Our Methods

Identify hyenas

Every hyena has a unique spot pattern. Individual hyenas additionally differ in their fur style and colour. While some have short, blond fur with large dark spots, others have fluffy, reddish fur with fuzzy spots. Because an individual’s spot pattern does not change with age, these characteristics allow us to distinguish spotted hyenas from each other and identify them individually.

Jedes Tüpfelmuster ist verschieden

The colour and length of the fur vary with age. This influences how easily an individual can be identified. Spotted hyenas are born with a black fur. At the age of about 1 month, the fur brightens and the spots appear, starting on the shoulders and front legs. By the age of 4 months, all spots usually have emerged. At about 7 to 15 months of age, the hairs grow longer, blurring the spot pattern and making identification a true challenge even for experienced observers. After this period, the hairs grow shorter again and the pattern reemerges. When hyenas grow very old, they may lose hairs and the hairs grow very short causing the spots to fade but the pattern usually remains recognisable.

After spending some time monitoring spotted hyenas, one gets to memorise the spot patterns of various hyenas, but knowing by heart all patterns of a population of up to 550 hyenas is difficult. And it does not help that the patterns of the two body sides of an individual differ from each other…

We use ‘ID cards’ that we compile for each hyena. These ID cards consist of printed photographs of both body sides of an individual and information such as the ID number, name and date of birth. The ID cards are sorted by clans to more quickly find a match when encountering a hyena in the territory of a given clan (but mind the intruders!).

Hyenas usually are identified by directly comparing the photograph on the ID card with the real pattern but when pressed for time, we take new photographs and compare the patterns later on. In this respect, digital cameras have proven to be an extremely helpful and important piece of equipment.

But what if the fur gets dirty? After all, hyenas are quite fond of taking baths in muddy puddles and ponds, especially on hot days. Distinguishing real spots from mud marks can be very tricky indeed. Luckily, spotted hyenas provide us with other cues such as ear notches and scars. And if one gets to spend a lot of time with them, they can also be recognised by their body shape, personality traits, and their way of walking.

top ^

Habituate and observe hyenas

Since the Ngorongoro Crater is replete with dangerous wild animals, all our work is done by car. To be able to approach hyenas with a car and observe their natural behaviour, they need to be habituated to the presence of the car.

Spotted hyenas are generally shy and cautious when approached by humans and vehicles – like most free-ranging animals. But they are also quite curious and can be habituated relatively easily if given a bit of time. Habituation works best when it is initiated when hyenas are still young. Once they gained confidence and trust the observers, they hardly pay attention to the observers in their vehicles.

Every hyena has its own character and undergoes different experiences. They behave differently towards conspecifics, competitors, prey and human beings. Hyenas thus also vary in their degree of habituation. For example, most members of the Triangle Clan are more wary than members of other clans because they regularly visit the Crater rim and encounter vehicles and people chasing them.

To monitor the natural behaviour of a hyena, it is crucial to acknowledge its personality and only approach as close as it accepts it. To assess the minimum distance tolerated by a hyena one simply has to pay attention to its behaviour – if the hyena becomes anxious or retreats, it indicates that one came too close and the respectful way to react is to retreat.

top ^

Determine the sex of hyenas

Young females and males are hard to distinguish from each other by external examination. First, females have an elongated clitoris or ‘pseudopenis’ that can be erected and that closely resembles a male penis. Second, their outer labia are fused and filled with tissue and closely resemble and are located at the same position as the scrotum of hyena males. Third, young females have very small teats that are barely visible, and contrary to common belief, there are no significant differences in body size and build between females and males.

It is therefore not very surprising that zoos regularly get confused, and report ‘male’ hyenas giving birth to cubs or that they suddenly discover, that an ‘infertile couple’ actually consisted of two females or two males.

The best way to sex a spotted hyena is to take a close look at the tip of the penis or ‘pseudopenis’ when it is erected: the penis of male spotted hyenas has a pointed tip and a clearly visible narrowing immediately above the glans whereas the female ‘pseudopenis’ has a rounded tip and lacks a narrowing. The best chance to see these characteristics is when two hyenas meet each other and perform the ritualised greeting ceremony.

Pseudopenis and penis in comparison

top ^

Determine the social rank of hyenas

Social interactions are essential to assess the dominance relationship between hyenas. To determine the hierarchy within an entire hyena clan every hyena has to be observed interacting with all other clan members. The dominance relationships between the two individuals are then established based on their behaviour and body postures. The dominant individual has its tail upright and ears cocked whereas the subordinate individual keeps its tail between the legs, has the ears backwards, the teeth bared, and the head downwards.

