"The dove came to him toward evening, and behold it had plucked an olive leaf with its beak"[Noach 8:11]
Rashi, quoting a Midrash, recounts that the dove said to Noach: "Let my food be as bitter as an olive - as long as it is provided by the hand of HaKadosh Baruch Hu - and not as sweet as honey - if it will be provided by the hand of flesh and blood."
Why, asked the Dubno Maggid, would the dove make such a statement to Noach before taking leave of him and the ark? Hadn't Noach so graciously provided for it and cared for all of its needs over the course of an entire year?
Rather, answered the Maggid, the dove was concerned that perhaps Noach would suspect that it had returned not because the flood had ended but because it knew that it would receive all of its food on the ark. This is why the dove told Noach, "I have not returned for food. For I prefer to be sustained with food that is as bitter as olives, as long as it is provided by Hashem, rather than with food that is as sweet as honey but provided by man!"
Source: Rabbi Y. Bronstein