This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain. Herpetofaunal Use of Four Habitats of the Middle Gila River Drainage, Arizona 1 Martin D. Jakle and Thomas A. Gatz 2 Abstract.--Data on reptiles and amphibians were gathered using pit-fall traps and by observation along the Gila River northeast of F!orence, Pinal County, Arizona. Four habitat types were sampled: desert wasn, desert upland, mature salt cedar, and mesquite bosque. A total of 104 individuals of 12 species were trapped and an additional seven species were observed. Based on trap data, species diversity was greatest in the desert wash, and lowest in the salt cedar habitat. Reptiles and amphibians showed little use of the salt cedar habitat which may reflect the lack of structural diversity in the herbaceous and shrub layers and reduced light penetration due to a dense canopy. INTRODUCTION The salt cedar habitat was a strip of mature trees bordering the Gila River. The strip was Increasing attention is being focused on approximately 350 m by 45 m, composed of an even-aged stand of mature trees. The stand had riparian habitat because of its recognized high little species diversity, being composed of almost values for wildlife and its rapidly dwindling 100 percent salt cedar trees (Tamarix pentandra) supply. Stream diversions, reservoir construction, ground water overdraft, grazing, which were quite dense, and formed a thicket. The density of the stand reduced light penetration and phreatophyte clearing, recreational demands, and precluded establishment of a herbaceous layer. other uses are taking their toll on a habitat type that naturally occupies a small percentage of the The mesquite bosque habitat also bordered the total landmass. Several workers have documented Gila River, adjacent to the salt cedar habitat and the importance of riparian habitats to birds in was approximately 1 km by 75 m. Mature mesquite the Southwest (Carothers et al., 1974; Stevens et trees (Prosopis velutina) were the dominant al., 1977; Szaro and Jakle, in press); however, species present, but the stand was a heterogeneous few researchers have studied the Southwestern mix which included Goodding willow (Salix riparian herpetofauna. This paper discusses the gooddingii) and cottonwood (Populus fremontii). herpetofauna of two riparian and two desert This habitat type had greater structural diversity habitats in Arizona. which included a shrub and herbaceous layer. The surrounding area consisted of two STUDY AREA AND HABITAT DESCRIPTION habitats: desert upland and desert wash. In the desert upland habitat the dominant tree species The study area is located in southcentral were foothill palo verde (Cercidium microphyllum) Arizona 21 km east of Florence, Pinal County, and saguaro (Carnegiea gigantea). The dominant at an elevation of 500 m. The dominant plant shrubs consisted of triangle leaf bursage community in this area is the Sonoran desert scrub (Ambrosia deltoidea), which was by far the most formation and, more specifically, the palo abundant, and ratany (Krameria parvifolia). The verde-cacti-mixed shrub series (Brown 1982). The herbaceous layer consisted primarily of an annual Gila River flows through this area and forms a grass, red brome (Bromus rubens), which grew riparian corridor. mainly under nurse plants. 1 The desert wash was located in a large sandy, Paper presented at the North American ephemeral drainage course, Donnelly Wash, which Riparian Conference, April 16-18, 1985, Tucson, emptied into the Gila River. This habitat was Arizo2-a. patchy, consis~ing of large sandy areas devoid of Respectively, General Biologist and Super­ any vegetation interspersed with vegetated areas. visory Biologist, U.S. Bureau of Reclamation, The dominant tree species were blue palo verde Phoenix, Arizona 85068. (Cercidium floridum), ironwood (Olneya tesota), and mesquite. Canyon ragweed (Ambrosia ambrosioides), wolfberry (Lycium andersonii), and gray thorn (Zizyphus obtusifolia) were the dominant shrubs; red brome dominated the herbaceous layer. 