Differing effects of isolation on evolution of bird songs: examples from an island-mainland comparison of three species

The present study investigated the effects of island isolation on songs of three species of Australian songbirds. The characteristics of songs recorded from mainland locations were compared with those recorded on Rottnest Island off the coast of Western Australia. In all three species, the characteristics of the island song patterns differed from those on the mainland. Each species exhibited a different kind of divergence on the island, including (1) differences in the structure of individual notes and syllables constituting songs; (2) differences in temporal patterns of song delivery; and (3) differences in the order of notes within songs. In two species, the island songs were less complex than mainland songs and this may be the consequence of a founder effect. In the third species, island songs were more elaborate and diverse, and this may be the consequence of sexual selection, although other explanations are plausible. For several of these populations, quantitative comparisons were made between samples collected 6–7 years apart. In two species, new recordings made in 2004 were compared with those made in 1998 and, in one species, recordings made in 1991 were compared with those made in 1998. For the nine comparisons available, similarity scores across years did not change significantly; thus, there was no evidence of systematic divergence with time.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 331–342.     

Mixed-species flocking of forest birds on Little Barrier Island

Abstract

Three aspects of mixed-species flocking of forest birds on Little Barrier Island were investigated. Whiteheads, fantails, parakeets, and grey warblers occurred more often in flocks than in “non-flocking” situations. Whiteheads were the main lead species, although parakeets formed groups within flocks and occasionally appeared to lead. Whitehead clumps defined the flock centre; only fantails were found commonly in the centre with whiteheads. Birds other than whiteheads generally orientated below or to the side of their nearest neighbours. We suggest that mixed-species flocking is a significant factor influencing the structure of forest bird communities in New Zealand during winter.