Grebe is a strange word. My Shorter Oxford English Dictionary says it is a French word of unknown origin.
It goes on to describe the characteristics of the bird genus and family to which it is applied as having a short body, flattened and lobed feet set far behind, and the virtual absence of a tail.
The grebes were probably underwater when the tails were given out. That's where they usually disappear to when I'm trying to photograph them.