Nesting habitats and nesting success of Hill Mynahs Gracula religiosa in Thailand

Abstract

Nesting habitats of Hill Mynah Gracula religiosa were studied in order to gain a perspective of habitat features which were favoured by natural selection. A total of 76 nest trees and 310 neighbour trees of northern Hill Mynah (G. r. intermedia) and 25 nest trees and 136 neighbour trees of southern Hill Mynah (G. r. religiosa) were studied in eight provinces of Thailand between 6° and 20°N from 1991 to 1999. Nest characteristics including nest height, nest size, nest depth, cavity entrance, angle of nest cavity and cavity entrance were recorded. The characters of nest trees, including condition types, the height, canopy and trunk were studied. Habitat characteristics were measured within a square plot of 20x20 m around nest trees. Number and the characters of neighbour trees around each nest tree, distance from nest trees to the nearest neighbour trees were recorded. The results showed that Hill Mynah nest trees were taller, bigger and had thicker canopies than their neighbour trees. Their nests were higher and farther from the tree boles in dense canopies. Nest trees were live and solitary in the areas with foliage cover. Habitats of successful nests were different from unsuccessful ones in the term of higher first branches, bigger canopies, more surrounding trees and farther from neighbour trees. Although the natural selection successfully shapes the form of Hill Mynah nesting habitats to avoid natural predators and unfavourable climates, heavy human interference is the major cause of nesting failure in this species. © 2006 Academic Journals Inc.