Answer:
Third Option: The Backyard Bird Count benefits birds and scientists.
Step-by-step explanation:
There are three to four ideas in this passage, but one idea connecting all others and hence the central idea of the passage is described in the line,
"the goal is not to see who can count the most birds. Instead, participants in this event work together to help bird experts get a good idea of how birds are doing"
This is not only the goal of the competition but also of the passage.
First option is not all-inclusive; it is just a step in achieving the main goal i.e. helping birds experts and birds themselves.
Second option is not mentioned anywhere in the passage.
Fourth option is not the central idea, but just a characteristic of the competition.