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?

(A) Female wood ducks will establish nests in nest
boxes only when natural nesting sites are not
available.

(B) Nesting female wood ducks who often see other
female wood ducks are the most successful in
their breeding efforts.

(C) The nesting boxes for wood ducks have less space
for eggs than do natural nesting sites.

(D) 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.

(E) Nesting boxes are needed to supplement the
natural nesting sites of wood ducks because of
the destruction of much of the ducks' habitat.

OA: D

Although after seeing the OA I could well relate, I am unable to understand how to arrive at the conclusion. I am confused between C and D. Someone please explain.