Defaunation and extinction undermine the resilience and functioning of ecological communities and ecosystems. Relative to other disturbances, overexploitation for the global wildlife trade presents a unique case of trait-based selection, as demand for specific individuals is often tied to unique morphological or aesthetic traits desired by consumers (“market traits”). Because evolutionary history leads to species that share both market and functional traits, we posit that non-random patterns of exploitation will result in non-random loss of functional diversity. 
We applied a trait-based framework to the global songbird trade for 4616 species, 148 of which are plausibly threatened by the trade. We quantified select market traits, such as unique coloration and song quality, and ecological traits related to body size, diet, and foraging strategy to assess whether the trade disproportionately threatens particular functional groups. We additionally looked for patterns of association between market traits and functional traits to assess whether selection on certain market traits could drive selection on associated functional traits.
We found that overexploited birds are a distinct functional subset of the global songbird pool, with the trade disproportionately threatening large bodied, frugivorous, and seed eating birds. Across all songbirds, there were multiple non-random associations between market traits and functional traits, with the strongest associations observed among trade-threatened birds; this was consistent with our theory that consumer-driven selection on market traits could theoretically result in selection on functional traits. However, there was mixed evidence for this hypothesis at a global scale, suggesting that disproportionate threat to functional diversity may be more likely in regions where there is heavy demand for associated market traits. 
Policy Implications: Our results highlight the need for increased focus on the mechanistic drivers of trait-based selection on the consumer side of wildlife trade, and how patterns of overexploitation can systematically affect ecological communities and ecosystem services.