RANGE AND TERRITORY IN BIRDS
All birds occupy territories within certain geographic ranges. Some folks use the words "territory" and "range" interchangeably, and this is not correct. Territory refers to individuals within the species. Range is more closely associated with the species as whole population. When birders speak of the bird's distribution, they are speaking of its range.
Territory, often fought for and highly protected, is the area that is "staked out" and defended against rivals where abundant food and/or nesting sites are found. Birds understand the well-defined limits of their territory, even without the aid of visual markers. When a rival bird enters a claimed territory, the possessor of that territory threatens the invader and causes him to leave. Particular calls and/or defensive displaying can accomplish this. Usually, the invading bird will recognize the warning that this territory is already occupied and leave to establish his own territory that isn't occupied by another bird. Sometimes the encroaching bird may turn out to be the dominant bird, either because of greater maturity, fearlessness, aggressiveness, or some other dominant characteristic. Occasionally, two birds will actually fight until there is a clear winner and the winner will claim the hard fought territory. The best territories, the ones that have the most to offer in regards to food and habitat, usually go to the dominant males.
But this is not always the case. Females, pairs of birds, families or even flocks can hold territories. Young, first season birds on their own for the first time, quite often have to settle for much less in terms of food, habitat, and the ability to attract a mate.
Territories vary widely in size but are usually relative to the amount of food and nesting possibilities that they offer. Some bird's territories, such as hummingbirds, are relatively small; thus ensuring that they can effectively patrol poachers and control selected food sources. Hummingbird territories can be as small as to be measured in square feet. On the opposite side of the spectrum, the territory of a Golden Eagle can be as large as dozens of square miles.
Range is something else altogether. All of the most commonly used field guides for bird identification have range maps for each species. The color codes may vary but generally blue is winter range, pink or red for spring and summer (sometimes referred to as breeding range), and purple usually refers to year-round range. Range maps should be used as general guidelines and not interpreted as absolute. Ranges are always changing in response to environmental factors and population fluctuations. Range maps are most useful when they are recent and up to date. Ranges are sometimes larger or smaller from one year to the next, depending on population changes within the species - the range expands with a growing population and recedes with a diminishing population. Another critical factor that is strongly related to shrinking range is habitat fragmentation and habitat destruction. Most all birds have particular habitats that are especially suited to those species. Remove or significantly alter the habitat and the bird's range changes as well. At the edge of its range, the bird is not seen in substantial numbers, but there are always some individual birds outside this edge, stretching the limits of the range. Also, range maps may show a continuous range, but birds may live only locally within that range. This is particularly true of species that live in specialized habitats. All birds are known to exist in particular geographic regions and areas. This applies to year round resident birds as well as to migratory birds. Ranges typically describe the northern, southern, eastern, and southern limits of each species.
In some cases, such as the Elegant Trogon, the United States range of the bird is severely limited to a relatively few mountain ranges in southeastern Arizona. Within the narrow confines of this range, Elegant Trogons can be found in canyons with streams and mixed woods, usually between 3500 to 8000 feet. Similarly, the range of the Buff-Collared Nightjar (which looks very much like the Common Poorwill) is extremely limited in North America to a few known canyons in extreme southeastern Arizona and just barely across the border into the southwestern corner of the New Mexico boot heel.
The trogon and the nightjar are species that have very specialized requirements about the habitat they live in, and this partly explains why their ranges are so limited in this country. Then there are other species that are not specialists. They seem to be more generalists in that they are very adaptable in many respects and therefore have adapted and adjusted to a wider variety of habitats and foods. Their ranges can be quite large. The perfect example of this situation is the common House Sparrow. Native to Europe, it was introduced to Asia, Africa, and the Americas and on each continent has kept expanding its range. This species is so adaptable that in North America its range now includes all the states in the US and almost the entire southern tier of Canada, coast-to-coast in both countries.
Birder's in southeastern Arizona are very well aware of expanding range as, over a period of time, more sightings of Mexican birds are seen here, both in resident and migratory species. For example, among resident year-round species, the Inca Dove was long associated with the Mexican villages, towns, and urban areas where they lived in close association with people. They were first recorded in the US at Laredo, Texas, in 1866 and then slowly spread their range north as far as Kansas and Arkansas, and as far west as southeastern California. Today their range seems to be increasing as they move up the eastern gulf coast of Texas. It's generally accepted that many species of birds have increased their range in recent years with the widespread popularity of birdfeeding, hummingbirds perhaps more noticeably so. The Sky Island mountains of southeastern Arizona offer good breeding habitat for several species of Mexican hummingbirds not commonly seen here. Partly due to the rise in popularity of feeders, we are able to document larger numbers of more species and demonstrate expanding range. Violet-crowned, Berylline, White-eared, Lucifer, and Plain-capped Starthroat are among the species who are expanding their range north into the United States.