Other snip off the leaves that they fed on during the day in an attempt to trick birds that search for them on partially eaten leaves. Birds are technologically advanced, highly motivated, extremely efficient, cost-effective insect pest controllers. Outbreak insects are often infected with parasites. Many birds can identify the infected insects, and often choose to eat those that are not parasitized. By preying only on healthy individuals, birds greatly add to the effect of parasites in reducing insect populations.
Birds can spread viral infections among the insect pests.
By eating beetles and their viruses and by defecating these viruses along tree trunks, birds inadvertently spread it to bark beetles in the same tree and throughout the forest. The breeding season for birds occurs when the insect populations are their highest. During insect outbreaks, some birds will increase the number of offspring that they raise to take advantage of the abundant food supply. Birds are highly mobile and many species of birds will take advantage of a local insect outbreak by moving into the infected area. Some of these invasions can increase the normal numbers of birds in an area by 80 times.