The transfer of ecosystem services across space is a common phenomenon, yet transfers are rarely included when estimating ecosystem services for a locality. We are investigating this topic in the context of the San Pedro River Basin, US/Mexico, and its desert riparian ecosystem, a rare remnant of a formerly extensive riparian network occurring throughout the American Southwest. One of the most widely recognized services provided by this ecosystem is the provisioning of stopover habitat essential to the survival of millions of migrating birds. The San Pedro, by supporting the hemispheric transfer of avian populations, enhances the persistence of many migratory bird species present in western North America. As such, economic valuation of the San Pedro riparian ecosystem requires consideration of more than just the services it yields locally; the supporting service of migratory species transfer must also be valued.

The value of the transfer service provided by a particular migratory habitat is a function of the total species value and the dependence of the species on the habitat in question, summed across each species the habitat supports during migration. Total species value is a function of its existence value, as well as the aggregate value of the ecological functions and services it provides, directly and indirectly, to humans throughout its range. We describe our exploration of combining geographic and ecological techniques to estimate service-related species value and dependence on the San Pedro Basin for selected migratory species.

Results/Conclusions

Each species utilizing or dependent upon the San Pedro riparian corridor for migration imparts value to the habitat. This value is derived from the ecosystem functions and services the species renders throughout its range. In effect, a major ecosystem service of the corridor is that it is responsible for supporting the transfer of ecosystem services across the continent. The methods explored to estimate the value of this service involve a combined ecological and geographic approach to estimate the dependence of migratory species on a particular habitat, as well as their provisioning of ecological functions and services throughout their range. Although presently data limited, the approach can be broadly applied to any type of habitat, and may be substantially refined as new information on migration patterns and ecological roles emerges.