Samuel K. Riffell

Does Repeated Human Intrusion Cause Cumulative Declines in Avian Richness and Abundance

Human intrusion, the mere presence of people in the environment, has be- come a dominant form of disturbance in many landscapes. Some forms of intrusion from recreationists and other groups occur repeatedly and can seriously alter avian reproduction, survival, and habitat use. Accordingly, repeated intrusion has the potential to cause impacts that accumulate through time and that are manifested as progressive declines in avian richness and abundance. From 1989 to 1993, we experimentally assessed whether or not temporally cumulative impacts occurred in Wyoming bird communities as a result of re- peated intrusion by solitary hikers; the intrusions lasted 1-2 h each week during 10 con- secutive weeks of each years breeding season. We tested a priori hypotheses about declines in overall richness and abundance, relative richness and abundance for sets of common and uncommon species, richness and abundance for six guilds, and separate abundances of four common species. Relative richness and abundance for the set of common species were the only metrics to exhibit significant declines between years during the 5-yr period. The declines in these variables, however, were not cumulative. At a statistical power level of 0.85, minimum detectable differences for many variables were small enough to have allowed easy detection of substantive declines, had any occurred. The yearly effects we detected for some richness and abundance variables may not have led to cumulative declines because individuals displaced one year may have been replaced in subsequent years, and some individuals each year may have habituated to or learned to tolerate the intrusions. For the avian communities and intrusion levels we studied, managers should focus on trying to preclude or ameliorate short-term impacts. Attempts to identify the types and intensities of intrusion that actually cause cumulative declines in richness and abundance should continue. Data about intrusions that do not generate cumulative declines, such as those presented here, are just as important as data about intrusions that do cause cumulative declines; managers need both to define the scope of intrusion disturbances that can lead to cumulative impacts in avian communities. Information about the cumulative effects of intrusion should be used by conservation biologists, wildlife managers, and land-use plan- ners to decide whether or how to control intrusion.

Effects of the Conservation Reserve Program on northern bobwhite and grassland birds

The Conservation Reserve Program (CRP) has converted just over 36 million acres of cropland into potential wildlife habitat, primarily grassland. Thus, the CRP should benefit grassland songbirds, a group of species that is declining across the United States and is of conservation concern. Additionally, the CRP is an important part of multi-agency, regional efforts to restore northern bobwhite populations. However, comprehensive assessments of the wildlife benefits of CRP at regional scales are lacking. We used Breeding Bird Survey and National Resources Inventory data to assess the potential for the CRP to benefit northern bobwhite and other grassland birds with overlapping ranges and similar habitat associations. We built regression models for 15 species in seven different ecological regions. Forty-nine of 108 total models contained significant CRP effects (P < 0.05), and 48 of the 49 contained positive effects. Responses to CRP varied across ecological regions. Only eastern meadowlark was positively-related to CRP in all the ecological regions, and western meadowlark was the only species never related to CRP. CRP was a strong predictor of bird abundance compared to other land cover types. The potential for CRP habitat as a regional conservation tool to benefit declining grassland bird populations should continue to be assessed at a variety of spatial scales. We caution that bird-CRP relations varied from region to region and among species. Because the NRI provides relatively coarse resolution information on CRP, more detailed information about CRP habitats (spatial arrangement, age of the habitat (time since planting), specific conservation practices used) should be included in future assessments to fully understand where and to what extent CRP can benefit grassland birds.

Using Fractal Analyses to Characterize Movement Paths of White-Tailed Deer and Response to Spatial Scale

Abstract It is often difficult to test hypotheses about how and why animal movement responds to environmental conditions, and at what spatial scales movement decisions are made, all of which are critical for sound management. We used fractal dimension (D) as a measure of tortuosity because it described animal movement patterns and was useful for testing hypotheses about effects of sex, home-range size, monthly rainfall, and reproductive phase on movement paths and for detecting changes in movement patterns of animals across a range of movement distances. We captured and fitted 33 (18 females and 15 males) white-tailed deer (Odocoileus virginianus) with global positioning system collars. We found that females moved more tortuously (D  =  1.75 ± 0.035 SE) than males (D  =  1.549 ± 0.025). These differences in movement were related to home-range size of females but not of males. Rainfall predicted D for females; thus, females may have been able to forage more intensively in a smaller area due to increased forage availability. Fractal D of females was greatest during the parturition period (1.468 ± 0.02), likely due to restricted movements in smaller areas or increased foraging. Home-range size of males was similar in spring and rut, but D was lower during rut, indicating that deer changed movement patterns within previously established home ranges. Movement patterns were similar at path lengths related to foraging patches and home ranges, whereas movement patterns changed as path length approximated the size of habitat patches.

A meta-analysis of bird and mammal response to short-rotation woody crops

Short‐rotation woody cropping (SRWC) refers to silvicultural systems designed to produce woody biomass using short harvest cycles (1–15 years), intensive silvicultural techniques, high‐yielding varieties, and often coppice regeneration. Recent emphasis on alternatives to fossil fuels has spurred interest in producing SRWC on privately owned and intensively managed forests of North America. We examined potential bird and small mammal response at the stand level to conversion of existing, intensively managed forests to SRWCs using meta‐analysis of existing studies. We found 257 effect sizes for birds (243 effect sizes) and mammals (14 effect sizes) from 8 studies involving Populus spp. plantations. Diversity and abundance of bird guilds were lower on short‐rotation plantations compared with reference woodlands, while abundance of individual bird species was more variable and not consistently higher or lower on SRWC plantations. Shrub‐associated birds were more abundant on SRWC plantations, but forest‐associated and cavity‐nesting birds were less abundant. Effects on birds appeared to decrease with age of the SRWC plantation, but plantation age was also confounded with variation in the type of reference forest used for comparison. Both guilds and species of mammals were less abundant on SRWC plantations. These conclusions are tentative because none of these studies directly compared SRWC plantations to intensively managed forests. Plantations of SRWCs could contribute to overall landscape diversity in forest‐dominated landscapes by providing shrubby habitat structure for nonforest species. However, extensive conversion of mature or intensively managed forests to SRWC would likely decrease overall diversity, especially if they replace habitat types of high conservation value.

