Oases in the Desert: What Do Altered Water Regimes Mean for Sonoran Desert Species?

Author: Clare Aslan

A coyote lopes across Silverbell Road in Tucson, crossing Christopher Columbus parking lot in the pale predawn of late spring. He pauses to drink at the fish-stocked Silverbell Lake. A hummingbird zips over his head, alights momentarily on a low branch, and takes off again. The tramp of light hooves announces the arrival of a family of javelina—two young in tow—at the water’s edge.

In strange contrast to the scene, the low hum of constant car traffic along Silverbell Road and I-10 permeates the air. Houses and industrial complexes can be seen in the distance. This oasis with its steady flow of wildlife is not a part of the open desert. Rather, it is a new ecological community, coalescing around an artificial water source created by human redistribution of water.

In the desert Southwest, urbanization increasingly alters the availability and distribution of water. Due to groundwater mining and surface water diversion, natural riparian and spring habitats are disappearing. To compensate for this loss of natural sources, artificial water sources in open deserts are commonly developed by wildlife managers and environmental impact mitigators. Water from natural sites is often sequestered in urban areas, which contain water-rich features such as parks, golf courses, and botanical gardens. Many native species visit urban water sources. Other species visit artificial water sources in the open desert but rarely or never enter urban areas.

It is clear that both artificial water sources themselves, as well as the moisture-loving vegetation in proximity to the water, can provide essential resources for a variety of desert species. For some species, the presence of artificial water may make urban areas critical stopovers along migratory pathways. For other urban-adapted species, the new concentration of resources in urban areas may generate high reproductive rates. But visitation to water sources in urbanized regions may also expose native species to urban dangers, such as window strikes, cars, domestic cats, and diseases. Urban areas could therefore represent ecological traps: attractive locations promising resources but delivering high mortality rates. If mortality exceeds successful reproduction in these sites, they become “sinks,” exerting an overall negative impact on species populations.

Importantly, climate change models predict increased drought severity in arid lands. This will lead to even further reductions in natural water sources and enhanced reliance on artificial water sources among desert wildlife.

In our capacity as a community-centered natural history center devoted to enhanced understanding of the Sonoran Desert, the Arizona-Sonora Desert Museum has a long history of conservation-relevant research in the region. One of our current research foci is the role of artificial water sources in the broader Sonoran Desert ecological community. Some of our specific research questions include:

• Which native species use artificial water in urban sites, open desert, and the transition zones between them?
• How do the presence and characteristics of artificial water affect the reproductive rates and body condition of desert species?
• How do the presence and characteristics of artificial water affect ecological processes such as pollination and seed dispersal?
• How do the presence and characteristics of artificial water sources affect mortality rates of desert species?

To explore these questions and others at artificial water sources throughout the Tucson region, we are partnering with citizen scientists including museum visitors, students, volunteers, and neighborhood associations. These partnerships increase the number of eyes on the ground, allowing us to gather a rich set of data that can help us more fully understand the circumstances under which artificial water sources can benefit desert species. The research can also help connect Tucsonans with the desert surrounding them. The project is just getting underway, with training of volunteers and listing of potential visitor species; preliminary findings are expected later this fall.

If you or your group would like to be involved in this effort, additional volunteer opportunities will be available soon. Together, we can build our understanding of the importance of our cities for the species of the Sonoran Desert.

Contact Kim Franklin at kfranklin@desertmuseum.org or Clare Aslan at caslan@desertmuseum.org for more information.