Baltimore orioles (Icterus galbula) and Bullock's orioles (Icterus bullockii) are migrating birds found throughout North and Central America, with a few in northern South America. The males are black with bright orange plumage and the females are black with a duller brown. Males are slightly larger than the females. They pair off monogamously and migrate north to lay eggs in the summer.
January Through Febuary
Baltimore orioles start off the new year in the tropics. Most are living together in social flocks up through February in Central America, Florida, southern coastal California. A few will be found as far down as northern South America, and fewer still may be found spending the winter in the central or northern states. Bullock's orioles spend the winter in Mexico, except for a few that stay in southern coastal California all year. In February, the first Baltimore orioles begin migrating north through Panama.
March Through May
Bullock's orioles are beginning their migration up through the coast from Arizona and California in March. A few begin breeding by the end of the month. Bullock's orioles finish migrating up the coast in May, settle in mountains and plains and begin breeding immediately. Some migrating Baltimore orioles are arriving in Mexico by March, though many are still south in Panama. By April some are arriving in Texas while others are reaching the central states. Most Baltimore orioles reach the northern states by May. April is the peak time for migration for Bullock's and Baltimore orioles, and continues through mid-May, which is peak nesting time for both.
June and July
In June, Baltimore orioles are nurturing their eggs and raising the young. Most of the babies hatch in June and become independent at the beginning of July. The adult orioles are shedding their old feathers in July and a few already begin their migration during this period. Bullock's orioles are busy taking care of their eggs and young. In July, they are still rearing their children and are beginning to molt their feathers.
August Through October
Migration peaks in August and September for Baltimore orioles. Throughout this time they are still shedding their feathers. Most reach their destination in the tropics by the end of October and have finished shedding their flight and body feathers. Bullock's orioles also are in the peak of their migration during August and September. A few are still molting their body and flight feathers through September. By October most have reached their destination for the winter in Mexico.
November and December
Baltimore orioles mostly have arrived at their wintering grounds in the tropics in November. A few stay behind longer and ornithologists think that most of the stragglers still found in the northern states in November and December end up perishing when the winter gets colder. Bullock's have reached Mexico by November and remain there through December, with the exception of those that live in Southern California year-round.
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