Humpback hunting tips shared socially

Humpback whale fluke
In many ways, it’s even more interesting if the behaviour is not functional and is spreading through the population arbitrarily. But we do suspect that it is ecologically functional and a response to a shift in the ecological regime of the prey.
Dr Luke Rendell
Research published this week in the journal Science offers further evidence that humpback whales are able to learn from each other, in this case passing on a hunting technique suited to a particular type of prey. The authors of the study found, via analysis of a rich observational database collected over three decades, that since it was first recorded this particular behaviour has spread across 40 per cent of the population concerned.

This population of humpback whales spend their summers in the Gulf of Maine – the area off New England bounded by Cape Sable in the north and Cape Cod in the south, encompassing the Stellwagen Bank National Marine Sanctuary. The whales arrive there every year to spend the summer feeding before making the return journey to breed in the Silver Bank off the Dominican Republic and in Bermuda.

Dr Luke Rendell, a Marine Alliance for Science and Technology Scotland (MASTS)-supported lecturer in the School of Biology at the University of St Andrews, spoke to ScienceOmega.com about the innovative hunting strategy and its implications for cultural transmission in these cetaceans.

Humpbacks around the world have been observed herding shoals of fish with underwater nets of bubbles, but ‘lobtail feeding’ involves the whale hitting the water with its tail before diving. It then blows bubbles below the disturbance it’s created before swimming up through the centre. It has been hypothesised that the surface disruption helps to herd the fish in some way, but it remains unclear whether this is the true purpose of the behaviour.

"It was first recorded in 1980 as part of a study of feeding behaviour in that population that was mostly done from an aeroplane," Dr Rendell stated. "Around 150 incidences of humpbacks feeding were observed. One incident, it was noticed, used this technique, although it wasn’t described as lobtail feeding at the time. The behaviour first appears in the records of the whale-watching observers in the following year – 1981 – when it was recorded five times." 


A response to ecological change?


Dr Rendell explained that it is difficult to pinpoint what necessitated the invention of lobtail feeding because researchers are not certain what the functional significance of the behaviour is. However, it is believed to be an adaptation for feeding on sand lance.

"There seems to be an uptick in the rate of individuals performing this behaviour when sand lance adundance is relatively high, and it was initially seen when the stock of herring in the area had crashed and the stock of sand lance was entering a boom period," Dr Rendell continued. "There was an ecological shift and we believe lobtail feeding was a response to that."

Other scientists involved in the paper include first author Jenny Allen, also from the University of St Andrews, Dr Will Hoppitt from Anglia Ruskin University, and Dr Mason Weinrich from the Whale Center of New England. From their perspective, Dr Rendell pointed out, which is to ask the question, ‘Is this behaviour an example of social and cultural transmission?’, its functionality or otherwise is of little consequence.

"In many ways, it’s even more interesting if the behaviour is not functional and is spreading through the population arbitrarily," he said. "But we do suspect that it is ecologically functional and a response to a shift in the ecological regime of the prey."

Humpback whales bubble net feedingIf behaviour is passed on by cultural transmission, it follows that the more you ‘hang out with’ a particular individual, the more likely you are to adopt the behaviours that they display. From the data collected over 30 years by the New England whale-watchers, the authors were able to build up a picture of the social network of the whales, including which ones spent most time together.

"We were able to determine when the behaviour was first observed in individual whales, and assumed that was some index of when they actually learned it," Dr Rendell related. "The analysis technique assumes that, if cultural transmission is responsible, you would expect animals which are socially connected to other animals that already know the behaviour to be more likely to learn it."

The technique – a network-based diffusion analysis – quantifies the strength of that relationship, allowing the investigators to compare models describing what would be expected if there was no social transmission going on, and what would be expected if the social network influenced the learning rate of individual whales. The cultural transmission model was the best fit for the data. Since it was first observed, lobtail feeding has spread through 40 per cent of the New England humpbacks via this process.


Complex cultural processes at work
 

"There has been a lot of debate and discussion about cultural processes in whales and dolphins over the last ten years. To my mind, this study highlights how crucial these learning processes are for the animals to be able to spread new feeding behaviours – which we think are responses to ecological change – through their population. This goes some way to explaining why the humpback whale is a particularly successful animal in its ecosystem. We think cultural transmission plays a vital role in their success."

Humpback whales are famous for their distinctive song. Each breeding population has its own song, which is sung by the males in the group and which changes over time.

"Sometimes they will throw out their song and replace it with an entirely new one that they’ve heard from another population and liked, for some reason," Dr Rendell said. "That can only be explained by cultural transmission; by the whales learning the songs from each other. Our results build on that, creating an increasingly complex picture of the cultural processes at work in these populations."

The database employed in this research has proven extremely useful in understanding how social relationships develop over time in humpback whales. It has, for example, allowed people to track the relationship between social networks and relatedness in terms of vulnerability to particular environmental effects.

"There was a case where a group of whales ate mackerel that had been contaminated by a red tide and ended up dying," said Dr Rendell. "The whales turned out to be significantly more highly related than would be expected, so it looked like the preference for mackerel had been transmitted within the family.

"It’s an amazing testament to Mason [Weinrich]’s hard work over the last 30 years that this database exists. We hope it will continue to be used to gain insights into the social processes going on in humpback populations."

At the moment, Dr Rendell is seeking funding for further research into song evolution in humpbacks, and may also be involved in Jenny Allen’s PhD studies on the cultural transmission of song among Australian humpback whales.

"I have a grant under consideration with some computer musicians from Plymouth," Dr Rendell went on. "We would like to generate music with the kind of agent-based models that they use on a regular basis to see if we can reproduce what the humpbacks do with their song. This is in the hope of gaining insights into how the whales learn from each other."

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