Despite their endearing trained performances for human audiences, killer whales (Orcinus orca) in captivity have been known to live up to their moniker. The SeaWorld trainer who was pulled into a tank and drowned by a 5,400-kilogram bull orca Wednesday in Orlando, Fla., was the latest in a string of incidents in the past two decades involving cetaceans that have harmed or killed a person.

But with more than 40 killer whales currently in captivity across the globe, the number of serious incidents might be considered low. "By and large, killer whales and dolphins have done well in captivity," Richard Ellis, a marine conservationist at the American Museum of Natural History in New York City, wrote Thursday in an online dialogue with Washington Post readers about the SeaWorld incident.

So what got into Tilikum, the killer whale that snatched 40-year-old veteran trainer Dawn Brancheau from a platform and dragged her underwater to her death? Even those who have worked with the species for years say that we will likely never know whether it was an act of aggression or overexuberant play—or even if, as some have suggested, it was premeditated. But looking to the whales' behavior in the wild can provide some clues. In their natural habitat, these toothed whales exhibit some big differences from their baleened, filter-feeding cousins. "They are called 'killers' because they kill their normal prey: whales, dolphins, seals, sea lions, penguins," Ellis noted.

We spoke with Brad Hanson, a wildlife biologist at the National Oceanic and Atmospheric Administration's Northwest Fisheries Science Center, who has been studying the social and feeding behavior of these whales to try to glean some clues as to why this and other captive killer whales might not be able to be trained out of their inclination to be natural born killers.


[An edited transcript of the interview follows.]

As someone who has studied these animals in the wild, should we be worried about attacks like this in captivity?
These are large animals. Their size and dentition are designed for taking down large prey. Given their size and strength they can do a lot of damage to anything in quick order.

Are attacks on humans common in the wild?
To my knowledge there have been none. There is one newspaper report out of California from around 1972. It's unclear what happened, but a surfer was lying on a surfboard and got bit. There are a lot of shark attacks out there, but there were suggestions that it may not have been a shark, based on the lacerations.

What is it about the captive environment that might lead these whales to attack more often?
It's important to remember that they are social animals. We do watch social interaction in the wild. They have very strong social bonds—not only with kind-specifics [their own species] but also in a captive situation they develop those with people they work with.

Even looking at them in the wild, it's clear that whales interact in ways that cause scarring. They do use their teeth to interact with other animals. Whether or not that is "aggressive" or "play" behavior—it's hard to just look at it and say. Part of the difficulty is just being able to see them in the wild when they're on the surface for a limited period of time. We have very little knowledge of what happens at depth.

In an instance such as this attack, is it possible to determine whether it was an instance of aggression or play?
They're big, strong animals. It's one of those things where the level in which they may exert that kind of force on the kind-specific would not have significant effects on those animals, but if you do that on a human it will be significant.

I had the unique experience of working with a killer whale orphan. Her mother was dead and she had ended up swimming into Puget Sound. She was about three years old and a little over 1,000 pounds. We went out and did health assessments on her every week. We tried collecting various types of data and soon veterinarians were saying we needed a blood sample—we thought we'd done well enough getting a breath sample. So we basically had to develop a bond with the animal in terms of socializing with it. But we were warned by one of the veterinarians at SeaWorld that you had to be extremely cautious going down that road with the animal. In order to make sure she didn't freak out during the sampling we did a bit of scratching her [with a scratching stick and our hands]. She then started rubbing on the bottom of the boat, so we had started on that slippery slope. They do want to bond. Obviously they're programmed to bond with members of their own species, but they can form a bond with other animals like humans.

It was a 30-year-old male killer whale that was involved in the attack. Is 30 old for a killer whale?
In many ways their life spans are sort of like ours. In the wild we have some females that are thought to be in their 80s and one male thought to be in his 50s. But most males tend to live into their 30s. Right now we're working off 30 years of data, which may sound like a lot, but when you're studying such long-living animals it isn't that much. We don't know if males we follow are dying at a relatively young age.

Do you think the age or gender might have played a role in this animal's behavior?
In resident-type whales, they're basically matriarchal societies, where the females are the center of the social structures. Up until puberty, males and females look pretty much alike, but at 15 years of age they sprout—and what we mean by that is their dorsal fins start to grow. Besides being larger in body size the males are very distinctively different looking animals. But is it for male–male competition or female selection? We don't know. But it may alter the way they or other animals relate to them.

How do these whales feed in the wild?
These animals will share their prey. We were doing a focal follow where we would pick an individual and follow in its food tracks, and one of the other whales would swim over and join up with it. We try to keep our distance from these guys to at least 100 meters or so, so we don't see it up close, but there appears to be cooperative foraging going on.

How smart are killer whales?
It depends how you define smart or intelligent. They can adapt to novel situations very quickly. I look at how quickly they learn behaviors in the wild. Killer whales in Alaska interact with longline fisheries up there. It's known that they can be several kilometers away from the fisheries and as soon as the hydraulics get turned on the whales swim toward them for fish that are coming off the lines.

A lot of people say they have big brains. But it's important to take into account that echolocation takes a lot of processing power, as well. A lot of that gray matter is designated to process those signals when they come back. Their ability to discriminate things with this system is impressive. They could find something the size of a BB in the bottom of a pool. They could determine the different densities of two objects of the same size.