GMAT TIGER wrote:
During the month of May, crabs arrive on Delaware's beaches to lay eggs. Certain shorebirds depend on these eggs for food during their annual spring migration to their northern breeding grounds. Delaware's crab population has declined recently. This decline, however, poses no serious threat to the migrating shorebird populations: by remaining longer in Delaware, the birds will be able to eat enough crab eggs to allow them to complete their migration.
Which of the following, if true, most seriously weakens the argument?
(A) No other food available to the birds on Delaware's beaches is as nutritious and accessible as are crab eggs.
(B) The decline in the number of crabs on Delaware's beaches is due to the harvesting of crabs by humans.
(C) There are more crabs on Delaware's beaches than in any other area that the migrating birds pass through.
(D) The crabs do not conceal their eggs.
(E) The earlier in the season the shorebirds complete their migration, the more likely they are to breed successfully.
In May, crabs arrive on Delaware's beaches to lay eggs.
Certain shorebirds depend on these eggs for food during their annual spring migration to their northern breeding grounds.
Delaware's crab population has declined recently.
By remaining longer in Delaware, the birds will be able to eat enough crab eggs to allow them to complete their migration.
Conclusion: This decline poses no serious threat to the migrating shorebird populations.
The issue is that some shorebird depend on crab eggs and crab population has gone down. The argument says that the birds can stay longer (so they will get enough eggs). Hence, the argument concludes that the decline in crab population is not a threat to these birds.
We need to weaken the argument. How can we do that? If we say that the birds will not be able to stay longer, that will weaken the argument.
(A) No other food available to the birds on Delaware's beaches is as nutritious and accessible as are crab eggs.
The argument is not relying on other food sources. It is saying that the birds will consume these eggs only. Just that they will stay longer to consume enough eggs. This doesn't weaken our argument.
(B) The decline in the number of crabs on Delaware's beaches is due to the harvesting of crabs by humans.
Irrelevant why the number of crabs has reduced.
(C) There are more crabs on Delaware's beaches than in any other area that the migrating birds pass through.
Irrelevant. We already know that the birds depend on crabs in Delaware.
(D) The crabs do not conceal their eggs.
Irrelevant.
(E) The earlier in the season the shorebirds complete their migration, the more likely they are to breed successfully.
Correct. This tells us that the birds will not be able to stay longer. If they will stay longer, they may not be able to breed successfully. Then there is a threat to the birds due to decline in crab population.
Answer (E)