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genera and 19 families have been recorded as prey items of A. nasuta; 41 of these trophic interactions are previously unpublished.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 the total number Levins’ measure of niche breadth (Levins, 1968) prey types consumed. We calculated BA for the A. nasuta 2 based on the equation B = 1/∑pi (where B is Levins’ species as a whole from the distinct record dataset and niche breadth and p is the proportion of individuals i also calculated BA for each biogeographic zone using consuming a particular prey type) and standardised this the subset of records with location data. We report the

values of B and BA for each biogeographic zone but do not make any interpretations of these values due to limitations in sample size. To illustrate the geographical distribution of our records in India, we created a density map containing the records with known locations (Figure 4). To do so we made use of the sp package (Pebesma and Bivand, 2005), the raster package (Hijmans, 2019) and the GISTools package (Brunsdon and Chen, 2014). We used a shapefile of India, accessible through the “getData()” function of the raster package. Density was calculated by dividing the number of records in India by the total area of India in square kilometres. The result was computed in quadrats by converting the India polygon into a raster layer with a resolution of 1,0. The quadrat raster was subsequently turned into a spatial polygon object and plotted along with the shapefile of India. In addition, we have mapped the records with known locations in the form of a point layer on the respective biogeographical Figure 3. Types of prey eaten by Ahaetulla nasuta eaten in zones of India (Vattakaven et al., 2016) using QGIS each biogeographic zone of India. v.3.10 (Figure 5). 838 Yatin Kalki & Merlin Weiss

literature and citizen science data suggest A. nasuta is a generalist predator (Fig. 2) that feeds primarily on frogs (37.4%, n=78) and lizards (32.5%, n=68), occasionally on snakes (19.9%, n=42), and rarely on birds (9.22%, n=19) and mammals (0.97%, n=2). The Western Ghats biogeographic zone had the most records (110) with the Coasts (28), Deccan Peninsula (6), and Semi Arid (1) regions following (Fig. 3). Ninety-six percent of the 172 prey items with a determined direction of ingestion were swallowed head-first. We estimated Levins’ measure of niche breadth for A. nasuta range-wide as

B = 3.403 which we standardised to BA = 0.601. Niche breadths for A. nasuta in each biogeographic zone were estimated as follows: Western Ghats (N=110; B=2.844;

BA=0.461), Coasts (N=28; B=3.086; BA=0.522), Deccan Peninsula (N=6; B=2.000; B =0.250), Semi Arid (N=1; Figure 4. Density map of records in India used in this study, A B=1; B =1). n=145. A Table 1 lists all of the taxa recorded as prey items of A. nasuta; 41 of these interactions are previously unpublished. At least 13 frog species, 14 lizard species, Results 14 snake species, 10 bird species, and 1 mammal species have been recorded in the diet of A. nasuta. A total of 209 records of Ahaetulla nasuta feeding behaviour were compiled. Social media records were Discussion the largest contributor (n=166), accounting for 79.4% of all records. This was followed by citizen science In general, our results are consistent with earlier records (n=30) at 14.4%, and then by literature records reports that Ahaetulla nasuta is a generalist predator (n=13) at 6.22% (Fig. 1). Broadly, the social media, that consumes a fairly catholic diet. Most authors state

Figure 5. Records used in this study in each biogeographic zone of India, n=145. Understanding the food habits of the green vine snake 839

Table 1. List of prey items recorded in the diet of Ahaetulla nasuta. Sources are classified SMR (social media records), CSR (citizen science records), and literature records. See Appendices 1 and 2 for direct links to original records on social media or Table 1. List of prey items recorded in the diet of Ahaetulla nasuta. Sources are classified SMR (social media records), CSR (citizen citizen science databases.science records), and literature records. See Appendices 1 and 2 for direct links to original records on social media or citizen science databases.

