CITY OF TUCSON

HABITAT CONSERVATION PLAN

Ground Snake and Tucson Shovel-nosed Snake Subcommittee

Meeting Notes

Topic: Stressors and threats to Ground Snake and Tucson Shovel-nosed Snake

Date: May 16, 2005, 1 pm

Location: U.S. Fish and Wildlife Service office

Participants: Cecil Schwalbe and Phil Rosen, University of Arizona; Trevor Hare, Sky Island Alliance; Marit Alanen, U.S. Fish and Wildlife Service; Ken Kingsley and Leslie Liberti, SWCA

The participants discussed both snakes intermittently and simultaneously. The primary concern for both species is that most of their former known habitat has been developed by agriculture, roads, and to a lesser but increasing degree, housing and industry. The remaining parcels of relatively undeveloped habitat may be too isolated and too poor in quality to sustain populations. Fragmentation by roads and agricultural fields, and now housing, is the primary cause of losses of these species. Increased traffic on roads results in roadkill and/or collecting. Most of the known records of both species are from specimens, alive or dead, found on roads. Specific resources needed by these snakes, the full suite of necessary components of habitat, and the size of parcels needed to sustain populations are among the unknowns. The two snakes do not usually occur in the same area, but there are examples of them being caught in the same pitfall trap (along the Hassayampa, where a study was done). They generally are found in different soil types. The ground snake is typically found in valley soils that have sufficient clay in them so that they crack after drying. The Tucson shovel-nosed snake is found in sandy soils that include small mammal burrows, primarily heteromyids (kangaroo rats and pocket mice).

In the 1970s, Avra Valley and Sanders Roads were the best places to find Tucson shovel-nosed snakes. There were a few remaining patches of relatively undisturbed land along these roads. It is not known whether these patches were, in fact, “good” habitat, or just the only habitat. What is known is that the snake has not been found there in the past two decades or so. The typical habitat for this species is creosote flats between the CAP canal and the Silverbell Mountains bajada. The typical habitat for the ground snake is floodplains. These habitat types in the study area have been subjected to many impacts, including development and major flooding in 1983 and 1993. Agriculture, including irrigation and drainage ditches, has undoubtedly had an impact on movement of snakes, and on the food resources used by them. It is not known whether there is sufficient existing undisturbed suitable habitat to sustain a population of either of these animals. It is possible that suitable habitat could be restored or created, but we do not currently have enough information to know exactly what to do.

One of the areas of greatest lack of knowledge is the abundance and distribution of food (prey animals). Much of the area of City lands and the former range of both species of snakes has been invaded by non-native insects, other invertebrates, and plants, with (presumed) concomitant loss of native species. Both species of snakes feed largely on invertebrates (insects, scorpions, spiders and centipedes). Little or nothing is known about the abundance, diversity, distribution, and population cycles of suitable prey species in this area, especially on land that has been disturbed. Although there is some information available on dietary items, identification of a wide range of samples has not been done beyond the most rudimentary (class, family) level, which is not particularly useful for understanding population dynamics and food requirements of prey species. A serious study of the invertebrates and burrowing rodents (which provide holes used by the snakes) would be an invaluable component of understanding and managing for the survival and recovery of these snakes and several other species (burrowing owls, cactus ferruginous pygmy-owls). Understanding the prey animals and hole providers may permit development of a food management plan for the snakes and owls.

Ultimately the best conservation approach would be to restore the disturbed lands to fully functioning natural desert communities. Unfortunately, the steps to get to that goal are not entirely known. Also necessary would be accurate mapping of soils and potential natural vegetation, separately distinguishing creosote bush dominated desertscrub and floodplain bottomlands. Restoration to the appropriate vegetation conditions to match edaphic conditions should be the goal. Introduction of plants, invertebrates, and rodents may be necessary before the snake could be reintroduced and established. This approach would also require examination of adjacent lands to evaluate conditions and potential for management and as sources of propagules.

Ground snake habitat could be created around recharge basins, but not shovel-nosed snake habitat. The areas between recharge basins could be planted and managed for floodplain vegetation that is characteristic of ground snake habitat.

It is possible that underpasses beneath roads in strategic areas might benefit one or both species of snake.

Unfortunately, not enough is known about either species to complete the threats matrix. The accompanying attempt is the best that can be done at this time.

A site visit by these experts would be valuable to clearly demarcate suitable and potentially suitable sites for management and restoration for these species.