Throughout May, crabs arrive on Delaware’s beaches to lay eggs. Migrating shorebirds that rely on these eggs for food stop there before continuing to their northern breeding grounds. The earlier in the season they reach those breeding grounds, the greater their likelihood of breeding successfully. Because the crab population was much smaller this year than last, the shorebirds lengthened their Delaware stay considerably in order to consume enough crab eggs to permit completion of their migration.
For which of the following hypotheses does the information given above provide the strongest support?The passage says the shorebirds had to stay longer in Delaware this year because there were fewer crab eggs available. Since reaching the breeding grounds earlier increases breeding success, a longer stopover likely means lower breeding success.
The supported prediction is about breeding success, not about whether the birds complete the migration.
A. The shorebirds will leave their northern breeding grounds earlier this year than they have in years past.
This is not supported. The passage discusses when the birds arrive at the breeding grounds, not when they leave.
B. The decline in the crab population was largely due to the shorebirds’ consumption of crab eggs in years past.
This is not supported. The passage says the crab population declined, but it gives no cause for that decline.
C. The average number of eggs laid per egg-laying crab will be significantly lower next year than this year.
This is not supported. The passage gives no information about future egg production per crab.
D. The proportion of the migratory shorebirds that breed successfully will be lower this year than it was last year.
This is correct. Because the birds stayed longer in Delaware this year, they likely reached the breeding grounds later. Since later arrival lowers the chance of breeding successfully, the proportion that breed successfully is likely to be lower.
E. Many fewer of the shorebirds will reach their northern breeding grounds this year than did last year.
This is too strong. The passage says the birds stayed longer so they could consume enough eggs to complete the migration. It does not suggest that many fewer birds will reach the breeding grounds.
Answer: (D)