Understanding bird ranges is critical for knowing where to find birds, how to identify them and how to attract them appropriately. Birds have different ranges, and birders who know what affects those ranges will have better luck in the field.
What Is a Range
Simply put, a range is the geographic area where a certain bird species can be reliably found. Different factors affect bird ranges, however, and birds' ranges will change over time.
Factors that affect ranges include:
- Season: Many birds migrate and change their ranges seasonally. These birds may live in completely different areas of the world in different seasons, and their different ranges may be thousands of miles apart.
- Climate: Birds can be uniquely adapted to live in specific climates. Some birds may be more heavily insulated with downy plumage and are easily able to live in colder areas, while others have lighter plumage adapted to hotter climates.
- Food: In many cases, a species' range will be limited or expanded based on the availability of food. A poor seed or fruit crop, for example, may force birds to expand their range in search of other foods or it may restrict them to a smaller area where food is still abundant.
- Habitat: Birds have adaptations to make the most of their habitats. Woodpeckers, for example, are adapted to pry food from the bark of trees, and an area of extensive grassland will limit their range because they cannot cross it and feed while they travel.
- Predators: Predators such as invasive animals, rodents and introduced animals can have severe impacts on bird ranges and may completely destroy bird populations in some areas. This is most visible in nesting ranges where predators may prey on eggs and hatchlings.
- Competition: An individual bird's range may be limited by its competition. Many birds are highly territorial and will harass, chase or even attack other birds that try to take over the same territory. When population numbers are high, the overall range for these types of species can expand as all the birds seek their own territories to defend.
Types of Bird Ranges
Birds have four basic ranges, though not every species will have each type of range.
- Breeding: This is the range where a bird species will construct nests, mate and raise young. Bird breeding ranges are often dictated by available food supplies, since mature birds will seek areas with ample food to give their young the best chance of survival. For many migratory birds, breeding ranges are often further north as they spread out to raise their families each year.
- Non-Breeding: A bird's non-breeding range is often called its winter range. This is the area where the birds congregate outside the breeding season. While they do not nest in their non-breeding range, family groups may stay together and juvenile birds continue to learn from their parents until the next breeding season begins.
- Migration: The migration range of a bird species is the transitory path the species will follow as it moves between breeding and non-breeding ranges. These ranges are most often found along major migration flyways, though they can fluctuate from year to year based on weather patterns. Similarly, the migration ranges of a species in the spring and fall can vary drastically depending on the routes the species uses at different times of year.
- Irruption: Bird irruptions are characterized by drastic changes in a species' range and can be caused by many different factors. In an irruption year, birds will have an expanded range, though the exact boundaries of that expansion can be difficult to predict and can vary from one location to the next and from year to year.
Of course, many birds stay in the same range throughout the year – their breeding and non-breeding ranges are the same, and because of that, they have no migration range. Some of those species still irrupt, however, and vagrant birds of any species are always possible well outside expected ranges.
How Bird Ranges Change
Over time, bird ranges can change drastically, and the birds that were once familiar in one area may become scarce or non-existent. This can be caused by…
- Hunting or invasive predators
- Climate change
- Long term pollution
- Urban growth and habitat change
- Changes in food sources
In some cases, this type of range adjustment means a smaller overall range for the bird species, which can lead to threatened or endangered status, or even extinction in extreme cases. Other times, adaptable birds will simply shift their ranges to more suitable areas without a significant population change.
Understanding bird ranges is essential for birders and conservationists alike. By knowing what factors affect different ranges and how those ranges can change, birders can better enjoy birding and conservationists can take steps to help protect all avifauna.
Photo – Long-Billed Curlew © Teddy Llovet