Background: Ixodid ticks are widely studied due to their epidemiological and epizootic importance. It is of great value to know vertebrate host preferences of ticks in order to understand their ecological relationships and distribution. Earlier studies report birds as important hosts of Ixodid tick and a total of 136 ticks species have been frequently found in birds worldwide. However, only few studies related to host preferences of ticks among wild birds in Bulgaria were conducted till now. Aim: To obtain new data on the host preferences of ixodid ticks among wild birds at three locations in Bulgaria. Material and methods: The study was conducted between 2010 – 2020 in three sites in Bulgaria – Biological Experimental Station Kalimok (Silistra region), near Brodilovo village (Burgas region), and the city of Sofia (city park). The birds were caught by mist nets and inspected for ticks. Ticks found were removed by fine tweezers or a special removal tool for ectoparasites. Tick identification was based on external morphological characteristics. Results: A total of 2419 individual birds belonging to 78 species were examined. Of these, 70 individuals (16 species) carried ticks, thus representing 2.9% infestation rate. A total of 262 ticks were collected and identified as: Ixodes ricinus, Hyalomma marginatum, Haemaphysalis punctata, Hae. concinna, Hae. sulcata and two specimens could only be identified to the genus Haemaphysalis. Ixodes ricinus was the most commonly encountered tick (224/262), predominantly nymphs, followed by Hyalomma marginatum (27/262). The highest prevalence of tick infestation was observed among the Eurasian Blackbird, Turdus merula (28.6%), followed by the common nightingale, Luscinia megarhynchos (12.9%) and the common chaffinch, Fringilla coelebs (11.3%). These three bird species harboured the majority of ticks on their heads – some single individuals were infested by 10 up to 25 ticks per bird. Conclusion: Ixodes ricinus was found as the predominant tick species in this study. Nymphs were the most frequently observed stage. Infesting both birds and humans, this tick species has the potential to spread local tick-borne infections.

During the vast distances in migration, sometimes through thousands of kilometers, the birds carry ticks very far away from their nesting sites. Up to this moment 136 species of hard ticks Ixodidae have been frequently found on birds. Larvae, nymphs and adults of 25 species of the genus Ixodes, parasitize on birds. By transporting of ticks infected with B. burgdorferi s.l., the birds introduce the infection indirectly to new geographical regions. Once imported, the spirochetes may adapt to the local ecological areas and reservoir hosts. Migratory birds which carry Borrelia spp. in their tissues or blood, are able to infect the ticks in the new area. This determines the reservoir competence of the birds and their participation in the ecology and the epidemiology of the Lyme disease. The selective transmission of Borrelia garinii from birds to ticks is detected; as well that migratory birds are able to carry Lyme disease as a latent infection for several months.