No threats to my kids – Fascinating nesting behavior of Sri Lanka Crested Drongo

Sri Lanka Crested Drongo is an endemic, unique species which is restricted to the wet zone of Sri Lanka. They are distinguished from the other Drongos in the area by their prominent crest and long tail feathers. They were previously thought to be a race of the Greater Racket-tailed Drongo that lives in the dry zone. It is usually found in pairs, and sometimes in mixed flocks, in the understory of humid forests in Sri Lanka’s lowlands and foothills. They are a “nuclear” member of the feeding flocks of mixed species. They stand out in forest habitats by frequently perching in the open and attracting attention with a variety of loud calls that include perfect imitations of many other birds.

This article focused on the fascinating nesting behavior of this species. Predation pressure has affected the development of various nest designs and nest placement in birds, as well as related life-history traits. The species nests on generally isolated trees in forest openings, and it returns to the same host tree annually. The nest and nestlings are fiercely protected by the parents. Canopy contact and an abundance of vines are recognized as important factors that facilitate snake predation, and such conditions are likely to allow access by nocturnal arboreal mammalian predators such as civets and rodents.

The stripping and cleaning behavior of the Sri Lanka Crested Drongo were observed primarily during the breeding season. The nest is made of moss and lichens and is built on an open branch. The drongo pair at the nest is constantly tearing and stripping leaves from both the host and adjacent trees, as well as removing loose bark and epiphytes from the trunks of the host trees. These host trees’ canopies did not touch those of neighboring trees and were devoid of creepers and lianas. As a result, the main trunk was the only point of contact between the host tree canopies and the ground or undergrowth vegetation. Drongos used their bills to strip leaves from small branches of the host and neighboring trees.
Small leaves were broken off their stems, and larger leaves were ripped off in pieces. Young shoots and buds were chewed and destroyed. The broken or torn leaves were not collected, but were left to fall. This leaf-stripping occurred only on peripheral branches where the canopies of the host tree and an adjacent tree came into contact or were in close proximity. As a result, either the host tree or the adjacent tree’s foliage was damaged. Leaf-stripping was observed throughout the host tree, not just near the nest. Emerging shoots and undergrowth branches that grew towards the exposed main trunk or lower branches of the host tree were equally damaged.
Drongos used their bills to remove mosses and lichens from host tree trunks and to break off loose bark. This activity was performed on the host tree’s main trunk between the points where it emerged from the undergrowth and where the first branching occurred. The birds pecked and scraped at the trunk while hovering for a few seconds. A bird would perch vertically on the trunk, splaying its tail for support, and clean the trunk for up to three minutes at a time. In general, the female drongo was more active than the male, who only outperformed her in trunk-cleaning activities toward the end of the incubation stage. The morning and evening hours were the busiest for stripping and cleaning.
 
All of these changes make it more difficult for snakes and small mammalian predators like macaques and civets to jump across to the host tree. The canopy distance between the host tree and adjacent trees appeared to be just out of their jumping range. They even swarmed humans who approached the host tree after the eggs were laid. During such mobbing, they frequently used raptor and toque macaque alarm mimicry.
Reference
RAJEEV, M., VIDANAPATHIRANA, D., WICKRAMASINGHE, L. and BENARAGAMA, B., 2018. Host tree canopy isolation by nesting Sri Lanka Drongo Dicrurus lophorinus. FORKTAIL, pp.52-57.
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