Contribution à l’étude de la structure de la population des hippopotames (Hippopotamus amphibius L.) au Parc National de la Bénoué (Cameroun)

Nje, Jean Ngog

doi:10.1515/mamm.1988.52.2.149

“…Drone height and weather affected hippo detection, based on surveys only done in the early morning [41]. However, time of day is critical, given hippo behaviour varies throughout the day [3,20,42–45]. We trialled the use of a relatively low-cost drone, testing its effectiveness to estimate hippo numbers, the percentage of hippos that could be assigned to age classes, and numbers of juveniles, subadults, and adults, comparing these estimates to counts from land.…”

Section: Introductionmentioning

confidence: 99%

Drone-based effective counting and ageing of hippopotamus (Hippopotamus amphibius) in the Okavango Delta in Botswana

Inman

¹

,

Chase

²

,

Leggett

³

2019

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Accurately estimating hippopotamus (Hippopotamus amphibius) numbers is difficult due to their aggressive nature, amphibious lifestyle, and habit of diving and surfacing. Traditionally, hippos are counted using aerial surveys and land/boat surveys. We compared estimates of numbers of hippos in a lagoon in the Okavango Delta, counted from land to counts from video taken from a DJI Phantom 4TM drone, testing for effectiveness at three heights (40 m, 80 m, and 120 m) and four times of day (early morning, late morning, early afternoon, and late afternoon). In addition, we determined effectiveness for differentiating age classes (juvenile, subadult, and adult), based on visual assessment and measurements from drone images, at different times and heights. Estimates in the pool averaged 9.18 (± 0.25SE, range 1–14, n = 112 counts). Drone counts at 40 m produced the highest counts of hippos, 10.6% higher than land counts and drone counts at 80 m, and 17.6% higher than drone counts at 120 m. Fewer hippos were counted in the early morning, when the hippos were active and most likely submerged, compared to all other times of day, when they tended to rest in shallow water with their bodies exposed. We were able to assign age classes to similar numbers of hippos from land counts and counts at 40 m, although land counts were better at identifying juveniles and subadults. Early morning was the least effective time to age hippos given their active behaviour, increasingly problematic with increasing height. Use of a relatively low-cost drone provided a rigorous and repeatable method for estimating numbers and ages of hippos, other than in the early morning, compared to land counts, considered the most accurate method of counting hippos.

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“…We followed the methodology applied by Ngog Nje (1988). All counts except one were conducted in the latter part of the dry season, when the Bénoué River is the Park's only remaining source of water and the area is easily accessible.…”

Section: Methodsmentioning

confidence: 99%

“…1). The surveys were carried out in the dry season, in a single day, generally during 09.00–12.00 (Ngog Nje, 1988). From our dry season count in 2013 we determined the number of hippopotamuses along the same stretch of river.…”

Section: Methodsmentioning

confidence: 99%

“…A survey in Faro National Park in North Cameroon (Tsi et al, 2011) revealed a hippopotamus population of 600 individuals, and an analysis of surveys carried out in Bénoué National Park revealed there were 400 individuals there in 1987 (Ngog Nje, 1988). The survival of the hippopotamus in North-Central Africa is intrinsically linked to these protected areas, which are part of the northern savannah zone complex that includes, from west to east, Faro National Park, Bénoué National Park and Bouba Ndjida National Park, and 27 safari hunting zones (Njoya, 2008).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Declining population of the Vulnerable common hippopotamus Hippopotamus amphibius in Bénoué National Park, Cameroon (1976–2013): the importance of conservation presence

Scholte

¹

,

Iyah²

2016

Oryx

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Populations of the common hippopotamus Hippopotamus amphibius have undergone widespread decline as a result of habitat conversion and hunting for bushmeat and, increasingly, for ivory. North Cameroon holds important populations of large mammals, including the hippopotamus. The species' status and population trend are poorly known, and led CITES to suspend trade in hippopotamus trophies in 2013. Using the methodology of surveys conducted during 1976–1987, we conducted counts of the hippopotamus in Bénoué National Park during the wet season of 2011 and dry season of 2013, and drew on unpublished biannual density counts conducted by the Garoua Wildlife College, Cameroon, during 1989–2010. Counts along the 100 km stretch of the Bénoué River in the Park indicated a reduction from 400 individuals in 1987 to 188 in 2013. However, linear densities along a 15–32 km stretch in proximity to the Park headquarters and two tourist camps were constant during 1976–2013 (c. 3.7 individuals km−1). Hippopotamus distribution was negatively associated with the presence of the camps of gold diggers, which occupied the northern half of the Park. Observations of antelopes suggested they had a comparable distribution, unlike primates, which were distributed relatively evenly. Our results show the importance of year-round conservation presence in the Park, which could be achieved with adequate personnel, a functional road system, and reinforcement of operations in neighbouring sport-hunting areas.

