The monarch butterfly population has declined due to a scarcity of :
Monarch Butterflies are one of the most beautifully colored butterflies with yellow and black lines, they migrate seasonally during the winter, Caterpillars of monarch butterfly feed on the leaves of milkweed which is a major source of food for Monarch butterflies.
The scarcity of milkweed will result in the decrease of the population of Monarch butterflies as the caterpillar will have nothing to feed on .
Hence we can conclude that the monarch butterfly population has declined due to a scarcity of milkweed.
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