355 METHODS DISCUSSION The herpetological array pit-fall trapping Based on pit-fall trapping data, the desert technique developed by Campbell and Christman wash habitat had the highest species diversity and (1982) and modified by Jones (1980) was used to equaled the desert upland as having the highest determine species composition and relative abundance of the four habitats studied. The high abundance of reptiles and amphibians in the four value of this habitat, i.e. palo verde-cacti-mixed habitat types. This method uses four 18.4 1 shrub, is supported by deVos et al. (1983). In a pit-fall traps. One trap is located in the center study west of Tucson, Arizona, this habitat had and connected to three peripheral traps by 7.2 m the greatest reptile and amphibian diversity of aluminum flashing which extends from the center the five habitats studied: palo verde-mixed trap at equal angles. Two arrays each were placed cacti, creosote-bursage, desert grassland, in the desert wash, desert upland, and mesquite mesquite bosque, mixed ripari~n woodland. bosque habitats, and one in the salt cedar habitat. Trapping commenced on March 23, 1983, in Although the salt cedar habitat had the the desert habitats and 6 to 15 days later in the lowest density and diversity of all habitats riparian habitats. Trapping ended May 5, 1983. studied, the occurrence of 3 individual li~ards of two species is noteworthy. K. Bruce Jones , in Traps were checked at least weekly. All captured several studies of salt cedar, has never collected lizards were toe-clipped, weighed, measured, any re~tiles in this habitat type. Jakle and sexed, and released at the capture site. Baucom conducted a bird census in a mixed salt Recaptured individuals were not used to determine cedar and Goodding willow habitat at Picacho diversity or abundance. Species diversity was Reservoir in central Arizona. During the census calculated based on the formula of Shannon and only two individuals--a desert spiny lizard Weaver (1948). (Sceloporus magister) and a coachwhip (Masticophis flagellum)--were recorded in 17 km of bird transects. Reptile populations were studied at RESULTS Whitlow Dam in central Arizona by Szaro and Belfit (in press). They reported low numbers of reptiles A total of 104 reptiles and amphibians ~ere and amphibians in a riparian habitat consisting of trapped during 406 trap days between March 23 and 78 percent Goodding willow and 22 percent salt May 5, 1985, an average of 0.26 individuals per cedar. trap day for all habitats combined. The desert upland and desert wash habitats had the highest trap success, 0.31 individuals per trap day. The These studies all report a depauperate mesquite habitat had the next highest trap herpetofauna in riparian habitats which were success, 0.22 individuals per trap day and the composed of either salt cedar or a mixture of salt cedar habitat had the lowest value with 0.06 Goodding willow and salt cedar. Szaro and Belfit individuals per trap day. There was a significant (in press) hypothesize that the recent development difference between the number of individuals of the riparian habitat behind Whitlow Dam (the captured in these two adjacent riparian habitats dam was constructed in 1959) and its isolation (Chi Square Test= p<.01). A total of twelve from other such habitats may explain the relative species were trapped (table 1). The greatest lack of reptiles. This area has no naturally species diversity (1.81) was found in the desert occurring relict riparian species nor has there wash and the lowest (0.63) was found in the salt been any recent colonization. Jones et al (in cedar (table 1). press) found that even naturally occurring riparian habitats rapidly lose "riparian or A total of 21 species of reptiles and upland" species as they become more isolated. amphibians were trapped or observed in the study However, another factor that all these habitats area (tables 1 and 2). Species which were only have in common is a dense canopy. The dense observed, and not trapped, were primarily large canopy reduces light penetration and inhibits the snakes. developmeent of shrubs and a herbaceous layer of ground cover. Indeed, Pianka (1966) studied Seven species of reptiles and amphibians were lizard populations in the western United States collected in only one habitat; five species were and reported a strong positive correlation between only trapped in the desert wash and two only in structural diversity and the total number of the desert upland. The western whiptail lizard lizard species. (Cnemidophorus tigris) was the most abundant species in all habitats except salt cedar, where 3 it did not occur. Two additional species, the Jones, K.B. 1983. Personal conversation, tree lizard (Urosaurus ornatus) and desert spiny U.S. Bureau of Land Management, Phoenix Training lizard (Sceloporus magister), were found in three Cente4, Phoenix, Arizona. of the four habitats. Jakle, M.D. and F.M. Baucom. 1983. An inventory of birds and fish of Picacho Reservoir. Unpublished report, Bureau of Reclamation, Phoenix, Arizona. 356 Table 1.--Summary of amphibian and reptile abundance based on pit-fall trap data from the four habitat types of the Florence study area, Pinal County, Arizona Habitat Type Desert Desert Mesquite Salt Cedar Total Species Upland Wash Riparian Riparian Individuals Bufo punctatus 1-~:/ ( . 008 )!/ 2 (.02) 3 (.007) caTiisaurus draconoides 6 (0.5) 6 (.05) Cnemidophorus tigris