If a bird power (brown or pink) could apply to multiple birds, can you choose to activate some and not others, or must you resolve all possible effects?
inferred
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Official Answer
You may choose to activate some and not others; all bird powers are optional.
This is stated on page 10:
Bird powers are always optional. For example, if you do not want to spend a card by tucking it under a flocking bird, you do not have to do so.
This applies to all types of bird powers, including brown ("WHEN ACTIVATED") and pink ("ONCE BETWEEN TURNS") powers. Therefore, if a power could apply to multiple birds, you may choose which ones to activate and which to ignore.
Source: page 10.
Source: Core Rulebook (pp. 1, 10, 7, 8, 9)