Yosef Karo

“ A minority of shochtim are careful to not shecht any duck in Tevet or Shvat unless they eat some of the heart, because of tradition that there is a time during those months when if he shechts a duck the shochet dies if he doesn't eat from it. ”

“ Contains four Seif
ובו ארבעה סעיפים:
Seif 1 You can always shecht whether day or night. Under what conditions? When an avukah (torch) is before him. But if an avukah is not before him, or in daytime in a dark place he may not shecht. But if he shechted his shechita is kosher. (And two candles are considered a torch. Maharil and Agudah)
לעולם שוחטין בין ביום ובין בלילה. במה דברים אמורים: כשאבוקה כנגדו, אבל אם אין אבוקה כנגדו, או ביום במקום אפל – לא ישחוט. ”