Seasonal Change in Social Structure, Behaviour and Habitat Use by Sarus Crane in the Semi Arid Region of North-Western India

Abstract

The seasonal change in social structure and habitat use by sarus cranes was examined in the semi arid region of North- western India. The study was conducted in Keoladeo Ghana National Park and in the surrounding areas in Bharatpur district of Rajasthan. The methods involved censusing of cranes in the park and in surrounding areas by moving on motorcycle in preidentified routes. The detailed methodology included quantification of habitat availability and focal and scan sampling for studying the behaviour of sarus crane. Eight sarus groups were intensively monitored to examine parent and juvenile relationships and juvenile weaning process. The mean encounter rate of sarus crane outside the park was greater than that of inside. Though the data was not tested for the lack of uniform effort in these two areas, the difference is likely to be statistically significant. The overall group composition during the study period differed inside and outside of the park. The agricultural areas outside had greater number of social family group sighted during the study period than within the park. The mean encounter rates had greater standard errors associated with them outside the park than inside the park. During the present study most of the social family, pair, congregation, and solitary crane were seen outside of the park except that of pair with juvenile. The seasons (winter and summer) had an influence on the sarus crane group composition apart from the fact that the groups were either seen within the protected area or outside. With the data from the present study it is not possible to test the effects of these two variables on the sarus group composition. However, in winter sarus cranes were seen in social family and pair with juvenile more often inside the park than outside the park. The other forms of groups of sarus such as social group, pair and solitary members were not very different inside and outside the park. In winter season, juveniles were not able to fly more than 0.61 m height and 45m distances restricting their movements within the park. During summer the juveniles could fly outside of the park in the 1st week of February onwards and were seen frequently outside of the park. Sarus cranes spent more time outside the park than inside, except pairs with juveniles. Inside the park the safety, food and space supported small groups and pairs all through the year. The group composition showed a dramatic change in summer where greater number of social family and pair with juveniles were observed outside the park than inside, while other forms of groups did not vary much in the two areas. During the study period a maximum of 67 sarus cranes were recorded inside the park in roosting areas. During the study period, wetlands were the most used habitat by sarus cranes than any other habitat types. Grasslands and dry wetlands were used distinctly by sarus next to the wetlands, and the agricultural fields have the least utilization. The later could be because of bias in sampling more inside the park than in the agricultural fields outside the park. During summer, the sarus cranes occurred more often in wetland and grasslands than in dry wetland or agricultural fields. During winter and summer sarus cranes mostly used wetland habitat (winter 20.5 % & summer 35%). In late summer, as all agriculture field were harvested and there was no water patches outside the park. The Forest Department pumped in water throughout the late winter and summer in the areas where group no (Block L), group no.4 (Block D) and group no.5 (Block E) spent more of their time. During summer, sarus cranes used this shallow water. The area where group no.3 (Block K) sarus stayed much of the time had very large grasslands. Within this area the wetland was closer to road and sarus crane appeared to be stressed while foraging in this wetland. The large expanse of grasslands used by group no. 3 (Block K) area, it prevented people to approach closer to the cranes and hence they used this grassland extensively during summer. Among the pair, the female was more the wary and cautious while using these water patches. Solitary sarus cranes preferred foraging in grasslands. In summer, water spread became small and narrow and sarus cranes spent more time in grasslands (winter 5% & summer 12%). Sarus crane did not use dry wetlands in summer due to lack of moisture in this area which, hinders growth of grasses and other aquatic flora and also insects in such dry wetlands were less. Generally, sarus crane used agriculture land more for foraging at the time of sowing and harvesting of cereal and pulses. The encounter rates (sightings/ hour) of sarus crane correlated with water level. During large water spread times, more cranes were encountered. Water depth was correlated with mean encounter rates (r= 0.77, N= 1 Z) , similarly water spread also had a significant positive correlation (r=0.64, N= 12). As expected water depth and water spread had a strong positive correlation (r=0.95, N= 12). At the beginning of the study in November the juveniles were estimated to be three months old, and when the study was concluded in May, the juveniles were nine months old and they continued to remain in the vicinity of the parents. Although the distance increased with time it is speculated that the quantum of time spent by the adults parenting the juvenile would diminish with time and also the distance between parents and juveniles. The major interaction between parent and juvenile during the observation period was "nursing" behaviour, where the parent fed the juvenile directly into its mouth. Subsequently, the parent "induced the juvenile to forage" by leading the juvenile to some areas in the wetland where food was abundant and the disturbance from tourists was low. From the last week of February juvenile started to move farther away from the parents and maintained an average distance of about 65 m. During this time the parents started courtship behaviour and paid less attention to the juveniles, even though the juveniles showed interest on their parents. In reciprocation of the lack of attention from the parents the juveniles continued to forage away from the parents. Till the end of the study period in May the juvenile still continued to tag along with the parents. To summarize, seasonal shift in sarus crane social structure was observed in the study area. Following factors appear to affect the sarus crane group structure and behaviour: (a) Availability and limitation of food.(b) Changes and availability of water in wetland. (c) Age of juveniles appears to be a factor for their attachment to parents.(d) The diurnal weather appears to be relative to sarus crane behaviour and social structure,which change on cloudy, sunny and rainy days .