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? ["The decline in the number of crabs on Delaware's beaches is due to the harvesting of crabs by humans.", 'The crabs do not conceal their eggs.', "No other food available to the birds on Delaware's beaches is as nutritious and accessible as are crab eggs.", 'The earlier in the season the shorebirds complete their migration, the more likely they are to breed successfully.']