Crocodylus Palustris Research Articles

Mugger Crocodile Crocodylus palustris (Lesson, 1831) predation on Brown Fish Owl Ketupa zeylonensis (J.F. Gmelin, 1788), with notes on existing literature regarding their predation on birds

Several observers have noted that Mugger Crocodiles Crocodylus palustris incorporate birds into their diet, though no authors have reviewed the full range of bird species subject to such predation. In the present study, the first observation of Mugger Crocodile predation on an owl, specifically the Brown Fish Owl Ketupa zeylonensis, is reported. Additionally, the existing literature regarding Mugger Crocodile predation on birds is summarized.

Population status and genetic assessment of mugger (Crocodylus palustris) in a tropical regulated river system in North India

For rewilding the depleted crocodylian populations in India, a targeted ‘one-species one area’ based conservation approach was adopted in the early-1970s. Suitable habitats were identified and designated as protected areas, specifically targeted to recover a particular crocodylian species. A ~ 610 km stretch of Chambal River in the Ganga River Basin was declared as National Chambal Sanctuary to restore the ‘Critically Endangered’ gharial (Gavialis gangeticus), where active management of mugger (Crocodylus palustris) was discouraged. In the present study, we examined the population trends, occupancy, and genetic status of mugger by conducting population monitoring and genetic assessment to understand the status of potentially competitive mugger in the Sanctuary. Our finding suggests that the mugger population has notably increased and colonised the Sanctuary. We observed a moderate level of genetic diversity in the mugger, which was relatively higher compared to the gharial in the Sanctuary. The rapid colonization of ecological generalist mugger raises concerns about potential competition with ecological specialist gharial threatening its long-term sustainability. Considering the coexistence dynamics between the species, it is essential to extend adaptive management strategies for mugger to ensure successful recovery of gharial population in the Sanctuary.

Osteology of Crocodylus palaeindicus from the late Miocene–Pleistocene of South Asia and the phylogenetic relationships of crocodyloids

Fossil crocodylian remains have been documented from India and other parts of South Asia since the mid-nineteenth century, but specimens attributed to several extinct and extant species of Crocodylus have largely been neglected in modern taxonomic treatments. Here, we present a detailed anatomical description of the extinct species Crocodylus palaeindicus, which we restrict to the late Miocene to early middle Pleistocene of India. Using an autapomorphy-based approach to species-level identification, we regard Crocodylus sivalensis as a junior synonym of C. palaeindicus and provide taxonomic re-identifications of all specimens previously referred to these two species. We present a new diagnosis for C. palaeindicus that facilitates its distinction from the extant mugger crocodile, C. palustris, which does not unequivocally appear in the fossil record prior to the Pleistocene. The lack of clear spatiotemporal overlap, coupled with the otherwise lengthy ghost lineage implied by their sister-taxon relationship in our phylogenetic analyses, provides tentative support that the extant species either is the descendant of C. palaeindicus or originated via budding cladogenesis. An expanded phylogenetic analysis recovers the late Miocene African C. checchiai and Pliocene South American C. falconensis as species within the Neotropical Crocodylus clade, supporting an African origin for this radiation. We also recover Kinyang, from the early–middle Miocene of Kenya, as a crocodyline, rather than an osteolaemine as originally described, and it is potentially the stratigraphically earliest known member of the Crocodylus lineage. Other notable results from our phylogenetic analyses suggest that crocodyloids might not have been present in North America prior to the late Neogene arrival of Crocodylus, with Albertosuchus knudsenii, Prodiplocynodon langi and ‘Crocodylus’ affinis all recovered outside of Crocodyloidea. Furthermore, we demonstrate that an alligatoroid placement for the recently erected latest Cretaceous–Palaeogene East Asian clade Orientalosuchina is highly labile, with relationships at the ‘base’ of Crocodylia unstable.

Current State of Mugger Populations.

The mugger (Crocodylus palustris) is a medium-sized crocodilian inhabiting South Asia. As a result of intensive hunting, its range declined drastically up till the 1970s. Currently, the world mugger population is fragmented and threatened mainly by habitat loss and the consequences of human-crocodile conflict, being classified as Vulnerable by the IUCN. The goal of this paper is to comprehensively determine the mugger's current range, and assess risks in notable habitats of the species across its range. To determine the range and notable habitats, extensive literature covering surveys, monitoring, population studies and reports of human-crocodile conflict was examined. Habitat suitability and risk assessment were performed by evaluating selected habitats using eight factors: the legal status of the area, elevation, surface water availability, water quality, salinity, availability of nesting and basking sites, interaction with humans and interspecific competition. Based on our findings, the chances of the mugger's survival varies greatly across its range and the threats they face are complex and often site-specific. Defining these threats is the first step for determining suitable risk mitigation efforts, some of which are explored in this review.

