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Leaping humpback whale off the east coast of Australia: A change in mating tactics may have contributed to the preservation of the population
Photo: Cetacean Ecology Group / University of Queensland
Humpback whale bulls off the coast of Australia are increasingly forgoing their characteristic song.
This is the conclusion reached by Rebecca Dunlop and Celine Frere from Queensland University in the journal »Communications Biology«.
The observation indicates that the animals have changed their mating behavior.
The researchers associate this with the whaling moratorium of the 1960s.
Dunlop and Frere analyzed data from 117 singing and non-singing male humpback whales collected off the coast of eastern Australia over a total of 123 days from 1997 to 2015.
It was found that the male humpback whales sang less and less frequently over the years to attract a mate.
Most of the male singing whales stopped the behavior the more competitors were in their vicinity.
Instead, the animals switch to a silent mating tactic.
The researchers write that there is a discussion among experts about the exact functions of whale songs.
However, there is broad agreement that the calls have something to do with attracting the females and with the competition between the bulls.
avoid competition
After singing, males will join a female and then accompany her on her way to be able to mate with her later.
Another tactic used by humpback whales is to approach a female without singing and then escort her as well.
When one of these pairs is joined by other males, physical combat, jostling and competition between the whalemen usually ensues, with the larger often prevailing.
Dunlop and Frere suspect that the animals with the silent mating tactics want to avoid that other males willing to mate are attracted by their sounds and then challenge them for their potential mate.
The strategy seems to be working: According to the study, the non-singing whales were almost five times more successful in finding a partner in the 2014/2015 season than those that started their underwater song.
For comparison: in 1997, when the population was much smaller, the singing bull whales still had an advantage.
Three nations still catch whales
Whaling, which killed about 1.8 million great whales in the Southern Ocean in the 20th century, primarily targeted adult whales at the time.
The number of East Australian humpback whales, which also search for food in the Southern Ocean, shrank to just 200 animals.
After whaling largely ended, the population recovered by eleven percent annually.
According to Dunlop and Frere, it is likely that changes in male mating behavior also helped prevent the extinction of the East Australian humpback whales.
Japan, Norway and Iceland are the only nations in the world that still catch whales.
The study authors point out that humpback whales are not the only wild animals capable of adapting their mating behavior to changing circumstances.
According to experimental studies, male ungulates, elephants, fish and amphibians would also use different tactics such as territorial behavior, guarding the partner or fighting in order to be able to reproduce successfully.
Which tactics the animals ultimately use also depends, among other things, on the size of the population.
However, empirical studies on wild animals on the subject are rare because the population size would have to change significantly.
jme/dpa