Until martins complete their second fall molt, young males are hard to tell from females. Dull blue feathering is easy to see on their heads and backs, but patches of gray and white remain over much of their bodies. Although sexually mature by 12 months of age, full adult status is not achieved until the birds molt into dark blue plumage when 15 to 17 months old. Adult martins measure about 7 inches in length. Life History Purple martins avoid harsh winter weather by migrating each fall to South America.
Brazil harbors the largest wintering concentration.
Literally millions of martins are found there during fall and winter months. Their annual journey to breeding grounds in North America usually begins, varying somewhat with weather patterns, curing January. Early arrivals, typically adult males, may reach the Gulf Coast as early as late January. Female and sub-adult, or first year, martins soon follow. Their inland migration to nesting sites, once reaching the North American coast, may extend into May. Many purple martins return to the same nesting area they used previously.