Critiques: On the first sighting report of Mugger Crocodile from Purna River, South Gujarat, India.

Critiques: On the first sighting report of Mugger Crocodile from Purna River, South Gujarat, India.

Observations on cooperative fishing, use of bait for hunting, propensity for marigold flowers and sentient behaviour in Mugger Crocodiles Crocodylus palustris (Lesson, 1831) of river Savitri at Mahad, Maharashtra, India

As far as animal cognition is concerned, in comparison with mammals and birds, reptiles have been underestimated and research in reptilian cognition hasn’t progressed much due to this bias. Though crocodiles are generally stereotyped as lethargic and lacking social interactions except for territoriality, parental care and prey ambush, they demonstrate discrete behavioural repertoire in a variety of situations suggestive of refined cognition. The observations presented here were recorded during a long-term study on Muggers Crocodylus palustris of Savitri River in Maharashtra, and indicate social behaviour of remarkable acuity among Muggers to optimize foraging, which clearly hints at cooperative fishing. Also, on many occasions here, the Muggers were seen to have sticks on their snouts or lay still in the vicinity of floating twigs presumably to lure birds that desperately scouted for nesting material; though only on one occasion the unsuspecting bird was ambushed successfully. Flight initiation distances (FID) of birds that forage and nest in crocodilian habitat have been measured to assess their wariness towards crocodile’s presence. We report the attraction of free ranging Muggers here to the yellow Marigold Tagetes erecta flowers. We also remark on apparent sentience involving a dog that was chased into the river by a pack of feral dogs, the ‘aquatic refugee’ having been seemingly nudged and escorted to safety of the bank by crocodiles. All these behaviours are discussed in the light of previous reports involving other crocodilian species elsewhere, to assess the cognitive faculty of this species.

Factors influencing the habitat selection of Mugger crocodile (Crocodylus palustris) and its conservation threats in the Rapti River of Chitwan National Park, Nepal

Mugger crocodiles (hereafter called muggers) are the apex predator and keystone species in slow flowing freshwater ecosystem. They play an important role in its functioning by distributing nutrients and increasing primary productivity. Muggers have a sympatric distribution with gharials in the Rapti and Narayani River of Chitwan National Park, but more research and conservation attention has been focused on gharials in Nepal. The inadequate availability of information on the occupied habitats of muggers restrict their evidence-based conservation and management. Therefore, we investigated the ecological factors affecting the habitat selection of muggers and its conservation threats in the Rapti River. We conducted a preliminary survey, followed by a detailed habitat survey, conducted in February and March 2022. During the detailed habitat survey, the pre-defined habitat characteristics were recorded at each station spaced at 500 m intervals along the river as well as the locations where muggers were sighted. We used a generalized linear model (glm) under the binomial family with a logit link function to analyze the factors influencing the habitat selection of muggers. The dependent variable was the presence or absence of muggers at sampling points and the independent variables included: river bank aspect, river width, mid-river depth, river bank substrate type, river bank slope, water current, invasive alien plant species, and anthropogenic disturbances. In addition, a relative whole-site ranking method was employed to determine the most prevalent threats to the mugger. During the survey period, we recorded a total of 46 mugger individuals, 71.8% were observed basking and 28.2% were observed submerged in the river. The highest percentage of muggers (39.1%) was observed on the sandy river bank, followed by the grass and forest bank (19.5%), and clay and sandy bank (15%), respectively. Only the river banks with moderate (15–25°) and moderately steep (25–35°) slopes were found to be the significant factors influencing the occurrence of muggers. Fishing and extraction of river materials, and disposal of garbage and solid waste were ranked as the most prevalent conservation threats. For the long-term conservation of muggers in the Rapti River, effective habitat management plans and strategies are required to control illegal anthropogenic activities such as fishing, sand mining, and boulder quarrying. Research on spatio‐temporal partitioning between mugger and gharials is recommended to understand how resources are shared by the species.

