Revisiting Packer et al. 1990

In a paper published in The American Naturalist in 1990, Craig Packer, David Scheel and Anne Pusey used field data on lions from Serengeti National Park to argue against a dominant idea at the time: grouping patterns are determined only by foraging success. Packer and colleague’s observations suggested, instead, that grouping patterns are linked to multiple factors, including, in particular, protecting offspring and maintaining territories over the long-term. Twenty-seven years after the paper was published, I spoke to Craig Packer about the motivation to carry out this study, his memories of field work, and what we’ve learnt since about grouping patterns in lions.

Citation: Packer, C., Scheel, D., & Pusey, A. E. (1990). Why lions form groups: food is not enough. The American Naturalist, 136(1), 1-19.

Date of interview: 6 January 2017 (via Skype)

Hari Sridhar: I wanted to start by asking you about the motivation to do the work presented in this paper. By looking at your publication profile, I came to know that you had started work on lions in 1978. This paper came out in 1990, but the work itself was done between 1984 and 1987. Could you tell us a little bit about what the motivation for this specific piece of work was in relation to the work you had done earlier on lions?

Craig Packer: Sure. I got interested in lions in the first place because I was interested in the evolution of cooperation. There were a lot of theories in the 1970s and 80s, from game theory into animal behavior and everything, but there were very few good examples about animals that behave in a way that you could use to assess the utility of some of these ideas. I previously worked on baboons, and they would occasionally cooperate with each other. But examples are pretty rare. They were so infrequent that you couldn’t get a very comfortable feeling of how well the theories worked. Lions had this reputation for being very cooperative, so I, initially, wanted to look at the lions to study different aspects of their potentially cooperative behavior. And then, in all of that, there was the simple notion of how big should a group be – Was there such a thing as an optimal group size? Would animals form groups of optimal size? – and there was almost a cottage industry of scientists, who were not primarily field workers, but were interested in data that George Schaller had published in his book in 1972, The Serengeti Lion. In contrast to when I came around, when there were a lot of theories that we wanted to test, Schaller was out there just getting baseline description of what was going on. And he was a wonderful descriptive biologist, and had no axe to grind; no ideas. He was just saying, well, this is what I’ve seen, and this is what it looks like. His book included a number of figures and tables, which a number of later authors then used to analyze to see if they can explain lion behavior. I was aware of all those, and I thought, whoa, they’re taking one problem that the lion needs to solve, which is to catch dinner, and now that’s going to be the only thing that the lions are doing. And by then, having watched the lions for the first five or six years that I was out there, I was convinced that it’s much more complicated than this. There were all these ideas out there, and everybody was publishing saying, Oh, we know why lions do what they do. And I said, I don’t think so. So, basically, we just wanted to get the right kind of data, because Schaller’s data were not collected with those hypotheses in mind, and so making assumptions about the circumstances where those groups were being formed, and how often they’re hunting and everything were likely to be gross oversimplifications. We needed to collect the right kind of data with which you could more rigorously test these ideas.  That’s what motivated it.

HS: How did this group of authors come together and what did each bring to this piece of work?

CP: Anne Pusey and I had been working on the lions together and collecting all the long-term data. We just had, as a kind of a procedure, that we’d be co-authors on anything either of us was doing at the time. David Scheel was a graduate student who I had explicitly recruited to come out and do this particular study, because of the difficulties in collecting the data. I went there thinking I’d see more examples of cooperation, but in fact, they’re very, very hard to study, because they don’t do much most of the time. We had to watch the lions 24 hours a day for four days in a row to get a good sense of how much they ate per day. Dave and I actually did the observation. We had this horrific schedule. We had radio collars on a number of the prides, and we would go out and stay with the pride of lions for 96 hours in 12 hour shifts. Dave would be on for 12 hours and I’d be on for 12 hours and he’d come back again and then I’d come back again. In that way, we were able to do the continuous observations. Those days, there was no such thing as GPS collars, so we had to follow and watch them continuously. In fact, we still would have to watch them to get the kind of data we collected. There’s no substitute for it. So, I’d asked Dave to come to Minnesota as one of my graduate students saying this is one of the things I wanted to study. But during that period of time, we were collecting other sorts of data as well. On this particular aspect of those long follows, I ended up being the lead author; other data that he and I collected he used for his thesis.

