184 T. O. W. Kamgaing et al.
TABLE 2 Per cent of dung piles of the duikers P. monticola and Cephalophus spp. disappearing or removed, by cause and season, in Nki National Park, south-east Cameroon.
Taxon/season Sample size
Philantomba monticola Major dry Minor wet Minor dry Major wet
Cephalophus spp. Major dry Minor wet Minor dry Major wet
50 74 33 61
68
101 81
123 1Scattered by birds or trampled by other animals.
negligible as inmost cases dung piles were.10mapart and we rarely found fresh dung piles within 5 m of each other on the same day. Weconducted all analyses in R 4.1.0 (R Core Team, 2021).
Weused a likelihood ratio test to examine individual effects, and we compared the full model with a reduced model lack- ing the factor to be tested (Barr et al., 2013). We examined the differences between the effects of explanatory variables using t tests. The level of significance was 0.05 for all statis- tical tests.
Results
We recorded a total of 288 dung piles of the blue duiker and 500 of red duikers, of which 216 and 373 met the final inclu- sion criteria, respectively (Table 1, Supplementary Table 2). The GLMs confirmed that dung survival time was positively associated with dung age at detection for both the blue dui- ker (slope coefficient 2.95 ± SE 0.44,P,0.001) and for red duikers (1.87 ± SE 0.33,P,0.001). The effect was strongest in the major dry season. Including dung older than 6 hours at detection resulted in a 4–348% positive bias in estimates of mean survival time for the blue duiker and 4–72% for red duikers (Fig. 2). This implies that dung detected at an older age tended to remain for a longer time than dung de- tected soon after defaecation (see Discussion). Therefore, to avoid biased estimation, dung piles older than 6 hours at detection were discarded from further analysis. Overall, 50% of blue duiker dung piles disappeared with-
in 1 day in all seasons, and other dung piles remained for 6– 34 days (Table 1, Fig. 3). Similarly, 50% of the dung piles of red duikers disappeared within 1–2.25 days in all seasons, and others persisted for 8–39 days. For both blue duiker and red duikers, dung piles survived for longer in the major dry season. Most dung disappeared as a result of removal by beetles, leaf cover, rainfall or decomposition (Table 2), with beetles
the most important factor for both the blue duiker (χ2 = 25.65,df = 9,P,0.005) and red duikers (χ2 = 35.81,df = 9,P,0.001) in all seasons. Overall, 70.6% of dung piles of the blue duiker disappeared as a result of removal by bee- tles, followed by leaf cover (11.0%), decomposition (9.2%), rainfall (8.7%), and scattering by birds or trampling by other animals (0.5%). Similarly, 66.8% of the dung piles of red duikers disappeared because of beetles, followed by de- composition (15.3%), rainfall (11.0%), leaf cover (6.2%), and scattering by birds or trampling by other animals (0.8%). Removal by dung beetles contributed the most to short-
ening dung survival time (Fig. 4, Table 3). The GLMs re- vealed a significant effect of main factor on dung survival time both for the blue duiker (likelihood ratio test, D1 = 120.82,P,0.001) and red duikers (D1 = 225.32,P,0.001). Season did not have a significant effect for the blue duiker (D1 = 7.7,P = 0.0502) and a marginally significant effect for red duikers (D1 = 8.4,P = 0.0447). Dung survival time was not correlated with dung pile diameter for either the blue duiker (D1 = 0.31,P = 0.5729) or red duikers (D1 = 3.7, P=0.0607). These results mean that the factors causing the disappearance of dung piles, most of which was ac- counted for by beetle activity, directly affected dung survival time and this was not influenced by dung pile size or season.
Discussion
Our estimates of mean dung survival time (6.83 days in the major dry season and 1.20–1.81 in other seasons for the blue duiker; 7.37 and 1.52–4.09 for red duikers) were substantially shorter than the values commonly used for the estimation of duiker density in Central Africa (i.e. 18 days for the blue dui- ker, 21 days for red duikers; Koster & Hart, 1988). As shorter dung survival times result in higher estimates of population density, previous studies based on Koster & Hart (1988)are likely to have underestimated duiker densities by an order of magnitude.
Oryx, 2023, 57(2), 180–187 © The Author(s), 2022. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605321001599
% of dung piles disappeared Beetles
Leaf cover
52.0 78.4 69.8 77.1
48.5 78.2 64.2 69.1
18.0 5.4
24.2 4.9
14.7 4.0 7.4 2.4
Rainfall
10.0 10.8 3.0 8.2
8.8 6.9 7.4
17.9 Decomposition
20.0 5.4 3.0 8.2
26.5 9.9
19.8 10.6
Others1
1.6 1.5
1.0 1.2
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