BackgroundInternational wildlife trade is the largest emerging source of vertebrate invasive alien species. In order to prevent invasions, it is essential to understand the mechanics of trade and, in particular, which traded species are most likely to be released or escape into the wild. A species’ economic value is a key factor, because we expect cheaper species to be less assiduously secured against escaping, and more likely to be deliberately released. Here, we investigate determinants of the price of species in the Taiwanese bird trade. Taiwan is an international hub for bird trade, and several native species are threatened by alien bird species.MethodologyWe investigated the relationship between the traded species sale price in Taiwan and the species availability for trade (the number of birds for sale, geographic range size and their origin, conservation and CITES status) and traits (body size, coloration, song attractiveness). We used phylogenetic generalized least squares models, with multi-model inference, to assess the variables that are best related to the price of birds in the Taiwanese pet trade.Principal Findings / ConclusionsWe found that species available for sale in larger numbers, native to Taiwan, not globally endangered, and small-bodied are all relatively cheaper, as too are species lacking yellow coloration and without attractive songs. Our models of price revealed high levels of phylogenetic correlation, and hence that closely related species tended to be sold for similar prices. We suggest that, on the basis of price, native species are more likely to be deliberately or accidentally released than alien species. Nevertheless, our survey of bird shops recorded 160 species alien to Taiwan (7,631 individuals), several of which are for sale cheaply and in large numbers. Alien bird species in trade therefore present an ongoing, non-trivial invasion risk on the island.

The invasion pathway is composed of a sequential series of stages that need to be quantified separately in order properly to understand the invasion process. Here, we examine the composition and characteristics of bird species being sold in the pet bird market in Taiwan. The bird trade in Taiwan is of high volume and financially lucrative. The identity of species in this trade is vital for informing later stages (introduction, establishment, spread) of the invasion pathway. We conducted interviews and surveys of 72 outlets selling pet birds from seven cities across Taiwan, from which we identified 247 bird species (within 34 families) for sale. Of these, 170 bird species (from 27 families) are exotic to Taiwan. Using randomization tests, we show that nine families are significantly over-represented in the pet trade (Psittacidae, Muscicapidae, Timaliidae, Sturnidae, Turdidae, Estrildidae, Chloropseidae, Zosteropidae and Fringillidae), and three after sequential Bonferroni correction (Psittacidae, Muscicapidae and Sturnidae). Species that have been identified in Taiwanese pet shops tend to have a larger native geographic range, originate further from the equator, are smaller-bodied, and have more aesthetically-pleasing songs than expected by chance. The native ranges of pet shop species are more likely to be situated in the Indo-Malay and Palearctic biogeographic realms, while fewer species than expected derive from the Neotropic, Afrotropic and Nearctic realms. Our results show that bird species for sale in Taiwan are determined by the interaction of species availability and societal demands.