Seabirds are among the most endangered of all vertebrate groups. Loss of Caribbean populations is ongoing; many documented colonies from the 1990s and 2000s are now inexplicably gone. We will use surveys and mark-recapture techniques to find out whether the birds have moved, suffered nesting failure from predation, or are changing their behavior. Our inventories have detected declines. Now we must discover what happened so that we can reverse the changes through conservation and management.