It has been observed at the federal level only since 1986.

Had been observed, in fact, since his entry to the park.

No more than five specimens have been observed since 1979.

Seals have been observed there since 2001, but never in such numbers.

It has not been observed alive in Canada since 1905.

They have been observed since 1969, with a single possible recorded observation in 1938.

Madam President, what have we been able to observe since 1963?

Notably, the higher than average population growth rate is a recent phenomenon, observed since the 1970s only.

However, no daylight saving time has been observed since 1979.

There has been a general warming trend observed, however, since the late 1980s.