Chapter 7

Territoriality and Migration

1. In choosing where to live, many animals actively select certain places over others. Ideal free distribution theory deals with the surprising observation that some animals may occupy less favored areas rather than competing for prime habitat. Hypotheses based on ideal free distribution theory predict that animals that choose areas where there is less competition may have the same fitness as those that have joined many others in using a favored habitat.

2. Territorial behavior results in clear costs to individuals that attempt to monopolize a patch of real estate against rivals. Defense of living space evolves only when individuals can gain substantial benefits from holding a territory—such as greater access to food or mates. As predicted, individuals abandon their territories when the costs exceed the benefits.

3. Territorial contests are usually won quickly by owners. The competitive edge held by territorial residents over intruders may stem from superior physical strength or energy reserves (which give residents higher resource-holding potential), or it may exist because residents have more to lose than intruders can gain (a payoff asymmetry) thanks to the dear enemy effect, in which familiar neighbors stop fighting with one another over territorial boundaries.

4. In many species, young individuals disperse from territories defended by their parents. Dispersal, like territoriality, comes with fitness costs such as increased mortality. Major benefits can include the avoidance of inbreeding with close relatives, escape from aggressive competitors, and the ability to find and exploit resources in short supply in the natal territory or home range.

5. Migration is the temporary movement of individuals between two well-separated areas. The ability to migrate very long distances may have originated in populations that had acquired the capacity for short-range migrations. The behavior may have adaptive value because migrants keep the costs of travel low while gaining major benefits from their long-distance journeys, such as access to greater resources that are available only during certain seasons.

6. Studying migratory connectivity (linking populations between the breeding and wintering grounds) has the potential to help identify regions of conservation importance that are critical to a species’ survival. Migratory connectivity in birds can be examined using a variety of technologies, including those that use markers that are intrinsic to the birds to indirectly track movements, as well as those that require the attachment of extrinsic markers on the bird to more directly track movement.

7. Some species of birds show variation in migratory behavior, both among populations as well as within populations. Understanding what drives this behavioral variation may enable scientists to help conserve species that are showing population declines only in portions of their breeding ranges.