Diversity and Diet of Babblers (Timaliidae and Pellorneidae): Possible Effects of Anthropogenic Disturbances and Environmental Characteristics at Pelagus, Sarawak (East Malaysia: Borneo)

Pang, Sing Tyan (2020) Diversity and Diet of Babblers (Timaliidae and Pellorneidae): Possible Effects of Anthropogenic Disturbances and Environmental Characteristics at Pelagus, Sarawak (East Malaysia: Borneo). PhD thesis, Universiti Malaysia Sarawak (UNIMAS).

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Abstract

Disturbed habitats tend to have impoverished bird communities compared to primary forests. This research focuses on the group known as babblers (Timaliidae and Pellorneidae) which are currently understudied in terms of how they persist in a multispecies community and what resource partitioning they utilise when in a continuous disturbed habitat. This study demonstrates a method to measure disturbance by quantifying the level of disturbance in selected sampling stations and was measured based on human and plant components. Based on the disturbance index, the disturbance was found to be varied in different forest types in Pelagus, Sarawak. In addition, the study also examined the babbler community and their potential prey in the areas with varying levels of disturbance; identifying which covariate(s) affect both babblers and prey the most. A total of 1,335 individuals of birds from 106 species were captured throughout this study. Amongst them were 328 babbler individuals, consisting of 16 different species representing from two families (Timaliidae and Pellorneidae). Chestnut-winged babbler was the most common species captured. Of the 17 orders of prey captured, Diptera was the most dominant order, followed by Hymenoptera and Coleoptera. Occupancy of babblers in Pelagus was found to be high (> 50%), despite netting probability being low (20%). Within the nine covariates measured with regards to occupancy and netting probability, eight had almost equal influence on babblers, except for the presence of domestic animals, such as dogs and cats, while canopy cover was the most influential covariate affecting prey abundance at all stations. Resource partitioning among babblers was also investigated by deploying double mist-nets with heights indicated by the ascending shelf (maximum height 3.6 m). The numbers of babblers netted was inversely proportionate to the shelf height of the mist-net, lower shelves (0–0.6 m) recorded the highest catches, implying that most babblers prefer to forage closer to the ground, despite the fact that a majority of vi potential prey being caught on sticky traps at 1 m and above. Sampling was conducted four times a year, with an interval of two to three months in between. Results show that the collective babbler abundance was significantly greater between March and April of 2016 compared to the other months in the same year, but there was no seasonal marked on prey abundance. This suggests that foraging activity among babblers could be more active compared to other periods as the foraging time was shorten due to raining. Thus, higher number of babblers were captured. The composition of babbler diets was investigated by analysing sample obtained from 110 regurgitated sample, 58 faecal samples and 27 stomach content. Eleven intact prey items were found from the regurgitated samples, while faecal and stomach content had one each. The results showed that babbler in this study are diet opportunist. and generalists. Their diets constitute of 11 prey groups. Caterpillars appeared to be the most preferred prey (Jacob’s Index), while Coleopterans ranked fourth (behind Orthroptera and Araneida), despite being frequently found in the diet samples. Prey body size was not an important factor affecting babbler prey choice, as the regressions between babbler weight against prey body length had no relation. Instead, babblers may be tracking nutrient content. The preferred prey, caterpillars are rich in phosphorus, while Orthopterans have the highest crude protein content. As human-induced disturbance is inevitable, it is critical to understand how bird groups such as babblers and their prey tolerate different levels of disturbance at the community level, and ultimately mitigate the disturbances that may impact other wildlife.

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