Dibamus nicobaricum

Chandramouli, S. R., Gokulakrishnan, G. & Sivaperuman, C., 2020, Status and distribution of the little-known and elusive Nicobarese worm lizard Dibamus nicobaricum (Fitzinger in Steindachner, 1867) (Squamata: Dibamidae), Bonn zoological Bulletin 69 (1), pp. 131-140 : 134-137

Dibamus nicobaricum

was recorded from three new localities during the present study, two of which are from Great Nicobar, where it is already known and a first record from Teressa Island. An adult male was recorded from Kalasi in Teressa Island, under the soil at about 5 cm depth in a coconut plantation (under exploitation) and a juvenile male was recorded from under a log in riparian habitat along the banks of a seasonal stream near Govind Nagar, Great Nicobar ( Fig. 4 ). Both these were in dense evergreen forests under thick canopy cover. The third individual was recorded from under a log in a littoral forest in Galathea Bay, Great Nicobar, forming the southernmost record for this species.

The MAXENT model predicted the distribution of D. nicobaricum in Great and Little Nicobar islands with occurrence probabilities ranging from 1 to 0.25 in Great and Little Nicobar islands and islands of the Central group, which diminishes to 0.12–0.25 in Car Nicobar, the northernmost island of the Nicobar archipelago. AUC (area under the receiver operating characteristic curve) value was 0.908 with significant contributions by the following variables: precipitation of the wettest month (45.8%), precipitation of wettest quarter (42.5%), precipitation of the driest month (4.7%), minimum temperature of coldest month (4.1%) and annual temperature range (2.9%). The other factors pertaining to climate and altitude did not have any influence on the prediction (Table 2, Figs 5–7 ).

(c) Behaviour

Behavioural observations were made on the recorded individuals of Dibamus nicobaricum to observe its pattern of activity in situ. The period of complete exposure of the organism was very meager when compared to the duration spent underground. Whenever the animal ventured under the soil surface, it always reached the bottom of the container, burrowing through the soil nearly 2–3 cm deep and resting underground. It voluntarily ventures out above the soil surface very rarely (during day time). This elusive behavior, its relatively small body size and cryptic colouration could chiefly be the reasons behind the very few records of this species till now. Majority of the local people were not familiar with Dibamus nicobaricum and could not recognize it based on the pictures shown.

(d) Status assessment of Dibamus nicobaricum

Based on the projected distribution maps and the number of individuals observed and reported in literature until now, it would be appropriate to regard Dibamus nicobaricum as an ‘Endangered’ species as per the norms of the IUCN criteria B1 (Extent of occurrence 3865 km 2, which is less than 5000 km 2) and B2 (Area of occupancy estimated to be 36.0 km 2, which is less than 500 km 2). However, data on population of D. nicobaricum and its fluctuation over a period of time are extremely difficult to establish owing to its rarity, relatively small body size, fossorial behaviour and elusive nature.

Figures

Fig. 4. Habitat of Dibamus nicobaricum near Govind Nagar in Great Nicobar.

Fig. 5.Predicted distribution of Dibamus nicobaricum based on occurrence points. Warmer colours denote higher occurrence probability.

Fig. 6. Jackknife test of variable importance to the model.

Fig. 7. Receiver operating characteristic curve for the MAX- ENT model predicting the distribution of Dibamus nicobaricum.