Occupancy Pattern and Food-Niche Partitioning Among Sympatric Kingfishers in Bhitarkanika Mangroves, Orissa

Abstract

Eight species of kingfishers, Common, Collared, White-throated, Pied, Stork-billed, Black-capped, Brown-winged and Rudy, - coexist in the mangrove forests of Bhitarkanika along the east coast of India. Sympatric species with similar resource requirements need to have niche partitioning as a strategy to avoid competition in order to coexist together. To understand the mechanisms underlying such species coexistence, it is vital to know about the food requirements, foraging habitat preference, and how the resources are shared between these sympatric species. The present study attempted to understand the potential mechanisms that might play a role in food-niche differentiation and examined the occupancy patterns of four sympatric kingfishers i.e. Common, Collared, Black-capped and Brown-winged kingfisher in Bhitarkanika mangroves. I conducted field study from January to May, 2011 in Bhitarkanika mangroves. The creeks were catgorized as primary, secondary and tertiary creeks based on the branching pattern. A total of 16, one km trails were selected in the intensive study area. Each 1 km trail was further divided into 10, 100 m segments for Sub-sampling. During the survey only seven among the 10 segments of each 1 km trail were surveyed which were selected randomly with replacement. A total of 160 creek segments of 100 m length were surveyed for six times during the study period and relevant habitat variables were recorded. For foraging behaviour observation, point count method was used i.e., an individual bird was followed till it captured a prey and relevant foraging variables were recorded. A total of 53 independent prey captures were recorded for the four species of kingfishers. Focal animal sampling method was used and observations were made opportunistically for time budget observation. Detection histories were constructed for each segment for bird survey and all relevant covariates. The two model parameters i.e., the probability that a segment is occupied by the species ('I') and the detection probability (P) were estimated and analysed in the occupancy framework. For foraging behaviour and time budget analysis, different parametric and nonparametric tests were used. Occupancy analysis confined that Collared and Black-capped Kingfisher occur seasonally in Bhitarkanika mangroves; Collared being more abundant in summer and Black-capped in winter. For all the four sympatric species river/creek width had a negative association with detection probability. Habitat type also affected the detection probability of all the species except Collared Kingfisher. The detection probability of Common and Black-capped Kingfisher decreased with the increase in depth whereas it did not affect the detection probability of Collared and Brown-winged Kingfishers. Water current and turbidity were negatively associated with the occupancy of Common and Brown-winged Kingfisher. However for Collared and Black-capped Kingfisher, it differed with vegetation layer. Perch height and foraging distance differed significantly among the four species of kingfishers. All the prey characteristics i.e., prey type, prey size and foraging substrate differed significantly among the four species of kingfishers. This study reveals that each of the four species of kingfishers in Bhitarkanika mangroves occupy foraging niches corresponding to their respective body sizes. The occupancy pattern and foraging behaviour of the smallest species, i.e., Common Kingfisher and the largest species, i.e., Brown-winged Kingfisher is more similar. As, both mostly forage in water to catch fish, their occupancy is also determined by water current. They segregate in terms of prey size, which is reflected by the respective body sizes. On the other hand, the foraging behaviour of Collared and Blackcapped Kingfisher is similar in terms of prey characteristics.