When are trees and shrubs most vulnerable to rabbit browsing?

FAQ
Question: 

When are trees and shrubs most vulnerable to rabbit browsing?

Answer: 

In the home landscape, rabbits feed on herbaceous plants (annuals, perennials, vegetables, and grasses) during the growing season.  Trees and shrubs become food sources in late fall and winter (December through March).  Damage to trees and shrubs is most severe in winters with extended periods of snow cover.