You will be given a definition of a task first, then some input of the task.
In this task, you're given a passage, further information available on a particular linked term from the statement, and an answer term. Your job is to generate a question that can use the information provided to obtain the given answer. You should use the information on both passage and link information to create the question. Note that the answer to the question should be exactly the given answer, and if the answer is none, the answer to the question shouldn't be obtainable from the passage or linked information.

Passage: The San Francisco Estuary is a major stop on the Pacific flyway for migrating waterfowl. Yet little is known about the flow of carbon in or out of the estuary via birds. Millions of waterfowl annually use the bay shallows as a refuge. Most of the birds are dabbling ducks that feed on submerged aquatic vegetation. Diving ducks (such as scaups) feed on epibenthic organisms like C. amurensis, representing a possible flow of carbon from that otherwise dead end. Two endangered species of birds are found here: the California least tern and the California clapper rail. Exposed bay muds provide important feeding areas for shorebirds, but underlying layers of bay mud pose geological hazards for structures near many parts of the bay perimeter. Piscivorous birds such as cormorants and pelicans also inhabit the estuary, but their trophic impact remains poorly studied.
Link Information: none Answer: none
Output:
Approximately how many California least tern remain?