One Spring, Your Friend Living in Minnesota Eagerly Sets Up

One spring, your friend living in Minnesota eagerly sets up her new hummingbird feeders, and is thrilled to watch hummingbirds feeding on the nectar. However, she is disappointed when after just a week or two the hummingbirds disappear. What advice would you give her?

A) Set up a bell (conditioned stimulus) near the feeders so the hummingbirds make an association with the food.
B) Set up flashing red lights that mimic the male neck feathers -- that should attract more males to the area.
C) Set up the feeders again in the fall. The hummingbirds may have briefly traveled through during their annual spring migration.
D) Wait till next year -- hummingbirds are a high-metabolism, semelparous species and have already reproduced and died.