The value of individual identification in studies of free-living hyenas and aardwolves

Abstract

From population estimates to social evolution, much of our understanding of the family Hyaenidae is drawn from studies of known individuals. The extant species in this family (spotted hyenas, Crocuta crocuta, brown hyenas, Parahyaena brunnea, striped hyenas, Hyaena hyaena, and aardwolves, Proteles cristata) are behaviorally diverse, presenting an equally diverse set of logistical constraints on capturing and marking individuals. All these species are individually identifiable by their coat patterns, providing a useful alternative to man-made markings. Many studies have demonstrated the utility of this method in answering a wide range of research questions across all four species, with some employing a creative fusion of techniques. Despite its pervasiveness in basic research on hyenas and aardwolves, individual identification has rarely been applied to the conservation and management of these species. We argue that individual identification using naturally occurring markings in applied research could prove immensely helpful, as this could further improve accuracy of density estimates, reveal characteristics of suitable habitat, identify threats to population persistence, and help to identify individual problem animals.

Supplementary information: The online version contains supplementary material available at 10.1007/s42991-022-00309-4.

Keywords: Aardwolf; Camera traps; Carnivores; Hyena; Individual identification; Mark-recapture.

Fig. 1

Photographs of two different hyenas in the Maasai Mara National Reserve, captured on different occasions. These photographs were all taken manually by observers in the field, using digital cameras. Contrast, brightness, and sharpness were edited to enhance visibility of spots. Shown here are reference photographs of the right (a, c) and left (b, d) sides of a female hyena named Pike. Spotted hyenas’ spots are not bilaterally symmetrical, so reference photographs should ideally show both sides. Her identity may be confirmed by comparison of her spot patterns on her right and/or left shoulder(s), flank(s), hip(s), and legs. Spots from multiple body parts should be used, but the specific parts used may depend on visibility (e.g., whether grass is in the way, whether the hyena is muddy, or depending on the animal’s posture or the angle from which the animal is seen). The right (e) and left (f) sides of a different hyena, a male named Kaikura, are quite distinct from Pike’s

Fig. 2

a A photo album of one of the Mara Hyena Project’s study clans in the Mara Triangle, Kenya. The photo album is organized by age–sex class. For each subject, photos of the left and right sides are shown together and oriented in the same fashion to facilitate comparison across subjects. These photos are updated throughout the hyenas’ lifetimes, and each photo is marked with the date taken. Photos are edited to increase contrast, so that spots are clearly visible. The position and shape of each hyena’s ear damage, if present, are noted on reference photos. Whereas a hyena’s spots never change, ear damage often varies over a hyena’s lifetime. Therefore, ear damage should be used to narrow the list of likely candidates, but final confirmation should always rely on examination of spot patterns. b Ears of eight different spotted hyenas in the Mara Triangle, Kenya. Ear damage is acquired while fighting with conspecifics or other large carnivores. Clearly, ear damage among individuals can be quite variable and distinctive, from a small nick to a missing ear. Photo credit for (a) to Erin Person

Fig. 3

Distinct ear damage on a spotted hyena cub with its natal coat. This cub, Black Bear, was the only cub at this communal den with a slit on this part of its ear (indicated by white arrow), so he could be clearly distinguished from the other cubs, including his littermate. This allowed researchers to identify Black Bear before he shed his black natal coat and developed spots

Fig. 4

A natural ear notch on the right ear of the same brown hyena at the ages of five (a) and 15 years (b). The shape of the original notch has changed, and new smaller notches have appeared over time

Fig. 5

The top row (a–c) shows the anterior surfaces of the forelegs of a male brown hyena named Kai-Alex, and the bottom row (d–f) shows those of a second male, Lloyd. Kai-Alex’s leg stripes are the same at six months (a) and 2.5 years of age (right foreleg, b; left foreleg, c). Similarly, Lloyd’s foreleg stripes are consistent from cubhood (d) to adulthood (right foreleg, e; left foreleg, f). Photos of leg stripes at 2.5 years of age were taken while hyenas were anesthetized

Fig. 6

A single female brown hyena, Alaika, is shown at the ages of five, eight, and 12 years. The first frame (a) shows the lateral view of Alaika’s right foreleg at five (left), eight (center), and 12 (right) years of age. We can see that the stripes are consistent over her lifetime. In the second frame (b), we see that the anterior view of the right foreleg looks quite different from the lateral view of the same leg, but, again, the stripes are consistent throughout her lifetime (5 years of age, left; 8 years, center; 12 years, right). Photographs in a and b were taken while Alaika was anesthetized for handling on three different occasions. c Remote camera trap images of Alaika with sufficient clarity to identify her using lateral stripes of right foreleg (left, center), and insufficient clarity for confident identification (right)

Fig. 7

Left sides of two known striped hyenas in a population near Shompole, Kenya. a, b Two images of the same individual, male M113, captured on different occasions. M113’s mane is erect in a, revealing some stripes on his left flank, but is not erect in b, thus partially covering and distorting these stripes. The stripes and spots on the fore- and hindquarters are more useful than the flanks or ears for identification of striped hyenas. c, d Two images of a second individual, male M114, captured on different occasions. In (c), M114’s legs are partially obscured by grass. Leg stripes may certainly be useful when visible, but they are more likely to be out of view than the shoulders and hips, which also have similarly variable and prominent markings. In this population, many hyenas have a single solid stripe over a double stripe on their left hip (white boxes; a, c). As an observer becomes more experienced identifying subjects in a given population, they should recognize interindividual similarities such as this and focus on more variable features (e.g., left thigh stripes, shoulder stripes). Therefore, slight similarities among hyenas should not necessarily lead to a reduction in accuracy, particularly if observers use patterns from multiple body parts to confirm each identification. Images captured by handheld digital camera (a) and remote digital camera traps (b–d) by Aaron Wagner

Fig. 8

Incidental photographic captures of aardwolves by remote camera traps used by the Brown Hyena Research Project in Namibia. a, b Two captures of the same individual, viewed from different angles. c A second individual. These two individuals can be easily distinguished by the stripes on their shoulders. While individuals can often be recognized even when viewed from different angles, applying bait or taking advantage of natural or man-made trails can help position animals relative to the camera lens for optimal visibility

Fig. 9

Variation over time in the sizes of six study clans in the Maasai Mara National Reserve, Kenya. For each time point, the annual mean clan size is shown (with standard error bars when multiple population counts were performed within the given year). Data for each of six study clans, represented by symbols indicated in the key at the top left, were included from the first year each was studied through 2013. The Talek West clan split into two daughter clans in both 1989 and 2000, indicated by horizontal black bars over the data points. Each of these two clan fissions resulted in a reduction in size of the parent clan, as a subset of this clan’s members left to form a new clan in each case. Reproduced from Green et al. (2018) with permission from Biodiversity and Conservation

Fig. 10

Representation among adult female spotted hyenas of the Talek clan at decade-long intervals (Holekamp and Strauss 2020) of descendants of the original 19 adult females studied by Frank (1983). Reproduced from Holekamp and Strauss (2020) with permission from Integrative and Comparative Biology