Behavioral and morphological evidence of an Allen's × Rufous hummingbird (Selasphorus sasin × S. rufus) hybrid zone in southern Oregon and northern California

Abstract

Allen's (Selasphorus sasin) and Rufous (S. rufus) hummingbird have long been suspected to hybridize, and potentially form a hybrid zone where their ranges overlap in southern Oregon. Migratory Allen's Hummingbird (S. s. sasin) breeds along a narrow strip of the California coast up to the Oregon border, while Rufous Hummingbird breeds from southern Oregon to Alaska. Analysis of behavioral and morphological data for 183 males and morphological data from 138 females showed that Allen's and Rufous hummingbird form a hybrid zone in southern Oregon and northern California. Linear discriminant function analysis and cline analysis of 20 phenotypic characters for males and 9 phenotypic characters for females suggested the center of the coastal transect of this north-south hybrid zone spanned from Bandon, Oregon (Coos County), to Port Orford, Oregon (Curry County). The contact zone extended north into the breeding range of Rufous (into Florence, Lane County, Oregon) and south into the range of Allen's (into Arcata, Humboldt County, California). Sporadic inland sampling suggested the hybrid zone extended at least 94 km inland from the coast. Behavioral data included courtship displays, which were composed of discrete, modular, behavioral elements. Sexual selection acted on these courtship displays, as behavioral clines related to courtship behaviors were more narrow than morphological clines. Some of the courtship behaviors analyzed included previously undescribed diagnostic behavioral characters for Allen's and Rufous hummingbird.