Conservation of the cao vit gibbon 779
TABLE 2 Group composition of cao vit gibbons recorded in 2007. Group composition
Group G13,4
G23
G33,4 G43 G5 G6 G7 G8 G9
G10
G114 G12 G13
G143 G15 G16 G17 G18
Adult male Adult female 1
1 1 1 2 1 3 2 1 1 1 2 2 1 3 2 1 1
2 2 2 2 2 2 2 2 1 1 2 2 2 2 2 2 1
Immature Adolescent Infant 4
2 2 3 2 2 1 3 1 1
2 3 2 2 2 1 1
1 1
1 1
1 2
Total Record1 8
6 5 7 7 5 7 9 3
2 2 1 2
(3)5 6 9 7 8 8 3
(2)5 Locality2
L, O North of Lung Gu L, O West of Lung Gu
L, O West of Lung Nha Nhung L, O West of Lung Ky Gia L, O North of Lung Nguom L, O West of Lung Chi
L, O North-west of Lung Che L, O North of Lung Dac L, O East of Lung Dac
3 O L
South-west of Lung Co (Nguom Dam) South-east of Lung Hoai
L, O West of Lung Nam (Tap Toan) L, O North-west of Tap Toan Lon L, O Between Nguoc Man & Nguoc Ri L, O Lung Gia Ray L, O Lung Bong Bip L, O Lung Tu Noc L, O China only
1L, listening; O, observation. 2Local name of the valley. 3These groups’ home ranges overlapped the border. 4The total number of individuals in these groups is uncertain because they were observed only briefly or were not seen at all (group record based on
vocalization only). 5The number in parentheses is the minimum number of gibbons in this group (for groups that were observed only briefly and not all members could be counted, or where group size was estimated by vocalization only).
carrying infants were observed in four of the 11 bi-female groups in
2007.In 2016 we recorded only one group with two females that both carried infants. In 2007 seven of 14 fully observed groups contained more than one adult male. In 2016 only one of 13 fully observed groups contained more than one male.
Discussion
Global population size of the cao vit gibbon Our results indicate the presence of c. 20 cao vit gibbon groups with a total population size of.100 individuals dur- ing the 2007 and 2016 surveys. It is unlikely that we missed any groups living in this area, for a number of reasons. Firstly, our survey posts covered all potential gibbon habitats in the study area. Secondly, during a study of three cao vit gibbon groups, individual groups sang on c. 70% of monitoring days (Fei et al., 2010). We monitored each survey point for 4–6 consecutive days. According to a detection function, the chance of detecting a group during
a 4-day survey is 1−(1−0.70)4.0.99. In addition, we conducted surveys in September, when cao vit gibbons vocalize most frequently (P.F. Fan, unpubl. data). Thirdly,
the steep karst hills and low canopy, an unusual habitat for gibbons, facilitated gibbon detection in this area. We observed most groups while theywere singing (Tables 2&3). In addition, we had monitored the population dynamics of gibbons on the Chinese side of the border every month since December 2007 and knew each of these groups, so this subpopulation provided a good control to evaluate the detection rate for our field surveys. We did not miss any known groups on the Chinese side during the surveys. Based on the transboundary survey in 2007 we estimated
the global population of cao vit gibbon to be .100 indivi- duals. However, population surveys recorded fewer than 40 individuals in Viet Nam prior to 2005 (reported population sizeswere 26–28, 37 and 27–35 in studies by Geissmann et al., 2002; Trinh Dinh, 2004; and Vu et al., 2005, respectively) and only 18 individuals in China in 2006 (Chan et al., 2008). It is unlikely that the gibbon population doubled during 2005–2007. Cao vit gibbons mature at 8–10 years of age and the interbirth interval is 3–5 years (Fan et al., 2015). The long juvenile period and long interbirth interval make gibbon population recovery a slow process. We there- fore conclude that surveys before 2007 must have underes- timated the population size, possibly because they did not cover the area completely. For example, the three groups
Oryx, 2020, 54(6), 776–783 © 2019 Fauna & Flora International doi:10.1017/S0030605318001576
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164
