Human perception relates to when endangered species are listed

The species endangerment listing process is governed not solely by causal factors but also by human perception, particularly as it relates to observability. Because human perception is important in species detection, we hypothesized that ecological indicators associated with human perception would change noticeably over time. Testing our hypothesis on species listed under the US Endangered Species Act, we found that - in general and across (not within) different taxa - body mass and geographic range of listed species decreased over time and that animals that produced vocalizations and exhibited grouping behavior were listed earlier than silent and solitary animals. Specifically, since the year of their listing, the body mass of birds, mammals, and reptiles decreased, whereas the body mass of amphibians increased; likewise, the geographic range of insects, mammals, and plants contracted, whereas the geographic range of amphibians, bivalves, birds, and fish slightly expanded. Our results demonstrate a temporal shift in endangered species listings, suggesting that approaches to listing species may need to be reevaluated and methodologically revised.