Most research on the variables that allow for introduced species to succeed and become invasive has focused on environmental and ecological factors. Fewer studies have assessed the roles of behavioral and cognitive traits. To help fill this knowledge gap, we studied neophobia, aversive behavior towards novelty, in the non-native Eurasian tree sparrow (Passer montanus), and compared results to previous work in a more successful invasive congener, the house sparrow (Passer domesticus). We assessed the neophobia of wild-caught Eurasian tree sparrows by measuring their responses to novel objects and novel foods and their ability to habituate to initially novel objects. We predicted that Eurasian tree sparrows, as less successful invaders, would overall be more neophobic than house sparrows. Although we did not observe differences in neophobia towards novel objects in the two species, Eurasian tree sparrows were significantly less willing than house sparrows to try novel foods. Eurasian tree sparrows were also slower to habituate to repeated presentations of the same initially novel object compared to house sparrows. Multiple factors certainly influence invasion success, but our results suggest that neophobia might limit the success of an introduced species in novel environments.

We captured wild Eurasian tree sparrows (Passer montanus) from a private field site in Illinois, United States. Sparrows were transported to Louisiana State University where we conducted neophobia trials. These behavioral assays consisted of three weeklong trials to assess responses to novel objects (week 1) and foods (week 2) as well as the sparrows' abilities to habituate to repeated presentations of the same initially novel object (week 3). We followed methods used in Kimball et al. 2022 (Novel objects alter immediate early gene expression globally for ZENK and regionally for c-fos in neophobic and non-neophobic house sparrows, published in Behavioural Brain Research). Behavioral trials were recorded, and then the recordings were watched by two observers (KJK and EBC). Video watchers noted the time during the hour-long trials at which each sparrow approached and fed from the food dish, where novel objects or foods were placed. Because male and female Eurasian tree sparrows cannot be distinguished by plumage characteristics, we determined the sex of each sparrow by examining gonads in the body cavity after the birds were euthanized after behavioral trials. 

We compared the Eurasian tree sparrows' behavioral responses to those of house sparrows (Passer domesticus) collected in a previous study (Kimball et al. 2022). Again, house sparrow data were collected using the same methods. The manuscript and its associated dataset for the house sparrow study can be accessed here: https://doi.org/10.1016/j.bbr.2022.113863. 

For more details on our methods, please read the associated manuscript.