Patterns of den occupation by the spotted hyaena (Crocuta crocuta)

1. What they did

Spotted hyaena cubs spend their first 8 to 12 months living at dens. Most start life in an isolated natal den used by one mother, then are moved to the clan’s communal den, which is shared by several litters and visited by many clan members. Hyaenas do not dig these dens themselves; they take over and modify holes dug by aardvarks or warthogs.

The researchers followed one well-studied clan, the Talek clan in Kenya’s Maasai Mara National Reserve, for ten years (1988 to 1998). Observers watched the clan every morning and evening on most days of every month, and from 1990 about half the adult females wore radio collars. Every hyaena was known individually, and the social rank of every clan member was known.

They mapped every den the clan used with GPS and aerial photographs in a Geographic Information System (GIS). They then measured:

• How long each communal den was used, and how often sites were reused.
• How far the clan moved between dens, and in which months.
• Where mothers gave birth, and how far each mother moved her cubs before they reached the communal den, compared with her social rank.
• Ticks in den dirt. To test whether parasites push hyaenas to move, they sifted dirt from den entrances for ticks and other small animals (July 1997 to January 1998).

Most den moves were not seen directly. A move was known when mothers and cubs were found at a new den and the old one was confirmed empty.

2. What they found

Communal dens

• The clan used 57 different sites as communal dens. Another 41 sites were used only as natal dens.
• Dens were spread over most of the territory. Most (67%) were within 0.25 km of a seasonal creek or river, although only 41% of the territory lies that close to water. Areas with no dens were mostly long grass with few prey.
• Half the communal den sites (28) were used once; the other 29 were reused, one of them 12 times. A few popular sites were used again and again, one in both the first and last years of the study.
• On average the clan stayed at a communal den for 31 days, so they moved about once a month. Stays ranged from a week or less (22 cases) to 8.1 months.
• Den holes lasted for years. A site could stand empty for up to 65 months before being used again.

Den moves

• Moves between communal dens averaged 1.5 km. Only ten were 3 to 5 km, and the longest was 6.2 km.
• Moves happened in every month (5 to 12% of moves each month), in wet and dry months alike. The fewest were in February to April, when few cubs are born; the most were in November (12%), the month with the most births.
• Observers saw females carrying or leading cubs to a new den 15 times. These moves often took a few days, with groups of females moving at different times. In 73% of them, the highest-ranking female at the den was among the first to move.
• On one occasion, observers found that a move was prompted by flooding.

Ticks and fleas

• Active dens had almost no ticks. Dens empty for at least a month had significantly more.
• At two of three dens sampled before and just after a move, there were no ticks either time. At the third, ticks appeared the day after the hyaenas left.
• Most ticks were a large soft-bodied species that seems to specialise on warthogs and has never been found on these hyaenas.
• Fleas were found at only two dens, both empty at the time. One had hundreds of fleas and the most ticks of all.
• Some empty dens were being used by warthogs and banded mongoose. Dens overgrown with plants and with spider webs across the entrances were probably not in use by any mammal.

Birth dens and social rank

• Of 79 litters from 39 mothers, 16 (20%) were raised at the communal den from birth and 63 (80%) were born at isolated natal dens.
• Natal dens were rarely reused (three of 41). Most (89%) were used by one mother. Three pairs of mothers shared a natal den: one pair were sisters, the other two pairs were unrelated.
• Birth dens were on average 1.7 km from the communal den. Low-ranking females gave birth farther away than high-ranking females did.
• Mothers moved their young cubs a total of 1.6 km on average before reaching the communal den. Low-ranking females moved them farther.

3. What they concluded

• Plenty of holes were available, but the clan reused only a few favourite dens again and again. These dens probably have qualities other than location that make them suitable.
• Talek hyaenas moved their communal den about once a month, only a little more often than Kalahari hyaenas (every 45 days), despite huge differences between the two ecosystems.
• In most cases, why hyaenas moved den remained unknown. Disturbance by lions or strange hyaenas, a cub’s death and flooding were sometimes followed by a move, but not always. Human activity did not necessarily cause moves: the clan sometimes used dens where cattle and herders spent hours each day. Once the researchers apparently triggered a move by putting vinegar and cayenne pepper around a den opening, but a second try failed. Ticks do not seem to be an important reason for most moves.
• High-ranking females seem more likely to lead den moves. Lower-ranking females may follow to keep their cubs with their peers.
• The clan often made short hops to dens they used for only a few days, which suggests the choice of den is not planned ahead. Mothers may judge a den after moving their cubs there.
• Low-ranking females raised their cubs farther from the communal den and moved them farther. Moving cubs over longer distances may be one reason low-ranking females raise fewer young. For them, an isolated natal den may mean less harassment and competition while cubs are most vulnerable; high-ranking females can push lower-ranking mothers away from the communal den entrance.
• Almost every cub will live through at least one den move, so den moves are probably one of the costs of living in groups. Living at several dens might help cubs get to know their clan’s territory.

6. Other technologies, skills or innovations

• Individual identification of every hyaena by their unique spots and other natural marks.
• Radio collars on about half the adult females from 1990.
• A Magellan Meridian XL GPS unit and a digitized map from aerial photographs (1:20,000) in ArcView GIS.
• Dirt sampling from den entrances, sifted for ticks and other invertebrates visible to the naked eye.