The ritualised greeting ceremonies are particularly useful to get an idea of the dominance relationship between individuals. When two hyenas meet, the subordinate animal erects its penis or ‘pseudopenis’ and is the first to lift its hind leg or lies down first to let the dominant animal examine its anogenital region. These rituals confirm the dominance relationships and strengthen friendships and coalitions. Hyenas initiate such greeting ceremonies from very early on (as early as four weeks old) and thereby learn which clan members are lower-ranking and which are higher-ranking.

top ^

Find the genetic father and mother

Knowing both parents of a cub is crucial. A key element of our research is to determine the reproductive success of our males and females and the establishment of a detailed pedigree. To do this, we need to assign a mother and a father to each cub. Because fathers do not provide care to their offspring and females (in rare cases) may adopt cubs from another female, we cannot rely on behavioural observations only and have to perform genetic parentage analyses.

Extraction of DNA from faeces, hair and tissue samples. We use three non-invasive methods to collect DNA samples from our study animals. Hyena faeces are covered with a thin layer of mucus that contains intestinal epithelium cells. This layer can be easily collected and stored in a small tube with a preservative solution. Faeces are collected immediately after defecation to ensure assignment to the correct individual. Hairs are collected when curious cubs approach the vehicle, and tissue when animals are found dead. DNA from the cells of the intestinal epithelium, hair roots and tissue is then extracted using standard commercially available kits.

Amplification of gene fragments and comparison of alleles of mother, cub and potential fathers. After DNA extraction, gene fragments of nine different areas or ‘loci’ of the hyena DNA are multiplied using Polymerase Chain Reaction (PCR). These fragments or ‘microsatellites’ vary in their length and each length corresponds to an ‘allele’; our loci have up to 16 different alleles. The lengths of these fragments are then measured and assigned to the alleles. Each individual has two alleles per locus, one that it inherited from the mother and one that originates from the father. Thus, to find out who the genetic mother and father of an individual is, we then simply have to compare the combination of alleles of the nine loci of the individual with that of the candidate mothers and fathers.

top ^

Collect ecological data

To better understand how spotted hyenas cope with changes in their biotic and abiotic environment, we collect detailed temperature and rainfall data and conduct monthly prey surveys across the Crater floor.

We monitor local weather and global climate change in the Crater. To track climate change in Ngorongoro Crater and understand how it may affect the spotted hyenas and their ecosystem we have constructed a network of 4 weather stations to record temperature and rainfall information. Three weather stations were installed on the Crater floor: station ‘Ngoitokitok’ is located close to Ngoitokitok picnic area, station ‘Acacia’ is by the ranger post in Lerai forest, and station ‘Jackal Hill’ is close to Jackal Hill. The fourth station ‘Lemala’ is on the Crater rim (2400m altitude) at our research station, close to Lemala ranger post.

We installed the stations between September 2021 and March 2022 and after some mishaps with the local wildlife (e.g. buffaloes being attracted to our meant-to-be repulsive nails, using them to scratch their itchy butts and bending our poles…) the stations are now up and running, reliably and accurately measuring air temperature, precipitation, relative humidity, and atmospheric pressure.

We openly share the weather data with local managers and researchers and organize regular hands-on workshops to ensure durable knowledge transfer. Feel free to get in touch!

We monitor the abundance and distribution of large herbivores. Ngorongoro Crater does not experience the same epic herbivore migration as the Serengeti, but this doesn’t mean that the number and diversity of large herbivores in the Crater never fluctuates or that the territory of each hyena clan holds the same prey density year round. To track the herbivore community in the Crater, and how the different species are distributed, we conduct monthly surveys to count those animals that make up most of the hyena diet in the Crater; e.g., buffaloes, Grant’s and Thomson’s gazelles, wildebeest and zebras.

These surveys span 23 transects that cover the territories of all eight study clans. With these surveys we learn not only about herbivores, but also about the wonderful ecosystem in which they live. Plus we sometimes get to see more cryptic animals like servals and honey badgers.

Let us know if you’re interested in using this prey data. We’re happy to share them!

top ^

Further Information

Wilhelm K, Dawson DA, Gentle, LK, Horsfield GF, Schlötterer C, Greig C, East M, Hofer H, Tautz D, Burke T (2002) Characterization of spotted hyena, Crocuta crocuta microsatellite loci. Molecular Ecology Notes 3: 360-362.