Abstract:
Tree cavities play a critical role in the life history of cavity-using species and thus are an
important structural feature of forests. This is the first study to address cavity resources in
tropical montane cloud forests in Sri Lanka. Therefore, nest-site availability of cavity nesting
bird species was studied at the Montane Cloud Forests of Horton Plains, situated in the highland
plateau of the Nuwara Eliya district. Study was conducted from September 2016 to May 2018.
Two habitats were selected as Cloud Forest (CF) and Cloud Forest Die-back (CFD). Line
transect method was used. All cavities were recorded and locations were marked using GPS
device. Cavity nests were located by searching the vegetation along transects. Tree species, nest
cavity height, diameter at breast height (DBH) were measured. Greater flameback
(Chrysocolaptes iucidus), Red-backed wood peacker (Dinopium benghalense psarodes) and
Lesser yellownape (Celeus brachyurus jerdonii), provided different sizes of nest cavities for a
suite of non-excavator species like Dull-blue flycatcher (Eumyias sordidus), Velvet-fronted
nuthatch (Sitta frontalis), Sri Lanka yellow-fronted barbet (Megalaima flavifrons). Total of 654
tree cavities were located. Live trees and snags with DBH>45 cm were favored as nest sites by
all species. This study indicates that cavities are an uncommon feature even in pristine habitats
with only 4.5% of the trees harboring cavities in both habitat types. Even more uncommon are
potentially usable cavities for avian cavity nesters. Only 2.98% of the trees have a potentially
usable cavity in the CF and only 1.42% in the CFD. In CFD there is a significantly lower density
of potentially usable cavities (2.8 cavities/ha in CF and 1.1 cavities/ha in CFD). More
specifically, in the CFD, large, decaying Rhododendron arboreum have a relatively greater
probability of having potentially usable cavities, while in the cloud forest potentially usable
cavities are disproportionably found in large, decaying Cinnamomum ovalifolium. Neolitsea
fuscata, Glochidion pycnocarpum were the other possible species with cavities. In both habitats,
snags are also very likely to harbor a potentially usable cavity. In order for habitats of the
montane region and some of their ecological value, it is necessary to protect the trees with
highest probability of becoming usable cavity trees. CFD habitats were much more extensive
than CF habitats, but birds strongly preferred CF as nesting habitats, presumably due to the
availability of nesting sites. Since the cloud forests of Sri Lanka are under various threats and
specifically since the cloud forest of the Horton Plains are susceptible to forest die back every
action should be taken to preserve the cloud forests as they present the last habitat for most
montane avifauna throughout the island.
