Avian insectivores of the tropical rainforest understory (“understory insectivores”) are common, diverse, and often sensitive to disturbance of tropical forest, making them useful as sentinels of rainforest ecosystem change. At the 2013 joint American Ornithologists’ Union and Cooper Ornithological Society meeting in Chicago, USA, researchers convened a symposium to address the ecology and conservation of understory insectivores. This Special Issue of Biological Conservation is the result of that symposium: a collection of articles that unites our efforts to further understand and conserve understory insectivores. In this introductory paper, we review the diversity and ecology of understory insectivores, identify threats to the guild, discuss hypotheses on drivers of population declines, and make suggestions for future research. Deforestation and forest degradation are the immediate threats to this guild, with agricultural expansion (particularly oil palm plantations), urbanization, road expansion and logging leading the list. Although vulnerabilities of this guild are most evident in the Neotropics, there are few studies from Asia and fewer still from Africa—we recommend increased geographic coverage. If we are to understand the vulnerabilities of understory insectivores from a pantropical perspective, researchers should prioritize understanding the most serious threats (e.g., edge effects, deforestation, fragmentation, etc.) and standardize efforts to gauge understory insectivores’ response to these threats (e.g., via species richness, abundance, demographic metrics). A coordinated approach by researchers working in tropical rainforests across the globe can help us understand the ecology of understory insectivores and meaningfully apply conservation and management actions.