HS: There is a mention of an unpublished manuscript on the group hunting of lions. I wanted to ask if that was later published as a paper.

CP: Gosh, give me the context of that.

HS: You say, “Once an individual is a member of a group of a particular size, whether or not to participate in a cooperative hunt is a separate decision.” And then you say, “Data on group hunting will be presented elsewhere.”

CP: Yeah, there were a couple of papers that came out on that. One Scheel & Packer paper and the other was a Packer & Ruttan paper. Those were asking, as that sentence implies: Are you going to actually make the effort to catch the prey, or are you going to wait and let your companion catch and then you’re going to parasitize from your kill?

HS: There’s another unpublished manuscript – Packer & Pusey – about group territoriality. Was that also published later on?

CP: Actually, that’s the funny one, because it took another 20 years before that paper came out. By the end of that paper, or by the end of that study, it was pretty clear that the grouping pattern of lions is really complicated. And it wasn’t just about getting their next meal. We knew that group territoriality was complex, but it was really hard to get it right. And so, I had another graduate student – Anna Mosser – who joined my lab later who analyzed our long-term data on that. She published those papers much more recently. The last one just came out, in 2015; very recently.

HS: The data that went into this paper was collected over three years. Was this analysis planned before the start of the data collection, or were you collecting this data for some other purpose?

CP: No, in that particular paper, we knew what we were going to be doing eventually. I knew, in broad strokes, how we’d be analyzing data. I didn’t know which statistical test exactly, but I knew how we would organize the data and what patterns we would need to assess.

HS: From the beginning, did you know you would need data over such a long period to be able to answer this?

CP: Yeah, because lions do things sort of in slow motion. It took us just an awful long time. I mean, in an ideal world, we’d still be doing it, but it was lethal. It’s so hard to collect this data. We went as long as I could afford to keep Dave Scheel and myself going on. It was very hard. By the end of that project, I was, literally, burnt out. I stopped going back to Serengeti for extended periods, just because it was so exhausting. We did that eight days a month, for six to nine months a year. I had small children at the time. It was tough.

HS: So, you’d spend six to nine months in Africa and the rest of the time in the US?

CP: Yeah, I’d teach here in Minnesota and then they’d let me go away and do all my field work.

HS: Tell us a little more about field work and your daily routine during this time.

CP: We had put radio collars on the lions, starting in 1984. Once we had those collars on, I knew we could do the study, because if they’re not collared, the lions could disappear in the tall grass or go into a river bed; you wouldn’t see them. Once we put the collars on, we decided that we would do this procedure of staying with the lions four days in a row. Also, the night vision devices that we had were not very good, and so we needed as much moonlight as possible. So, we scheduled it such that it’d be just before the full moon for four days – we would take the full moon off – and then the four days right after that. We had a colleague in Serengeti with an aircraft. We would fly and look for as many prides as we could find, at the beginning of that sequence, and then we’d say, Okay, this pride, they’re in groups of two, or they’re in groups of three or whatever. We’d follow them for four days, and then we’d have the full moon. Anne Pusey would also tell us if there are any groups that we would be interested in, on the full moon, and then we would go out again the day after the full moon. So, we chose the prides in advance, just based on their group size, because that was the most important variable. The lion pride is different from the group because the pride is a fission fusion society. We would start out with a group of two, but then the group might team up with somebody over time. We had to deal with all of those complexities later.

The first few we did in a single car. That was horrible. The cars – these were Land Rovers; long live Land Rovers! – were outfitted with a mattress in the back. So, it’d be one person lying down at the back trying to get some sleep and the other person trying to watch in front. So, if the lions moved a lot, and they often did at night, you’re bouncing around and you couldn’t sleep. Then you had to be back on duty for 12 hours. During the day, it’d be really hellishly hot. We did that a few times, but then I managed to get another car and so we would do it in two different cars. So, we would be by ourselves, and the other car would be parked somewhere. And, during your break, you could either go home, or you could sleep or whatever, and show up at the right time to take over. There was the difficult matter of somehow paying attention to the lions for 12 hours, when they’re sleeping 19 hours a day, and then trying not to miss anything. It was especially stressful at night because you didn’t want to flash your lights. If you use your lights, that would give away the lions to the prey, and then they wouldn’t get anything to eat. So we had to stay in the darkness, and somehow guess when they might be moving. And, in fact, we often didn’t see them catch. We just would find that, Oh, they’ve got it. We didn’t care so much about the details of who did the work; so much was about how much they caught. That was the key variable: how much food was obtained per hour per day, and that’s why some of those ideas we said we would do in other papers. In the observations we were making, we didn’t always know who caught it or many lions were involved in the hunt? All we cared was, for example, there is four of them, they caught a wildebeest, and a wildebeest weighs so many kilos, so they have so many kilos divided by four.

