In these times when America seems possibly more divided than at any time since the Civil War, is it good to discover how much more civilized our world than that of our primate cousins?
Or is bad to have the idyllic myth of nature’s Eden again shattered by the reality that humans aren’t the only animals who kill their own kind and that, in fact, some of our distant cousins make us appear, well, civilized?
Consider the news that comes now from scientists studying the mountain gorillas of the Virunga massif at the border of Uganda, Rwanda, and the Democratic Republic of the Congo.
Conservationists have long been trying to save those animals as the ever-growing human population of Africa squeezes the big apes out of their habitat. But now they’ve run into a problem.
The gorillas, it appears, don’t get along well.
“A sudden increase in social group density observed in 2007 caused a threefold increase in the rate of violent encounters between social units (groups and solitary males). A fivefold increase in the rate of infanticide and seven cases of lethal fights among mature males were subsequently recorded, and the annual subpopulation growth rate declined by half between 2000 and 2017,” they reported in Science Advances this week.
Their peer-reviewed study concluded that an analysis of 50 years of data on the gorillas “reveals that social behavior changes observed at high group density” – not food shortages or shrinking habitat per se – might now be the major factor limiting population growth.”
The findings, they warn, suggest the gorillas might become a harder species to save as their habitat continues to shrink, adding to the already well documented food and predation problems confronting isolated or so-called “island populations” of wildlife.
Alaska is home to a classic case of the latter that illustrated both the problems of trying to keep hungry, isolated populations from destroying their own habitat either by devouring all the edible vegetation or, in the case of predators, killing all their prey.
With Sitka blacktail deer overrunning, Coronation Island – an isolated, 28-square mile forested outcrop in the Gulf of Alaska just off the Panhandle south of Sitka – the Alaska Department of Fish and Game 60 years ago decided to try to “balance” nature.
Armed with good intentions, the agency released four wolves – two males and two females – on the island in October 1960. By 1964, 13 wolves were thought to be living there, and deer were reported absent on the north side of the island.
“But fresh tracks occurred on steep slopes on the south side of the island and on the higher peaks,” noted Alaska research David Klein reported in a 1992 paper presented at a North American wolf symposium “(State biologist Harry) Merriam equated these locations with escape terrain, where rough terrain and dense vegetation provided the best opportunity for deer to escape from wolves.”
Unfortunately, nature being the kill or be killed world that is, the deer couldn’t escape the growing wolf populations for long.
When Merriam returned to the island in December 1967 “with new snow and good tracking conditions, there was evidence of only one wolf, indicated by urination marks to be a female,” Klein said. “No deer tracks were seen. Three wolf scats collected contained deer in one, seal in another, and rodents and chitons were in the third.”
Three years later, Merriam spent 10 days on the island and found a single, fresh wolf track but no tracks of deer. The wolf had been reduced to eating nothing but seals, birds, rodents and marine invertebrates.
The diet might have been enough to sustain foxes. It was not enough to sustain wolves. By the 1980s, the last wolf was gone from the island.
Klein’s study concluded the island was “too small to sustain populations of both deer and wolves.”
Other studies have reached similar conclusions. Herbivores inhabiting small ranges must be managed to prevent them from destroying the vegetation on which they depend, and if predators are added to the mix, they must sometimes be controlled to keep them from killing off all the prey.
But the African case appears to be the first in which scientists have encountered social conflict as a population limiting problem, although the African researchers noted past studies suggesting the “frequency of aggressive behaviors is expected to increase when group density increases, which may have negative consequences for the population growth rate.”
The new study says the negative consequences are now documented. The researchers found that as the density of gorilla social groups – what one might call tribes – grew, the gorillas began to wage war on each other with both the males leading social groups and lone males especially targeting young gorillas.
“The proportion of infanticide committed by group silverbacks (68 percent) and solitary males (32 males) was consistent with the proportions of group-group encounters and group-solitary male encounters,” thet wrote, “revealing that solitary males were not more likely to engage in infanticide than group males.
“Because infants represented 22 percent of the study subpopulation on average between 2000 and 2006, the increase in infanticide was responsible for an estimated 1.54 percent decrease in the growth rate of the study subpopulation. The annual growth rate dropped from an estimated 5.05 percent in 2000 to 2.37 percent in 2017, corresponding to a 2.68 percent decline.”
It wasn’t just young gorillas that got killed, however.
