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. 2025 Sep 5;15:32366. doi: 10.1038/s41598-025-01484-3

Alert distance as a measure of tolerance and effect of human intervention on the behaviour of Rhinoceros unicornis in Kaziranga National Park

Sangita Medhi 1,✉, Malabika Kakati Saikia 2
PMCID: PMC12413440  PMID: 40913028

Abstract

The prospective for conflict between wildlife conservation and human interference are apparent from many restricted areas. The animals changed behavioral response to human presence can be considered as a tool/index to measure the disturbance. This study is an attempt to find out the strength of animal’s behavioural responses to human intruders through disturbance distance of Indian rhinoceros in Kaziranga National Park and help in fulfilling the dynamic function. The study was carried out in Kaziranga National Park from 2016 to 2018. Road transect method was used and the data was collected by scan animal sampling. The collected data was then analyzed with the help of SPSS. Different types of bahavioural response were recorded at various distance. The alert distance, flushing distance and chasing distance were found to be significantly different. Various other factors like habitat and wind direction influence the disturbance distance. Woodland shows less disturbance distance, while short grassland shows the highest. The disturbance distance was found to be higher when there was no wind and when the wind direction was from animal to observer. This is probably due to the strong hearing power and sense of smell respectively. The general linear model shows the contribution of all the variables on disturbance distance. Implementations of buffer zones based on the alert distance can increase the tolerance of the animals and reduce the disturbance.

Keywords: Rhinoceros, Conservation, Disturbance distance, Behaviour

Subject terms: Behavioural ecology, Behavioural ecology

Introduction

Protected areas are the main part of in-situ conservation of wildlife species and simultaneously provide opportunities for visitors to experience the nature creating a political capital to government’s budget1,2. Maintaining both the objective is a big challenge for the management. The ratio between economic benefit and environmental cost is dynamic3. Several studies have shown both qualitative4–6 and quantitative7–10 human impacts on wildlife. Human disturbance may alter the animal’s behaviour resulting in altered foraging pattern11. The wildlife managers have been trying to minimize the human disturbance by determining the minimum approaching distance at which the animal shows escaping behaviour and designate the boundary limit for the tourists12. Changes in behaviour against human interference can be used to estimate animal tolerance and guide management of restricted areas13. Disturbance distance is widely studied among the bird communities. It is regarded as flight distance14, displacement distance15, threshold distance16, set-back distance12, alert distance17,18, flight initiation distance19–21, etc. in different studies. Flight initiation distance has been using as a quantitative measurement in bird’s assessment of risk22,23. Human induced disturbance has been reported to change in habitat use24, reduce parental care25, reproductive failure due to compromised parental defense26 among many species. A number of studies has also documented physiological changes, such as changes in heart rates, body temperature, plasma corticosterone level etc.27–34. Nature of response to disturbance are different in different species and in different ecological condition. It also differs with the size of the animal19,35–37. Larger species has higher predator risk owing to have higher delectability19 and require more time to escape36.

Indian Rhinoceros is a large herbivore and Kaziranga National Park holds its highest population with diverse habitat. The park is highly attracted by the tourist from various parts of the world by this charismatic species, which create a high revenue which can be helpful for constructing various conservation strategies. Hence it is important to study the disturbance limit to guide the tourists so that the animals are less disturbed and recreation and conservation can coexist. The non-lethal disturbance stimuli due to humans are predicted to have effects on behavioural change and the intensity of these changes are predicted to be the results of many interacting factors. The environmental elements like (1) structure of vegetation cover, wind (2) social factors, like position in the group (age-sex), (3) the behavior of intruders are expected to be some factors interacting with the disturbance stimuli22. Variation in individual state both in relation to individual perception and habitat quality or types influences behavioural responses38. The human interference may disturb and displace wildlife or trigger aggressive and threatening behavior towards people. The habituation of wildlife to tourists has also been linked to an increased risk of their being depredated or changed behaviour39. The differences in behaviour profile would definitely define this hypothesis. However, as the larger species has lower disturbance distance, estimating the minimum approaching distance in turn will cover the smaller sized species also40. But no such work has been carried out in case of large mammal species so far or estimate what is the minimum approach distance of Indian rhinoceros in Kaziranga National Park. Hence, this study has been formulated to find out the disturbance distance of Indian Rhinoceros. The study also attempts to find out the affects of habitat type, wind direction, age-sex and tourist- non tourist area on the disturbance distance and effects of tourism in behavioural profile.