HS: Could the people in different vehicles communicate with each other?

CP: We had radios. That was the other thing. During those hours when we were hoping to get some sleep, we had to leave the radio on, in case the other guy got stuck. So, if Dave got stuck at 3 o’clock in the morning and the lions had wandered off somewhere, I had to make sure that he can catch up with them again, so he didn’t miss anything. And so, you know, I’d be trying to sleep with our radios on. And these were radios with a lot of static, so they’d crack and pop and then each other’s voices would be highly distorted because we were using hf radios. It’s not like what you use today; there was no cell phone coverage at that point. And so, hf radios probably were best for communicating with somebody about 1000 miles away, because the signal would bounce off the stratosphere and come back down. But in our case, we could sometimes not even hear each other very well because we’re too close! We’d get a lot of static. The communications was possible, but it meant a lot of discomfort while you’re doing so. But the worst thing of all was just sitting there when it was your turn to be on duty in the dark, not knowing what was going on. You couldn’t listen to radio because you had to listen to these damn beeps all the time. So, it’s like this deprivation just sitting there. Horrible.

HS: Did you ever get out of the vehicle during this time?

CP: When we are on duty, we would stay in the car so as not to disturb anything. During the day, when the lions were asleep, when they were really in a deep sleep because it’d be really hot, we might get out of the car, just to stand and stretch beside the car.

HS: Did anyone other than the two of you take part in fieldwork?

CP: Well, towards the end, I was getting so burned out by it. I was a nervous wreck. I also had an obligation to go to a conference in Los Angeles; or maybe it was something else. Anyway, I managed to get an assistant to do my shifts for a couple of the last ones.

HS: What was the assistant’s name?

CP: There’s one fellow named John Fanshawe. I hope we acknowledged these people.

HS: Yes, John Fanshawe is on the list.

CP: Yeah, he did one or two of them. He was a lifesaver. I owe him a lot for my sanity.

HS: Who loaned you the plane?

CP: The Frankfurt Zoological Society. They were contributing to our project by flying once a month, so we could locate all the lions. We used those flights not only to figure out where everybody was, but to decide which group to follow. Markus Borner is mentioned in there too. He was the pilot.

HS: Could we quickly go over other names in the Acknowledgements to get a sense of how you knew these people and how they helped?

CP: Sure.

HS:  David Babu

CP: He is the Director of National Parks. We always acknowledge the people who give us the permission to do the work in an African country.

HS: K.N. Hirji

CP: Yeah, he was the head of the Wildlife Research Institute. Another official.

HS: Barbie Allen

CP: Barbie Allen was our lifesaver. She would send us supplies from Nairobi so that we were well-fed and felt like we could live in the Serengeti during tough times. This was during a period of time when the border with Kenya was closed. Tanzania was a failed socialist experiment, so we never got decent supplies in Tanzania. We’d always come to Nairobi and she always gave us a place to stay and helped organize spare parts for cars when they broke down. She was our fairy godmother, really.

HS: Was she also a biologist?

CP: No, just a good citizen and a good heart.

HS: Bruce Davidson

CP: Oh, Bruce. I forgot about him. He did another one of the all-night follows instead of me. He was a photographic assistant for Alan Root, who’s a filmmaker.

HS: Jon Grinnell

CP: Jon Grinnell was… oh that’s right, he was another one of my graduate students. He might have also done one of the all-night follows.

HS: Larry Herbst

CP: Larry Herbst was another graduate student who had helped collect some long-term data.

HS: Richard Matthews

CP: Filmmaker. So, I guess Bruce Davidson was Richard Matthews’s assistant.

HS: Marcel Proust!

CP: You know Remembrance of Things Past, this incredibly long book; like thousands of pages. During the daytime, that’s how I passed my time; I read Proust.

HS: Samantha Purdy

CP: She was with Richard Mathews. Richard and Samantha assisted Bruce Davidson, did one of the all-night follows, but they were also out finding lions. They would sometimes tell us where there was a group that we wanted to go and do an all-night follow on.