“Violent encounters between social units also increased mature male mortality. During the 2007–2017 period, seven mature males died after being wounded during an encounter with another social unit, compared with one in the 2000–2006 period,” the scientists said. “These deaths will likely not have the same direct, long-term demographic consequences as infant mortality because female fertility does not depend on the number of males. However, dominant males protect their group’s infants against extra-group males, and their death is often followed by a rise in infanticide.”
The scientists warned that bad behavior is now threatening to stall the growth in the population of gorillas around the Dian Fossey Gorilla Fund’s Karisoke Research Center, where the number of gorillas has been on the upswing since 1968.
The scientist said it is possible food plays some undefined part in the gorillas’ troubles, but it isn’t an obvious problem “as feeding competition is low overall, and there was no evidence of an overall decline in food availability in the study area between the 1980s and 2010.
“In a study focusing on five key food plant species accounting for 70 percent of the gorilla diet, (another researcher) found that the biomass of three species increased between 1988–1989 and 2009–2010, while the biomass of the remaining two species declined.”
Home range sizes, likewise, remained stable between 2000 and 2012 and “group size had little impact on group home range sizes, which indicates that feeding competition was likely low during this period,” the study said.
The most obvious problem appears to be that gorilla social groups just can’t get along, a problem often witnessed with wolf packs that regularly go to war in Alaska.
The study would indicate that members of social units are better at moderating their behavior within the group than they are at controlling themselves when they have to interact with other groups.
The study, they wrote, “suggests that the amount of space a species may require will vary depending on its social organization at any one moment in time. For example, in gorillas, three groups each containing 20 animals may require less space than six groups containing 10 animals. This is of particular relevance for the mountain gorillas in the near future.
“The Virunga gorilla population is still growing at a high, 3 percent annual rate, and we can expect group density to keep increasing in the future. As a consequence, aggressive encounters between social units will likely become more frequent. Protected-area managers should expect infanticides, injuries, and overall stress to increase. The decrease in animal welfare will have ethical implications that will affect conservation policies in place in Rwanda, Uganda, and the Democratic Republic of the Congo.”
Gorilla tourism is a significant and growing business in Africa.
The Volcanoes National Park in Rwanda, the Virunga National Park in the Democratic Republic of Congo, and the Bwindi Impenetrable National Park in Uganda is “where gorilla tourism prominently takes place,” according to the journal Africagrowth Agenda.
“The cost of a permit is placed at $1500 in Rwanda with a special package of $15,000 for a group with a personalized park ranger which is the highest. The next in line is $600 in Uganda while the cheapest is $400 in DRC Congo. These permits are for one hour of watching gorillas in their natural habitat. Rwanda has been able to develop their tourism product so well that the African Wildlife Foundation (in 2019) reported that visits to the Volcanoes national park has increased by over 80 percent and the country’s tourism growth has been ranked as one of the top five in Africa and a major influence is the gorilla tracking package.”
Rwanda has generally been good to the threatened gorillas, and the gorillas have generally been good business for Rwanda. The new study doesn’t specifically say that it’s bad for business to have the gorillas beating on each other for in front of the tourists, let alone killing baby gorillas.
But the warning about the “decrease in animal welfare” and the associated “ethical implications” comes close. This might be the way nature works, but it’s not exaclty something tourists want to see.
“Infanticide: An ugly side of nature” was how photographer Ed Mackerrow headlined a post on his blog after an experience at Katmai National Park and Preserve in 2018 where grizzly bears also engage in the practice.
“This uglier side of nature, infanticide, the killing of baby bears by an adult (usually male) bear, is something I never wished to witness,” he wrote below. “In past years at Katmai National Park, I watched a couple of close calls where an adult tried to kill a cub.
“Well, infanticide does indeed exist in nature and this past July I, unfortunately, witnessed a large male bear kill a cub, and then brutally attack the mother of the cub when she tried to intervene.”
Bears do it. Gorillas do it. And yes, sadly, sometimes humans do, too.
But the research would indicate we don’t do it nearly as often as the bears, our distant primate relatives the apes or even as often as our less distant human ancestors once did.
Archeologists in 2014 found evidence that led them to conclude human infanticide was common in ancient Rome, a mere 1,800 years ago. We’ve come a long way since then.
Infanticide is now rare in the Western world and though Americans might now be shouting at each other and engaging in mighty wars of words, we aren’t warring either – another behavior all too common among our species until not all that long ago.