Revue de Primatologie (Jan 2016)
Ranging patterns of a large western Gorilla group at Dipikar Island in the Campo—Ma’an National Park, Cameroon
Abstract
The study site, Dipikar Island (2° 10’-2°18’N, 2° 17’-2°14’E), is located in the Campo Ma’an National Park (CMNP), in South Region, Cameroon. In late 2010, after assessing the feasibility for gorilla habituation, the World Wide Fund for Nature’s (WWF) Kudu—Zombo Program, in collaboration with the Ministry of Forestry and Wildlife of Cameroon (MINFOF), selected this site in order to develop a controlled ecotourism program for gorilla viewing. We began the preliminary phase of fieldwork in May 2011 with the priority of establishing an extensive trail system, developing and refining the habituation protocol and identifying gorilla groups within the study area. From March 2012, the trail of the focal group Akiba was followed with varying success from nest to nest. We rarely noted signs of other gorilla groups during our consecutive monitoring of the Akiba group. The group size was extrapolated based on nest counts and the average nest size was 32.4. We superimposed a 500 m x 500 m grid system on the map to allow comparative measurements of home range size. Home range, monthly range and the frequency of quadrant use by the Akiba group were calculated as the sum of all 500 m x 500 m quadrants entered. The “core area” was defined as the sum of quadrants that, in descending order of entry, cumulatively accounted for 75% of the group’s total quadrant entries. Daily path length (DPLs) was calculated from the maps by measuring the distance traveled between each consecutive nest site. From March 2012 through December 2014, the Akiba group was followed during 596 days, representing 74% of the effort days, when the teams were in the field (n=807 days). Group Akiba entered a total of 256 quadrants, resulting in a contiguous home range of 64 Km2 over three years and an average annual home range of 40.4 km2 with an annual home range of 39.8 km2 in 2012 (Y1), 45.5 km2 in 2013 (Y2) and 36 km2 in 2014 (Y3). For the total number of quadrants entered by Akiba, 62% was visited in Y1, 71% in Y2 and 56% in Y3. However, the size of the area used on a monthly basis was smaller averaging 11 Km2 (N = 29, range = 5.8 - 20.5, SD = 3.4). Of their total home range, the Akiba group intensely used an even smaller area, resulting in a core area of 3.5 Km2: 75% of the group’s visits were concentrated in 5.5% of the total home range visited throughout the study period. On a monthly basis, Akiba group moved in limited areas, with frequent visits outside in neighboring quadrants. For the total number of quadrants visited by the group during the period of study, it appears that the group concentrated its movements around the core area. In fact, 30% of the quadrants, including the core area, were visited in the three years, while 8% in Y1 and Y2, 5% in Y2 and Y3, 16% in Y1 and Y2. Only 18. 4% of quadrants were visited exclusively in Y2, 15% in Y3 and 7.4 in Y1. Throughout the study period, the mean daily path length (DPL) was 1600 m (N = 502, range = 180-5300 m, SD = 858). Interestingly, the group’s home range seemed to gradually decrease after the first year of follows and a mean monthly DPL of 1845 m (N=12, range =1408–2273 m, SD = ± 275 m) was recorded between March 2012 to February 2013 (P1) and a mean monthly DPL of 1268.3 m (N= 17, range = 958.4-1637 m, SD = ± 225 m) was recorded between March 2013 to December 2014 (P2), excluding August 2014). The difference between the mean monthly DPL during P1 and the mean monthly DPL during P2 is significant (P <0.05). The result seems to indicate that DPL decrease after the 1st year of following, suggesting that the group Akiba became more habituated or tolerant to the teams following their traces. The group seems to have a very large home range but not really long DPL. Even with the large home range, they still range mostly around their core area.Je remercie le WWF — CCPO (Cameroon Country Programme Office) qui a initié le projet d’habituation des gorilles au Parc National de Campo Ma’an (PNCM) et son partenaire le ministère des forêts et de la faune du Cameroun qui a autorisé cette initiative sur le terrain. Plus spécifiquement, je remercie le programme Kudu-Zombo du WWF-CCPO et le service de la conservation du PNCM pour le soutien et la facilitation qu’ils m’ont apportés sur le terrain. Mes remerciements vont également à l’endroit du Programme de Compétitivité des Filières de Croissance (PCFC) de la Banque Mondiale, du WWF International (Fondation Segré), du WWF — Allemagne en particulier Dr Ilka Herbinger pour le support financier. Je remercie les pisteurs du projet d’habituation des gorilles du PNCM particulièrement, Assembe Dieudonné, Mana Jean, Olé Pierre, Mba Joseph, Bilendé Jean Sondo, Ndoungou Paul, Doungué Lucien, Tsimi Kossi Francis et Edjo Martin pour leurs efforts remarquables dans le suivi des gorilles et la collecte des données. Un merci très particulier à Nomo Maurice Nomo pour le soutien moral et les encouragements au quotidien.
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