HS: Alan Root, you said, was a filmmaker.

CP: Yeah, he’s the filmmaker who’d hired Richard and Samantha.

HS: Steve Scheel

CP: Oh right, Steve Scheel was Dave’s brother. I think he also did an all-night follow one time, when I was teaching in Minnesota.

HS: Charlie Trout

CP: Charlie trout was another pilot for Frankfurt.

HS: CW Clark

CP: Oh right, Colin Clark. Clark of Mangel & Clark. They have written one of those theories about why lions live in groups because of foraging and all that. Clark was very helpful in letting me know how he had done the dynamic programming model. Finally, we get to scientists!

HS: You also thank the National Geographic Society for the loan of their vehicle. Were they filming in your study area at the time?

CP: No, there was a friend of mine who had a custom-built Mercedes four-wheel drive vehicle. He had custom-built it to drive from Cairo up to Lake Victoria or vice versa. He did a lot of projects for National Geographic as one of their photographers. After he’d finished his assignments, the car was just sitting at Barbie Allen’s place in Nairobi. So, I asked Geographic if I could borrow it, so we could have that second car. National Geographic let us use it for a couple years.

HS: Do remember what this person’s name was?

CP: The filmmaker was Robert Caputo He just let me know that they had it, that I should ask them, and then they gave me permission to use it.

HS: What do you remember about the writing? Where did you write it and long did it take you?

CP: I wrote it back in Minnesota. After that year in 1987 when I got so burnt out, I never went back to Tanzania for a long period again. I was back there in 1988, just for a few weeks, and I didn’t go back at all in 1990. And beginning in 1991, I was only there for about a month at a time. For the next 10 or 15 years, I really focused. It was really my graduate students who did all the field work; because I was burnt out.

So, I wrote it in Minnesota. It was a paper that went through various drafts, because, by then, that whole cottage industry was a lot of the big names in behavioral ecology of the day; like Clark and Mangel. And other people had written on that subject of optimal group size,  like Giraldeau and people. And so, they didn’t want to hear that all of their musings on the back of an envelope were not appropriate extrapolations of the data. People looked at our data with a very critical eye. There was a lot of back and forth with The American Naturalist. The American Naturalist also had a real backlog in their publications, and their editor at the time was not pushing things very fast. So there’d be this long delay back and forth, back and forth. We’d be asked to do some edits, and I would edit it; never anything serious. It was just a matter of word crafting so that people weren’t offended. All I was trying to say was, look, these are animals that you’re looking at; a female animal. And yeah, sure, she’s got to get enough to eat today. But she’s also got to look after babies. She can’t be too far away from them. She’s got to defend her territory. She’s got to worry about males who might kill the babies. All these different things they have to do at the same time. It is much, much more complicated. And that’s why the title became ‘Food is not enough’. I was struggling to find a good catchy title. I still don’t know that I like that title very much. In fact, that was suggested to me by Marcus Feldman, the editor of The American Naturalist at the time. We were like, Okay, sure, this is what we’re trying to say.

HS: Do you remember what your initial title was?

CP: No, I don’t.

HS: I noticed that it was submitted in August 1988 and finally accepted a year later in 1999.

CP: When did it finally come out?

HS: July 1990.

CP: Okay, so yeah, it was a long time. Nowadays, there are all these online journals where you get things published much more quickly, but back then there were relatively few journals. They all wanted to print. And, you know, it was a growing field, so there were many more manuscripts being processed than being published. And so, the process, even if you got accepted, took a long time.

HS: Was American Naturalist the first place you submitted this to?

CP: Yes. I always wanted it to go to Am. Nat. That was the preeminent journal in those days for that kind of work.

HS: At the time when the paper came out, do you remember how it was received? Did it attract a lot of attention? Was it considered controversial when it came out?

CP: Um…I don’t know. I think people got it. I think, on the whole people, recognized that, yes, those prior analyses were not with the best data, and that they were oversimplifications. I think that’s kind of been a hallmark of a lot of the things I’ve written over the years: whoa, wait, you know, the real animals are more complicated than this. And, you know, I know a lot of people were disappointed that there weren’t simple explanations for complex behavior. But I don’t remember that people were really hostile to it. I think they were more like, oh, well, shucks, we’ll move on to something else.

HS: Was publishing this paper an important point in your career? Did it have a strong impact on the course that your research took after this?

