Ahaetulla Nasuta): a Crowdsourced Approach
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Herpetology Notes, volume 13: 835-843 (2020) (published online on 16 October 2020) Understanding the food habits of the green vine snake (Ahaetulla nasuta): a crowdsourced approach Yatin Kalki1,2,* and Merlin Weiss1,3 Abstract. A total of 209 observations of Ahaetulla nasuta feeding on prey were compiled from social media platforms, citizen science websites, and from the literature in order to gain insights into the food habits of this arboreal colubrid, and to construct an inventory of the prey species recorded in its dietary spectrum. The diet of A. nasuta consists primarily of frogs (37.4%) and lizards (32.5%), occasionally snakes (19.9%), and rarely birds (9.22%) and mammals (0.97%). At least forty-four species spanning 38 genera and 19 families have been recorded as prey items of A. nasuta; 41 of these trophic interactions are previously unpublished. These data serve as a preliminary exploration into the food habits of A. nasuta and can be used as a baseline for future hypothesis-driven research. Keywords. Ahaetulla nasuta, Green vine snake, Diet, Predation, Prey Inventory, Feeding Ecology Introduction Making in-situ observations on snakes feeding in the wild is difficult due to their inherently secretive nature Documenting the food habits of a snake species and the infrequency with which they feed. One way is a crucial prerequisite to understanding its natural to study the feeding ecology of a snake species is to history, role in the ecosystem, and evolutionary history (Greene, 1983; Toft, 1985; Mushinksy, 1987). Dietary dissect preserved museum specimens and examine their information can provide valuable insights into the stomach contents (Rodriguez-Robles, 2002; Greene and ecology, biology and even phylogenetic relationships Rodriguez-Robles, 2003; Wiseman et al., 2019). While of snake species (Shine, 1991; King, 1993; Vincent et this method is indeed useful, it provides only a limited al., 2006; Henderson et al., 1988). Correlation between picture of the species’ food habits, does not account for morphology and feeding behaviour of vipers and marine temporal shifts in dietary composition, and is highly snakes, for instance, provided an important insight into sensitive to the method of collection and locality. their evolutionary history (Pough and Grooves, 1983; Furthermore, this method can only be implemented Voris et al., 1983). Additionally, studies on the prey with species that have a large number of representative spectrum of various pit vipers have indicated how their preserved specimens stored in museums. Another venom has developed (Daltry et al., 1996; Andrade technique is to palpate wild specimens in the field and et al., 1999). Furthermore, understanding the natural document regurgitated prey items and expelled faecal history (i.e. diet composition) is a fundamental first step matter (Daltry et al., 1998; Gregory and Isaac, 2004). in implementing any conservation strategy (Greene, Like the previous method, this technique cannot detect 1994; Dorcas and Willson, 2009). temporal changes in diet beyond the time during which the study was carried out. Furthermore, both of these methods are quite invasive; the first method requiring the euthanasia of the snakes and the subsequent dissection of the specimens; and the second method causing the 1 Agumbe Rainforest Research Station, Agumbe, Karnataka potential loss of a meal, which can be energetically 577411, India. costly to the snakes. Finally, published observations 2 Madras Crocodile Bank Trust and Centre for Herpetology, may be widely scattered in literature, especially for Mamallapuram, Tamil Nadu 603104, India. 3 Van Hall Larenstein University of Applied Sciences, geographically widespread and common species that Leeuwarden, Friesland 8934 CJ, Netherlands. have gone by multiple scientific names (van den Burg, * Corresponding author. Email: [email protected] 2020). 836 Yatin Kalki & Merlin Weiss With the advent of digital photography and the internet, prey, the direction of ingestion, the observer’s name (not which allows for the quick and easy dissemination included here for privacy reasons), the location along of information via social media, yet another method with latitude and longitude of the nearest city/town/ has arisen: “crowdsourcing.” By compiling and village (whenever possible), and the URL (Appendix consolidating observations posted online by multiple 1). Prey identity was determined cautiously based on individuals, researchers can construct an inventory of geographic location and morphological characters the prey items recorded in the diet of a certain snake visible in the photographs. Identification was made at species. This method can be used not just for feeding the genus, family