|Dolphins are social animals|
Parental care naturally involves things such as suckling the young, protecting them from predators, and so forth, and it can also include helping them to survive injury. Without the advent of first aid, this may often be ineffective, but it has been observed in a number of species. It becomes particularly dramatic - and, from a human perspective, distressing - when it is apparent that the juvenile is already dead. Here, there is no possible benefit to the young, and likely at least some apparent detriment to the mother in wasted effort, if nothing else.
So why does it happen? Clearly, since it isn't adaptive, nurturing behaviour directed towards deceased offspring is the product of something else going wrong. And it isn't necessarily the obvious reason, either. Can animals feel grief? To what extent can they understand the concept of death? Or are we actually mistaking some behaviour for attempted care, when it's really something else entirely?
To try to understand this, we need data on instances where it has happened. It's not the kind of thing you can easily study, especially if you want to know how animals act in the wild, rather than in the restricted confines of captivity; it's not as if you can ethically set up a study where you surreptitiously kill baby animals just to see what happens. Instead, you're going to be forced to rely on anecdotes of past occurrences, albeit preferably ones backed up by video footage or similar solid evidence to get as impartial and accurate a view as possible.
This sort of behaviour has probably been observed the most in primates. We perhaps don't find it surprising that chimpanzees and gorillas have both been seen attempting to care for deceased offspring, for example by carrying them about, grooming them, and so forth. In some instances, this can continue for a long time - even months. But it's not just apes, since monkeys have been shown to sometimes act in similar ways following a bereavement. Moving further across the primate family tree, lemurs do seem to attempt to give some form of care to their young for a few hours after death, for example, by licking or calling to them, but don't appear to display the same prolonged dysfunctional attachment that can be seen among monkeys and apes.
But, if prolonged care for the deceased is apparently absent among the "lower" primates, are there other groups of animals where we might expect to see it? It's a natural bias that we'd tend to look at animals that share some similarities with us, especially in the sense of being relatively intelligent. And, in fact, this does appear to be the case. Rodents, for instance, don't show this sort of behaviour that we know of, while elephants do, by some analyses, show compassion to the dying and a particular interest in corpses of their own species. More surprisingly, perhaps, giraffes have been seen to examine their own dead, and to stand guard over them for some days.
But, if it's large brains and complex behaviour that we're looking for, an obvious place to start is among the cetaceans. Behaviour similar to that among primates has been reported among several marine mammal species, including both dolphins and whales. But such reports are, by their very nature, somewhat sporadic. However, a collection of fourteen new reports of cetaceans handling the dead adds significantly to our knowledge base, including adding a number of species never before observed to act in this way.
A typical such report concerns a group of short-finned pilot whales (Globicephala macrorhynchus) seen off the coast of the Azores in 2003. One of the adults in the group was swimming a short way off from the others, accompanied by the body of a calf, which it kept nudging with its head, and occasionally carried about in its mouth. The behaviour continued for the 109 minutes of the encounter, and presumably for some time thereafter. More notably, perhaps, the carcass was already badly decayed, and must have been dead for some considerable time.
Many of the other reports are similar, with an adult - always a female, where it was possible to determine the sex - swimming about in close proximity to a dead infant, or actually carrying it, whether by holding it (or its fins) in their mouth, or by attempting to balance it on their head or back. The majority of the deceased animals were newborn, although many were older, and none were themselves adults.
The timespans involved also seem to be somewhat variable. A killer whale seen off Washington state was carrying what was likely a stillbirth, still with the umbilical cord attached, and which cannot have been dead for long; when she was seen the next day, the corpse had already gone. Whereas, with the pilot whale mentioned above, the behaviour must have been continuing for far longer than that.
All but one of the fourteen accounts referred to members of the dolphin family, with the one exception being a sperm whale. We do know of similar reports from other non-dolphin species, but none at all for baleen whales, such as humpbacks. It's unclear whether that's just because its difficult to observe them at this time of their life, due to some physical limitations in their ability to carry young (for instance, having no teeth to grip fins with), or an actual behavioural difference.
We can't, of course, know what's going on in these animals' heads. Indeed, in most cases, we don't even know if they are the mother of the deceased, since we do know of instances among primates were other close female relatives have attempted to tend to dead infants. But we can make some reasonable inferences, and perhaps exclude a few possibilities.
For instance, one theory is that this isn't even remotely what we perceive it to be, and is really no more than an animal playing about with an object that they've found, in much the same way that they might play with a skull they happen to come across. This isn't as far-fetched as it sounds, and there is some evidence to support it in at least some instances among primates. In the case of the cetaceans, though, it seems unlikely, since the adults aren't normally 'playful' in that way, all of them that we know of 'just happen' to be female, and they obviously haven't come across the carcass by coincidence (if they did, most of them would presumably be of different species).
It's more likely, then, that this is to do with the complex social bonds that these animals have in life. Helping one another is just part of what they do, even when the child isn't theirs. This doesn't necessarily mean that it's 'mourning' for the dead in the way that we'd understand it, though - although, to be fair, we can't rule that out, either. It could be an inability to truly comprehend death, especially in those instances where the infant has not been dead for long. Even where it has obviously begun to decompose, which you'd think would be a major clue, the maternal hormones sloshing around in the mother's bloodstream might just not allow it to 'let go'; the social bonds are so strong between mother and young that they can't be denied, even when it's far too late.
If even we humans sometimes have difficulty accepting the death of a loved one, how much harder must it be for an animal that can't truly understand the concept? An animal that doesn't really understand why its infant has stopped responding, but is driven, partly by biology, and partly, perhaps, by the altruistic drive so often needed to maintain complex social groups, to keep offering help for as long as it can?
[Photo by Serguei S. Dukachev, from Wikimedia Commons.]