The American Redstart (Setophagaruticilla)is in Serious Decline

The American redstart (Setophagaruticilla) is in serious decline.Scientists have been able to correlate health and breeding success to levels of ¹³C in their blood (a chemical signature indicating the source of their diet) .Birds with lower levels of ¹³C in their blood return to their spring breeding ground sooner,weigh more and produce more offspring.Based on this,what would you expect to find in the wintering grounds of the American redstart? Check all that apply.

A) Limited availability of habitat in areas where plants have low¹³C
B) Higher insect biomass in areas where plants have low¹³C
C) A lack of territorial behavior being displayed by American redstarts
D) Differences in food quality correlating with levels of ¹³C in the habitat
E) Similar flora and fauna in all redstart habitats,unrelated to levels of ¹³C