Review on Mugger (Crocodylus palustris) mortality by vehicle collisions in Gujarat State, India

Review on Mugger (Crocodylus palustris) mortality by vehicle collisions in Gujarat State, India

First confirmed record of Mugger Crocodile (Crocodylus palustris) from the Purna River, Tapi District, Gujarat

First confirmed record of Mugger Crocodile (Crocodylus palustris) from the Purna River, Tapi District, Gujarat

Population trends of Mugger Crocodile and human-crocodile interactions along the Savitri River at Mahad, Maharashtra, India

In this paper, we report monitoring of a resident population of Mugger Crocodile Crocodylus palustris (Lesson, 1831) along a stretch of 3.5 km of the river Savitri on the outskirts of Mahad town of Raigad District in Maharashtra, on monthly basis from 2014 to 2021. This river is increasingly becoming a sink of anthropogenic wastes emerging from adjacent settlements impacting its habitat value, and puts the reptile side by side with humans and human-wastes that could be a cause of rising incidents of crocodile mortality in the recent times here, as also reported from elsewhere. Savitri River has been a fishing ground for local indigenous communities, who also use the river bank for washing clothes and utensils, and for swimming. Such proximity between people and crocodiles creates a potential for negative interaction. This long term study monitored the Mugger population trends for the last eight years at four transect stretches along the river. Counts are suggestive of a healthy viable population of Mugger in this river currently, but a future conflict situation cannot be ruled out. Being generalist feeders, Muggers can sustain themselves on fish, and scavenge on dumped carrion and other anthropogenic organic wastes. With the exception of a few sporadic incidents of aggression by the Muggers at this location, no human casualties have been reported thus far, however, this does not rule out fatal reciprocal interactions in future and hence a few practical mitigation measures have been suggested.

Identification of free-ranging mugger crocodiles by applying deep learning methods on UAV imagery

Individual identification contributes significantly towards investigating behavioral mechanisms of animals and understanding underlying ecological principles. Most studies employ invasive procedures for individually identifying organisms. In recent times, computer-vision techniques have served as an alternative to invasive methods. However, these studies primarily rely on user input data collected from captivity or from individuals under partially restrained conditions. Challenges in collecting data from free-ranging individuals are higher when compared to captive populations. However, the former is a far more important priority for real-world applications. In this paper, we used Unmanned Aerial Vehicle (UAV) to collect data from free-ranging mugger crocodiles, Crocodylus palustris. We applied convolutional neural networks (CNNs) to individually identify muggers based on their dorsal scute patterns. The CNN model was trained on a data set of 88,000 images focusing on the mugger's dorsal body. The data was collected from 143 individuals across 19 different locations along the western part of India. We trained two CNN models, one with an annotated bounding box approach, the YOLO-v5l, and another without annotations, the Inception-v3. We used two parameters, True Positive Rate (TPR) and True Negative Rate (TNR), to validate the efficiency of the trained models. Using YOLO-v5l, TPR (re-identification of trained muggers) and TNR (differentiating untrained muggers as ‘unknown’) values at the 0.84 decision threshold were 88.8% and 89.6%, respectively. The trained model showed 100% TNR for the non-mugger species, the Gharial, Gavialis gangeticus, and the Saltwater crocodile, Crocodylus porosus. The performance of the CNN model was reliable and accurate while using only 125 images per individual for training purposes. Inception-v3 underperformed for both the parameters, thus, showing that a bounding box approach (YOLO-v5l model) with background elimination is a promising method to individually identify free-ranging mugger crocodiles. Our manuscript demonstrates that UAV imagery appears to be a promising tool for non-invasive collection of data from free-ranging populations. It can be used to train open-source algorithms for individual identification. Further, the identification method is entirely based upon dorsal scute patterns, which can be applied to different crocodilian species, as well.

Status, distribution and habitat use by Mugger crocodile (Crocodylus palustris) in and around Koshi Tappu Wildlife Reserve, Nepal