Materials and methods

Study site

Kaziranga National Park (KNP) is located between latitudes 26°30′ N to 26°45′ N, and longitudes 93°05′ E to 93°40′ E. KNP is a flood plain area and is in the southern part of river Brahmaputra. As KNP is on the river bank, it contains newer alluvium41. This is the reason why KNP supports high grassland and a favorable habitat for mega herbivores including Indian rhinoceros. The park covers an area of 859.4 km2. including all the additions42. The present study includes 482.9 km2 area43. KNP mostly consists of short grassland, tall grassland, wetlands and semi evergreen forest. The park experiences four seasons with only winter season as tourist visit (December to February) covering the full tourist route. Pre-monsoon, monsoon and post monsoon are affected by rain and flood which restricts the visitors to enter the park. The flooding in the park restricts the animal to use less dry areas and reduce resource availability.

Methods

The study was carried out from May 2016 to July 2018 (covering two tourist season from December to February) in Kaziranga National Park (KNP), Assam, India. The study was initiated with a pilot survey of two weeks. To study the disturbance distance, survey was conducted in both core area and area with human interference (tourism area). Transect method was done according to Fernandez-Juricic et al., (2001) and Burger & Gochfeld (1991) with few modifications. The disturbance distance was estimated by approaching the individual through walk towards it and different sites were selected owing to point transect in the studies of Fernandez-Juricic et al, (2001) and Burger & Gochfeld (1991). In the current study, road transect method were opted and instead of approaching towards the animal, the observer passed through the road and the changes were recorded. Six transects of 10 km were taken three in each core area and area with human interference. The distance of the transect was measured by plotting it in the Google earth and the GPS point of starting and end point of the transect was recorded for reference point (Fig. 1). The road transect was conducted by gypsy at a speed of 10–20 km per h.

Fig. 1.

Fig. 1

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Line transect for disturbance distance in both tourist and non-tourist area at Kaziranga National Park (Map prepared in ARC GIS 9.3).

To find the Indian rhinoceros’s distance of disturbance, road transect method have been used with few modifications and the data was collected through scan animal sampling at an interval of 5 min. The transects were carried out both in the morning (7–11am) and evening (3–5 pm) during the tourist season of the study period. The survey was started 7.00 am in the morning and 3.00 pm in the evening. The ending time was not fixed as it depended upon the sample numbers. However, it took three to four hours to end. The study was carried out three days a week from December to February in both the years. As the observers encounters a rhino during the transect, they record the behaviour change (Gradual and changed behaviour) and measures the distance with the range finder (ParGate, PG 2000 TPX) and proceed with the transect. A reference point near the rhino was recorded so that if the rhino runs away the distance can be measured. The distance measured during the pilot survey was also manually measured to test the accuracy and to maintain data standardization. Habitat type, wind direction (Fig. 2), tourist and non-tourist area and age-sex were the other factors recorded during the data collection. The behavioural responds of rhinos on the intruder’s presence were based on Fernandez-Juricic et al., (2001) with few modifications.

Fig. 2.

Fig. 2

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Determination of wind direction in the field during data collection.

Visual or morphological characteristics to classify age-sex

During the study, age-sex were classified into “adult male, adult female, sub-adult and calf38. Visual or morphological characteristics to classify age-sex was as per Laurie, 1978 and experience during the pilot survey. The adult consists of the age class more than 6 years, sub-adults from 4 to ≤ 6 years, and calf up to 3 years44,45.

Adult male & adult female

The adult male and adult females were distinguished with the help of genital organ in open areas. In the dense area, it was identified through the shape of the head. The head of the female is slenderer than the male and the neck folds are thicker in case of males38. Moreover, presence of mammary glands and bulging belly represents adult female.

Sub-adults

Sub-adults were distinguished from adults by smaller body size, horn size and absence or less scars on skin. The collar also contains very less folds in comparison to adults.

Calves

Calves are small in size. They almost reached the belly height of the mother. The horns are almost underdeveloped. Infants appeared pinkish in color.

