Perspectives on Drought Impacts on Diverse Southwest Ecosystems:

U.S. Fish and Wildlife Service

May 2003

What do we know about drought?

Drought is a regular occurrence in desert ecosystems, but the severity of the current drought is not. Drought can have mild to severe effects on wildlife species. For threatened and endangered species already stressed by other factors, drought can drive these species closer to extinction. Of the 42 listed or proposed animal species in the state, almost two-thirds are aquatic or riparian-dependent. Management has ranged from simply monitoring the effects of drought on populations to extreme hands-on measures aimed towards rescuing individuals.

What information is available and what is still needed?

Sonoran pronghorn are in a crisis situation. In the U.S., the population has declined from an estimated 142 animals in 1998 to 21 in December 2002. Although the spring range conditions have improved, many does may not have bred last year. The fawn crop will be poor, and survival will probably be low.

The number of known cactus ferruginous pygmy-owl nests has dropped from a high of 13 in 2001 to 3 in 2002. Only one young bird survived to dispersal. Due to drought, trees did not leaf out last summer, most of the normal cover was absent, and the young were easy targets for predation. Lack of prey may have also left them weaker and caused them to fledge earlier.

Fish are also affected by reduced stream flows or complete loss of water in channels, loss of pools, fewer aquatic invertebrates, and higher predation from non-native species. Positive effects have also occurred. Fewer external parasites were observed on fish during winter survey counts on the San Bernardino/Leslie Canyon NWR. And the drying of pools in Sabino Canyon meant a reduction of invasive predators such as bullfrogs, crayfish, and green sunfish, and an increase in populations of native frogs.

What drought plans are in place?

Emergency projects are underway to enhance Sonoran pronghorn survival. These include development of forage enhancement plots, reconstructing a water catchment to improve its reliability, and planning a semi-captive breeding program in order to enhance reproductive success and survival.

A population of Chiricahua leopard frogs east of Camp Verde was rescued by hauling water to two stock tanks. All frogs from a third tank were salvaged and held in captivity at the Arizona-Sonora Desert Museum. This strategy was successful in saving a handful of frogs, but it is not a long-term solution for maintaining populations. A better strategy is to continue to renovate stock tanks in this area to increase their water-holding capabilities and to identify natural springs that are holding water and can serve as habitat for the species.

A similar rescue effort occurred near the San Bernardino NWR when a population of the San Bernardino springsnail on private land was almost lost because flows at a spring dried up last summer. This species (an Arizona Wildlife Species of Special Concern) has been extirpated from most of its range. Monitoring is underway to learn more about its habitat requirements. This particular spring has not been managed in a condition to ensure that adequate flows exist to maintain the springsnail population throughout the year. A garden hose kept the population alive until flows returned.

Last year, Fish and Wildlife Service, Forest Service, and Arizona Game and Fish Department salvaged most of the known Little Colorado spinedace from the East Clear Creek Watershed. As creeks dry, this fish is limited to small pools within drainages that normally hold water until the monsoon rains arrive. Last year as the few pools we knew about dried up, the fish were salvaged. With only holding area, we risk losing all the broodstock should something happen to this pond. We are trying to develop additional holding sites, but holding fish in captivity is not the preferred management strategy.

Drought contributed to the loss of two long-lived, reestablished populations of Gila topminnow in the San Pedro Watershed. Although we could better monitor sites like this and rescue populations before they are lost, a better long-term strategy is to determine why these sites fail and manage them to limit failures. Long-term management includes continuing work to restore watersheds, increasing water flows within drainages, and controlling non-native fish and crayfish in these habitats.

What are drought related issues?

Besides the issues related to management of threatened and endangered species, several of the national wildlife refuges in the state depend on water diversions or stream flows to maintain refuge operations and habitats. Continued drought may limit their ability to divert water for wildlife habitat, especially when pitted against human and agricultural purposes.

As water in Arizona becomes even more scarce and competition for that water increases, drought will continue to hamper efforts to recover threatened and endangered species, avoid the future listing of species, and manage our refuges. Long-term planning is needed to better manage our water resources, reduce the spread of both plant and animal non-native species, and restore watersheds so these species can better survive the next drought cycle.

Brenda Smith

Assistant Field Supervisor

Flagstaff Ecological Services Sub-Office