Brood parasites are organisms that rely on others to raise their young. It's the equivalent of having a baby, placing him/her in a basket, and then leaving it on a random person's front porch. While this may seem strange to us, it's not uncommon to some species of birds. One of nature's shrewdest examples of this behavior comes from cowbirds. Not only do they lay their eggs inside the nests of other birds and expect them to rear the foster chicks as their own, scientists have found another way these birds may be harming their hosts -- their extra-thick eggshells can crack the hosts’ own eggs when they falls into the nest.

To test this idea, researchers of recent study gathered 157 freshly laid cowbird eggs and dropped them onto host eggs fro ...