Robert D. Ohmart

Use of exotic saltcedar (Tamarix chinensis) by birds in arid riparian systems

Avian use of saltcedar (Tamarix chinensis) along the middle Pecos River was compared with similarly collected data along the lower Colorado River and Rio Grande. Use of saltcedar ranked high among all bird groups in all seasons on the middle Pecos River. In contrast, many species do not occur in saltcedar on the lower Colorado River, while few species winter in saltcedar on the lower Rio Grande. Occurrence of granivores and insectivores during winter in saltcedar on the Pecos River may be explained by seed-producing shrubs and annuals within or adjacent to these habitats. Most breeding birds on the Pecos River are summer visitors. These breeding species, though present, do not occur in saltcedar on the Colorado River despite abundant food resources and occur in intermediate abundances on the Rio Grande. Densities of several summer-visiting insectivores have declined markedly on the Colorado River since the proliferation of saltcedar, whereas they have remained relatively stable in other river valleys to the east. Biogeographical considerations, specifically elevational (climatic) gradients, are suggested reasons for this phenomenon.

The Effects of Timber Harvesting on Breeding Birds in a Mixed-Coniferous Forest

within a year and in three years the numbers of both species and individuals had increased. The purpose of our investigation was to determine differences in individual avian species densities, species occurrence, and diversity values in a virgin mixed-coniferous forest and in a recently harvested forest. In the logged portion of the study area most of the trees forming the forest canopy were removed. We wanted to determine whether selective

Habitat Selection Attributes of an Avian Community: A Discriminant Analysis Investigation

Habitat use characteristics of all bird species occurring in the lower Colorado River valley were studied. Seventy—two transects, each through homogeneous stands of vegetation and together representing all riparian habitat types occurring in the area, were censused three times monthly for 2 yr (1977, 1978) to provide distributional records for all species. From the census data we divided the transects into three groups for each bird species each season: transects where the species was recorded in both 1977 and 1978, transects where the species was absent both years, and transects where the species occurred in only one of the years. We used discriminant analyses to classify the habitat on each transect as suitable or unsuitable for each species, using a set of eight species composition measures, four foliage density measures, and foliage height diversity (FHD). Mean habitat discriminability of all species varied from a low of 86% in summer to a high of 91% in late summer. Most species showed extensive variability among seasons in both the degree of habitat selectivity and the criteria used in habitat selection. This variability reflected both changes in population structure of the species and responses to changing resource and climatic pressures. Ecological attributes of the species were examined to determine which factors shaped the habitat use patterns of each. Feeding guild played only a small role in both the degree and criteria of habitat selectivity, except for highly specialized feeders such as nectivores and frugivores. Species with restricted distributions were usually habitat specialists, but species with widespread distributions included both habitat generalists and specialists. During spring and summer nonresident, short—stay species showed greater habitat selectivity than did extended—stay species, but during nonbreeding seasons both short—stay and extended—stay species showed equivalent habitat selectivity. That both the mix of habitat generalists and specialists and the habitat selectivity of individual species varied seasonally implies that the organization of habitat use of the community is the dynamic product of many interacting factors. The importance of individual habitat attributes was also examined. Species showed preferences for particular habitat attributes significantly more frequently than they avoided habitat attributes. FHD was the most frequently important variable in differentiating areas used from areas not used. Proportions of honey mesquite, cottonwood, and willow in the vegetation were also frequently important variables in habitat selection by avian species, but usually in conjunction with FHD. Foliage density characteristics were less frequently significant, but for species where these measures were important, they tended to be the primary habitat selection criterion. In summer and late summer, habitat selection criteria of individual species seemed independent of the selection criteria of the other species in the community. In other seasons there was evidence of species interactions in these habitat selection patterns. These empirical findings for an entire avian community over all seasons are an advance in our understanding of how habitat use patterns of communities are organized. The extensive seasonal variability in habitat use by avian species and variability of distributions of individual species between years imply that studies of community organization can best be done with large—scale, long—term studies.