Behavioural response due to disturbance

Disturbance distance is the distance at which the rhino felt disturbed due to certain unusual external factors like presence of any intruders or human beings that leads to change their normal behavioural activity. Indian Rhinoceros showed three types of responds or behavioural change to the existence of external factors during the study period at KNP. Those were such as-

Alert behaviour

It is the behaviour when the animal felt the existence of some intruder, they stop their normal activities and immediately try to identify and locate the source of disturbance by moving their head on either direction with ears erected or act as if scanning the intruder. While being not able to identify the problem or if the animal felt safe from the intruder, they were found to be continue the previous activity. This type of behaviour was regarded as alert behaviour and the distance at which the animal shows such behaviour has been regarded as alert distance.

Flushing behaviour

It is the behaviour when the animal felt some disturbance on the existence of some intruder and ran away from the point of disturbance creating source, such type of behaviour was regarded as flushing behaviour and the distance at which the animal flushed away has been regarded as flushing distance.

Chasing behaviour

It is the behaviour when the animal felt the disturbance due to the existence of some intruder and chased towards the disturbance creating source, such behaviour was regarded as chasing behaviour and the distance at which the species started to chase has been regarded as chasing distance. In this behavior the animal tried to attack the source of disturbance.

Age and sex

For different age & sex group, adult male and adult female, sub-adult and calf were considered.

Tourist and non-tourist area

The road transects were selected three in tourist area and three in non-tourist area. The tourist area was considered where the tourist visit was allowed and the non-tourist area were the places where the tourist was not allowed. Only the authorities used those for specific works.

Habitat type

The habitat type considered for the study was woodland, tall grassland and short grassland (wetland were not considered as they were distantly located to the roads). As Kaziranga has a diverged habitat it had effects in the feasibility on the rhino encounter.

Wind direction

Wind direction was a factor influencing the disturbance distance. The eye sight of rhinos is poor but the sense of smell is very prominent and the speed of wind is higher during the winter season. Hence, the wind had an effect on the rhinos on feeling the presence of an intruder. As there are four directions and it varied with due respect to the time and place of the transect, for the current study the directions were considered as observer to animal, animal to observer, along the transect and opposite to the transect (Fig. 2).

Activity budgeting was done as per the methods of Laurie (1978), through scan animal sampling. The behavioural nomenclatures were used as per Laurie (1978) and Medhi & Saikia (2020), which included feeding, resting, walking, vigilance, wallowing, locomotion and other miscellaneous. Diurnal study was conducted from 06:00 h in the morning to 18.00 h in the evening maintaining uniformity in both tourist and non-tourist area. Direct observation of Rhinoceros unicornis were made along the roadsides transacts, in and around the water holes and from the convenient watch towers of the park. Behavioural data were collected when encountered, in an interval of 5 min through scan sampling method (i.e. 5 min scan and 5 min gap procedure, as per Altmann46).

A total of 179 sample data for disturbance distance and 5091 scan samples for behavioural data were collected during the study period. The collected data were then pooled together and analyzed using M.S. Excel and SPSS respectively. Kruskal–Wallis test was done to find out the significant variation of disturbance distance with different response. One Way ANOVA was done to find out the variation of disturbance distance in relation to habitat, wind direction, age-sex and the areas of human interference (tourist and non-tourist area) and general linear model was done to see the contribution of the variables on the change of disturbance distance. One-Way ANOVA was also done to find the significant variation among different behaviours in tourist and non-tourist area.

Results

Activity pattern of Rhinoceros unicornis in tourist and non-tourist area

The activity pattern of Indian Rhinoceros was found different in tourist area and non-tourist area. The feeding (Mean% ± SD; 66.01 ± 1.81), locomotion (9.92 ± 1.51), vigilance (10.98 ± 1.68) wallowing (6.14 ± 0.76) and other (1.02 ± 0.53) activities were found to be higher in tourist area, whereas resting (23.15 ± 1.84) was found higher in non-tourist area (Fig. 3). Statistical analysis of activities in tourist and non-tourist area showed significant variation among locomotion (One Way ANOVA; F = 66.825, df = 9, p < 0.01), vigilance (One Way ANOVA; F = 89.503, df = 9, p < 0.01) and resting (One Way ANOVA; F = 290.373, df = 9, p < 0.01).

Fig. 3.

Fig. 3

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Mean percentage of activity pattern of R. unicornis in tourist area and non-tourist area.

