Animal grief may look nothing like human sorrow

Grief is considered a deeply human response to loss. Across cultures, people mourn with rituals, social withdrawal, and emotional upheaval. But are we alone in our experience of grief? A new study by UCL anthropologists suggests animal grief may differ entirely.

The study, published in the journal Biology Letters, examined how rhesus macaque mothers respond to the deaths of their infants. What the researchers found could shift our understanding of animal emotion.

While many assume that animals grieve similarly to humans, this research provides a more nuanced view. The macaque mothers did not withdraw or show signs of emotional collapse. Instead, they exhibited an unexpected and short-lived burst of activity.

This pattern, absent of lethargy or appetite loss, may reflect a different process altogether – one that lacks the prolonged sorrow seen in human grief.

Restlessness instead of withdrawal

The researchers observed 22 female rhesus macaques living on Cayo Santiago, Puerto Rico. Half had recently lost their infants, and the others served as non-bereaved controls.

Using smartphone software to track behavior, the team recorded how much time each mother spent resting, grooming, feeding, and engaging in displacement behaviors such as self-scratching or pacing.

In humans, grief often leads to decreased energy and motivation. Lethargy, sleep disturbance, and withdrawal from social interaction are common.

However, the macaque mothers in this study behaved differently. In the two weeks following their infants’ deaths, bereaved females spent significantly less time resting than controls.

“Following the loss of an infant, we had expected the macaque mothers to spend more time resting, as is common among bereaved humans,” said Dr. Alecia Carter, a co-author of the study.

“What we actually observed was the opposite. The bereaved macaque mothers spent less time resting in the first two weeks after an infant’s death and there was no difference of their time spent foraging, grooming, or doing displacement behaviors.”

Animal grief may involve agitation 

This surprising pattern led the researchers to rethink their expectations. The idea of a two-phase grief response – protest followed by despair – is well-established in studies on mother-infant separation.

In primates, both infants and mothers show early signs of agitation when separated, a phase known as protest. Among infants, this is sometimes followed by despair, marked by low activity and reduced engagement.

In the macaque mothers, only the protest-like phase was observed. There was no evidence of a longer despair stage. “The mothers’ period of restlessness was surprisingly short,” noted Dr. Carter.

“But this short-term response can also be seen in primate mother-infant separation studies, which show a relatively short period of ‘maternal disturbance’ after separation from their infant.”

Rather than a full grieving process, the macaques may simply experience a short-lived behavioral disruption. This suggests that grief, as understood by humans, may not be a universal feature of mammalian life.

The absence of longer-term emotional change raises a critical question: do non-human primates truly grieve, or do they merely react to disruption?

No clear signs of animal grief

Emily Johnson, the study’s lead author and a master’s student at UCL, approached the research with a central question in mind.

“Death is an inevitable part of life and how we respond to death can vary greatly, even among humans,” she said. “We wanted to explore how the behavioural response to death, the experience of grief, differs between primates and humans. Is grief a uniquely human experience?”

The researchers carefully distinguished between bereavement and grief. Bereavement refers to the state of having lost someone.

Grief, by contrast, is the emotional and behavioral reaction to that loss. In this study, the mothers clearly experienced bereavement. But the evidence for grief, as defined by emotional withdrawal and behavioral changes, was lacking.

“Anthropologists have long questioned whether animals are capable of experiencing grief, and many pet owners will report their beloved cat or dog grieves after the death of a fellow pet,” said Johnson.

“But these are reports from owners who are often themselves grieving. Grief-like behaviour, such as reduced activity, could simply be because they have lost a playmate.”

Bereaved mothers rested less

The team collected data over 93 days, capturing a total of 2,528 minutes of observation time. Each macaque mother was watched for a median of 158.7 minutes across several sessions.

The infants who died were, on average, just 9 days old. Most bereaved mothers did not carry the corpses of their infants for long. In fact, only two mothers did so, and for less than two days.

There was only one statistically significant difference between the bereaved and control groups: resting time. Bereaved mothers rested less in the first two weeks after their infants’ deaths.

This effect disappeared in the following weeks. There were no differences in feeding, grooming, or displacement behaviors. The findings suggest that any response to loss among the macaques was immediate and short-term, not prolonged.

This lack of extended change is important. It mirrors findings from studies on baboons and other primates, which often show physiological stress after a loss but no consistent behavioural markers of grief.

In some cases, primates may even expand their social networks post-bereavement, as seen in chacma baboons.

Grief signs may be missed

While the study offers compelling results, the authors acknowledge alternative explanations. One is that the sample size – just 11 bereaved mothers – may have been too small to detect subtle patterns. Another is that the age of the infants at death mattered.

Since all of the infants were very young, mother-infant bonds may not have been fully established. In cattle, for example, stronger grief responses are observed when calves are removed after several days, not immediately after birth.

Individual variation may also play a role. Just as grief in humans can vary widely across individuals and cultures, the same could hold true for non-human primates. Some macaques might grieve in ways not captured by the study’s methods.

More detailed data, including hormonal and neurological measures, might uncover hidden aspects of grief.

New direction for animal mourning

The authors propose a shift in how researchers approach animal grief. Instead of expecting a mirror of human sorrow, scientists might look for evidence of protest-like responses and recognize that not all species – or even individuals – will enter a despair phase.

“Our findings show no behavioural markers of grief in the way humans understand it among the macaque mothers, so we recommend further study in this area and greater data collection on primates’ responses to bereavement,” said Johnson.

By recognizing protest and despair as separate stages with different expressions, future research can develop more accurate models. This framework could help distinguish true grief responses from other stress-related behaviors.

Animal grief may be brief

The study does not prove that macaques cannot grieve. It shows that if they do, their grief may look nothing like ours.

The absence of lethargy or appetite loss challenges our assumptions about shared emotional landscapes between humans and other primates.

Rather than sadness, macaque mothers may respond with brief agitation and then return to normal. That may not mean they feel nothing. But it does mean we must question what grief really looks like across species – and whether our human model applies at all.

The study is published in the journal Biology Letters.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–