Diet exposure to technical hexabromocyclododecane (HBCD) affects testes and circulating testosterone and thyroxine levels in American kestrels (Falco sparverius)

► Testis mass was larger in HBCD-exposed male kestrels compared to controls. ► Testes of HBCD-exposed males also tended to have more tubules with final spermatids. ► HBCD-exposed males demonstrated increased circulating testosterone than controls. ► HBCD-exposed males demonstrated reduced circulating thyroxine than controls. ► Perivitelline sperm counts did not differ between HBCD-exposed and control males.