Mugger crocodile is found in various locations of Nepal, ranging from Eastern to Western lowlands, and is also a resident crocodilian of the Koshi Tappu Wildlife Reserve (KTWR). Fewer studies have been carried out on the status and distribution of this crocodilian with limited information on its habitat characteristics. This study sets forth to highlight the population status, distribution and habitat use by mugger crocodile in and around KTWR. Detailed surveys were conducted in the rivers, natural and private ponds of the KTWR in December 2020. Every 500 m along the survey transects, habitat characteristics were recorded in each habitat station as part of the habitat survey. The dependent variables were presence or absence of mugger crocodile in each habitat station. Meanwhile, the independent variables included habitat predictors such as; water depth, slope, elevation, distance to roads, distance to settlements, bank substrate, and human disturbance. Generalized Linear Model under binary logistic regression was employed to test variables associated with presence and absence of muggers for statistical significance. The population survey of the muggers was assessed by day counts either using dugout canoe or walking along transects. During the research period, 35 individuals of muggers were recorded. The probability of mugger sighting augmented with increased slope and depth. 34 muggers (97.14 %) were basking, while 1 (2.85%) were seen swimming out of the total muggers detected. In private and public ponds, 22 muggers were sighted, while 13 were sighted in the main Koshi river, its branches, and the Moriya river. Sixteen muggers (45.71 %) were sighted within the reserve, while the remaining 19 muggers (54.28 %) were sighted in the buffer-zone areas. The probability of mugger sighting varied considerably with regard to slope and water depth among the seven habitat predictors examined. In lieu of prevailing fishing pressure in the river systems of the KTWR and easy availability of prey species for muggers in private fishponds; the muggers are likely use private fishponds more frequently. In order to subdue the muggers inside the KTWR, the reserve authority has a vital role for proper habitat management decisions and regulation of fishing activities.

Physicochemical assessment of Wetlands and its Impact on Marsh Crocodiles Crocodylus palustris (Lesson, 1831) of Terai Landscape, Uttarakhand, India

Water is the basic life line of all living organism on this planet. The study revealed that the significance of water quality is good at the Terai Arc Landscape (TAL) rivers which passes through the Terai landscape of Kumaun, Uttarakhand, India. Water is essential for drinking, domestic, irrigation and industrial purposes. The Terai Landscape of Uttarakhand is rich in water resources and which is utilizable for all purposes. Rapid industrialization has led to low quality of water due to wastewater flowing in natural wetlands of the area. Water and their ecosystems are major indicators of the strength of forest and aquatic fauna. This was achieved by analyzing 12 water quality parameters from samples collected at 13 study sites between the Kosi and Sharda river stretch of different water bodies on monthly basis for a period of 12 calendar months. The water physicochemical variables are analyzed using standard methods during May 2015 to April 2016 and its assessment is carried out. The 12 parameters included Average depth, Temperature, pH, Transparency (turbidity), Dissolved Oxygen (DO), Total Hardness, Total Alkalinity, Chloride, Nitrate, Fluoride, Total Iron, Phosphate and presence and absence of Coliforms. We observed that the range of contagion, vicinity of pollution sources and water quality of sites suggest that the species is under threatened category in Terai landscape, Uttarakhand. Amongst the 13 sites chosen for assessment, the physicochemical properties of different water bodies in reference to usage of wildlife such as Marsh crocodile, tiger, leopard, elephant, sloth bear and many species of herbivores at present is acceptable.

Estimation of the Population Size of Crocodile Crocodylus palustris (Lesson, 1831) from Two Incomplete Survey Methods-Daylight Ground Counts and Night Counts

The population count of crocodiles was undertaken from the Warana basin of Maharashtra, India for successive two years 2013-14 and 2014-15. Two main survey methods Daylight Ground count and Night Count were used to access the population. As the Crocodile is a shy animal and the study area is so big it was impossible to locate every crocodile from the study area as well as to cover the whole study area. Hence population statistics was applied to calculate the population size of the Crocodile. The statistical approach explained by W. E. Magnusson (1978) was used for the present work. The calculation of probabilities for two survey methods estimated that the study area has about 182. It has an approximate variance of 806 and hence a standard error of ±28.39.

Status and distribution of Mugger Crocodile Crocodylus palustris in the southern stretch of river Cauvery in Melagiris, India

A study was conducted to examine the population estimate and spatial distribution of Mugger Crocodile in the southern stretch of river Cauvery, Hosur Forest Division from February 2019 to May 2019. In total, 53 basking sites and 45 Muggers were encountered by direct sighting in the 24-km river stretch using daytime ground based survey approach. N-mixture models estimated an average Mugger density of 2.05 individuals per kilometre for daytime survey. A night spotlight survey across the seven segments of river stretch was also conducted which yielded direct sightings of 54 Muggers with an average encounter rate of 2.25 individuals per kilometre. Two crocodile nests with hatched egg shells were also observed on the sand banks of the river. We concluded that a potential healthy and breeding population of Mugger inhabits the studied stretch of the river. Multiple corresponding analysis was also performed, which demonstrated that Mugger responds to sandy banks alongside deep water pools for basking in contrast to river segments with shallow depth and dense riparian cover.

