Sensitivity of Tropical Insectivorous Birds to the Anthropocene: A Review of Multiple Mechanisms and Conservation Implications

Epigraph: “The house is burning. We do not need a thermometer. fire hose.” (P. 102, Janzen and Hallwachs, 2019 ). Insectivorous birds are declining widely, for diverse reasons. Tropical insectivorous birds, more than 60% of all tropical particularly sensitive to human disturbances including habitat loss fragmentation, intensive agriculture pesticide use, climate change; the mechanisms incompletely understood. This review addresses multiple, complementary sometimes synergistic explanations insectivore declines, by categorizing into ultimate vs. proximate, direct versus indirect. Ultimate Anthropocene activities evolutionary history these birds. history, synthesized Biotic Challenge Hypothesis (BCH), explains birds' vulnerabilities many proximate threats as function both feeding specialization poor dispersal capacity. These traits were favored evolutionarily diversity clades competing intensely prey co-evolution with arthropods over long time periods. More ecological include bottom-up forces like insect populations, top-down meso-predator increases, plus underlying factors, especially agricultural intensification, change. All conditions peak in lowland, mainland Neotropics, where bird declines have been repeatedly documented, but also occur other locales continents. multiplicity interacting factors informs conservation implications recommendations birds: (1) Why they so global change phenomena no longer enigmatic, (2) distinguishing stressors matters, (3) life-histories predispose be Anthropocene, (4) regions continents vary respect sensitivity, (5) biodiversity concepts stronger incorporation species' histories, (6) protecting will require more, larger reserves multiple reasons, (7) greater value generally recognized.