Seasonal Fluctuation in Thermoregulatory Behaviour of Long-Billed Vulture (Gyps indicus) by Wing Stretching at Southern Rajasthan, India

Long-billed vulture is warm-blooded and they regulate body temperature by solar radiation. Thermoregulatory behaviour plays an important role for organism survival and its fitness. It also plays a major role in removal of ectozoons, cleaning of body and feathers, elimination of sand particles, wing flexibility and is also helpful in long distance flight. Maximum thermoregulation time recorded in winter were (680±95.65) and minimum were (516.07 ±68.66) seconds in summer in per day. Maximum thermoregulation time’s record in winter was due to low environmental temperature, high humidity and low wind velocity. In winter maximum average temperature was (27.12±2.88°C) and minimum was (8.63±3.03°C), while thermoregulation time minimum recorded in summer due to high environmental temperature. In summer season maximum average temperature was recorded (39.34±2.10°C) and minimum was (23.08±4.49°C). Thermoregulation is influenced by various ecological parameters liketemperature, rain, sunshine period, wind velocity and cloudy weather. Thermoregulatory times reduced when environmental temperature increased. In summer long billed vulture protect nestling from direct sunlight. Current World Environment www.cwejournal.org ISSN: 0973-4929, Vol. 15, No. (2) 2020, Pg. 353-362 CONTACT Nadim Chishty nadimchishty@gmail.com Wildlife, Limnology & Toxicology Research Laboratory, Department of Zoology, Govt. Meera Girl’s College, MLSU, Udaipur, Rajasthan, India. © 2020 The Author(s). Published by Enviro Research Publishers. This is an Open Access article licensed under a Creative Commons license: Attribution 4.0 International (CC-BY). Doi: http://dx.doi.org/10.12944/CWE.15.2.23 Article History Received: 19 March 2020 Accepted: 08 August 2020


Introduction
Sun-bathing or basking is a behaviour seen in birds for many kinds of reasons  Columbiformes, Ciconiiformes, Corvidae and passerine birds. The thermoregulatory behaviour is performed by many avian species and reported in more than 170 species of birds belonging to 48 families . Sunbathing is not only used to maintain body temperature, but also plays a vital role in maintaining flight muscle, healthy wing, able to fly longer distance , aerial flight and searching food and water for its survival. It also plays a key role in survival of warm-blooded animals like reptiles, birds and other organisms living in dry and cold environment. Vultures have special characteristics to maintain body temperature by absorbing sunlight (Heath, 1962;Curry-Lindahl, 1970;Kushlan, 1973;Tom J. cade, 1973). Thermoregulation is an important adaptive phenomenon in birds, and they play a key role in its survival like plumage maintenance, sunbathing, sun basking, and water bathing (Slessers, 1970).Vultures spend most of their time preening and maintaining plumage. Vultures absorb high portion of solar radiation in comparison to other birds, by spreading wings in position of sunlight with an intention to dry the feathers, removing sand particles and ectozoons from feathers (Clark and Ohmart, 1985) and their dark colored wings absorb maximum heat from sunlight (Hamilton and Heppner, 1967;Lustick, 1969;Marder, 1973) at low wind velocity (Walsberg et al., 1978). Vultures stretch their wings to more time duration in winter as compared to summer season (A.G. Clark, 1969;Mueller, 1992). Many studies have been done on energy demands by organism for different types of activities and functions. Some scientist have focused on thermoregulatory behaviour and adaption by warm-blooded animals to live in dry and cold environmental conditions (Schmidt-Nielsen, 1964;Scholander, 1955;Scholander et al., 1955;.
The study was mainly focused on fluctuation of time according to seasonal variation in thermoregulation behaviour in long-billed vulture. Study will provide details observation of environmental factors liketemperature, humidity, wind velocity and season on thermoregulation behaviour of long billed vulture.

Materials and Methods Study Area
An intensive study was made in the region of high hills and rocky cliffs of Aravalli hills of southern Rajasthan at an elevation of 600-700 meter, where annual precipitation was 600.8 mm. Southern Rajasthanin cludes Chittorgardh, Udaipur, Sirohi, Jalore, Pratapgarh, Banswara and Dungarpur district, situated between 24°34'48.00N'' latitude and 73°40'48.00E'' longitude. Udaipur division has temperature ranging from 5.6°C in winter and temperature rising during summer up to 43°C. The annual rainfall is approximately 89-93% of total rainfall in the division caused by monsoon season from June to October (RCA, Udaipur, 2018).

Method
Study was supported by repeated direct observations using binoculars Nikon 8X40, and photography and video-graphy done by Nikon Coolpix P900, Canon D-60 camera with sigma150-500mm lens. Data were collected in early morning to late evening. For thermoregulation behaviour two long billed vulture colonies were observed. Data were analysed with the help of MS-Excel and SPPS software tools.

