When it comes to finding avian vagrants (species found outside their usual range), fall and winter are perhaps the best seasons for birders; many species wander widely as they head for wintering grounds and a variety of irruptive species grace Temperate latitudes during the colder months. In addition, waterfowl, loons, grebes and other aquatic birds move in concert with open water sources and food availability, sometimes veering far off-course (or off-schedule) from their usual migration patterns. By contrast, spring migration and activity, driven by the chemistry of procreation, tends to be more direct and predictable.
In summer, once the breeding season has ended (or even beforehand in the case of juveniles), southern species often wander north of their usual range, seemingly enjoying a bit of adventure while the weather is warm and food is plentiful. Mexican songbirds often turn up in the American Desert Southwest during the summer months and southern waders (such as roseate spoonbills, little blue herons and white ibis) may wander up the coasts or along major rivers; their appearance in the Heartland or New England is a special treat for avid birders.
Late summer is a good time to observe these summer vagrants, now joined by the first waves of migrant shorebirds that have left their Arctic breeding grounds. While oppressive heat still lies ahead, these travelers offer an early sign that the glorious days of autumn are just around the proverbial corner.