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“…Drone height and weather affected hippo detection, based on surveys only done in the early morning [36]. However, time of day is critical, given hippo behaviour varies throughout the day [3,20,37–40]. We trialled the use of a relatively low-cost drone, testing its effectiveness to estimate hippo numbers, the percentage of hippos that could be assigned to age classes, and numbers of juveniles, subadults, and adults, comparing these estimates to counts from land.…”

Section: Introductionmentioning

confidence: 99%

Drone-based effective counting and ageing of hippopotamus (Hippopotamus amphibius) in the Okavango Delta in Botswana

Inman

¹

,

Leggett²,

Chase

³

2019

Preprint

View full text Add to dashboard Cite

Accurately estimating hippopotamus (Hippopotamus amphibius) numbers is difficult due to their aggressive nature, amphibious lifestyle, and habit of diving and surfacing. Traditionally, hippos are counted using aerial surveys and land/boat surveys. We compared estimates of numbers of hippos in a lagoon in the Okavango Delta, counted from land and video taken from a DJI Phantom 4 TM drone, testing for effectiveness at three heights (40 m, 80 m, and 120 m) and four times of day (early morning, late morning, early afternoon, and late afternoon). In addition, we determined effectiveness for differentiating age classes (juvenile, subadult, and adult), based on visual assessment and measurements from drone images, at different times and heights.Estimates in the pool averaged 9.18 (± 0.25SE, range 1 -14, n = 112 counts). Drone counts at 40 m produced the highest counts of hippos, 10.6% higher than land counts and drone counts at 80 m, and 17.6% higher than drone counts at 120 m. Fewer hippos were counted in the early morning, when the hippos were active and most likely submerged, compared to all other times of day, when they tended to rest in shallow water with their bodies exposed. We were able to assign age classes to similar numbers of hippos from land counts and counts at 40 m, although land counts were better at identifying juveniles and subadults. Early morning was the least effective time to age hippos given their active behaviour, increasingly problematic with increasing height. Use of a relatively low-cost drone provided a rigorous and repeatable method for estimating numbers and ages of hippos, but not in the early morning. Introduction1 Hippopotamus or hippo (Hippopotamus amphibius) are Vulnerable on the IUCN Red List 2 of Threatened Species, numbering 115,000-130,000 [1]. Habitat loss and hunting for meat and 3 ivory are driving declines [1], but much of the population data originates from aerial surveys, 4 which can be inaccurate [2-6]. Reliable and accurate spatial and temporal data on abundances 5 and demographics of hippo populations are essential for effective conservation management 6 [1,7,8] but hippos are inherently difficult to count because individuals regularly submerge and 7 surface throughout the day and have uniform appearance. They are also among the more 8 dangerous animals in Africa [9-11], limiting effectiveness of on-land and water methods of 9 counting [12]. 10 Hippos are usually surveyed from the air [9-12], but also from boats and land [9,13,14]; 11 each method has advantages and disadvantages. Aerial surveys cover large areas [4] but with 12 limited time to scan waterbodies and count hippos, given their speed. Also, aircraft noise may 13 cause hippos to submerge [19], contributing to underestimation [20]. Aerial surveys are costly 14 and logistically difficult, resulting in long intervals between surveys [21-24]. Slow, low-flying 15 microlight aircraft or helicopters capturing images may overcome some of these challenges [25] 16 but remain costly and potentially logistically difficult, ...

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Contribution à l’étude de la structure de la population des hippopotames (Hippopotamus amphibius L.) au Parc National de la Bénoué (Cameroun)

Cited by 6 publications

References 3 publications

Drone-based effective counting and ageing of hippopotamus (Hippopotamus amphibius) in the Okavango Delta in Botswana

Drone-based effective counting and ageing of hippopotamus (Hippopotamus amphibius) in the Okavango Delta in Botswana

Declining population of the Vulnerable common hippopotamus Hippopotamus amphibius in Bénoué National Park, Cameroon (1976–2013): the importance of conservation presence

Drone-based effective counting and ageing of hippopotamus (Hippopotamus amphibius) in the Okavango Delta in Botswana

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