Prey No. Records Source

Amphibians

Unidentified Anura 4 CSR, SMR

Anura (Tadpoles) 1 Kunte 1998

Clinotarsus curtipes 2 SMR

Euphlyctis aloysii 1 SMR

Euphlyctis sp. 1 SMR

Hoplobatrachus tigerinus 3 SMR, Wall 1921

Indirana sp. 17 CSR, SMR

Indosylvirana sp. 2 SMR

Minervarya sp. 20 CSR, SMR

Polypedates maculatus 1 SMR

Polypedates occidentalis 1 SMR

Polypedates sp. 2 SMR

Pseudophilautus sp. 2 SMR

Raorchestes bombayensis 1 SMR

Raorchestes luteolus 1 SMR

Raorchestes sp. 8 CSR, SMR

Rhacophorus malabaricus 9 SMR

Sphaerotheca sp. 1 CSR

Birds

Acritillas indica 1 Balakrishnan 2009

Copsychus saularis 1 Kartik 2018

Emberiza melanocephala 1 CSR

Lonchura punctulata 2 CSR

Nectariniidae 1 SMR

Parulidae 2 SMR

Passer domesticus 5 Ali and Abdulali 1938, SMR, CSR

Phylloscopus sp. 1 Panneerselvam and Rajan 1984

Ploceus philippinus 1 Shivanand and Kumar 2004

Pycnonotus jocosus 1 SMR

Unidentified birds 3 Panneerselvam and Rajan 1984, SMR

Lizards

Agamidae 4 SMR

Calotes calotes 1 SMR

Calotes liolepis 1 SMR

Prey No. Records Source

Calotes mystaceus 1 SMR

Calotes versicolor 25 CSR, McCann 1934, SMR

Cnemaspis sp. 5 CSR, SMR

Cyrtodactylus albofasciatus 3 SMR

Eutropis sp. 10 CSR, SMR

Hemidactylus sp. 3 SMR

Monilesaurus rouxii 8 SMR

Ophisops beddomei 1 SMR

Ophisops leschenaultii 1 SMR

Otocryptis weigmanii 1 CSR

Riopa sp. 1 SMR

Ristella sp. 1 SMR

Scincidae 1 CSR

Mammals

Mus booduga 1 SMR

Unidentified Rodentia 1 SMR

Snakes

Ahaetulla nasuta 1 CSR

Amphiesma stolatum 3 CSR, Primrose 1904, SMR

Calliophis nigrescens 2 CSR, SMR

Chrysopelea ornata 1 SMR

Coelognathus helena 1 SMR

Dendrelaphis grandoculis 1 Praveen and Palot 2017

Ploceus philippinus 1 Shivanand and Kumar 2004

Pycnonotus jocosus 1 SMR

Unidentified birds 3 Panneerselvam and Rajan 1984, SMR

Lizards 840 Yatin Kalki & Merlin Weiss Agamidae 4 SMR

Table 1. Continued. Calotes calotes 1 SMR Calotes liolepis 1 SMR

Prey No. Records Source

Calotes mystaceus 1 SMR

Calotes versicolor 25 CSR, McCann 1934, SMR

Cnemaspis sp. 5 CSR, SMR

Cyrtodactylus albofasciatus 3 SMR

Eutropis sp. 10 CSR, SMR

Hemidactylus sp. 3 SMR

Monilesaurus rouxii 8 SMR

Ophisops beddomei 1 SMR

Ophisops leschenaultii 1 SMR

Otocryptis weigmanii 1 CSR

Riopa sp. 1 SMR

Ristella sp. 1 SMR

Scincidae 1 CSR

Mammals

Mus booduga 1 SMR

Unidentified Rodentia 1 SMR

Snakes

Ahaetulla nasuta 1 CSR

Amphiesma stolatum 3 CSR, Primrose 1904, SMR

Calliophis nigrescens 2 CSR, SMR

Chrysopelea ornata 1 SMR

Coelognathus helena 1 SMR

Dendrelaphis grandoculis 1 Praveen and Palot 2017

Fowlea piscator 3 SMR

Hebius beddomei 3 SMR

Hebius monticola 3 SMR

Melanophidium wynaudense 2 SMR

Oligodon taeniolatus 1 SMR

Rhinophis sanguineus 1 Wall 1921

Uropeltis macrolepis 9 SMR, Datanwala and Durso 2020

Uropeltis mahabaleshwarensis 3 SMR

Uropeltis sp. 8 CSR, SMR

Invertebrates

Hirudinea 1 Karunarathna and Amarsinghe 2009

Understanding the food habits of the green vine snake 841 that A. nasuta’s diet is chiefly made up of lizards, small and Amarasinghe, 2009). Consequently, the chances mammals and birds, and that frogs and snakes are only of leech predation being observed and documented occasionally eaten (Wall, 1905; Wall, 1921; Smith, 1943; are smaller than those of other prey types. As this was Whitaker and Captain, 2004; Das and Das, 2018). Our the only reported case of invertebrate predation by A. results indicate that frogs and snakes are important and nasuta, we neglected invertebrates in our graphs and frequently eaten prey items for A. nasuta, especially in calculations. Further observational or experimental the Western Ghats rainforests. The proportion of snakes studies are required to fully understand the nature of the in the diet (20.4%) was especially surprising as there are interaction between A. nasuta and invertebrates such as very few published records of ophiophagic behaviour leeches. in A. nasuta. Twenty-three of the 41 snakes eaten were During the course of our internet searches, we fossorial (56.1%), 15 were terrestrial (36.6%), and only identified four feeding records belonging to Ahaetulla 3 were arboreal (7.3%). Morphologically similar snakes, anomala Annandale, 1906 which had been misidentified Thelotornis spp., also have catholic diets (Shine et al., as A. nasuta. Ahaetulla anomala is visually similar to A. 1996) which include arboreal, terrestrial and fossorial nasuta but can be differentiated by its dermal appendage snakes (Akani et al., 2002; Maritz et al., 2019). The covered in many small scales (vs. dermal appendage proportion of snakes in the diet of Thelotornis