Ecomorphological relationships and invasion history of non‐native terrestrial bird species on O‘ahu, Hawai‘i, suggest ecological fitting during novel community assembly

The widespread introduction of species has created novel communities in many areas of the world. Since introduced species tend to have generalized ecologies and often lack shared evolutionary history with other species in their communities, it would be expected that the relationship between form and function (i.e., ecomorphology) may change in novel communities. We tested this expectation in a subset of the novel bird community on O‘ahu, Hawai‘i. By relating foraging behavior observations to morphology obtained from live birds at four sites across the island, we found many relationships between species’ morphology and foraging ecology that mirrored relationships found in the literature for native‐dominated bird communities. Both movement and certain foraging behaviors were related to a species’ tarsus‐to‐wing ratio. Further, bill morphology was related to gleaning, frugivory, and flycatching behaviors. The commonness of significant ecomorphological relationships suggests that, within O‘ahu's novel bird community, form is strongly related to function. We hypothesize that ecological fitting likely played a major role in the assembly of this novel community conserving the relationships between form and function found in many other bird communities. To further support this hypothesis, we used niche data from EltonTraits 1.0 to determine whether the establishment of bird species introduced to O‘ahu was related to the distinctiveness of their ecological niche from the incumbent community. Introduced species were more likely to establish on O‘ahu if their diets were less similar to the bird species already present on the island. Our results support the idea that ecological fitting is an important mechanism in shaping ecological communities, especially in the Anthropocene, thereby influencing novel community assembly and functioning.