Composition of mix species foraging flocks of birds in Riverstan of montane region, Sri Lanka

Abstract

Mixed-species flocks (MSF) are an important form of the social organization of birds throughout the world, particularly in the forested tropics. Montane zone flock system is distinct from that of low land wet zone of Sri Lanka, although some species are present in both systems. The present study identified the mixed species flocks of birds in Riverstan at Knuckles Region, Sri Lanka. Monthly transect counts and opportunistic observations were made between January to May, 2012. Data were analyzed using MINITAB (version 16).

A total of 72 flocks and 27 bird species were uncounted at Riverstan during the study period. The flock size vary between 2-13 species and 4-58 individuals and six species per flock had high percentage and high percentage of individuals per flocks consisted of 11-20. The number of bird species that contributed to the flocks at Riverstan range from 2 to 26. The mean number of species per flock was 6.03 ± 2.25 and the mean number of individuals in a flock was 4.77± 1.59. The flock size was positively correlated with the number of species present at Riverstan (r = 0.756, P <0.05 ). Grey-headed Canary Flycatcher (Culicicapa ceylonensis) was the most abundant species (mean 2.68±1.02 birds per flocks) encountered with 169 individuals and 63 flocks while Sri Lanka White eye (Zosterops ceylonensis) was the most frequent species (mean 5.69±3.92 birds per flocks) encountered with 269 individuals and 52 flocks encountered, among 1472 individuals encountered in 78 flocks observed at Riverstan. Grey-headed Canary Flycatcher and Sri Lanka Scimittar Babbler (Pomatorhinus horsfieldii) were the nuclear species in Riverstan and Sri Lanka Scimittar Babbler form small MSF and they form flocks when absent Gray Headed Canary Flycatcher. The leading species were Sri Lanka white eye (Zosterops ceylonensis) and Sri Lanka Yellow- eared Bulbul (Pycnonotus penicillatus) at Riverstan Different bird species used different heights within flocks. According to the associations of Foraging heights there were mainly two clusters at Riverstan. MSF at Riverstan represented resident, endemic and migrant bird species and their mostly preferred fruiting trees were Eurya nitida, Ilex knucklesensis, Eleocarpus glandulifer . Present study indicated that they were being effected due to fragmentation, visitor entrance and forest fires at Knuckles region