CP: Yes, it definitely did. Getting back to my initial concerns – a lion as a cooperative species – there are a number of different ideas that I had, besides foraging efficiency, as to why lions might live in groups. I wanted to test them one after the other. That one was kind of the cornerstone. It was the very first one to say, okay, sure, hunting is also really complicated. People somehow assume, when they imagine all these game theoretical models of cooperation, that there’s always a temptation to cheat. One of those papers that I came up with about that same time was like, whoa, wait a minute, you don’t expect even partners in a lion pride are necessarily gonna cooperate with each other. If you can get the other guy to do the work, it’s great; you can parasitize him. And so, this was like the empirical side of that broader investigation of group hunting, and how cooperative it is, and if it is cooperative, when is it and when is it not cooperative? And so that that was a series of papers I wrote where I felt like I was starting to really make a new body of knowledge having to do with social carnivores and species in general, as to why they did what they did in terms of being cooperative or being social or not. The next thing we did after that had to do with infanticide. And then came group territoriality. And it was going to be 1, 2, 3. But then group territoriality just proved to be so complicated. We did publish it, but it took a decade longer you know, to get that stuff out. But, definitely, I was well-enough known by then that people were going to take me seriously. If I’d been somebody completely unknown, maybe there would have been a bit more pushback. I’d published a number of things that people respected and, therefore, they said, okay, right, it is more complicated.

HS: Today, 26 years since this paper was published, would you say the main conclusion still hold true more-or-less?

CP: Yeah, more or less is a good way of putting it. One of the things that have come up since then is that we couldn’t find any really strong advantage of group hunting in our lions in most circumstances that we were watching. But there were some other circumstances – which are in one of these other papers – the Scheel & Packer paper – where they definitely cooperate. They need to cooperate to catch buffalo, but this is a separate issue. This is why I was trying to separate them in this Am. Nat. paper. One was how big of a group should you be in given your per capita food intake rate? Second issue is should you cooperate or not? And so, this is kind of related to each other. But as far as this one goes, yes, I stand by it. I don’t see any reason to change it at all. But when we did those observations, we didn’t have as much information as we do now about when they should cooperate or not. We had a few gleanings, like: when they’re hunting buffalo they have to cooperate, because trying to catch a buffalo by itself is gonna fail. This was the gist of our game theoretical work, and it holds up really pretty well. There was one other study that came out of southern Africa, from Etosha. That kind of proved this right, but in a way we weren’t really expecting initially And it was a study in Etosha where the prey was not big and dangerous like buffalo where obviously you’d have to cooperate, but something really small but really hard to catch. The principle, in a way, is the same: you have to hunt together. And so, what we come to recognize is that in different areas, different conditions may lead them to cooperate less or more. What I’ve obtained since doing this study is to definitely be open, and I have always said that the answers we got in the Serengeti may look different in other places. But as far as their actual grouping patterns, that narrow question we addressed in the Am. Nat. paper. Does their decision to be in a group of 2, 3, 1 or 5 – whatever – maximize their daily intake rate? But what we’ve learned since we actually did that field work, is that it’s not about the grouping, but about when they cooperate or not.  Our general principles are right; I’m happy with that. But what I hadn’t realized is how Serengeti was, kind of, like anywhere else. A good expression for this is all ecology is local. I love that expression. The solution is universal, but all ecology is local; or something like that. And so, you know, the ecology of Etosha – hunting Springbok – is such that they really need to cooperate. Whereas in the Serengeti, the same size prey as Springbok is Thomson’s gazelle, but they never cooperate to catch a Thomson’s gazelle.

HS: Was the work in Etosha was also done by you?

CP: No, that was done by a Namibian scientist named Phil Stander.

HS: If you were to redo the study today, would you do anything differently, given the advances in theory and the techniques available?

CP: Yeah, I guess with unlimited funding, the ideal way to do that would be to have GPS collars with accelerometers on every member of the group. The problem is you still have to get there and see what they catch and what they eat. And if you’re not there watching it yourself, you don’t know if they scavenged it or if they caught it. And that’s a big difference. You can then go and measure them on a regular basis and see how much they have eaten, because you can estimate their food intake rate from the profile of their belly. It gets really distended after they’ve had a big meal. The problem is now there is very few people with that kind of money for that kind of work.

HS: Do you continue to work in that site today?