spp. was formed by rostral scale only in A. nasuta; Mohapatra et also greatly underestimated before the inclusion of social al., 2017). The first was a literature record that had been media data (Maritz et al., 2019), however, bias towards published as a dietary record of A. nasuta feeding on ophiophagic records in social media is a concern which a Bengal monitor (Varanus bengalensis; Chowdhury et can only be addressed through comparison with data al., 2017). The second was a social media record of A. from museum specimens or field-based studies. anomala attempting to feed on a Common Kingfisher The inventory of prey items recorded in the diet of A. (Alcedo atthis). The third and fourth were citizen science nasuta encompasses a variety of taxa but it is probably records of A. anomala feeding on a Common Tailorbird far from complete. Certain biogeographic regions (Orthotomus sutorius) and a Red-whiskered Bulbul where A. nasuta occurs, such as the Deccan Peninsula (Pycnonotus jocosus) from India Nature Watch. and Semi-Arid regions, were greatly underrepresented The niche breadth of A. nasuta range-wide was in our dataset, as were regions outside of India, which estimated as BA = 0.601 which indicates that it has a have a widely different prey composition. Increased fairly wide niche and is a generalist (Lewis et al., 2006). sampling from those regions, either through field Even when compared to other generalist snake species, studies, museum specimens or localised internet A. nasuta has a fairly wide dietary breadth, i.e., niche searches will undoubtedly increase the dietary breadth breadth (Diller and Wallace, 1996; Layloo et al. 2017; Di of A. nasuta. Being a popular ecotourism destination, Pietro et al., 2020). Niche breadths of A. nasuta in each the Western Ghats was the most highly represented biogeographic zone varied greatly as did the number of zone in our dataset with 109 records and prey items of records from each region. Limitations in sample sizes all classifications except mammals were represented from the Deccan Peninsula, Coasts and Semi-Arid in this zone. However, Duttaphrynus melanostictus, a regions are likely to bias the estimates of niche breadth. common anuran eaten by many sympatric snakes of the Greater sampling from these regions through field or genera Fowlea, Hebius, Amphiesma, Naja, Bungarus, specimen-based studies is warranted. and Ptyas (pers. obs.) was not recorded as a prey The fact that 41 of the 53 dietary interactions of item of A. nasuta even though many other sympatric A. nasuta were previously unpublished and largely terrestrial anurans were. It is likely that A. nasuta avoids sourced from social media observations demonstrates feeding on D. melanostictus due to the latter’s toxic both the lack of published literature on the diet of the nature (Keomany et al., 2007; Reilly et al., 2017). An species and the utility of social media as a repository for A. nasuta in captivity was offered D. melanostictus such natural history data (Maritz and Maritz 2020). The which it bit but immediately spit out (K. Murthy pers. layperson is generally not inclined to find out if their comm.). Leech predation has been reported from Sri observation is novel or to then publish it in a journal. It is Lanka (Karunarathna and Amarasinghe, 2009) however up to researchers to use methods like crowdsourcing to no such observation has thus far been reported from compile and publish these observations and make them India, not even from the Western Ghats, where leeches available for the scientific community to utilise. Citizen are abundant. Leeches are smaller than other prey items science data is incredibly useful as it usually has reliable and are consumed quickly (60 seconds; Karunarathna location data, a feature often lacking in social media 842 Yatin Kalki & Merlin Weiss observations. Although citizen science records did not Chowdhury, S., Maji, J., Chaudhuri, A., Dwari, S., Mondal, contribute greatly to our dataset, they provided much A.K. (2017): Ahaetulla nasuta (Green Vine Snake). Diet. valuable information that was lacking in the literature. Herpetological Review 48(2): 444. Daltry, J.C., Wüster, W., and Thorpe, R.S. (1998): Intraspecific This study expanded the known prey composition of A. variation in the feeding ecology of the crotaline snake nasuta by 77%. Calloselasma rhodostoma in Southeast Asia. Journal of On the whole, the crowdsourced approach is an Herpetology, 198–205. inexpensive, efficient and novel way to compile Daltry, J.C., Wüster, W., Thorpe, R.S. 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