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  1. Abstract

    Hummingbirds utilize visual cues to locate flowers, but little is known about the role olfaction plays in nectar foraging despite observations that hummingbirds avoid resources occupied by certain insects. We investigated the behavioral responses of both wild and captive hummingbirds to olfactory cues of hymenopteran floral visitors, including native wood ants (Formica francoeuri), invasive Argentine ants (Linepithema humile), and European honeybees (Apis mellifera). We demonstrate for the first time that hummingbirds use olfaction to make foraging decisions when presented with insect-derived chemical cues under field and aviary conditions. Both wild and captive hummingbirds avoided foraging on feeders with defensive chemicals ofF. francoeuriand aggregation pheromones ofL. humile, but showed no response to honeybee cuticular hydrocarbons. Our experiments demonstrate the importance of olfaction in shaping hummingbird foraging decisions.

    Significance statement

    Recent reviews reveal that avian olfaction is not just limited to vultures and a few taxa. We demonstrate that a very charismatic group, hummingbirds, avoid defensive and aggregatory chemical cues from insects present at nectar resources. Olfactory cues can provide critical information about the presence and potential threat of insect floral visitors. This study raises new questions about the underrated importance of olfaction in avian foraging and specifically, hummingbird foraging.

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  2. 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. 
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