Daf Yomi Day 2: - Not Particularly Good Simanim, Now, Are They?

Rabbi Eliezer says in the Mishna that one can only say Shema at night until the first mishmar. As we see in the gemara, there are 3 mishmarot at night, and R Eliezer gives simanim, signs, for recognizing when a mishmar occurs. The first, the donkey brays. The second, dogs howl. The third, the infant nurses from the breast of its mother, and a woman converses with her husband.

bavli brachot 3a
עד סוף האשמורה:

מאי קסבר ר' אליעזר
אי קסבר שלש משמרות הוי הלילה
לימא עד ארבע שעות
ואי קסבר ארבע משמרות הוי הלילה
לימא עד שלש שעות
לעולם קסבר שלש משמרות הוי הלילה
והא קמ"ל דאיכא משמרות ברקיע ואיכא משמרות בארעא
דתניא ר' אליעזר אומר שלש משמרות הוי הלילה
ועל כל משמר ומשמר יושב הקב"ה ושואג כארי
שנאמר (ירמיהו כה) ה' ממרום ישאג וממעון קדשו יתן קולו שאוג ישאג על נוהו
וסימן לדבר
משמרה ראשונה חמור נוער
שניה כלבים צועקים
שלישית תינוק יונק משדי אמו ואשה מספרת עם בעלה.
מאי קא חשיב ר' אליעזר?
אי תחלת משמרות קא חשיב
תחלת משמרה ראשונה סימנא למה לי אורתא הוא
אי סוף משמרות קא חשיב
סוף משמרה אחרונה למה לי סימנא יממא הוא
אלא חשיב סוף משמרה ראשונה
ותחלת משמרה אחרונה
ואמצעית דאמצעיתא
ואב"א כולהו סוף משמרות קא חשיב
וכי תימא אחרונה לא צריך למאי נפקא מינה
למיקרי ק"ש למאן דגני בבית אפל ולא ידע זמן ק"ש אימת
כיון דאשה מספרת עם בעלה ותינוק יונק משדי אמו ליקום וליקרי.

The entirety of the sugya I cited, including the citation of the brayta (though perhaps the citation originally stood on its own), stylistically appears to be stamaitic.

Now, one thing that struck me about this is the inadequacy of the simanim given by R Eliezer. After all, someone is supposed to be able to use them to figure out what time of night it is, which means that he witnesses the event and he knows what ashmora it is. According to the second asnwer, a man would see the baby suckling and know it is morning such that he would say kriyat Shema.

If so, how can you have confusion? The (stama de) gemara does not know if by siman ledavar, R Eliezer meant the beginning, the end, or the middle of each respective mishmar! Why not see when the baby suckles, see when a man speaks with his wife, see when the donkey brays, and see when the dogs howl? Does the baby suckle while it is still dark, or when the day breaks? Does the donkey bray in the beginning of the night or 1/3 into it. The simanim don't seem so good.

(Perhaps the simanim were good for there time but were no longer calculable at the time of the give and take in the gemara?)

Update: My father made an interesting suggestion, which I'll expand upon here. Perhaps this whole idea of actually checking the matter empirically, that is, via direct observation, was not something that would have occurred to them, since it would not be in their cultural milieu. For example, Aristotle wrote that women had fewer teeth than men. Now, this is not so, and he probably could have asked Mrs. Aristotle to open her mouth so he could check, but instead he comes to this (false) conclusion philosophically. Now, there were Empiricists, who relied only on direct observation, but this was not the only school of thought. (Read Galen here.) Chazal felt that truth could be derived from tradition, not just direct observation, and on occassion darshen the existence of natural phenomena. We see in the end of Sanhedrin that the student who did not trust the drasha of his rebbe and doubted it until he witnessed it firsthand seems to be considered an apikores, since if he had not witnessed it he would not have believed. Perhaps they would not investigate in the manner I suggested, but will only arrive at truth by considering the possibilities and seeing which is the logical interpretation.