Result and Discusion
The key result of sunbathing by wing spreading behaviour represents cleaning of the body and feathers, elimination of sand particles, removal of ectozoons and maintaining the flexibility of the feathers, they also helpful in maintain healthy wing and body. Maximum activities of vultures is recorded in warmer time with the sunrise, environment temperature rises and simultaneously human activities also start and with that in towns & villages vulture activities also start (Sonika K. and Amita K. 2010).Vultures have a larger wing span which help them in flying and a highly specialized mode of flight, they avoid flight in extreme high temperature or afternoon time. They do not fly in day time when the temperature increases above normal range, as well as cloudy weather. According to Cade, sunbathing behaviour by wing spreading of certain raptors develop not only associated with maintaining body temperature but also with features maintains and cleaning, to provided elasticity of flight muscle James A. mosher, 1976).Vulture also spread wing their various other function like drying, maintaining buoyancy, body temperature maintain (Hennemann, 1982). Vulture changes their position according to time during sunbathing to maintain rate of heat exchange that adjust the angle of occurrence of solar transmission rate. Organs such as bald head, skin of neck and interior thigh region play greater important role in heat conversation (Marsha A. S., 1997).
Long-billed vultures spent most of their time in sunlight to gain solar radiation for preening, sunbathing, sun basking and drying wings. Thermoregulatory behaviour of long-billed vultures is generally seen in morning hours and warmer time of day in cloudy and winter season. They used to live in rocky hilly areas, old large trees and old historical monuments and they also use rocks, stones and old trees for sunbathing. The sunbathing behaviour of long-billed vulture included fully extension of both wings and keeping face against sunlight. Sunbathing behaviour is performed by young adults and juvenile. They kept open both the wings for more than a minute and this behaviour is repeated many times in a day.  (Table 1). Sunbathing time is influenced by various climatic conditions like-temperature, rainfall, humidity, wind velocity and sunshine period. The average time of thermoregulation of long-billed vulture was 679.60 second in winter season and 516.8 second during summer season ( Table 2, 3).

Pearson Correlation and Regression Analysis
A Pearson product moment co-relation was run to determine the relationship between difference in temperature and rainfall. There was a strong, negative correlation in temperature and rainfall, which is statically significant (r= -0.832, p= 0.01) ( Table-4); Temperature and thermoregulations time in winter season was negatively correlated and statically significant (r=-0.956, p=0.05)( Table-5). Pearson co-relationship in temperature and thermoregulation time in summer season was negatively co related and statically significant (r= -0.781, p = 0.05)( Table-6). The regression analysis between thermoregulation, temperature and rainfall during study period, it was observed that difference in temperature increase statically significant of β= 3.74 decrease in rainfall, p=0.02.

Regression Analysis of Different Variables
Regression analysis between another variables like winter season temperature and humidity were observed and found no significant increase β= 0.248 times in humidity was observed, p= 0.676. The regression analysis between difference in winter season temperature and wind velocity were observed and found that difference in temperature increase statically non-significant effects of β= 0.007 times in wind velocity observed, p= 0.945. The regression analysis between the temperature and thermoregulation time in winter season; it is observed that as difference in temperature increase statically non significant decrease β= 13.737 time in thermoregulation time is winter season is observed, p= 0.124.
The regression analysis between difference in summer season temperature and humidity, it is observed no significantly effect of β= 0.0777 in humidity was observed, p= 0.922. The regression analysis in temperature and wind velocity were observed that as difference in temperature increase statically significant decrease of β=-0.435 in wind velocity (kmph) was observed, p=0.001). The regression analysis in between the temperature and thermoregulation time in summer season; it is observed that as difference in temperature increase non statically significant increase β= 4.60 times in thermoregulation time in summer season is observed, p= 0.357).

Relationship Between Environmental Factors and Sunbathing Times
During study period we observed over all maximum average temperature was (36.66±6.02°C), minimum was (11. 53±7.45°C) and the average difference in temperature was (     Note -* = Correlation is significant at the 0.05 level (2 tailed); **= Correlation is significant at the 0.01 level (2 tailed).

Discussion
There was a significant difference in maximum sunbathing time recorded in winter season (680±95.65) seconds and minimum was recorded (516.07±68.60) seconds in summer season. Maximum sunbathing time was observed in winter, p<0.0001 (Table 7). Maximum sunbathing time was recorded in winter season due to low environmental temperature, high humidity and low wind velocity, this leads to increase thermoregulation time in long billed vulture during winter, but in summer season thermoregulation time decrease due to higher environment temperatures, high wind velocity and low humidity. Note -* = Correlation is significant at the 0.05 level (2 tailed); **= Correlation is significant at the 0.01 level (2 tailed). Note -* = Correlation is significant at the 0.05 level (2 tailed); **= Correlation is significant at the 0.01 level (2 tailed).  Acknowledgment I ( Narayan Lal Choudhary)as research scholar is extremely thankful to CSIR-UGC for financial support. We want to thanks Principal Govt Meera Girls college, Udaipur for providing us infra structure and facility needed to carried out our research work. We sincerely thankful for Dr Satish sharma for their valuable suggestions. Last but not least Dr Nadim chishty (Assoc Professor) acknowledges to Commissionerate of College education-Jaipur Rajasthan for encouragement to do research work.

Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.