Bawean warty pig and Bawean deer 897
TABLE 2 Details of the four camera-trap surveys and of the combined surveys, camera trapping parameter estimates, adjustment factors (used to estimate total population size and number of mature individuals), and model output and adjusted model output for the random encounter model for the Bawean warty pig over four periods in 2015, and combined for the whole period.
Survey period
7 Feb.–14 Apr. (67 days)
Truncated operation length (days)
No. of camera traps
Parameter estimates Trap rate1
Day range (km/day)2,3 Radial distance (km)2,4 Angle2,4 (radians)1
Adjustment factors Mean group size
Proportion immatures
27 12
0.398
12.069 0.004 0.392
1.78 0.419
Model output Density (individuals/km2) 13.81–24.59
Estimated no. of mature individuals
Adjusted model output Estimated population size 635–1,146 369–666
22 May–1 Aug. (72 days)
18 16
0.618
12.069 0.004 0.392
2.29 0.502
19.95–45.69 930–2,219
463–1,105
29 July–19 Oct. (83 days)
49 19
0.536
12.069 0.004 0.392
2.08 0.547
14.94–31.06 696–1,448
315–656
21 Oct.–3 Dec. (44 days)
36 21
0.050
12.069 0.004 0.392
1.78 0.378 1.62–2.88
75–134 47–83
8.41–16.82 392–784
234–467
1Total number of independent captures divided by total number of camera-trap days. 2From Rademaker et al. (2016). 3Defined as the mean speed of movement of animals in front of the camera in m/s, extrapolated to km/day and multiplied by the proportion of time spent
active. 4Radial distance and angle of detection to the camera were measured at the time of detection of the animal in front of the camera.
protected area, orwhether this is a relic of population dynam- ics in a very small population, requires investigation. Neither Rahman et al. (2017a) nor our study detected
deer in the interiors of protected areas. The lack of records may be attributable to (1) a genuine absence or extreme rarity in these areas, (2) secretive behaviour, with a strong preference for moving in dense habitat that is difficult to monitor with camera traps, (3) adverse habitat conditions that are not suitable for Bawean deer, or (4) good conditions outside these areas attracting the deer. Similarly, Bawean warty pigs appear to be less abundant in the interiors of pro- tected areas. It is important to understand the reasons for the lower abundance or absence of species in the protected area interior, to plan effective conservation measures.
Population estimates of Bawean warty pigs
Population estimates per survey period for the Bawean warty pig fluctuated considerably across the duration of our study. Our lowest estimates were at the end of the dry season and beginning of the rainy season, whereas the high- est estimates were recorded in the dry season when the re- productive season was at its peak. Other studies have shown that pig densities seem to fluctuate in response to resource availability (e.g. Hancock et al., 2005). Significant climatic seasonality on Bawean Island, particularly in terms of
precipitation and associated occurrence of fires, could result in large fluctuations in population sizes. Hunting pressure, spatial restriction on dispersal and an absence of predators may exacerbate these changes. Based on the findings of Rademaker et al. (2016),
which indicated a small and geographically restricted population numbering ,250 mature individuals, the Bawean warty pig was categorized as Endangered on the IUCN Red List based on criterion D (IUCN, 2012). Our new estimated mean of 350 mature individuals ex- ceeds this threshold. However, in line with IUCN guide- lines we suggest that because seasonal population sizes are well below the threshold, the species may continue to fulfil criterion D. Additionally, criteria B1,2(a,b(i,iii)) may qualify the species as Endangered based on the small extent of occurrence and area of occupancy (IUCN, 2012).
Population estimates of Bawean deer
Rahman et al. (2017a) calculated a population size of 227–416 Bawean deer, suggesting a population equal to that of warty pigs (based on this study and Rademaker et al., 2016). The authors recorded 118 independent camera-trap images of deer from 75 camera positions during 9 months in 2014. A subset of the data was used to derive population
Oryx, 2020, 54(6), 892–900 © 2019 Fauna & Flora International doi:10.1017/S0030605318000996 Combined periods
7 Feb.–3 Dec. (266 days)
18 68
0.471
12.069 0.004 0.392
2.04
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