Ecological Relationships Among Arboreal Desert Lizards

Three arboreal desert lizards (Urosaurus graciosus, U. ornatus, and Sceloporus ma- gister: Iguanidae) occur in close association in riparian habitats of central Arizona. The lizards were studied over 2 yr, to determine patterns of resource utilization. Urosaurus graciosus and U. ornatus are similar in body size, but Sceloporus magister is much larger. Juvenile S. magister are, however, similar in body size to adults of both Urosaurus. Ratios of head and body size (larger species:smaller species) reveal similarities between the Urosaurus species and between both species of Urosaurus and juvenile S. magister, but large differences be- tween Urosaurus species and adult S. magister. Active body temperatures of all three species were similar, and the only significant difference in time of activity was between S. magister and U. ornatus. The habitat of U. graciosus reached higher air and substrate temperatures than that of U. ornatus and received greater incident radiation (S. magister occurred in both habitats). Urosaurus ornatus and S. magister avoid extremes of temperatures by entering crevices in trees, retreating under loose bark, or entering mammal burrows or nests, whereas U. graciosus retreat to shaded portions of tree trunks and are thus less able to avoid extremes. Urosaurus graciosus occur in relatively small trees and forage in the canopy; U. ornatus inhabit large trees and forage on trunks and large limbs; S. magister occupy trees of all sizes but forage primarily on trunks and large limbs, and on the ground. Prey sizes were significantly different among species and with one exception (S. magister), signifi- cantly different within species among years. Diets of all three change seasonally and yearly, presum- ably in association with resource availability. Diet overlaps are often high but fluctuate seasonally and yearly. Data on resource availability suggest that all species exploit the temporally abundant insects. Data presented on habitat utilization, activity times, body temperatures, and food eaten reveal partitioning of the arboreal habitat in three dimensions between U. graciosus and U. ornatus and partitioning of prey size between the two Urosaurus as a group, and S. magister.

Water Economy of Two Desert Canids: Coyote and Kit Fox

Water loss rates (W1) were determined by tritium dilution for free-ranging kit foxes ( Vulpes macrotis ), for unrestrained desert coyotes ( Canis latrans ), and for kit foxes in a naturally landscaped outdoor enclosure. Coyote W1 was much greater in summer than in winter ( P < 0.001). Seasonal variation of W1 was not statistically apparent in kit foxes. The weight-specific water loss of kit foxes was intermediate between summer and winter rates in coyotes. Kit fox W1 was 65% of that predicted on the basis of body weight, whereas W1 for summer coyotes was 155% of predicted. Metabolic water was estimated to contribute 18% of total daily water requirements for kit foxes and approximately 10% for coyotes in summer. For both coyotes and kit foxes, the acquisition of preformed water was calculated to require substantially more prey than was required to meet energy demands.

Nonlinear relationships between birds and vegetation

We tested for the presence and importance of nonlinear relationships among bird species abundances and vegetation characteristics of the lower Colorado River valley. We transformed vegetation variables into polynomials and then ran multiple regressions, with bird densities as the dependent variables. Polynomial variables were selected in 36% of first steps and 45% of second steps in the regressions. In a significant number of cases there was a response to a polynomial variable but not to the original linear variable. Importance of curvilinear responses varied among bird species. This method offers a more comprehensive examination of responses to envirnomental gradients because unimodal and some skewed relationships can be detected. See full-text article at JSTOR

Resource Utilization by Desert Rodents in the Lower Sonoran Desert

Four species of heteromyid rodents were studied in 5 communities in the Lower Sonoran Desert to examine differences in resource utilization by heteromyids in terms of: (1) collection of seed species, seed size and seed type (shrub—tree, forb and grass) and (2) association with amount of perennial cover of habitat. These rodents were not allocating resources by seed species or seed size. These rodents were collecting seeds to some degree by seed type, however, this was related to foraging in particular microhabitats. We found no correlation between numbers of each species of seed in cheek pouch contents and energy content per seed species. These heteromyids were opportunistic in collecting seeds as shown by considerable variation in seed species collected by populations and species among habitatas and seasonal variation in seed species collected. These heteromyids appear to partition seed resources by specializing on particular microhabitats. If these heteromyids use microhabitats optimally as granivores, they cannot allocate resources by seed species, size or type without risking local extinction due to the high variable production of specific seed species and sizes in the desert. The regular distribution of body sizes among heteromyids in a community appears to be a consequence of exploiting particular microhabitats in the desert community rather than allocating resources by seed—size selection.

Cutaneous Water Loss in the Roadrunner and Poor-Will

Avian physiologists have generally assumed that since birds lack sweat glands, cutaneous evaporation is negligible. However, recent data indicate that the skin represents a major avenue of evaporative water loss (EWL) in the Painted Quail (Excalfactoria chinensis), Village Weaver (Ploceus cucullatus), Budgerigar (Melopsittacus undulatus), Zebra Finch (Poephila castanotis) (Bernstein 1969, 1970, 1971a, b), and the Domestic Pigeon (Columba livia) (Smith 1969; Smith and Suthers 1969). Not all birds lose large amounts of water through the skin. SchmidtNielsen et al. (1969) state that the skin plays a minor role in EWL in Ostriches (Struthio camelus), contributing less than 2 percent of total evaporation at 400C. The purpose of this study was to examine cutaneous evaporation in two North American desert-inhabiting birds, the Roadrunner (Geococcyx californianus) and the Poor-will (Phalaenoptilus nuttallii). Oxygen consumption and EWL have been studied previously in both species over a wide range of ambient temperatures (Bartholomew et al. 1957; Bartholomew et al. 1962; Calder and Schmidt-Nielsen 1967; Lasiewski 1969; Lowe and Hinds 1969).