Disturbance distance of Indian Rhinoceros

A total of 179 samples for disturbance distance (DD) in Indian rhinoceros were collected and analyzed during the study period in Kaziranga National Park. The mean alert distance (AD) was found to be higher (Mean AD in meter ± SD; 72.19 ± 68.79) than flushing distance (FD) (FD: 67.19 ± 54.78) followed by chasing distance (CD) (CD:40.18 ± 19.70; Fig. 4). Kruskal–Wallis test of disturbance distance with different response showed significant variation (X = 6.630, df = 2, p  < 0.05). The mean disturbance distance in non-tourist area (Mean DD in meter ± SD; 68.88 ± 66.22) was found to be more than tourist area (58.61 ± 37.11). Whereas, the maximum disturbance distance in tourist area was 136 m and 419 m in non-tourist area (Fig. 5a, b). Variation was also found in different age/sex groups. The mean disturbance distance was found to be higher in sub-adult (90.82 ± 117.74) followed by male (78.47 ± 66.05), female (62.94 ± 45.42) and calf (60.93 ± 38.31). The mean alert distance was found to be higher in male (98.2 ± 73.32) followed by sub-adult (86.12 ± 135.10), calf (77.86 ± 34.68), and females (57.31 ± 32.69). However, mean flushing distance was found to be higher in sub-adult (103.33 ±) followed by female (79.82 ± 65.30), calf (49.86 ± 38.29), and male (31.67 ± 17.55). Whereas, the mean chasing distance is higher in male (50 ± 12.2) followed by female (47 ± 20.91) and calf (20 ± 9.1).

Fig. 4.

Fig. 4

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Alert distance, flushing distance and chasing distance of Indian Rhinoceros in KNP.

Fig. 5.

Fig. 5

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(a) Mean disturbance distance in tourist and non-tourist area, (b) Maximum disturbance distance in tourist and non-tourist area (c) Mean disturbance distance in different habitat and (d) Maximum disturbance distance in different habitat of R. unicornis in KNP

Effect of habitat, wind direction and human interference in disturbance distance of Indian Rhinoceros

The mean disturbance distance of Indian rhinoceros was found to be different in different habitat. The mean disturbance distance in short grassland (80.75 ± 11.16) was found to be highest followed by tall grassland (66.26 ± 20.42) and woodland (47.71 ± 47.71). However, the maximum disturbance distance found in woodland was 98 m, tall grassland was 165 m and short grassland was 419 m (Fig. 5c, d). Kruskal–Wallis test of disturbance distance in different habitat showed significant variation (X = 19.028, df = 2, p < 0.01). Moreover, the disturbance distance was found to be lowest when there was no wind (60.26 ± 41.99) followed by observer to animal (67.91 ± 53.08), animal to observer (76.51 ± 57.82), along the transect (79.4 ± 69.9) and back to the transect (89.19 ± 54.39).

The mean disturbance distance of tourist area and non-tourist area with habitat showed that the disturbance distance is lowest in woodland of non-tourist area (46.92 ± 29.40), while it is highest in short grassland of tourist area (97.88 ± 49.25). However, both in tourist and non-tourist area the disturbance distance was higher in short grassland followed by tall grassland and woodland. Moreover, the mean alert distance was highest in short grassland (93.95 ± 95.92) followed by tall grassland (76.64 ± 40.62) and woodland (41.94 ± 11.63). Flushing distance followed the same sequence (short grassland-47.10 ± 42.61) tall grassland-55.36 ± 55.30, woodland- 47.10 ± 32.82, while chasing distance was found higher in tall grassland (50.00 ± 0) and lower in short grassland (38.00 ± 21.34; Fig. 6).

Fig. 6.

Fig. 6

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Alert distance, flushing and chasing distance in different habitat of R. unicornis in KNP.

Variation in the disturbance distance was found in different wind direction. The disturbance distance was found to be lowest in woodland when the wind direction was from the observer to the animal (38.88 ± 4.32). When the wind direction was along the transect the mean disturbance distance was 53.43 ± 29.84 in woodland, 164.2 ± 107.93 in tall grassland and 49.12 ± 45.59 in short grassland. During the wind direction from animal to observer, the mean disturbance distance found in woodland was 57.08 ± 41.71, in tall grassland it was 83.78 ± 63.44 and 134.89 ± 127.10 in short grassland. While the wind direction was opposite to the transect, the mean disturbance distance found was 82.67 ± 56.58 in tall grassland and 90.69 ± 56.13 in short grassland. However, when there was no wind the mean disturbance distance found was 41.62 ± 24.81 in woodland, 62.41 ± 41.55 in tall grassland and 134.22 ± 53.01 in short grassland (Fig. 7).

