Heard shiur that did not say where but that Rav Yosef Engel says look when chickens lay eggs to see when bayn hashamashos is..... Where what sefer and page does he discuss this?
HG, Spring Valley
The answer to your question is in the Gilyonei Hashas Bechoros 8a. Mahari Brona (149) writes that based on the rule that a chicken does not lay eggs at night, if fruit fell from a tree during Bein Hashmashos but at the same time a chicken laid an egg, the fruit wouldn't be muktzeh because it obviously fell during the day. Ikrei Hadat (Rabbi David Tirani Orach Chayim 11:8) postulates even further that we could theoretically do a Bris on Shabbos for a baby born Bein Hashmashos if we knew that a chicken had given birth at that point in time.
However Gilyonei Hashas (Rabbi Yosef Engel) writes that evidently no chicken ever laid eggs during Bein Hashmashos as if so there would not be a dispute between Tannaim over Bein Hashmashos.
Rabbi Elyashiv writes in his He'aros that we would not rely on the Ikrei Hadat as this is D'Orayso but regarding Mahari Brona we could rely on this as it is D'Rabonon.
Yoel Domb