Please explain why can't I use Math strategy on the 1st blank

While the cerulean warbler’s status may be particularly (i) __________ , it is just one of the many species of migrant birds whose numbers have been (ii) __________ for years. Increasingly, biologists investigating the causes of these (iii) __________ are focusing on habitat loss in the Tropics, where the birds spend the winter.

In the first blank I see the contrast word "WHILE’ which is (-ve) and I see (,) so left side and right side says the same thing. For 2nd blank I figured out the ans to be declining/falling which is (-ve) so,
(-ve) x (+ve) = (-ve). So 1st blank should be a positive word. But my answer is wrong.

Contrast is highlighted by the phrase “Just one of the many species”, this mean that though there are many species of migrant birds only this species (Cerulean Warbler) birds population is dwindling.