Spotted Hyena Census Using Calling Stations
From the annual report submitted to the Government of Botswana by The Botswana Predator Conservation Program (Dr. J. W. “Tico” McNutt, Director and Project lead Gabriele Cozzi)
In this census project conducted in the eastern Moremi Game Reserve and adjacent Wildlife Management Areas for four days in October 2007, spotted hyenas (Crocuta crocuta) were attracted to a site through broadcasts of various recordings of hyena calls. The objective was to obtain a density estimate from the number of hyenas attracted to the calling stations. Calling stations were distributed in the survey area according to an estimated maximum response distance of spotted hyenas from elsewhere. This procedure has an established history for estimating hyena densities in varied habitats.
After nightfall, the team broadcasted hyena calls for six-minute periods, alternating with four minutes of silence over a 30-minute sample period. The calls used included hyena whoops, the sounds of several hyenas vocalizing at a kill, wildebeest (Connochaetes taurinus) alarm cries (when captured by a predator), vocalizations of an encounter between two hyena clans, and hyenas mobbing lions (Panthera leo). This variation was intended to maximize the number of hyenas attracted to the calling stations by including those not only motivated by a possible feeding opportunity but also those motivated by a territorial challenge.
A grid with 13 calling stations set a minimum of 7.5 km apart was laid out, covering all habitat types in the sampling area. Furthermore, BPCP used knowledge of clan territorial boundaries (established from multiple hyenas fitted with GPS radio collars) to ensure that the same clan’s territory was sampled with successive calling stations on the same night. These measures minimized the risk of double counting hyenas at different calling stations.
Using hyenas fitted with GPS radio collars, we monitored the response of specific individuals over known distances. A total of 47 hyenas were counted at the 13 calling stations, yielding a density estimate that is considerably greater than previously reported habitat specific estimates. There are a number of possible explanations for an underestimate deriving from known individuals. The most probable cause is that clan membership is considerably larger than the number of adults we have identified in the vicinity of den sites. Also contributing to an underestimate is that the analysis does not assess territory overlap among neighboring clans, resulting in a cumulative overestimate of the sampled area.
Nevertheless, our results here compare well with previous studies using the same sampling method and suggest that our survey area supports a hyena density that is intermediate in the range of densities reported from other regions.