How Do Animals Recognize Each Other?

To be a giraffe among giraffes, or a pigeon among pigeons, is to live at all times in that scene from Being John Malkovich—a world in which everyone you know looks pretty much exactly like you. However wondrously varied the animal kingdom might be, on a species-level its residents tend to look more similar than not—at least, from a human perspective. I’m not saying that all squirrels look identical—just that being a squirrel, and trying to distinguish your squirrel-spouse from your squirrel dad from your squirrel-mailman, seems like it would be pretty hard work.

And yet anyone who’s seen a nature documentary knows that despite their surface similarities, animals recognize their own all the time. Sight might play some role here, depending on the species, but it can only take a given animal so far. Presumably, other processes have to pick up the slack. This week on Giz Asks, to figure out what, exactly, those processes are, we reached out to a number of experts—among them biologists, psychologists, and environmental scientists—who detailed the wide range of behaviors which help animals of the same species recognize one another.

Jill Mateo

Associate Professor in the Department of Comparative Human Development and head of the Adaptive Research Lab at the University of Chicago

Most animals recognize their family and ‘friends’ by sight or by smell, although other cues could be used, such as sounds. Odors are used as cues to familiarity or genetic relatedness in mammals, birds, amphibians, fish and insects. These odors could come from general sweat glands or from specialized glands in the skin. In some cases, odors are influenced by the major histocompatibility complex (MHC), a collection of genes involved in the immune system. Family members have similar MHCs, and therefore have similar odors.

Another question we could ponder is ‘why do animals recognize each other?’. Recognizing familiar individuals, such as neighbors, can help to avoid unnecessary fights or to promote alliances. Recognizing relatives can be important to avoid inbreeding, or to recognize previously unfamiliar kin, such as paternal half-siblings in species which have multiple paternity. Furthermore, animals which engage in nepotistic behaviors—risky behaviors that benefit kin —certainly need to be able to recognize how closely related they are to the individuals who might benefit.

The ‘how’ and ‘why’ of animal recognition are well understood for Belding’s ground squirrels, a small, group-living mammal found in high elevation meadows of the western United States that I have studied for 25 years. Adult females are highly nepotistic, but risk their lives only to benefit mothers, sisters and daughters. Their litters are comprised of full- and half-siblings, creating a need for squirrels to recognize kin they did not encounter growing up, such as their father, a paternal half-sibling, or a cousin. Belding’s ground squirrels have a variety of glands that produce odors useful for recognition. Oral, dorsal, pedal, anal and supra-orbital glands produce individually distinct odors, and oral- and dorsal-gland odors are kin distinct. That is, these odors co-vary with kinship and allow squirrels to quickly assess their relatedness to others. Indeed, when two squirrels first encounter each other, they smell each other’s oral glands, and look as if they are kissing as they do so. After their seven-month hibernation, squirrels still recognize their kin, but no longer recognize their previously familiar neighbors, telling us that each spring squirrels use their own odor as a referent or a template of what their family smells like.

Lauren Highfill

Associate Professor in the Department of Psychology at Eckerd College

Being able to tell a family member from a non-family member is very important and seems to happen in many species. Nepotism, or favoring kin, as well as the avoidance of close inbreeding is seen throughout the animal kingdom, which suggests the importance of being able to distinguish family from others. There are a variety of mechanisms used, and sometimes multiple mechanisms within a single species. For example, bank swallows first use their nest site to recognize where their chicks are (and they will feed non-kin chicks placed in their nests). However, once their own young fledge (around 2-3 weeks), the parents shift their discrimination strategy to recognizing the individual call of their chicks (and will no longer feed a non-related chick).

Bottlenose dolphins produce “signature whistles” which are characteristic of a particular individual. When a dolphin is separated from its group it is more likely to produce its signature whistle than when it is not separated. Dolphins also seem to remember the signature whistles of their “friends” after years of separation.

Other strategies include visual cues (e.g. behavior and morphology) and chemical cues (e.g. odors). Research also suggests that pandas may use their distinctive facial fur pattern for individual recognition.

Joshua Plotkin

Assistant Professor, Department of Psychology, Hunter College, SUNY

Humans are members of the primate order, and like our ape cousins—chimpanzees, gorillas, orangutans, bonobos—we primarily absorb our physical world through our visual experiences. Our ability to recognize people that we know is based largely on the integration of our visual system with our memories. This doesn’t mean we don’t also use our sense of smell and hearing in our interactions with others (humans have language and primates certainly communicate with each other using sound and smell), but vision is our primary sense.

But how do other animals, non-primates in particular, experience their physical and social worlds? For more than a decade, I have studied the behavior of Asian elephants in Thailand. My research focuses largely on how elephants think and make decisions in both their physical and their social worlds. How do elephants make decisions about where to go to find food, or which elephant to cooperate with? Although elephants can see (my colleagues and I did a study that showed they can recognize themselves in mirrors, for instance), research on elephant behavior indicates that elephants’ interactions with others—specifically, within their social groups—may rely more heavily on their use of sound, smell and touch.

In one study, scientists Lucy Bates, Richard Byrne and their colleagues were interested in looking at African elephants’ memory for family members and the elephants’ understanding of where the family members were located in relation to themselves. The interesting part of this study is that they tested this using urine, and found that the elephants may have been able to identify a large number of individuals simply by “smelling” what they left behind.

I think it’s pretty clear from research like this, and decades of research from other elephant behavior scientists in Africa and Asia, that elephants are multimodal communicators; they can use the complement of visual, acoustic, olfactory and tactile information in their social interactions with other elephants. In addition to detecting, identifying and communicating with individuals through sound calls, elephants often use their trunk, which is an extremely sensitive olfactory organ, to both touch and smell other elephants. Although we’re still studying this, I’m convinced that the elephant’s sense of smell plays a huge role in their ability to make all sorts of decisions in their daily lives. The non-human animal world can tell us so much about how sociality and communication evolve, and we still have so much more to learn!

