Abstract

Adaptive radiation represents one of the most compelling examples of evolutionary diversification, particularly evident in isolated island environments where ecological opportunity drives rapid speciation and niche partitioning. This study examines behavioral and morphological evolution in island avian species across three archipelagos : the Galápagos Islands, Hawaiian Islands, and Lesser Antilles. We analyzed morphometric data from 847 specimens representing 73 species across 12 genera, combined with behavioral observations totaling 2,340 hours of fieldwork. Phylogenetic analyses based on mitochondrial and nuclear DNA sequences revealed rapid diversification events occurring within 0.5-2.3 million years post-colonization. Morphological analysis demonstrated significant adaptive divergence in bill morphology, wing characteristics, and body size, with coefficients of variation 2.8-4.2 times higher than mainland relatives. Behavioral studies revealed novel foraging strategies, altered mating systems, and modified anti-predator behaviors. Principal component analysis identified three major axes of morphological diversification : feeding apparatus specialization (43.2% variance), locomotory adaptation (28.7% variance), and body size scaling (18.1% variance). Behavioral innovations included ground-foraging in typically arboreal lineages, cooperative breeding systems, and loss of flight in predator-free environments. Phylogenetic signal analysis indicated stronger behavioral lability compared to morphological traits, suggesting behavior acts as a precursor to morphological adaptation. These findings provide insights into the mechanisms driving adaptive radiation and highlight the importance of ecological release in promoting evolutionary diversification.