Chulin 139b - Searching after mitzvos

The gemara says that one may have thought that they would be required to search after the mitzvah of shi'luach ha'kein and put in effort to find a birds nest on mountains and hilltops, to which the gemara responds that it only applies when you chance upon it. There is a great debate among the achronim regarding the mitzvah of shiluach ha'kein, whether it is an absolute obligation to send away the mother bird even if one has no particular interest in the baby birds, or is it a mitzvah more similar to divorce where if one wants to do something i.e. take the babies, or divorce their wife, the torah prescribes a format that must be followed. The Chacham Tzvi (83) and Chasam Sofer (100) suggest from this gemara that thought to demand searching after the mitzvah on mountain tops, that it is an absolute obligation. Although the gemara concludes that one isn't obligated to go to the extreme of trying to locate a birds nest, the underlying assumption that it is an absolute imperative even if one has no interest in the babies is never rejected.

On a bit of a different note using the same source, the Mekor Chaim (Nesivos on Hil. Pesach Siman 432) which I cited in my sefer Nasiach B'chukecha (195) proves from our gemara that one is required to invest effort into searching after mitzvos from the fact that the gemara required a specific pasuk to exempt the assumption of searching after the mitzvah on hilltops. Therefore, other mitzvos that don't have a pasuk exempting this level of effort, would demand that extreme amount of effort. However, in my edits on my sefer I pointed out that from Rashi we would be able to prove the exact opposite. Rashi writes - 

שנאמר שלח תשלח ב' פעמים, שומע אני לחזור אחר המצוה הזאת עד שתבא לידו. Rashi explains that the default position for having to put tremendous effort into searching after this mitzvah is not a gobal requirement or assumption that would be by all mitzvos. Rashi says that since we have the double language of שלח תשלח I would have understood that this mitzvah would require one to search after it in order to fulfill it, to which the gemara responds that כי יקרא implies the opposite. Therefore, other mitzvos which have no pasuk specifically implying that it demands an extreme level of effort, one would not have to put in tremendous effort to attain the mitzvah.