This explains why these marsh hens are seen less frequently than other species. Because of their special camouflage, they are spotted rarely even though they are common.

This does not explain why this marsh hen is spotted less frequently than other species. A harsh repetitive call would attract attention and make the marsh hen more likely to be spotted, not less.

This explains why this marsh hen is seen less frequently than other species. The others move around the banks, making them visible to human visitors, while the marsh hen is stationary and therefore harder to spot.

This explains why the marsh hen is seen less frequently than other species of birds. It is active at night, when the cover of darkness makes it difficult to see.

This explains why the marsh hen is seen less frequently than other species of birds. Other species travel often and in groups, making them more easily sighted by visitors, while the marsh hen is more solitary and sedentary.