Avian Community Structure Changes in a Mature Floodplain Forest after Extensive Flooding

Effects of flooding on the vegetation and avian communities of the Bill Williams River, Arizona, were evaluated from 1976 to 1983. High water flows in 1978 through 1980 caused the death of 99% of all Fremont cottonwoods (Populus fremontii) and 64% of all Goodding willows (Salix gooddingii) on a 120-ha area near the confluence with the Colorado River. By 1982, cattails (Typha spp.) had become the dominant vegetation. Groundand canopy-dwelling avian insectivores and cavity nesters decreased, whereas passerine marsh insectivores and rail-like species increased. Water released from Alamo Dam resulted in loss of the last remaining large stand of mature cottonwood-willow habitat in the lower Colorado River valley, causing declines in numbers of some bird species possibly threatened with local extirpation. Need for flood management procedures to conserve vegetation is paramount when beleaguered habitats are involved. J. WILDL. MANAGE. 51(2):495-502 Creation of reservoirs and channelization of rivers have extensively altered plant and animal communities along many major water courses. In some areas controlled water releases in spring and early summer have resulted in a spread of native riparian tree species, as along the Platte River in Colorado and Nebraska (Williams 1978), thus increasing riparian wildlife in that area. However, in other areas, water flow management has been detrimental to both native vegetation and wildlife, as along the Missouri River (Anderson 1971, Johnson et al. 1976). Such problems are encountered also in the Southwest, where a prolific exotic tree, Chinese tamarisk (Tamarix chinensis), largely has replaced native tree species in many areas (Horton 1977). The lower Colorado River and its tributaries are such areas and serve as dramatic testimonials to the ecological consequences of heavily managed riverine systems. Examination of historical records shows that until the mid-1800s, the lower Colorado River was lined with gallery forests consisting of cottonwoods and willows. Channelization of the river, cutting of trees for firewood, fires, and land clearing for agriculture removed most of these forests (Ohmart et al. 1977). Cessation of natural floods and high soil salinities have prevented the return of these communities. Today, most Fremont cottonwood and Goodding willow areas that remain in the lower Colorado River valley are decadent and form mixed stands with exotic tamarisk, screwbean mesquite (Prosopis pubescens), honey mesquite (P. juliflora glandulosa), and arrowweed (Tessaria sericea). Only along the Bill Williams River does the cottonwood-willow forest remain relatively intact in the lower Colorado River mainstem and adjacent tributary deltas. A water release from Alamo Dam (near the confluence of the Bill Williams and Big Sandy rivers, Mohave County, Arizona) of unusually long duration flooded a 120-ha stand of cottonwood and willow on the Bill Williams River at its confluence with the Colorado River during October 1978-April 1981. Management of native vegetation is presently given very low priority in flood control procedures. This study was conducted to determine the effects of longterm flooding in a riparian forest and to denote subsequent changes in the avifauna. Results from this study will be useful in planning management options during future flooding events. Special thanks are due R. W. Engel-Wilson, M. J. Kasprzyk, J. M. Jackson, and D. Krueper for organizing and assisting with the fieldwork. D. E. Busch provided water flow data and insightful views into the workings of water management agencies. K. V. Rosenberg, A. W. Laurenzi, and V. C. Hink critically reviewed the manuscript and helped with interpolation of preand during-flood bird and vegetation data. S. M. Cook and J. R. Durham provided editorial assistance, and C. D. Zisner typed the manuscript. The research was funded partly by the U.S. Bur. Reclamation, Contract 7-07-30-V0009.

Metabolism and Body Temperature of Two Desert Canids: Coyotes and Kit Foxes

Oxygen consumption (VO2) and body temperature (Tb) of desert coyotes ( Canis latrans ) and kit foxes ( Vulpes macrotis ) were measured at ambient temperatures between —10° and +43°C. Measurement of VO2 established a thermal neutral zone between 22° and 26°C for coyotes, between 19° and 31°C for kit foxes in summer, and between 23° and 33°C for kit foxes in winter. Within the zone, metabolic rate for coyotes was 0.0015 watts per gram (W/g) or 79% of the predicted weight-specific basal metabolic rate; kit fox metabolic rate was 0.0034 W/g in summer and 0.0028 W/g in winter, or 117% and 97% of predicted, respectively. Kit foxes exhibited high thermal conductance, which varied seasonally. High thermal conductance in the kit fox is hypothesized as an adaptation for dissipating exercise heat loads by nonevaporative means. Kit foxes made minimal use of evaporative cooling for dissipation of metabolic heat. The Tb of both species was elevated at warm ambient temperatures.