In b, if being was excluded and it read:

begun investigating nesting boxes erected by volunteers, ferried out to the island last month.

Would this be correct, or would "ferried out to the island last month" modify volunteers, not nesting boxes?

I have a doubt on the logical structure of modifiers. Consider Option C (I understand it is an incorrect option due to the reasons explained in the earlier posts):

A team of researchers reported that five endangered bird species had resumed nesting or (c) investigating nesting boxes, erected by volunteers, ferried out to the island last month.

Now, breaking down as follows (please ignore the correct intended meaning for the time being. This is just an example for reference to understand what modifies what in a sentence like this):
1. A team of researchers reported that five endangered bird species had resumed nesting or investigating nesting boxes,
2. erected by volunteers,
3. ferried out to the island last month

My understanding is:
1. "erected by volunteers" (which is framed inside the comma pair) refers to the "boxes".
2. I have a doubt on this one-
(A). Does "ferried" refer to "volunteers"? As per the touch-rule, the verb-ed modifier would modify the closest noun entity in the previous sentence (hence, "volunteers" here).
or, (B). Does "ferried" refer back to "boxes"? As "erected by volunteers" is inside the comma pair and can be considered non-essential (ommitted) for the time-being.

Request to please share your expert inputs here. Thanks in advance.
AndrewN
zhanbo

Hello, Pankaj0901. You should indeed have doubts about (C). The double commas tell us that the modifier erected by volunteers is non-essential, so we should be able to remove that modifier without distorting the meaning of the main clause. But that creates a problem, since the sentence would then be saying that nesting boxes had been ferried out to the island. I suppose the boxes could have been ferried out, but then that leaves the information about the volunteers in an awkward spot. If the sentence means to convey that those volunteers were ferried out to the island, then such information should be restrictive, presented without commas: by volunteers ferried out. Since (C) wedges a comma between volunteers and ferried, we can only interpret the sentence as saying that boxes were ferried out, and, in case we were curious, those same boxes were built by volunteers.

In general, I would urge you not to pursue a line of reasoning that divorces grammar from meaning. The two are often intertwined, as is the case above, and sometimes perfectly grammatical answers still fall flat in terms of the meaning they convey.

- Andrew

Thank you so much! Your responses are really appreciated! AndrewN