Frank P. Howe

A SEVEN-YEAR COMPARISON OF RELATIVE-ABUNDANCE AND DISTANCE-SAMPLING METHODS

Abstract We used data from statewide surveys of riparian birds in Utah, 1992–1998, to compare relative-abundance and distance-sampling methods. By generating relative-abundance indices with point-count methods and density with point-transect sampling methods, we examined whether the assumptions underlying each method were met during field surveys for four bird species (Brown-headed Cowbird [Molothrus ater], Bullocks Oriole [Icterus bullockii], Warbling Vireo [Vireo gilvus], and Yellow Warbler [Dendroica petechia]). Point-count methods failed to reasonably meet the fundamental assumption of constant proportionality, with estimated detectability varying 3- to 5-fold despite the use of widely accepted and well-standardized methods. Population trends based on relative abundance were subsequently unstable, often varying in both magnitude and direction with the survey plot radius used (25 m, 50 m, or unlimited distance). Distance-sampling methods appeared to meet critical assumptions, were robust to assumption violations, allowed methodological self-assessment, and were demonstrably efficient in a large-scale, multispecies survey setting. Our data show surveys of birds without estimations of detectability are likely biased because the assumption of constant proportionality is violated to a degree that precludes strict inference and may confound trend analyses.

Climate and density-dependent drivers of recruitment in plains bison

Abstract In semiarid ecosystems ungulate densities can compound the effects of drought on forage availability, which can feed back to regulate reproduction and offspring recruitment. Climatic changes in the frequency and severity of drought could thus exacerbate these effects. Here, we use long-term data sets to examine the dual influences of population density, cohort, and climatic variation on recruitment in the Henry Mountains bison (Bison bison bison) population. We found that 1-year lagged annual precipitation had a positive effect on recruitment (&bgr;  =  0.032, SE  =  0.009) and population density had a negative effect (&bgr;  =  −0.0023, SE  =  0.0004), but did not detect cohort effects. Furthermore, the effect of population density seemed to be more severe in dry relative to wet conditions, indicating that competition for forage could be severe in drought conditions. These results could help managers gain insight into the effects of climate change on bison population dynamics, and help guide the management of bison abundance on rangelands shared with cattle.

Effects of Sagebrush Treatments on Multi-Scale Resource Selection by Pygmy Rabbits

ABSTRACT The effects of widespread sagebrush removal treatments on pygmy rabbits (Brachylagus idahoensis) are not well understood. Due to reliance on sagebrush, pygmy rabbits are among the species for which these treatments may be detrimental. Our objectives were to evaluate the effects of experimental sagebrush treatment on 8 radio-collared pygmy rabbits between and within home range habitat selection using Monte Carlo simulation from null models. Pygmy rabbits were not extirpated from plots containing habitat treatments, and we found no evidence that treatments affected home range placement. The mean treatment distance of observed home range centers did not differ from repeated trials of random points. However, we found evidence of within home range selection against treatments from 2 of 8 rabbits located close to the treatments. The mean treatment distance of all observed locations for these 2 rabbits was greater than expected based on a null model. We also used snow tracking to show that pygmy rabbits entered treatments in 4 out of 21 trials, which was less often than expected by chance (G 2 = 8.662, P = 0.003). Conservatively, sagebrush removal treatments should not be conducted on active or recently active pygmy rabbit burrows. Elsewhere near known pygmy rabbit sites, treated patches should be small and connected by untreated corridors to prevent potentially limiting movement of rabbits among the untreated habitat.

