Australian humpback whales sing less (wanna hear?) and fight more | Biodiversity

A ban on commercial whaling in 1986 triggered an exponential growth in the humpback whale population in the Southern Ocean. Where there were 200 individuals, now more than 20,000 swim. In view of this change, a study published in the journal Communications Biology this Thursday, the males adapted their mating strategy.

​When a humpback whale sings in an attempt to attract a female, it may also attract the attention of other males, i.e. competition. When there were only a few hundred whales this didn’t seem to pose a big problem. Now that there are more than 20,000 in the Southern Ocean, your singing could “warn the competition” and get them in trouble. Therefore, they are singing less.

The most common behavior became to accompany and escort the female and try to mate with her. Which does not prevent the conflict. Due to the high population density, competitive groups are formed, that is, three or more adult males seeking the attention of the same female, in which case the males can fight to get the best position in the group.

Despite migrating, these animals continue to have breeding behaviors
University of Queensland Cetacean Ecology Group

“Male humpback whales have successfully adapted to extreme changes in their population,” concludes the report. study Australian. He adds that alternating between singing and competitive strategies, depending on the existence of competition, may even have “decreased the risk of extinction of this animal” and contributed to the strong population growth.

The song has become a waste of effort

A humpback whale (Megaptera novaeangliae), known as “the most vocal of all” was close to extinction in the 1960s due to commercial hunting. At that time, there were estimated to be around 200 humpback whales in the Antarctic Ocean. Now, the scenario is different, essentially due to the ban on commercial whaling that came into force in 1986 by decision of the International Whaling Commission (CBI). In 2015, states the study of Rebecca Dunlop It is Celine Frerethe estimated number of humpback whales in the Antarctic Ocean it was more than 20 thousand.

The data from this investigation, published in the journal Communications Biology, were collected over four time periods, in 1997, 2003 and 2004, 2008, 2014 and 2015 at the time of the “annual migration of humpback whales from breeding grounds on the Great Barrier Reef”. coralsfor feeding zones in the Southern Ocean”, more specifically, in September and October of each year.

In the initial period of the study, in 2003 and 2004, it was found that 2 out of 10 males used the chants as a “form of sexual signaling to attract females”. The proportion drops to half in 2015, at the end of the collection. The seduction technique ceased to be very successful.

Humpback Whale Song Can “Warn Off The Competition” And Get Them In Trouble
University of Queensland Cetacean Ecology Group

In contrast, competitive groups have become much more common. These changes, in the eyes of the investigation, are possibly a “phenomenon dependent on the density of the population that increased from 3500 individuals when the study began, to more than 20 thousand, when the study was completed”.

The author of the work Rebecca Dunlop confirms to PÚBLICO that the growth of the population of humpback whales, after the prohibition of commercial hunting, altered “the mating behavior of the males”. And as whale numbers increased, she adds, the chants became “less and less useful in mating rituals.”

The justification that Rebecca and Celine found for these changes was that using the song as a mating ritual brought an added cost: “the potential attraction of other males that join the singer, which can interrupt him and potentially lead him to leave the area , which is to say the song was a waste of effort.”

They then opt for physical competition, that is, explains the study, “they go looking for females” and do not sing so as “not to attract other males to the group”. But even so, due to the high population density, competition arises, leading to aggressive behavior among males.

Buoys for recording the song

These animals are between 12 and 16 meters long and weigh around 26 tons, but their size does not prevent them from being somewhat acrobatic. It is species Whales live throughout all oceans, and even in harbors and rivers, and make long migrations to feeding grounds in summer and mating in winter.

During the migration to the feeding grounds, the researchers used an acoustic recording system, from which they were able to track the whales, along with “observation of other whales from a land station based on the mountain”.

The acoustic recordings were made by means of “three to five hydrophonic buoys” (which detect sound waves under water), anchored in “18 to 28 meters of water”, the signals received by the buoys were then transmitted to the base station on the coast and later used by researchers to cross-reference data from different buoys and determine the most likely position of the singers.

The collected data says Rebecca Dunlop, allowed the team to create “a picture of the mating behaviors of humpback whales, in terms of which ones sing, which ones are male, as well as their social environment”.

This study sought to understand how “flexible are animal behaviors in the face of a major ecological impact, in this case, the near extinction of the humpback whale due to whaling and whether animal populations are able to recover” from these impacts and reached the conclusion that adaptation from the mating rituals of this species to its population density “may have reduced the risk of extinction of this animal and contributed to its recovery”.

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