Preserve Selection and Design Considerations: Most landscape level relationships for this species are unstudied. Area requirements, use of corridors, and relationships to ecological processes such as fire are unknown. Apparently benefit from forest fragmentation that promotes shrub successional stages, at least for a time (Rosenberg and Raphael 1986, Stiles 1980), but fragmentation and loss of shrub habitats would be detrimental. As towhees often use brushy riparian habitats, they may naturally use stream and river courses as corridors.
The genetic variation evident in this species should be a consideration in conservation. As a group the "red-eyed" towhees (P. ERYTHROPHTHALMUS, P. MACULATUS, and P. OCAI) display complex patterns of geographic variation and hybridization. For P. MACULATUS alone, nine subspecies are recognized in western North America north of Mexico, and another twelve are known in Mexico and Guatemala (Greenlaw 1996). In the Great Plains, Spotted Towhee interbreeds with Eastern Towhee, and in Mexico interbreeds with Collared Towhee (P. OCAI). See Greenlaw (1996) for more detail on patterns of hybridization, subspecies variation, and gene flow. Sibley and Sibley (1964, cited in Greenlaw 1996) suggest that in Mexico, hybridization between species may have been promoted by human alterations of landscapes that modified ecological barriers (such as the altitudinal zonation of vegetation) and created new ecotones where species would overlap.
Management Requirements: Management should focus on maintaining shrub and sapling layers in preferred forest and shrub habitats, particularly extensive areas of dense, woody thickets and riparian willows and brush (Greenlaw 1996). Management activities may be beneficial or detrimental, depending on how shrub habitats are affected. Towhees will coexist with humans where landscapes are lightly to moderately altered and shrub habitats remain, but heavy development, urbanization, and land conversion destroy habitat (Greenlaw 1996). The prevalence of domestic cats in residential and rural landscapes may increase mortality of adult birds and nestlings (Greenlaw 1996). Brood parasitism by Brown-headed Cowbirds (MOLOTHRUS ATER) is a particular concern. Cowbirds are likely affecting productivity in some areas, with possible long-term consequences for local populations.
FOREST MANAGEMENT: Towhees will occupy forest interiors, forest edges, riparian areas and shrub successional stages of harvest units, and natural openings wherever brushy growth provides foraging and nesting habitat. Management activities that remove shrub layers (e.g., timber harvest, grazing, or fire) would be detrimental in the immediate term until shrubs return. On the other hand, timber harvest, prescribed fire, and wildfire that eventually promote shrub growth or increase the area of favored shrub habitats would be beneficial for the time shrub successional habitats remain. Thus management impacts should be analyzed in a context of habitat patterns across landscapes and cumulative effects. Unfortunately, quantitative information on towhee relationships to management activities and ensuing habitat changes is slim.
In Washington, Stiles (1980) found towhees present in early successional stages of Red Alder (ALNUS RUBRA) up to 12 m in height, but absent in older stands with taller alder. In California valley-foothill hardwood, valley-foothill hardwood-conifer, and valley-foothill riparian habitats towhees are associated with shrub understory of sapling age classes with sparse canopy and 10-24% closure (USFS 1994). In California fragmented Douglas-fir (PSEUDOTSUGA MENZIESII) forests, towhees were associated with recent clearcuts and showed significant positive correlations with percent clearcut, total edge, and insularity (degree to which remaining forest stands were surrounded by clearcuts; Rosenberg and Raphael 1986). However, in a Giant Sequoia (SEQUOIA GIGANTEUM) forest, they disappeared from plots where the living and deadwood understory was removed by cutting and prescribed burning (Kilgore 1971). In Colorado pinyon-juniper woodlands, found in natural openings and chained sites where the tree overstory had been removed and shrubs remained. Positively associated with distance to a habitat edge and with shrub height, but negatively associated with tree canopy height and richness of grass and forb species (Sedgwick 1987).
GRAZING: There is little quantitative information available on grazing effects; response would depend on grazing intensity, timing, and subsequent changes to shrubby vegetation. Also of concern, however, is that towhees are frequent cowbird hosts. Cowbirds are attracted by the presence of livestock and cowbird brood parasitism impacts on host bird productivity can be substantial. Thus towhee presence and vegetation structure by themselves are inadequate in determining livestock effects and productivity must be monitored. Cowbird parasitism rates may also be affected and compounded by landscape patterns at different spatial scales (Tewksbury et al. 1999), but this is unstudied in relationship to this species.
Showed a positive response to grazing in aspen (Page et al. 1978, cited in Saab et al. 1995). Sedgwick and Knopf (1987) found that moderate late-fall grazing of cottonwood bottomland plots in northeastern Colorado did not affect densities in the short term (three years). Densities did vary in parallel from year to year in the control and treatment plots.
However, a comparison of grazed and ungrazed pinyon-juniper with oak understory in New Mexico showed that abundance levels are deceptive in determining the effects of grazing. In the first two years of the study, towhees were more abundant in "ungrazed" plots that had been rested from grazing for 20 years than in moderately grazed plots (three-season grazing November-June with 1.3 ha per animal unit month), but no difference was found in abundance in the second two years. However, nest success was lower in grazed plots. Towhees in grazed plots suffered nest failure from weather and brood parasitism by cowbirds (which are attracted by the presence of livestock), whereas birds in the ungrazed plots did not. Twenty-six percent of nests (n = 23) in grazed plots were parasitized. Nest predation rates were the same in the two treatments. Interestingly, the authors found no differences between means of vegetative measures in grazed and ungrazed plots (Goguen and Mathews 1998).
Management Research Needs: Quantitative information is needed on relationships to habitat types, vegetation structure, landscape patterns, and vegetation change over time. Very little information available on the effects of land management activities, and further study is needed of current forest management practices, effects of different grazing regimes in different habitats, and habitat loss to land conversion at local and regional scales. Information needed on rates of brood parasitism and effects on productivity and populations, particularly in relation to landscape patterns. Also need information on rates of predation on eggs and young. Landscape relationships, use of corridors, area and patch size requirements, seasonal movements, and all aspects of ecology during migration and nonbreeding season need further study.
Biological Research Needs: There have been few quantitative studies on the species, the existing studies mostly coming from the Pacific Coast and Mexico, and our knowledge comes largely from anecdotal information (Greenlaw 1996). More information is needed on basic biology and description, genetics, breeding biology, territoriality and territory size, site fidelity, behavior, demography, phenology, migration patterns and pathways, wintering areas, and general ecology. Geographic variation among subspecies and patterns of hybridization need to be studied with genetic methods (Greenlaw 1996).
