Sexual selection in the yellow-vented bulbul (Pycnonotus xanthopygos)

The Yellow-vented bulbul (Pycnonotus xanthopygos) is originally described from the Lebanon and found from the Arabian Peninsula to the Turkish Mediterranean region and its range is expected to expand further into northern Anatolia. Yellow-ventedbulbul is a territorial and socially monogamous passerine bird and pair bonds in this species persist throughout the breeding season, over the whole year or frequently through multiple years, which makes the choice of a reproductive partner important. On the other hand, particularly outside the breeding season, bulbuls flock in social units of about 5 to 50 individuals, suggesting that their social environment is important as well. The sexes of the species similarly ornamented and yellow under-tails are important in mate choice and social interactions. In this study, therefore, we examine sexual size dimorphism, mate and social choice, territory and pair fidelity and extra-pair paternity in yellow-vented bulbul. In this context, both field observations and experimental methods were used. The breeding population of the species were observed during 2013-2014 breeding season and pair were marked with aluminum and colored plastic rings to observe birds in the next breeding seasons. Furthermore, blood samples were taken from bıth adults and nestlings to determine extra pair paternity. Moreover, to understand the role and interaction of ornamentation and familiarity in mate choice and social choice in both male and female, experimental tests were performed for preferences for familiarity and/or experimentally manipulated ornaments in an aviary four-choice test. In this sense, four parameters (familiar increased yellow, unfamiliar increased yellow, familiar decreased yellow and unfamiliar decreased yellow) were used in the sexual and social choice experiments. While sexes of the of the species similarly ornamented, sexual size dimorphism in ten morphometric characters, except for bill characters, were detected. Males were heavier, longer and larger than females. Furthermore, it is found that yellow-vented bulbuls were assortatively mating by wing and tarsus length. These means that both sexes attempt to gain the best quality partner possible. We found that yellow-vented bulbuls are able to discriminate between familiar and unfamiliar conspecifics as well as variations in plumage colour intensity in this study. In the mate choice test, females preferred unfamiliar males with increased yellow. However, there were no significant differences in male preferences based on familiarity or intensity of patch colour. In the social choice test, females preferred to associate with familiar females. Males also preferred to associate with familiar males but also significantly preferred to associate with less ornamented males. The results suggest that ornamentation and familiarity are important features, playing different roles in males and females, in both social and sexual selection processes in yellow-vented bulbul. Moreover, we found that pair and territory fidelity in yellow-vented bulbul. Some pairs bred in the same territory in the following breeding periods. On the other hand, we observed that some males divorced and paired other females in the next breeding period in thesame territory. Long-term pairs were used the same territory and only onelong-term pair dah the second clutch. In this context, long-term monogamous pairs gained direct benefits through territory and second clutch. These results also support that yellow-ventedbulbuls are socially monogamous species with long-term pair bonds. The occurrence of the extra-pair paternity in the yellow-vented bulbul (Pycnonotus xanthopygos) is for the first time reported in this study. Although the species forms socially monogamous pair bonds during the breeding season, we found that 16 (22,8%) of 67 offspring had a different father than social father and 11 (42,3%) of 26 nests had an extra pair offspring. Furthermore, four of the socialmonogam males sired extra pair offsprings outside of their social partners. We found that females with the extra pair offspring were produced more males in a clutchandwhen females were in better body condition comparing to their partner, they produced more males in a clutch. These results may imply that females allocate the offsprings sexes through extra-pair copulations.