The lack of a role of body asymmetry in shaping tick load in European robins (Erithacus rubecula) during autumn migration

Data to reproduce the analysis performed in The lack of a role of body asymmetry in shaping tick load in European robins (Erithacus rubecula) during autumn migration currently in final review at Ibis.

Abstract:
Fluctuating asymmetry (FA) of the body, reflecting developmental instability, has been linked to fitness traits in birds. However, its potential role in shaping susceptibility to ectoparasitism remains largely unexplored. We investigated the relationship between FA in tarsus length and tick parasitism in European robins Erithacus rubecula during autumn migration on the Baltic Sea coast in northern Poland. We examined 198 robins for tick infestations. FA was quantified as the difference between lengths of the left and right tarsus. The prevalence of tick-infested birds was 49.5%, with ticks predominantly identified as Ixodes ricinus (98.5%). Negative binomial models revealed that migration period was the sole predictor of tick abundance, with early migrants carrying significantly more ticks than late migrants. We found no association between tarsus FA and either total tick load or body side-specific tick presence. Although our results are correlative, they suggest that moderate asymmetry in robin leg morphology may not influence susceptibility to ticks. However, this susceptibility might depend on the context, e.g., the condition, sex and age of birds, or their stopover length, which suggests directions for further research. Our results highlight the importance of seasonal factors in host-parasite dynamics.