Besides laying eggs in her own nest, any female wood duck will lay an egg in the nest of another female wood duck if she sees the other duck leaving her nest. Under natural nesting conditions, this parasitic behavior is relatively rare because the ducks' nests are well hidden. However, when people put up nesting boxes to help the ducks breed, they actually undercut the ducks' reproductive efforts. These nesting boxes become so crowded with extra eggs that few, if any, of the eggs in those boxes hatch. The statements above, if true, most strongly support which one of the following? ['The nesting boxes for wood ducks have less space for eggs than do natural nesting sites.', 'Female wood ducks will establish nests in nest boxes only when natural nesting sites are not available.', 'Nesting female wood ducks who often see other female wood ducks are the most successful in their breeding efforts.', 'The nesting boxes would be more effective in helping wood ducks breed if they were less visible to other wood ducks than they currently are.']