Seasonal reproduction of Megascops choliba males in Southeastern Brazil (Aves, Strigidae): an endocrine and molecular study

Reproductive activity in animals is regulated by variations in plasma levels of steroid hormones, which respond to both geophysical and social-environmental cues. Changes in testosterone (T) levels play a crucial role in coordinating the morphological, physiological, and behavioral adaptations among males, orchestrating gonadal recrudescence and regression in response to seasonal shifts in environmental factors. Although these reproductive neuroendocrine processes have been extensively examined in various bird species, they remain largely unexplored in owls. The Tropical Screech Owl is widely distributed across Central and South America, and it exhibits regional variations in the timing of chick hatching. This study hypothesized that male Tropical Screech Owls (Megascops choliba) exhibit fluctuations in testosterone levels and corresponding seasonal expression of reproductive genes, potentially linked to reproductive activity, including the presence of semen. To investigate this seasonal reproduction, a group of seven adult male owls was monitored for 14 consecutive months under ex-situ conditions. These owls underwent cloacal electrostimulation and subsequent massage to collect semen, as well as blood sampling to measure serum T levels. The expression of aromatase (CYP19A1), androgen receptor (AR), and estrogen receptor (ESR1 and ESR2) genes was also assessed in gonadal and hypothalamic tissues from four reproductively active and four non-reproductive males collected in-situ from a wild population. Serum T levels in males were significantly higher in July and August, coinciding with the presence of sperm. No significant difference was observed in the hypothalamic tissue transcripts of reproductive versus non-reproductive males. However, non-reproductive males exhibited higher expression of AR and ESR1 genes at the gonadal level. These results confirm the reproductive seasonality of M. choliba males during the winter season in São Paulo State.