Learning how to build a nest plays an important part in the breeding

Official Explanation

Remember, to weaken an argument, typically you must show that a suppressed premise is false. The premise of the argument is that all other things being equal the breeding success of blackbirds increases with experience. To weaken the argument, we need to show that not all things are equal. Choice (B) does this, suggesting that as blackbirds mature they lay more viable eggs. This alone could explain the breeding success of older blackbirds. The answer is (B).

B
When it asks for ^weaken^,we should ask "why the nesting exp only?" why not anything else but nesting ? this way we will attack the author's position that nesting exp only was the factor in success.
using this methodology, i was expecting some ans choice that talk abt anything but nesting n here is B that exactly does that.
examined once more and dismissed rest as incorrect

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Learning how to build a nest plays an important part in the breeding success of birds. For example, Dr. Snow has recorded the success of a number of blackbirds in several successive years. He finds that birds nesting for the first time are less successful in breeding than are older birds, and also less successful than they themselves are a year later. This cannot be a mere matter of size and strength, since blackbirds, like the great majority of birds, are fully grown when they leave the nest. It is difficult to avoid the conclusion that they benefit by their nesting experience.

Which one of the following, if true, would most weaken the argument?
(A) Blackbirds build better nests than other birds.IRRELEVANT
(B) The capacity of blackbirds to lay viable eggs increases with each successive trial during the first few years of reproduction.INSTEAD OF NESTING EXPERIENCE , THIS COULD BE THE REASON FOR BETTER BREEDING LATER...CORRECT
(C) The breeding success of birds nesting for the second time is greater than that of birds nesting for the first time.ITS ALREADY GIVEN IN STIMULUS .....IT IS JUST A PREMISE...
(D) Smaller and weaker blackbirds breed just as successfully as bigger and stronger blackbirds.THIS STRENGTHENS THE ARGUMENT..NOTE "This cannot be a mere matter of size and strength, since blackbirds, like t.........
(E) Up to 25 percent of all birds are killed by predators before they start to nestIRRELEVANT


KUDOS IF U PLEASE.....

The key to (B) is understanding the term "capacity." In this context, it means ability - kind of like in a physiological context. In other words, (B) says that it is NOT the nesting experience that leads to more success in breeding but RATHER it is the adaptation of their bodies - every time they lay eggs, they get better!

-Year 2 of breeding was more successful than Year 1; Year 3 was more successful than Year 2
-This cannot be explained by size and strength
-It must be explained by their nesting experience

I simply want to show why it is NOT the nesting experience that led to this. Maybe the blackbirds get progressively healthier during their first years of nesting. Either way, I just want to show an alternative explanation as that is basically the best way to weaken this claim.

(A) "Other birds?" Who cares?

(B) Yea! If the ability to lay more viable eggs increases, then it is NOT the nesting experience but rather their physiology that explains the uptick in success: their eggs are more viable!

(C) We basically already knew this: premise booster.

(D) This actually strengthens by ruling out an alternative explanation. It says that strengthen and size don't matter! Thus, we couldn't just say, "well during the 2nd and 3rd years the birds were stronger or bigger!" to weaken this claim because (D) says, "not so fast! Those things don't matter!" Whenever we rule out an alternative explanation, we are strengthening the argument if just by a little.

(E) "All birds" is too wide of a scope and we don't care about happens before they start to nest - we care about what happens after!

The very first sentence marks the conclusion?
I was equally confused as some others with the structure of the argument.

Somehow totally narrowed in on the "nest-building" part while negleting the breeding part.

Tough!

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