CP: No, unfortunately, I’ve been thrown out. For the longest time, I just did basic research there. That was no threat to the authorities. And then, through time, I got more interested in conservation of lions. It turns out that lions are a very political species. You may be familiar with the politics of lions in Gujarat, for example. In Tanzania, they have a very different thing because sport hunting is big business, and sport hunting runs right through the heart of the government. They allocate the hunting blocks and so there’s plenty of scope for bribery, misbehavior, over-hunting and everything. So, in some of my later research, I found out too much about how hunting was being mismanaged in Tanzania. And that mismanagement was really the result of a lot of corruption that went to the highest levels of the government. .I exposed that corruption to my own American government, not as a spy, but as a citizen who was informing the American government when they were considering whether to put the lion on the endangered species list. And my government official that I gave the information to, or rather indicated I had information I liked to talk to them about, published my confidential email on a public web page. The hunting industry informed the Tanzanian government, who then got rid of me.

HS: When was the last time you visited the site?

CP: I was in Tanzania in April 2015. I was checking to see if I could, at least, visit as a tourist, and I found out, No, I’m not even allowed in the country.

HS: If you compare this site during the last time you visited to the time when you worked there for this study, what are the major changes that have happened in the site?

CP: Oh, well, you know, the study population that we were working on in the 80s is right in the middle of Serengeti National Park. So, it’s well protected against habitat loss and poaching. The lion population there is still thriving.  It would have still been possible to do that work again; probably even now. Given the technology of the 1980s we could have only done that study in the Serengeti, because it’s the only place that’s open enough. You could see what they were doing driving around at night. There was another study I mentioned earlier that was done in Etosha, but that was only one group. We needed a large population where we could sample different group sizes. So, with the new technology, it would probably be possible to do that sort of work even in places like Botswana or Libya. But you need a lot of resources.

HS: Do you think the prides that you studied during are likely to still be around?

CP: Either their descendants or neighboring prides might have taken over the area over the years. The population is pretty stable.

HS: In one place in the paper you say that during prey scarcity, females should forage alone or in groups of five or six females. What’s your current thinking on that? Is it still useful to think in terms of optimal group size, and if it is, do those numbers still hold?

CP: In that population, I would say, yeah, that’s what they want to do. What happens is  – we sort of indicated this  – if you’re in a group of three or four, and you’re trying to raise your cubs together, you’re forced, by the needs of protecting your cubs, to be in a group that’s too big. What you can do is you can dart out, you can go off by yourself for a few hours or even a day, catch food and come back. And so, they would go off and they would forage alone. What we said there was really restricting it to the females. We were pointing out it’s more complex, but we didn’t point out how utterly complicated it is. It’s utterly complicated in that females do not live alone; there are also males. And it’s not just the dangerous males that we talked about, with the risk of infanticide; it’s also their husbands. Their husbands can be really good providers, and they catch the buffalo. And so, when you make the calculations, it gets much, much more complicated. One could think about that, but we were just trying to go along within the framework that had been established by prior papers, asking what females do. And so, we set up our study to see what happens with females. But in the real world for the lions, there is going to be that wild card. If your husband’s there, he can put down his beer cans for a minute, or whatever, and just go get some dinner.

HS: You define a female group as all females from the same pride that are less than 200 meters apart. Would you still use that definition?

CP: Yeah, that definition works well because, in fact, they’re almost always lying on top of each other. They might spread out when they’re hunting, but they typically stay within about 200 meters. It’s a good rule of thumb, loosely applied. Its fuzzy logic, you know, a fuzzy 200.

HS: Towards the end of the paper, you talk about factors in addition to foraging that could affect line grouping patterns – cooperative cub defense, territoriality and female reproductive patterns. Today, do we have a better sense of the relative importance of these factors in determining grouping patterns? You also say that it will be useful to build a dynamic model that incorporates all these factors? Has that happened?

