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
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
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.