Bird eggs.

I once spent a summer studying gulls on Appledore Island in the Gulf of Maine, off the east coast of the United States. The rocky island is a breeding colony for herring gulls (Larus argentatus) and great black-backed gulls (Larus marinus), so I had a front-row seat to the dramas that unfolded as birds paired up, laid and incubated eggs, and raised chicks. I saw chicks hatch from large speckled eggs (Figure 1A), a Herculean feat that took over an hour. Eggs and chicks are extremely vulnerable, and many gull offspring do not survive. Now, when a gull soars past - or pilfers my sandwich at the beach - I appreciate the hurdles it overcame just to reach adulthood.