Relationship between Fat Status, Stage of Gonadal Maturity and Hormonal Variation of Turdus philomelos (C.L. Brehm, 1831) Wintering in Apulia during 2018–2020

Simple Summary The European Birds Directive (2009/147/EC) mandates that migratory game birds “are not hunted during their period of reproduction or during their return to their rearing grounds”. For each huntable species, the study of the onset of the reproductive phase is important in order to plan the hunting season. The purpose of this study was to evaluate the development of the fattening status and reproductive activity of the song thrush. To achieve this goal, the chemical and fatty acid compositions of the pectoral muscle were analyzed in relation to the fattening status of the birds. In addition, reproductive status was evaluated through anatomical and pathological examinations of tissues and the assessment of sex steroid profiles. The results showed that the fattening statuses and fatty acid profiles of the song thrush increase from December to February, corresponding with low ambient temperatures and the approach of spring migration. The change in fatty acid profile may also be related to their diet, which switches from insectivorous to vegetarian, during the winter. The sex hormone profiles and histological examination show that both male and female song thrushes were in a reproductive quiescence phase during the period under consideration. Abstract In this study, we aimed to evaluate the development of the fattening condition and the reproductive status of the song thrush from December to February. For this purpose, the chemical and fatty acid compositions of the pectoral muscle were analyzed in relation to the fattening state of the birds. Moreover, their reproductive activity was evaluated via the anatomical and pathological examination of tissues and through the assessment of sex steroid profiles. One hundred ninety-five thrushes captured by local hunters during the 2018–2019 and 2019–2020 hunting seasons in different provinces of the Apulia region in Italy were used. The first step was the measurement of bird body mass, and the amount of subcutaneous body fat was estimated visually. During post-mortem examinations, the pectoral muscle was excised and used for chemical and fatty acid analysis and a hormone assay, respectively. Moreover, ovaries and testicles were evaluated to determine the degree of maturation and thus the reproductive status of the birds. The results regarding fattening status and fatty acid profile confirmed that in January–February, thrushes change their diet, increasing their intake of oleic acid, likely to better cope with low temperatures and prepare for long-distance migration. In both male and female thrushes, the concentrations of sex hormones confirmed a phase of reproductive quiescence from December to February, which was also confirmed through histological examination of the gonads.