Fig. 7.

Fig. 7

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Disturbance distance with different wind direction and habitat of R. unicornis in KNP.

On the other hand, the mean disturbance distance in woodland was highest when the wind direction was animal to observer (57.08 ± 41.71) and lowest was when the wind direction was from observer to animal (38.88 ± 4.32). Among tall grassland the mean disturbance distance was highest when the wind direction was along the transect (164.2 ± 107.93) and lowest when there was no wind (62.41 ± 41.55). Whereas in case of short grassland, the mean disturbance distance was higher when the wind direction was from observer to animal (228.94 ± 214.15) and lowest when the wind direction was along the transect (49.12 ± 55.59; Fig. 7).

General linear model showed that habitat, wind direction, human interference and age/sex group had a great contribution in the variation of disturbance distance of Indian Rhinoceros (R squared = 0.579; Fig. 8a, b, c). The contribution of the habitat (F = 7.499a; p  < 0.001), human interference (F = 6.641a; p  < 0.001) and wind direction (F = 3.345a; p  < 0.021) was found to be significant.

Fig. 8.

Fig. 8

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(a) GLM plot of Alert distance with tourist & non-tourist area and habitat. (b): GLM plot of flushing distance with tourist & non-tourist area and habitat. (c): GLM plot of Chasing distance with tourist & non-tourist area and habitat.

Discussion

Indian rhinoceros are significantly affected by the disturbance of human interference. In the present study, changes in the normal behaviour were observed in the presence of intruders. The usual behaviour altered into alertness, flushing or chasing as a respond to the stimuli. These behavioral changes occurred at varying distances, with alertness being observed at the highest distance, followed by flushing and then chasing. The alert distance can be considered as the tolerance limit of rhinoceros against human disturbances13,47. However, flushing and chasing behaviour indicates higher level of disturbance which is intolerable and defensive. The behavioural aspects are well elaborated in various studies such as wild reindeer Rangifer tarandus tarandus and mountain goats Oreamnos americanus48,49. Rodgers & Smith (1995) have considered alert distance as high conservative indicator of tolerance. The present study is also evident for the change in behavioral percent between tourist and non-tourist area. Increase in vigilance, locomotion and decrease in resting behaviour in tourist area is attributed to disturbances caused by intruders. Displacement from a resource is anticipated to affect wildlife survival and reproduction in arid regions, such as northwest Namibia, where plant growth and water availability are patchily distributed and inadequate39.

The distance of disturbance varied between tourist and non-tourist area. It was found to be lower in tourist area and higher in non-tourist area. This is likely due to the impact of human interference, indicating higher disturbance levels in tourist areas. However, the animals in the non-tourist area become alert at a longer distance compared to animals in the tourist area. In non-tourist area having less disturbance by the human interference, the animals can detect the stimuli from a longer distance. However, the behavioural aspects of the human intruder like group size of intruders50, tangential approach51–53 and clothing color54 also influence the response behaviour duration of the animal. Escape behaviour is reasonably expected to be influenced by the life-history characteristics of birds55. Previous research into the behaviour of the black rhinoceros suggests a strong avoidance of chronic human-induced disturbance56. The behavioural response of Indian rhinoceros also varies among different age and sex groups. Lower alert distance and higher flushing distance in females and calf indicates that rather than flushing away the female try to examine the problem as females were mostly found with calves. Hence, providing security to the calf is their prior duty rather than escaping. Escaping in such situation may mislead the calves track and enhance straying of calves which will further lead them against various threat. Moreover, lower chasing distance in females than male is most likely due to providing protection against the calf. Higher alert distance and lower flushing distance in males is the sign of lack of responsibility. The overall disturbance distance was found to be higher in case of sub-adults and lowest in calves followed by females. This indicates that the sub-adults show less response to the stimuli than other groups. Whereas, lower disturbance distance in calves shows their fearful nature. Females show lower disturbance distance as a part of parental care and protection towards the calf. Weston et al. (2012) have also stated the change in the magnitude of flight initiation distance among different age and sex group.

