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

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.

Keywords: Turdus philomelos; endocrine status; fat status; gonadal maturity.

Figure 1

Primordial and primary oocytes in a female song thrush hunted in December (H&E, 200×).

Figure 2

Oocytes with acidophilic and homogeneous ooplasm and central nucleus from birds hunted in late January.

Figure 3

Secondary oocyte with follicular theca in a female song thrush hunted in February (H&E, 400×).

Figure 4

(a) Testicles: seminiferous tubules with primary and secondary spermatocytes (H&E, 100×); (b) Details of the seminiferous tubules with the germ line in different maturation stages (H&E, 100×).