In winter, the White-throated Sparrow migrates to the southern and eastern United States. They are differential migrants with females migrating farther, increasing the proportion of females at lower latitudes in the Atlantic flyway. Females are smaller so they would not perform as optimally at colder, higher latitudes, and females avoid competition with the dominant males of the winter hierarchies by migrating farther. There is also no benefit for females to be among the first to return after winter, so migrating farther allows the males to return and establish territory a few weeks before their arrival. It stays year round in the Atlantic provinces of Canada. This bird is a rare vagrant to western Europe. Alongside some other species such as the cardinal, dark-eyed junco, song sparrow and chickadees, this species ranks among the most abundant native birds during winter in eastern North America.
The Song Sparrow has been the subject of several studies detailing the physiological reactions of bird species to conditions such as daylight length and differing climatic conditions. Most birds gain mass in their reproductive organs in response to some signal, either internal or external as the breeding season approaches. The exact source of this signal varies from species to species – for some, it is an endogenous process separate from environmental cues, while other species require extensive external signals of changing daylight length and temperature before beginning to increase the mass of their reproductive organs. Male specimens of M. melodia gain significant testicular mass in response both to changes in the daily photoperiod and as a result of endogenous chemical signals. Females also undergo significant ovarian growth in response to both photo-period and endogenous signals. Hormone levels in both males and females fluctuate throughout the breeding season, having very high levels in March and late April and then declining until May. These studies suggest that there are multiple factors at work that influence when and how the song sparrow breeds other than just increasing day length.