Multiple factors cause species endangerment. However, the species endangerment listing process is not solely governed by causal factors, but also by human perception. Because human perception is important in species detection, we hypothesized that four indicators related to human perception, body mass, geographic range, animal calling, and animal congregating behavior would observably change over time. Specifically, we predicted a negative correlation would exist between these indicators and time of species listing as threatened or endangered as defined by the U.S. Endangered Species Act. We tested our hypothesis on species listed from 1967-2018 and included taxonomy and Hawaii/Continental US as covariates.
Results/Conclusions
In general, body mass and geographic range of listed species decreased over time, however different trends emerged when considering taxonomic groups and island/mainland context. Birds, mammals, and reptiles exhibited negative relationships with body mass, whereas amphibians had a positive relationship. Likewise, insects, mammals, and plants exhibited negative relationships with geographic range, with amphibians, birds, and fish showing a slight increase. Animals that called and exhibited grouping behavior were listed earlier than silent and solitary animals. Our results demonstrate a temporal shift from listing larger-bodied, more cosmopolitan species towards smaller-bodied, more local species and vocal and social animals to quiet and solitary animals. The one outlier group, amphibians, demonstrated an opposite relationship that may be due to increased attention focused on the rapid decline of this group across the US. These trends suggest human perception affects species listing, which should be considered in the species being considered for listing.