CP: No, I haven’t done that yet. And yeah, thanks for reminding me of that because, as I mentioned, I was trying to do foraging, then we tried to do cub defense, then we did group territoriality, and it just took a little while longer to get through all those different things. Take group territoriality, for example. If you think about the landscape that the lioness occupies anywhere  – and they do they pass through almost every square inch of their territory – there’s some parts of that territory  that are intrinsically more valuable than others: a waterhole where they’re going to ambush a prey or to get a drink themselves or their cubs can get a drink; or it’s a hiding spot for their cubs. It’s a fluke of the geography. The prey gets funneled through it and then they can ambush them or they can wait for them. And so, you can visualize that there is a landscape that, literally, on a 100 meter by 100 meter basis, or a hectare by hectare basis, has higher value or lower value. And so, in another one of these papers we did that took so long, we constructed a lion real estate map based on how lions had occupied the landscape over the last 40 years. Whenever they occupied a particular hectare, their average reproductive rate was such, whereas when they occupied the next hectare it was lower. And so, we actually constructed a lion real estate and showed areas of high real estate value and low real estate value. And then, we looked to see what happens when your pride is big: do you tend to occupy more of those high value areas? And, do you gain high value areas at the expense of your smaller neighbors? So, it’s a little like – again I’ll use an Asian thing – it’s like how power gets resolved in Kashmir. That’s going to be a debate between the two sides.  It’s not like back in the old days, when it would have been by whoever has a larger army. It’s the same idea, but the lions are doing that in gangs. They’re disputing the boundaries of their territories with their neighbors all the time. And when they’re, temporarily, stronger than neighbors, they can expand; weaker, they lose it. This shifts back and forth. And where we see the extreme value of group territoriality, we can simulate what happens with a relatively few assumptions. What does the landscape need to look like that it pays lions to live in groups as opposed to being solitary? That’s the paper we published just in the last year or two. It happened too late but it’s finally out. And that one shows that the circumstances require that the landscape have very heterogeneous resource distribution.  You kind of sharply go from a really high valuable area to a pretty lousy area, such that those high peaks are really worth fighting for, and there are enough of them adjacent to each other that you can feed your family. The reason I was thinking of that is that we did it without any acknowledgement of the hunting – whether they hunted as a group or not. It’s purely imagining them in their fight against their neighbors to get what we roughly know about how well they’ll be able to reproduce, by whatever means.

I’m right now actually working on a synthesis of all the lion studies. I got a grant from the National Science Foundation a few years ago to synthesize everything we’ve ever done. It’s been taking me a lot longer than I anticipated. I’ve been very slow to put everything together. I’m working on this right now, and, thanks to you, I’m wondering whether I need to go back and think about some sort of dynamic model that includes these other aspects. In a way, I thought we answered it with that Mosser et al. paper, but I may have to think about whether I want to put group foraging in there as well.

HS: Will the synthesis come out as a book or a paper?

CP: It’ll be a book. It’s taking me so long. It’s just that, now that I’m finished with Serengeti, I want this to be the final word. And so, I’ve been analyzing the data to get answers for just about everything that I’ve always been curious about, on top of bringing together all of our prior publication. I’ve been doing this analysis now for two years and three months. It’s been going on for a long time.

HS: I look forward to reading the book.

CP: So do I! You know, they said that when EO Wilson was writing Sociobiology, he would go around campus wearing a football helmet because he had all this knowledge in his brain, which he didn’t want to lose. I’m starting to feel like that; I don’t want to come out on the slippery streets. I got to get this all out. Not that anyone would care about me, but I’d be so pissed off if I don’t.

HS: In one place in the paper, you say that whether foraging efficiency has any effect on grouping preferences can best be clarified by looking at comparable data from lions in different parts of Africa. Has that been done?

CP: Not explicitly. Because, again, like that study in Etosha where they showed this incredible amount of cooperation; that was just one group.  There wasn’t the variation – you couldn’t compare a solitary with a pair, with the trio, the quartet. You only had these six females and what they did every night.  And right now – part of the reason I was thinking about GPS collars with accelerometers – there’s a study being done by a group from the UK in Botswana. They have similar stuff like that except they don’t have cameras, so they can’t be sure whether the lions hunt or they scavenge or whatever, because they just get the GPS readings back three months late; they don’t really know what happened. But again, that’s just with one group. The thing about the Serengeti study that made it so important, scientifically – it’s always been the strength of that study – is we had so many different animals. We were looking at 20 different prides – we had solitaries, we had pairs, we had groups of 12, 15. And so, we could make these comparisons. No one else has done that.

HS: The paper includes some natural history observations on lions. I want to ask if these observations have been updated in any way. For example, you assume that each male eats twice as much as a female. Would you still make that assumption?

CP: Yeah, I wouldn’t change that.

