In an environment in which insect populations are decreasing, which bird, small insect eater, cactus eater, seed eater, bud, leaf and fruit eater population might also decrease over time? why?

The reduction occurs in the population of insect eater birds due to unavailability of food.

Explanation:

If reduction occurs in the population of insects in an ecosystem, so the organisms which feed on them i. e. insect eater birds also reduced and die due to hunger. In an ecosystem, every organism is the food of other organism, if one organism is eliminated or reduced in population, then the other organisms will also be affected.