IntroductionThe common hippopotamus Hippopotamus amphibius L. is a vulnerable species that requires efficient methods to monitor its populations for conservation purposes. Rapid evolution of civil drones provides new opportunities but survey protocols still need development. This study aims to determine the optimal flight parameters for accurate population estimates. A second objective is to evaluate the effects of three environmental factors: wind speed, sun reflection and cloud cover.MethodWe estimated the population of two main hippo schools (Dungu and Wilibadi II) located in Garamba National Park in Democratic republic of Congo. Eight observers reviewed 252 photos taken over the Dungu school, representing a total of 2016 experimental units. A detection rate and a level of certainty were associated with each experimental unit, and five parameters were related to each count: flight height, three environmental parameters (sun reflection on water surface, cloud cover, and wind speed), and observers’ experience.ResultsFlight height reduced the observers’ confidence in their detection ability, rather than the detection itself. For accurate counts of large groups an average height of 150 m was shown to be a good compromise between animal detection without zooming in and the area covered in one frame. Wind speed had little influence on the counts, but it affected the performance of the UAS. Sun reflection reduced the detection rate of hippos and increased level of certainty, while cloud cover reduced detection rates slightly. Therefore, we recommend flying when the sun is still low on the horizon and when there is little cloud, or when cloud cover is light and even. This last point reinforces our recommendation for flights early in the day. The counts also showed large differences between groups of inexperienced and experienced observers. Experienced observers achieved better detection rates and were generally more confident in their detection. Experienced observers detected 86.5% of the hippos on average (confidence interval = ±0.76%). When applied to data from the second site, the detection was 84.3% (confidence interval = ±1.84%). Two correction factors were then calculated, as the inverse of the detection rate, based on the estimated number of hippos present during one flight (Factor 1) or in the general population respectively (Factor 2). Factor 2 especially was consistent with previous studies using traditional aerial counts (1.22 vs 1.25). Factor 2 was found to be appropriate for use by experienced observers. These results confirm the use of correction factor 2 for hippo surveys, regardless of the study site, as it accounts for hippo behavior. Optimum counting and cost efficiency were achieved with two trained observers counting 7 pictures.ConclusionThis study is a promising approach for routine surveys of the hippopotamus which is a species usually ignored in wildlife counts. Drone technology is expected to improve rapidly; therefore UAS could become a very useful and affordable survey tool for other species ...
Les aires protégées de la République démocratique du Congo (RDC) sont mena-cées par diverses pressions anthropiques nécessitant un suivi fréquent et précis. Le mini-drone Falcon équipé d’un appareil photo numérique Sony NEX-7 a été utilisé pour cartographier et suivre la dynamique d’un terroir villageois dans le Domaine de chasse de Mondo Missa à l’est du Parc national de la Garamba, au nord-est de la RDC. Un total de 3 143 photos acquises en avril et juillet 2015, avec une résolution au sol de 8 cm/pixel, a été orthorectifié. La cartographie a porté sur une zone de 114 ha. Les ortho-images ont d’abord été segmentées, les segments étant ensuite classés manuellement par photo-interpré-tation. Des changements notables ont été constatés entre les deux dates. Les zones des forêts et savanes ont perdu 6,5 ha (86,6 à 80,1 ha). Les jachères sont pas-sées de 16,9 à 8,2 ha, les défriches de 4,1 à 10,0 ha. Les cultures saisonnières ont connu une variation allant de 3,2 à 11,8 ha. La taille moyenne des parcelles cultivées est de 0,2 ha (s = 0,14 ha ; n = 50). Enfin, la surface occupée par les arbres isolés a peu évolué (de 1,3 à 1,9 ha), celle des implantations humaines étant constante (1,7 ha). Ces résultats traduisent le fait que l’expansion de l’agriculture itinérante sur brûlis induit une conversion des habi-tats naturels et une modification de la composition végétale. Les aéronefs sans pilote à bord permettent de réaliser une cartographie précise et une surveillance rapide des changements d’affectation des terres à petite échelle dans les aires pro-tégées des forêts et savanes tropicales. Ils offrent donc une solution efficace pour évaluer la déforestation et la dégradation au sein des espaces occupés par les com-munautés locales. Cette évaluation repré-sente un enjeu important dans le proces-sus REDD+ qui envisage de quantifier avec précision ces évolutions.
The Luki's Biosphere Reserve (LBR), latter remnant Mayombe's forest in Democratic Republic of Congo, is exposed to a prominent human pressure. After the independence process that occurred in the country, the "zaïrianization'' policy of nationalization lead to the agro-industrial collapse. Face to that situational configuration and then compelled to unemployment, the population turned on forest activities, such as, slash and burn shifting cultivation, carbonization, operating timber and hunt, which tend to be their main basic live hoods means. The problem of this study is, based on how local populations tend to survive despite the crises and above any lack of support? Responding to that preoccupation, an investigation focus on systemic analyses of various ways of subsidence had been realized in four (04) local villages of the reserve: Kinzua-Mvuete, Kikalu, Kiyalala, Kiyangala. Data's collecting through a systemic approach and analysis shown a serious dependence toward forest resources; in a stamped context of demographical progression, generalized by poverty and weaknesses of environmental governance, the populations have developed several strategies of survive in terms of, intensification, diversification and migration. Those assorted activities consisted especially to the non-respect of the fallow period, the land dispute, the felling of small diameter trees, the modification of land use, conducting to deforestation and to degradation, increase therefore misery. In order to reconcile the objectives of development and conservation: agroforestry, fish farming, beekeeping, and sensitization have been suggested.
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