Why Were Ecologists Concerned About the Shift in the Peak

Why were ecologists concerned about the shift in the peak caterpillar season from June 3,1980,to May 15,2000?

A) The caterpillars would have eaten much of the foliage of the trees where flycatchers would have nested,rendering their nests more open to predation.
B) The earlier hatching of caterpillars would compete with other insect larval forms that the flycatchers would also use to feed their young.
C) The flycatcher nestlings in 2000 would miss the peak caterpillar season and might not be as well fed,leading to population reductions.
D) The flycatchers would have to migrate sooner to match their brood-rearing to the time of peak caterpillar season.