. Animal Behaviour, 63(2), 201–208. https://doi.org/10.1006/anbe.2001.1895