This classification means that there are less than 1000 mature birds, and that the species was found in five locations only.

The yellow collar develops as the bird ages, with more vibrant colors found in mature birds.

Its egg weighed twenty pounds, and a mature bird up to half a ton.

In 2003, the number of individuals was estimated to be over 2,500, with more than 750 mature birds, possibly as many as 1,500.

Shelter Island's mature bird had not been spotted for more than a week as of last Monday.

In 2000 the population was estimated to comprise about 80 mature breeding birds.

That is considered risky because mature birds are attached to their territory and might well panic outside of it.

In the case of several species the estimated populations are as low as a few 1000 mature birds, spread over a considerable area.

Overall their population stands at between 17,000 and 21,000 mature birds, based on a 2001 estimate.

The current population is estimated 50 to 249 mature birds.