Vagrancy in Birds

 

A species’ known, expected geographical range is usually a useful clue in an identification, but the appearance of vagrants, birds far out of their typical range, complicates matters. Most vagrants reported in North America are birds that have strayed a few hundred miles out of range but that breed within North America; all such species are depicted in this guide. A small minority of vagrants come from Eurasia, South America, or Africa, and these species are usually not depicted.


The study of bird vagrancy is relatively new. Some theories suggest that vagrants have a faulty navigation system and confuse, for example, north and south, leading them to migrate northward instead of southward in the fall. Most such strays are long-distance migrants, often passerines or shorebirds that spend the winter in tropical regions of the world. Other vagrants have been blown off course by weather systems; for example, European Golden-Plovers returning to Iceland in spring sometimes make landfall in Newfoundland because of strong easterly winds. Some vagrants are transported to North America on large ships; on rare occasions hummingbirds, rails, and even owls have been found in large shipments of plants. Seabirds — especially the tubenoses, such as petrels and shearwaters — are particularly prone to wander far out of range; there are few barriers to their travel over the open ocean, and strong weather systems such as hurricanes can also displace them great distances.

Aztec Thrush
Aztec Thrush is a species normally found only in Mexico; this vagrant male was photographed in Arizona.

In some cases, vagrants may be pioneering individuals or flocks of birds that are testing out new breeding or wintering areas; they may remain in areas well out of range and establish breeding populations or become part of a growing wintering population.


Reporting vagrants

Birders relish the sight of a new or unusual species in their area. Anyone might discover a vagrant species, sometimes just by looking out a window and seeing something unfamiliar. Vagrants are of special interest to ornithologists because they contribute to the collective picture of a species’ natural history, including range expansion, responses to weather and climate, and migratory patterns. All states and most provinces have bird records committees that keep track of, review, and archive reports of rare birds; such committees are grateful to receive well-documented reports of unusual species or subspecies. Upon finding an unusual-looking bird, then, it is a good idea to take notes as well as a video or photographs, in order to study the bird in detail afterward and so that others can review the notes and images.

 

 

Learn more about how to identify birds

Birds in Action

Birds in Flight

Identifying birds by ear (bird songs, bird calls)

Limits of field identification

 

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