Subsidized Mammals: Understanding the mammalian interactions with garbage sites around Western- Rajaji Tiger Reserve, Uttarakhand

Abstract

Anthropogenic food subsidies in the form of garbage dumps are widespread across the globe. When such sites are found around protected areas/wildlife habitats, wildlife is observed to exploit these subsidies as food resources. Foraging on such human-derived foods may have a negative or positive impact on individual to community/ecosystem levels. It becomes important to know the species associated with garbage dumps when found around protected areas and understand the interactions happening at the garbage dumps. This study was conducted aiming to know the animals at risk and also increase our understanding of these novel setups. I deployed 13 IR camera traps at total 10 garbage sites resulting in a cumulative effort of 437 trap nights at the garbage site. The camera trap data was processed using Megadetector & SpSeg packages in python. This data was used to get the Relative Abundance Index with respect to 437 trap nights. Sambar (RAI= 8.35) was the species with the highest visitations at the garbage site, followed by Indian crested porcupine (RAI= 2.70) and spotted deer (RAI= 2.15). Synanthropes like rhesus macaque (RAI= 1.78 ) and wild pig (RAI= 1.67) were the most visitors following spotted deer. I hypothesised that synanthropic species will have higher visitations because of distribution outside protected areas, followed by omnivores from the forest area as compared to herbivores and carnivores from the forest areas because of their ability to exploit larger variety of food resources. The data from this study rejected this hypothesis as forest dwelling species like sambar and Indian crested porcupine visited these sites more as compared to other synanthropes. Lesser visitations by omnivores like golden jackal, small indian civet, small indian mongoose; carnivore like common leopard along with scavenger striped hyena was a result of the less percentage of poultry waste (0.33% at only one site) in the garbage sites. I collected data on variables such as distance of the garbage site from the protected area, human infrastructure and waterbody, also quantified the size of the garbage site in terms of perimeter, NDVI difference between the protected area and garbage site as a surrogate of vegetation cover, relative abundance of each species in the adjoining protected area and calculated the composite RAI values of human, dogs/cats and livestock as a disturbance measure . I quantified the garbage in broader categories using a 1 m2 quadrat which was divided into smaller sets of 25x25 cm2. A total of 39 plots were laid for all the garbage site. The categories quantified were food wrappers & food disposables, food materials, religious offerings, agriculture discards, dung plates, sanitary waste, construction waste, carcass & poultry waste, pharmaceutical waste, cloths and plastic and others. The relation between relative abundances within protected area and visitations at the garbage site was assessed using Spearman correlation test along with Wilcoxon test p-values. With the available dataset I used ANOSIM using ‘vegan’ package in R program v4.1.2 to investigate the effect by considering the dissimilarity of the communities between sites based on the RAI values of the species for each garbage site. Relative abundance from protected area was not related to visitation of the species at the garbage site. Out of the selected variables, the ANOSIM values suggested the effect of ‘distance between garbage site and protected area’ on forest species and synanthropes. The effect of the ‘size of garbage site’ on the species could not be tested as there was not much variation in the sizes of the garbage sites. Human, dogs/cats and livestock presence affected the forest species, suggesting their sensitivity towards disturbances, while synanthropes were found to have affinity with the NDVI difference between protected area and garbage sites (vegetation cover at the garbage site) and the ‘percentage of food materials available in the garbage site’. To understand the co-occurrences at the garbage site, I modified the probabilistic models for co-occurrences (Veech, 2013) to get pair-wise associations at the temporal scale of one hour. A total 13 mammals avoided co-occurring with humans (and vehicle) while nine with livestock and dogs. Co-occurrences were found to be there between sambar and Indian crested porcupine at two out of three religious sites and at a household site, suggesting high tolerance levels to each other’s presence at the garbage site to exploit the resources. One of the sites was visited by barking deer with spotted deer group/herd. This association by solitary living barking deer can be for foraging effectively by reducing vigilance efforts in a group.