The disturbance distance and response to the stimuli is affected by habitat or vegetation structure. Fernandez-Juricic et al. (2001) explained about the positive association of grass cover and openness in the disturbance distance of birds. The disturbance distance was found to be higher in short grassland and lower in woodland which prevails that animal at a longer distance in the short grassland shows reaction towards the intruder. Whereas, in woodland it decreases with the decrease in the visibility due to dense canopy. However, in tall grassland it was found moderate. These changes are enhanced by the visibility of the source of disturbance. Availability of higher vegetation cover and consequently lower perceived risk of predation increases the tolerance distance23,57,58. Modification of alert distance according to the availability of cover in birds are evident from different studies11,40,59. Knight and Temple60 have also documented similar changes of alert distance in different habitat in case of birds. However, no studies have been carried out on mammal disturbance distance. Many species have less access to and quality of food in the winter, which makes it harder for them to move away from populated areas. Additionally, because vegetation in alpine and sub-alpine environments regenerates slowly, habitat degradation may have an impact61.

Wind direction is another factor which effects the disturbance distance. The disturbance distance was found to be lowest when the wind direction was from observer to animal. Moreover, the disturbance distance is less when there is no wind. The Indian rhinoceros has a strong sense of smell and power of hearing. The wind helps to spread the smell of the observer (human intruder) and when there is no wind, they can detect the sound more quickly. These are most likely the possible reason for the above observation. However, along with the wind direction the habitat also has a parallel impact. The disturbance distance in woodland is lower than grassland as because the trees act as the obstacle and pretend the wind which reduces its velocity. Fruziski62, have mentioned the influence of weather on the flight initiation distance of birds. However, many researches are evident, which explains various other factors that influences the disturbance distance like type of riding (gypsy safari of elephant safari etc.) and speed of movement in birds63.

Recreational habituation is reported in many studies and it usually produced positive responses in the coding system (e.g., habituated animals reduced flight initiation distances). However, it is unclear whether habituation benefits animals (e.g., by lowering expensive behavioural responses to humans) and needs more research61. However, as the current study area allows very less time for tourism habituation may hardly likely take place. Hence, we can conclude that there is different behavioural response against the disturbance (stimuli) found in Indian rhinoceros in KNP. The disturbance distance is influenced by the habitat structure, age and sex group, wind direction etc. However, there are many other factors which may affect the disturbance distance like, the intruder’s behaviour, its clothing, type of riding source, speed of the vehicle etc. and hence needs more intense study.

Conservation implications

The increased recreational activity and decreased wildlife habitat has created a challenge for the wildlife. The significant difference between alert distance and flushing distance call attention to consider the alert distance as a tolerance limit12. Fernandez-Juricic et al. (2001) have mentioned this difference (alert distance and flushing distance) of disturbance distance as a buffer zone and the animal is capable to adapt to the intruder in this zone. The decision maker of the management can build a limit of approach distance in the park and implement some law for the vehicle drivers to maintain the behaviour of the peoples. Providing behaviour education to the drivers will enhance them knowledge regarding the human behavioural effects on animals and can control the tourist accordingly. The viewers should maintain the minimum of 100–200 m of distance. However, if the wind direction is from observer to animal, then it will be 200–400 m. This distance will gradually decrease in tall grass land and woodland. The alert distance in different habitat with different wind direction may consider as a buffer zone for Indian Rhinoceros. The viewers should also be conscious in woodland and tall grassland as the visibility is less and hence the chasing was found more in comparison to short grassland. Being a large animal, the buffer region of the Indian rhinoceros will help in protecting other small species. However, the disturbance distance for Indian rhinoceros may not be 100 percent applicable for other species. The perceptual range, visual acuity and the detection ability are not similar in all wildlife species and varies with the size and type of the animal64,65. Therefore, a detailed study of disturbance distance in other animals are also mandatory for the reduction of human interference on wildlife.

Supplementary Information

Supplementary Information. (1.5MB, pdf)

Acknowledgements

The Authers are very much thankful to the Forest department of Assam, India to providing permission to carry out the research work. The Authers is also indebted to Mr. Robin Sarma, Research Officer, Kaziranga National Park for assisting in the entire work.

Author contributions

S.M., did the research work as a part of the PhD degree from the Department of Zoology, Gauhati University, Assam India. She did the data collection, analysis and preparation of the manuscripts. M.K.S. supervised the entire work. Both the authors reviewed the manuscript.

Data availability

The Authers assures that the date used in the manuscript is available and any required data for queries will be provided at any time. Dr. Sangita Medhi will be the primary contact for any future data-related issues.

Declarations

Competing interests

The Authers declares no financial and non-financial competing interest.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-025-01484-3.

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