Mourning Dove Movements during the Reproductive Season in Southeastern Idaho

We determined movements of mourning doves (Zenaida macroura) in relation to selected manmade ponds on the Idaho National Engineering Laboratory (INEL) in southeastern Idaho using radio telemetry during June-August in 1984 and 1985. Maximum distances were measured from dove feeding and loafing sites to watering sites (? = 3.1 km) for 40 doves and to nest sites (t = 3.7 km) for 12 doves. The daily maximum distances from feeding and loafing sites of individual mourning doves to their known watering sites and nesting sites averaged 0.5-2.0 km (n = 8) and 1.1-3.8 km (n = 5), respectively. Movements of adults indicated that mourning dove populations in desert areas would be enhanced by establishing additional permanent watering sites where distances between existing sites are >6 km. Movements of adult doves also indicated minimal opportunity for transport of radionuclides from contaminated ponds in INEL to areas outside INEL during the reproductive season. J. WILDL. MANAGE. 52(3):477-480 Mourning doves on INEL in southeastern Idaho are dependent on water sources made or manipulated by man. Some mourning doves use man-made ponds on INEL that have been contaminated with radionuclides (Arthur and Markham 1978, Halford and Millard 1978); relatively low levels of Cesium-137 contamination have been reported in some of these doves (Markham and Halford 1982). Because of their potentially high mobility, doves using man-made ponds on INEL are capable of feeding and/or nesting in areas adjacent to INEL. Doves using contaminated ponds may thus provide a potential pathway for radionuclide transport to areas off the site. Our objective was to determine daily movements of mourning doves in relation to their watering sites and nests in a cold desert ecosystem. Particular attention was given to doves that used the Test Reactor Area (TRA) radioactive leaching pond to discern whether they were providing a pathway for contaminant transport to areas off INEL. Mourning doves were also monitored at the Naval Research Facility (NRF) This content downloaded from 157.55.39.107 on Wed, 30 Mar 2016 06:44:29 UTC All use subject to http://about.jstor.org/terms 478 MOURNING DOVE MOVEMENTS * Howe and Flake J. Wildl. Manage. 52(3):1988 where none of the ponds were used for radionuclide leaching. Most studies of mourning dove movements have been based on recaptures and band returns. For example, Channing (1979) and Leopold and Dedon (1983) reported movements, based on band returns, of nonmigratory mourning doves in central California. Tomlinson et al. (1960) studied the local movements of mourning doves in Missouri by recording recaptures in walk-in traps placed at 0.4 km intervals over 1,295 ha. Few studies of movements of mourning doves have been conducted using radio telemetry. Hitchcock and Mirarchi (1984) and Grand et al. (1984) did extensive telemetry studies on fledgling doves in Alabama, and Sayre et al. (1980) used radio telemetry to determine daily maximum movements and activity patterns of adult mourning doves in Missouri. We are grateful to O. D. Markham, K. F. Higgins, T. R. McCabe, and C. G. Scalet for project and manuscript review. We thank W. L. Tucker for guidance on statistical design and analysis. We are obliged to INEL staff and technicians who assisted in the collection of data. This research was funded by the Office of Health and Environmental Research, U.S. Department of Energy. This is a contribution of the INEL Radioecology and Ecology program.

RODENT-MEDIATED INTERACTIONS AMONG SEED SPECIES OF DIFFERING QUALITY IN A SHRUBSTEPPE ECOSYSTEM

Abstract. Interactions among seeds, mediated by granivorous rodents, are likely to play a strong role in shrubsteppe ecosystem restoration. Past studies typically consider only pairwise interactions between preferred and less preferred seed species, whereas rangeland seedings are likely to contain more than 2 seed species, potentially leading to complex interactions. We examined how the relative proportion of seeds in a 3-species polyculture changes rodent seed selectivity (i.e., removal) and indirect interactions among seeds. We presented 2 rodent species, Peromyscus maniculatus (deer mice) and Perognathus parvus (pocket mice), in arenas with 3-species seed mixtures that varied in the proportion of a highly preferred, moderately preferred, and least preferred seed species, based on preferences determined in this study. We then conducted a field experiment in a pocket mouse—dominated ecosystem with the same 3-species seed mixtures in both “treated” (reduced shrub and increased forb cover) and “untreated” shrubsteppe. In the arena experiment, we found that rodents removed more of the highly preferred seed when the proportions of all 3 seeds were equal. Moderately preferred seeds experienced increased removal when the least preferred seed was in highest proportion. Removal of the least preferred seed increased when the highly preferred seed was in highest proportion. In the field experiment, results were similar to those from the arena experiment and did not differ between treated and untreated shrubsteppe areas. Though our results suggest that 3-species mixtures induce complex interactions among seeds, managers applying these results to restoration efforts should carefully consider the rodent community present and the potential fate of removed seeds.