For example , the greater scaup has a wider black nail than does the very similar lesser scaup .
The shape or color of the nail can sometimes be used to help distinguish between similar - looking species or between various ages of waterfowl .
The greater scaup has a wider black nail than does the very similar lesser scaup .
The shape or color of the nail can sometimes be used to help distinguish between similar - looking species or between various ages of waterfowl .