Beware of hitchhiking ticks? Clarifying the variable roles of bird families in tick movement along migratory routes

Ticks are blood-feeding parasites which act as major vectors for various pathogenic microorganisms affecting both animal and human health. Hard ticks are known to “hitchhike” on migratory birds as they transit from breeding to overwintering grounds in spring and autumn, potentially leading to exchange and establishment of non-endemic tick species in novel environments. Even though, there is a lack of understanding of which migratory bird families play a role in movement of specific tick genera and what influence migratory season may have. To fill this knowledge gap, we performed a systematic literature review regarding primary data of ticks moving on migratory birds within the African-Western Palearctic flyways. In total, 34 studies were found which showed 123 bird species from 37 families connected to potential movement of 26 tick species representing six genera (Amblyomma, Dermacentor, Haemaphysalis, Hyalomma, Ixodes, Rhipicephalus). Statistical analysis showed bird families which carried above average number of ticks were only found for interactions with Hyalomma and Ixodes ticks with below average estimates found for all tick genera besides Rhipicephalus. Contrary to expectation, no tick genus, which was found in both migratory seasons, was estimated to have increased numbers in one season or the other. In certain cases, tick genera (e.g., Amblyomma) were only found on birds during spring migration. This pattern could highlight that the assemblage of ticks present on a bird at capture does not represent the ticks present at the point of migratory departure, highlighting an understudied importance of stopover sites to potential tick introduction or turnover. Taken together, the results presented here provide guiding information for further analysis into species specific interactions which will allow for the integration of individual level variation into understanding the risk of tick movement with migratory birds and potential for emergent disease. Data included here are the studies and the raw collected data in relation to the above mentioned project.