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Biology

Gulls in Argentina bully whales into changing their behavior

Paper: Fazio, A., Argüelles, M. B., & Bertellotti, M. (2015). Change in southern right whale breathing behavior in response to gull attacks. Marine Biology, 162(2), 267–273. doi:10.1007/s00227-014-2576-6

Introduction

If you’ve ever been on a whale watch, you’ve seen how whales breathe: they come up to the surface slowly, clear their blowhole with a spectacular spout, breathe in through the blowhole, then slowly arch their back and dive back down to the depths. If you’ve never seen it before, here’s a video of a right whale breathing in the Bay of Fundy – see it calmly come up, expose its entire back to the air, then calmly go back down.

Right whales in the waters off Patagonia in Argentina are not usually as calm when they’re breathing because in that moment, they come under attack by kelp gulls. The kelp gulls will sit in the water until they see a whale come up, then they’ll fly over, perch on top of the whale, and start pecking at the whale’s skin with their beaks. They’re searching for a type of parasite, called a cyamid, which feeds on the whale’s dead skin. The bird’s pecking rips the skin, leading to painful wounds on the whale’s back.

Figure 1: Main players – mother whale and her calf | example of gull predation, inset: cyamid

Figure 1: Main players – mother whale and her calf | example of gull predation, inset: cyamids

While this situation doesn’t represent a predation risk or something that would be seriously harmful to the whale, the assumption is that these wounds cause the whales discomfort. Much like when people feel discomfort, the whales have developed a breathing behavior in order to avoid the pecking by the gulls. Moreover, the behavior has progressed from completely absent to widespread in the population, suggesting that these whales are learning the behavior from other whales. This paper investigated the novel breathing behavior, tracked its appearance in the population, and examined its prevalence with regards to the number of gull attacks.

Methods

The researchers spent a lot of time on whale watch boats, watching a lot of whales, to collect all the data for this study over a period of four years. They recorded all observations of a whale surfacing to breathe and took note of how long the whale’s breath was, how many gulls (if any) were attacking it, and what method of breathing the whales were using. Normal breathing is the behavior shown in the video at the beginning of the article, whereas the new behavior is called “oblique breathing,” shown in the video below.

During an oblique breath, the only part of the whale that breaks the water line is its head; the rest of its body stays underwater to avoid being pecked at. The whale does this breath repeatedly and quickly, suggesting to the researchers that this is not a restful behavior for them. This oblique breathing behavior has increased over time (~30 years) as both the gull and the whale populations have increased: the first observation was recorded in the 70s, and now the behavior is widespread throughout the population.

Results & Discussion

The researchers found a correlation between the number of attacks seen and the number of oblique breaths observed. The oblique breathing behavior was more prevalent in places where there was a higher attack rate, even after the attack rate had decreased (Figure 2).

Figure 2: These two graphs show the percent of sightings in which whales used oblique breathing (bars) and the attack rate of the gulls (line) over two years.  When the attack rate was high, there was oblique breathing behavior, but the behavior increased in prevalence after the attack rate had declined.

Figure 2: These two graphs show the percent of sightings in which whales used oblique breathing (bars) and the attack rate of the gulls (line) over two years. When the attack rate was high, there was oblique breathing behavior, but the behavior increased in prevalence after the attack rate had declined.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The authors suggest that this increase in avoidance behavior, even after the gulls stopped attacking the whales as frequently, was due to learning. Because this region in Argentina is a breeding ground, the whales here are mostly mother-calf pairs, and whale calves are very receptive to imitating the behavior of their mothers. The mothers are displaying the oblique breathing behavior to avoid the gulls in this reproductive area, and the calves are seeing that behavior from the day they are born. Interestingly, adults breathe obliquely even when there aren’t gull attacks, which could mean that they’re showing their calves how to avoid those attacks when they eventually happen.

The oblique breathing reduces the amount of damage that the gulls can do, but it doesn’t come without a cost to the whale. The different breathing behavior could require more energy because it’s a rushed breath and the whale’s body isn’t held in the most streamlined manner of normal breathing. If oblique breathing does indeed carry that extra cost, the calves would be the most affected because they have to breathe twice as much as their mothers. There has been an increase in calf mortality in the study area, and the researchers hypothesize that the oblique breathing behavior may be a factor in that. The good news, though, is that oblique breathing behavior is effective at reducing gull attacks, which keeps a healthier whale population in a highly reproductive area, presumably resulting in a healthier population overall.

What do you think?

Should humans intervene to try to fix this problem? Gulls are a part of the ecology of the area, but these whales are an endangered species. Do you think we should take some action to help the whales or let nature take its course?

Discussion

Trackbacks/Pingbacks

  1. […] of their mothers,” sea scholarship consultant Erin McLean, who was not concerned in a work, recently explained. “Interestingly, adults breathe obliquely even when there aren’t gull attacks, that […]

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