Ongoing assessment of the Marsh Crocodile (Crocodylus palustris) population in the wetlands of Anand and Kheda Districts, Gujarat, India

Ongoing assessment of the Marsh Crocodile (Crocodylus palustris) population in the wetlands of Anand and Kheda Districts, Gujarat, India

Anecdotal observations of ‘double clutching’ behaviour in captive Mugger crocodiles (Crocodylus palustris)

Abstract Animals modulate their behaviours in accordance with their local environment and in the process, undergo different behavioural and physiological adaptations to better survive in a given ecosystem. One such behaviour that plays an important role in survival and sustenance of a species is the breeding behaviour. In this article, we present anecdotal information on breeding strategies of Marsh or Mugger crocodiles. Mugger crocodiles mostly lay single clutch during a year and have an elongated courtship and mating period lasting for 3–4 months. However, we show anecdotal data covering a period of 2 years for a Mugger crocodile producing double clutches annually under captive conditions. The laying of multiple clutches in captive Mugger crocodiles may indicate higher nutritional status and/or breeding strategies of the females under resourceful conditions. We suggest the need for future work on understanding proximate mechanisms underlying the ‘double clutching’ behaviour of Mugger crocodiles.

Population status, habitat occupancy and conservation threats to Mugger crocodile (Crocodylus palustris) in Ghodaghodi lake complex, Nepal

Mugger crocodile is a keystone species of slow flowing fresh water ecosystem. Few studies regarding status and distribution of Vulnerable Mugger have been conducted in Nepal. However, studies on ecology and other aspects of the species are limited. The goal of this study was to determine the Mugger crocodile's population status, habitat occupancy, and conservation threats in the Ghodaghodi lake complex, located in the western lowlands of Nepal. A detailed survey was conducted on 18 lakes of the lake complex in February, 2021. The population status of the Mugger was surveyed by walking along the entire boundary line of each lake. For habitat survey, perimeter of all the lakes of the complex was divided into the number of stations spaced at 500 m intervals. Habitat factors associated with the presence and absence of the Mugger were analyzed using Generalized Linear Model under binary logistic regression and likelihood ratio test was performed to test predictors for statistical significance. During the survey, 26 muggers were recorded. The probability of sighting Mugger in the lake complex was significantly differ by distance to settlement, distance to river, and human disturbances, among the nine habitat variables examined. Similarly, habitat modification and illegal fishing were ranked as most severe threats to Mugger crocodile in the lake complex. The concerned authorities, responsible for managing the lake complex shall pay attention on controlling the major identified threats like habitat modification, illegal fishing, unmanaged infrastructure development, and pollution in the lake complex in order to support future conservation of Vulnerable Mugger population in the area. Furthermore, a detailed and extensive study is suggested to investigate the movement of Muggers between different lakes of the complex as well as from Ghodaghodi lake complex to the nearby rivers during breeding season in order to support effective planning and execution of habitat management activities of this Vulnerable species.

Basking Behaviour and Use of Riparian Tunnels by Mugger Crocodiles Crocodylus palustris (Lesson, 1831) of Savitri River at Mahad, Maharashtra, India

This study has recorded observations on maintenance behaviour pertaining to basking and use of tunnels by Mugger crocodiles Crocodylus palustris (Lesson, 1831) of river Savitri at Mahad in the Indian state of Maharashtra. The Mugger shuttles between the land and water guided by a circadian rhythm, primarily to regulate its body temperature. This amphibious reptile was seen to be meeting its thermal preferences by a combination of heat-seeking and heat-avoiding behaviours that largely revolve around immersion in water, basking and retreating in tunnels. The ascendance from water body to bask on dry ground also included intermediate postures taken by the Mugger like pre-basking, surface basking and shallow water basking; and the relative amount of time spent in each of these behaviours varied seasonally. Also, the Mugger crocodiles were seen to excavate separate tunnels on the river banks for purpose of resting and nesting. These observations recorded over a span of nine years are discussed in the context of ethology. The study also documents behaviour of Mugger with conspecifics and other species that share its habitat. It is emphasized that understanding of crocodile behaviour helps in discernment of species-specific natural history, and is also important from the perspective of its conservation management.

Roads and railways: An emerging threat to the Mugger (Crocodylus palustris) populations of Gujarat, India

Roads and railways: An emerging threat to the Mugger (Crocodylus palustris) populations of Gujarat, India