On a more somber note, species such as chimpanzees, gorillas, bonobos, orangutans and Asian and African elephants are endangered; we are running out of time to learn more about these remarkable animals. New knowledge about their behavior and cognition not only informs our understanding of our own evolution but also may play an important role in helping scientists and conservationists develop better protocols for protecting them and their habitats.

Noah Perlut

Associate Professor, Department of Environmental Studies at the University of New England

There are many different methods of communication and individual recognition among animals. There are scent-markings: for instance, a deer might urinate down its leg, which catches the smell, and gives off an individual identification A grey fox will very intentionally poop right in the middle of a trail or on top of a rock in a place that’s really obvious, as a way of saying ‘I was here, this is who I am.’ A bird [communicates through] song or calls or other types of vocalizations, as well as through actual displays—the way that they fly up in the air and make a particular pattern, usually linked with a sound while in the air, or a call. These are ways that they all can distinguish individuals, and then they can make choices about what sort of relationship they have with those individuals, whether it’s to ignore them, whether it’s aggressive, whether it’s a friendly relationship—or if it’s courtship. Courtship is really key here.

There are a number of mammals that can also communicate by sight as well: the way a squirrel moves its tail can give signals to other squirrels about who they are, as well as their relative health and their body condition, and things like: are they stressed, are they prepared to mate, etc. Things like that provide very complex signals.

It’s really complex signals that are provided in things like that.

Marc Bekoff

Professor Emeritus of Ecology and Evolutionary Biology at the University of Colorado and the author of the forthcoming Canine Confidential: Why Dogs Do What They Do

A number of nonhuman animals—i.e., animals—have the ability to recognize themselves. Of course, what they actually know about themselves and whether they actually say something like “Wow, that’s me” when they see, hear, or smell themselves, isn’t known. So, while we don’t know if other animals have a true sense of “I-ness,” as do humans, they do show the ability to know something about their own body: for example, this tail is mine. Thus, they have what I call a sense of “body-ness” and a sense of “mine-ness.” Different studies have been conducted on nonhuman primates, dolphins, elephants, and magpies using what is called the “red dot” test. During these experiments, called the “mirror test,” a red dot is placed on the forehead of an individual when they are anesthetized or otherwise unaware that someone has marked them. Then, after they previously have been trained to interact with a mirror, a limited number of members of these species make self-directed movements toward the red spot. These movements are taken to mean they have some sense of self-awareness or self-recognition.

But we really don’t know how dogs recognize other dogs as the individuals who they are, and likely there’s more than one way they do so. I’m sure that dogs have individual and unique scents—so one way in which my dog Jethro, for example, might recognize his good friend Zeke and other dogs would be by what they smell like. For me the interesting questions are how dogs recognize other dogs as individuals with whom they don’t have all that much contact, or how they recognize them from a distance. Dogs might also use sight — visual clues such as size, shape, coat color, the type of ears and tail an individual has, and gait, for example, and perhaps what another dog sounds like when they vocalize. It’s also easy to imagine that dogs use what are called “composite signals” in which they use cues coming in simultaneously from the different senses to identify individuals. Numerous people with whom I spoke when I was researching my book told me that they simply knew their dog recognized other dogs—but hard data on this question is really lacking. This would be a wonderful topic for future systematic research.

Prof. Jenny Morton

Department of Physiology, Development and Neuroscience at the University of Cambridge, her recent research on Huntington’s disease led her to her discovery that sheep can recognize human faces

Sheep tell each other apart from face recognition, sound and smell. So, pretty much as a dog does. Which sense prevails depends upon how far away one animal is from another and how dark it is. Smell is more important for lamb recognition, and less important for adults.

Lars Chittka, PhD, MSc

Professor of Sensory and Behavioural Ecology, Berlin Institute for Advanced Study

[Bees] don’t—to our knowledge, there is no individual recognition in bees (but there is recognition of colony membership by scent). But some wasps recognize each other individually through distinct facial features. And bees can be trained to recognize images of individual human faces.

Elizabeth Tibbetts

Professor of Ecology and Evolutionary Biology at the University of Michigan

Social bees and wasps have a colony-specific scent that they use to figure out which individuals are nestmates vs non-nestmates. Workers also identify the queen using her scent. The fertile queen smells different than infertile workers. Some bees and wasps use other mechanisms for recognition. For example, Polistes fuscatus paper wasps have unique facial features. These wasps use each other’s unique faces for individual recognition. It’s similar to the way that you identify people using variation in human facial features.

Tamás Faragó Ph.D.

Biologist and research fellow, Department of Ethology, Eötvös Lorand University, Budapest, studies bioacoustics

The short answer is we don’t really know much about this. [Dogs] certainly use smell, visual and acoustic features. There is one study showing that they look longer at pictures showing the face of dogs they have already seen compared to novel ones suggesting that they are able to discriminate other dogs’ faces (Racca et al 2010). Another study showed that they react differently to familiar and unfamiliar territorial barks: when the researchers played back a bark from an unknown individual outside the fence of the garden, the subjects approached it, and reacted with barks, while when they heard the bark of a familiar individual they oriented to the house where it was actually located during the playback (Pongrácz et al 2014). Finally, they also seem to react differently to a familiar and unfamiliar dog’s separation whines. The subjects showed more affiliative behaviors to the familiar dog when they heard its whines before compared to hearing an unfamiliar individual’s whine (Quervel-Chaumette et al 2016). However we don’t really know what features they actually use to differentiate other dogs.