Visiting the coasts of West Africa (along the Namib Desert), I had the opportunity to see a colony of sea lions (Class: Mammalia). Before I arrived on the coast, I was definitely excited. I would finally have had the opportunity to interface with marine animals that I have always considered “sweet.”
A total failure. An incredible stench, deafening noises, promiscuous pairings and an aggressiveness that actually no one expects until you observe them closely.
Group breeding in social pinnipeds is one of the most dramatic examples of gregariousness in female mammals. Yet, colonial living is associated with disease, inter-female aggression, and infant mortality. Many pup deaths are due to injury and starvation following permanent separation from the mother; other die because of the aggression wounds.
We will not speak specifically of African otarids, but of studies carried out on stable colonies in North America, precisely in Alaska. We are talking about the population of Steller sea lion Eumetopias jubata (which has a WORLD population of 250,000 individuals) of Lewis Island.
Like most mammals, there are populations with a certain “stable” social hierarchy (but which can undergo shifts), territorially speaking. In fact, on this island, and on others in Alaska, 3 types of territorial males have been defined with reference to high tide line:
- Terrestrial fertile male with territories above the high tide line;
- Semiaquatic fertile male with territories partially above and partially below the high tide line (winning strategy);
- Aquatic fertile male with territories below the high tide line.
These territories are well defined but they can shift with high frequence at the beginning and at the end of the breading sesason. This creates new and well defined boundaries (relatively stable). These shifts are also much more present when we observe changing territories like rocky shores (because of the high dinamic processes that invole these places).
But the social structure is not only a prerogative of the males but also of the fertile females. The hierarchical scale is determined by a lot of factors like physiognomy, temperament, aggressiveness and not to exclude the size of the organism.
This well defined society is a function of the reproductive success of an individual. Here, are the females that have to ravish the fertile male (polygamous society) and therefore induce him to copulate. The dispays have some precise characteristics. Movements and postures of the female are highly exaggerated. The female moves slowly its head and neck swinging almost 180 degrees from side to side, passing through the most crowded places within the colony.
While doing this, she vocalizes loudly, mouth wide open, vibrissae erected and salivating strongly. She applies also behaviours with clear sexual intention. Vaginal display, with dilated vagina, sometimes swollen vulva and intermittent urination were observed. The vigor and length of one display, and the frequency of consecutive displays, presumably has a strongly stimulating effect on the fertile male. Also, the fertile male could have a stimulating effect on the female by means of nipping and chasing of the fertile female and by the intensive licking of her genitalia.
With the copulation that lasts approximately 16.3 minutes, females chose a place used by other fertile females that have already given birth. The natal place shows some common characteristics like:
1) Sufficient space above high tide line, and so located that shelter is provided during storms.
2) Easy access to protected shallow water
3) Gentle slopes that facilitate the movement of pups
4) Locations which provides protection against strong solar radiation.
For this population the delivery season is accentuated in May-June (peak 7-10 June).
The first recognition mother-offspring depends on the mother that can recognize the pup within 12 hours after birth. Than she refines its capability to recognize its progeny with different sensorial modalities: olfaction, vision and audition. Surely, the acoustic channel appears the most utilized in gregarious mammals because it can cover short and long range of diffusion, and is linked to an accurate discrimination.
The pups’ vocalization, with time, go under a higher selectiveness, changing gradually. This graduality allows the establishment of the “new” call between mother and calf.
Instead, the pup can develop the ability to recognize its mother after a longer period (generally 2-3 months). The pup, effectively, increases its possibilities to survive if he responds to every vocalization coming either from his mother or another.
This different recognition timing is given by the different pressure that involves the two part of this dyad. Effectively, the pressure on the mother is much higher than that on pups, because it determines her genes continual propagation. Instead the pups will most probably be taken care of by any mother. So the rapid onset of recognition behaviour (by mothers) depends on the pressure given by the colony.
The bond between mother and offspring frequently lasts for more than a year. This can occur in four main ways:
1) Females do not give birth each year and retain the bond with their young into the second year.
2) Females renew the bond with their last young after loss of a pup.
3) Females reject the newborn pup and keep the subadult.
4) Females keep both the pup and the yearling.
Just in these days I was asked to write about these animals, and I remembered all those behaviors so far from our ideal; because they must certainly have a significance for the survival of the species. And their behavior actually makes sense, and that experience, in my corner of memories, has been transformed from being unable to remove a disgusting stench from clothes to being able to understand that the survival of the species requires bizarre actions, to determine the true winner deed to life.
Special thanks to my lab colleague Alessandra 😉
- Anbn. Behav., 1992, 43, 541-548
- ” Breeding And Maternal Behavior Of The Steller Sea Lion (Eumetopias Jubata) In Alaska” by Sandegren, Finn Eskil.
- Pitcher BJ, Harcourt RG, Charrier I (2010) Rapid Onset of Maternal Vocal Recognition in a Colonially Breeding Mammal, the Australian Sea Lion. PLoS ONE 5(8): e12195.