HS: Then, you say a cub less than one year consumes about one third as much as an adult female.

CP: Yeah, again, I wouldn’t change that. That’s reasonable.

HS: Finally, you say that they consume five to 8.5 kilos in a day.

CP: Yeah, I haven’t seen any difference from that either.

HS: Have you ever read this paper after it was published?

CP: Yeah.

HS: In what context?

CP: Well, I just wanted to make sure about what we said about their grouping patterns. We actually published another paper that was similar to that one, about how they actually form groups in different circumstances. And, actually, I was just thinking about that paper for something else recently, too. So, I check it every now and then when I’m talking about grouping patterns. That’s pretty much still the cornerstone of a lot of things I’ve looked at, although, I’ve got more data, and I’ve updated it. But we don’t have, like, three times as much data. It doesn’t change things much. I can subdivide it by area, instead of combining all the data. I could say, well, let’s do it in this part of the Serengeti plains versus this part of Serengeti woodlands. We can disaggregate the data in interesting ways. But we never went out again. It’s just so lethal watching them 24 hours a day; we never did that again. So, that’s it.

HS: Would you count this paper as one of your favorites among all the papers you have written?

CP: I have such mixed feelings about that paper, because it always reminds me of going mad in the middle of the night, in the middle of the Serengeti. But I also like it, because it was a way to present how lions as they are; not just two dimensional. It’s not just food, like the title says, so I like it from that perspective. And so, it’s on that list of papers in which I was able to be more integrative and holistic. I like it from that point of view. I just wish we had 10 times as much data.  If we did, error bars on some of those things would have shrunk, and we could have also separated out by habitat, or we could have done a much more sophisticated analysis. Just doing those 39 different follows, that’s an N of 39. And that’s not enough, if you want to use really sophisticated statistics, look for interactions, all these sorts of things. You want to have 10 times as much data. In almost everything that I’ve ever done, I’m always happiest when I have the most data. So, this paper is on my list of: Oh, yeah, that was really cool, but I wish I had more data. That’s how I feel about it.

HS: What would you say to a student who’s about to read this paper today? Would you guide his or her reading in any way? Would you point them to other papers they should read along with this? Would you add any caveats to their reading?

CP: It was a work of its time. And during that time, there was still a lot of excitement about behavioral ecology, and how some fairly simple models might explain some fairly complicated behaviors. What we were trying to do is to issue a corrective saying, well, you know, your model is only as good as the assumptions. The reality of these animals is that they lead far more interesting and complicated lives than just worrying about their next meal. It is important to keep in mind that this paper is from its own time. There are other things they should read; my synthesis, if I ever get that thing done. There are two other papers. There was a Science paper we wrote around 2000-2001 that was about egalitarianism and African lions. That is one I really love, because it was so holistic. It’s pointing out all the different dimensions along which lions interact with each other. The thing about egalitarianism is this – there’s a temptation to be the 1%, right? We’d all love to be Bill Gates. In an animal society, if an individual is too greedy like that, then everyone else is inclined to say, well, I’m not gonna put up with this. I’m going to occupy Wall Street or whatever. There’s an interaction that has to take place so that despotism isn’t too horrible. And, in fact, despotism is really common in animals, especially where you have kin groups. For example, worker bees are going to do what the queen says because their options are terrible as a worker bee. What are they going to do? Start their own hive? No, not a chance. Dog packs are like that; you’ve got the dominant female and the dominant male. Wolf packs are like that. Hyenas are like that. Lions are weird in that they are kin groups too, but they’re completely egalitarian. Why is that? It turns out that, well, they’re cats, and cats can do very well on their own. But, wait a minute, you got to be in that game. You need your partner; your partner’s absolutely essential. And so you have to try not to be too despotic because you need your companions in so many ways. It’s that needing of companions, that’s what I love about lions. I love lions because they are so egalitarian. There’s no dominance hierarchy in the females. That’s because they need each other; they’re necessary companions. If our lives were that gloriously simple, it would be great. Early humans had that too. This is why it’s interesting, because hunter gatherer bands tend to be egalitarian as well. Lions are like early humans.

I really love that paper. I also really love these real estate papers that have 40 years of data on 20 prides. That’s a massive amount of information. I believe the Am. Nat. data well enough except that there should be more. With the recent landscape stuff, we got it. I’m really happy with that. On basic lion ecology, I’d say those are the ones I love the most.

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