or order level whenever characteristic ecology studies (Layloo et al., 2017, Maritz and Maritz, traits were not visible. Citizen science records of A. 2020), but also to study mating behaviours, conflict nasuta feeding (Appendix 2) were gathered from potential (Miranda et al., 2016) and occurrence records the websites iNaturalist (Available at https://www. (Marshall and Strine, 2019). Here, we present a dietary inaturalist.org. Accessed on 10 August 2020.), Reptiles synopsis for Ahaetulla nasuta (Lacépède, 1789) from of India (Khandekar et al., 2020), India Biodiversity crowdsourced data. Portal (Vattakaven et al., 2016), and India Nature Ahaetulla nasuta is an arboreal colubrid found in Watch (Available at https://www.indianaturewatch.net. southern and southeast Asia known to feed on lizards, Accessed on 10 August 2020.). We did not use a neutral small rodents, birds and occasionally snakes (Smith, IP address or incognito browser for internet searches as 1943; Whitaker and Captain, 2004). However, few many of the feeding records were on private Facebook publications have specifically identified prey items groups which we could only access by joining the and the relative compositions of prey categories in its groups. Published literature records were also added diet remain unknown. In India, A. nasuta is common to the dataset from the references listed on Reptile in a variety of habitats and is a species tourists and Database (Uetz et al., 2020), Google Scholar, and the photographers encounter frequently in the tropical Biodiversity Heritage Library. rainforests of the Western Ghats (pers. obs.). Given The records were collected in Excel v.16.0, and that A. nasuta is commonly encountered and hunts cleaning and analysis of the data was completed in R diurnally (Kartik, 2018), many people have observed v.3.6.3 (R Core Team, 2020) and R Studio v.1.2.5042 (R and photographed wild A. nasuta feeding—and some Studio Team, 2020). In order to clean our data, we used of these photos have been posted on social media or the dplyr package (Wickham et al., 2020) and for the citizen science websites. To a researcher studying the visualisation we used ggplot2 (Wickham et al., 2016). food habits of A. nasuta, these online platforms can act First, we created separated data frames representing as repositories of valuable information. the respective relations illustrated later, starting with types of records as per source, i.e. social media, citizen Methods science and literature. The same was done for the different groups of prey animals, thus records per type In order to identify and compile social media records of prey classification (birds, frogs, lizards, mammals and of A. nasuta feeding, we searched Facebook using snakes). Here we first filtered out repeated observations the keywords “Ahaetulla nasuta feeding”, “Ahaetulla using the “distinct()” function of the dplyr package, nasuta eating”, “Ahaetulla nasuta kill”, “green vine meaning observations that had been posted by the snake feeding”, “green vine snake eating”, and “green same observer on multiple platforms as well as records vine snake kill”. We then examined the photographs and of the same individual A. nasuta posted by multiple their captions to determine the legitimacy of the records individuals who had observed the feeding together. The and disregarded any observations of captive A. nasuta same applied to citizen science and literature records, feeding (background obviously a terrarium or location some of which had also been posted in social media. We listed as a zoo). Additionally, we searched Youtube then visualised the respective data frames in the form and Flickr using the same keywords and compiled of bar charts (Figures 1 and 2) in order to keep visual records that met the above criteria. We searched biases to a minimum. We calculated the percentage that Instagram using the keywords “#ahaetullanasuta” and each category contributes to the whole dataset in both of “#greenvinesnake” and compiled valid photographic the data frames. Additionally, we created a stacked bar records of wild A. nasuta feeding by examining the chart illustrating the preferred prey of A. nasuta in each photographs in the “Top” and “Recent” sections. From biogeographic zone of India (Vattakaven et al., 2016) each feeding observation, we collected the identity of the (Figure 3). Understanding the food habits of the green vine snake 837 Figure 1. Types of records used in this study: social media, Figure 2. Types of prey eaten by Ahaetulla nasuta. citizen science and literature records. measure to range between zero and one (Lewis et al., Using frequencies of different prey types (birds, frogs, 2006) using the equation BA = (B−1)/(n−1), where BA lizards, mammals and snakes) consumed, we calculated is standardised niche breadth, and n is