Repeated human intrusion and the potential for nest predation by gray jays

Through attraction of avian nest predators, human activity near nests is known to cause lower nesting success or nest failure in some species. This is a significant conservation issue because many wildlands are subjected to repeated intrusion by recreationists, ecotourists, and other user groups during avian breeding seasons. Yet, wildlife scientists still have limited knowledge about the extent to which repeated human intrusion attracts avian nest predators. We studied this topic in subalpine forest in Wyoming, USA, and experimented with the gray jay (Perisoreus canadensis), a nest predator that is known to approach recreationists. During 1989-1993, we implemented intrusions within 20 circular 1-ha (113-m-diam) sites for 1 or 2 hr each week during a 10-week period when potential passerine prey were breeding. Simultaneously, 10 circular 1-ha control sites did not receive experimental intrusions. The average number of gray jays on intruded sites was higher than that on control sites by 156% (1989), 225% (1990), 59% (1991), 13% (1992), and 29% (1993). The probability of gray jay recurrence on intruded sites was higher than that on control sites by 125% (1989), 300% (1990), 20% (1991), 33% (1992), and 20% (1993). By increasing the number and recurrence of gray jays, relatively low levels of repeated intrusion can increase the potential for nest predation by gray jays. We caution that additional work is necessary to assess whether attraction of gray jays actually leads to increased nest predation. Knowledge of when intrusion does and does not attract gray jays is important because information about both events is necessary to define the levels and circumstances of intrusion that are influential. Wildlife managers can use knowledge about intrusion-induced attraction of avian nest predators to help decide whether or how recreational activity in wildlands should be managed.

Survival and Habitat Use of Feral Hogs in Mississippi

Abstract Sus scrofa (Feral Hog) can cause extensive damage to agricultural crops and native vegetation, is a potential disease vector, and competes with other wildlife for food resources. Without site-specific information about survival and habitat use, habitat management and control efforts may not be effective. We examined home-range size, habitat use, and survival of 29 Feral Hogs in central Mississippi using radio telemetry. Dry-and wet-season survival rates were 80.8% and 41.4%, respectively. Hunting (primarily during the wet season) was the major cause of mortality. Dry-season home ranges were larger (6.4 km2) than wet-season home ranges (3.0 km2). During the dry-season, Feral Hog home ranges (2nd-order selection) were associated with dense vegetation types (seasonally flooded old fields, old fields, and managed openings). During the wet season, old fields and agricultural fields were selected, but seasonally flooded old fields and managed openings were not. Within home ranges (3rd-order selection), hogs selected old fields and managed openings during the dry season. All habitats were used randomly within home ranges during the wet season. Flooding of preferred habitats, changes in food availability, and hunting pressure likely caused these changes in habitat use and home-range placement.

Assessing Multiregion Avian Benefits from Strategically Targeted Agricultural Buffers

Mounting evidence of wildlife population gains from targeted conservation practices has prompted the need to develop and evaluate practices that are integrated into production agriculture systems and targeted toward specific habitat objectives. However, effectiveness of targeted conservation actions across broader landscapes is poorly understood. We evaluated multiregion, multispecies avian densities on row-crop fields with native grass field margins (i.e., buffers) as part of the first U.S. agricultural conservation practice designed to support habitat and population recovery objectives of a national wildlife conservation initiative. We coordinated breeding season point transect surveys for 6 grassland bird species on 1151 row-crop fields with and without native grass buffers (9-37 m) in 14 U.S. states (10 ecoregions) from 2006 to 2011. In most regions, breeding season densities of 5 of 6 targeted bird species were greater in the 500-m surrounding survey points centered on fields with native grass buffers than in landscapes without buffers. Relative effect sizes were greatest for Northern Bobwhite (Colinus virginianus), Dickcissel (Spiza americana), and Field Sparrow (Spizella pusilla) in the Mississippi Alluvial Valley and Eastern Tallgrass Prairie regions. Other species (e.g., Eastern Meadowlark [Sturnella magna], Grasshopper Sparrow [Ammodramus savannarum]) exhibited inconsistent relative effect sizes. Bird densities on fields with and without buffers were greatest in the Central Mixed-grass Prairie region. Our results suggest that strategic use of conservation buffers in regions with the greatest potential for relative density increases in target species will elicit greater range-wide population response than diffuse, uninformed, and broadly distributed implementation of buffers. We recommend integrating multiple conservation practices in broader agricultural landscapes to maximize conservation effectiveness for a larger suite of species.

Response of non-grassland avian guilds to adjacent herbaceous field buffers: testing the configuration of targeted conservation practices in agricultural landscapes

Summary 1. A substantial part of the world’s land base is dominated by agriculture, and forest habitat often consists of discrete patches of forest and linear woody corridors. These natural components provide habitat for some forest birds, but make conservation of these species difficult. In-field practices applied outside forest patches, such as specific juxtapositions of herbaceous field buffers adjacent to forest habitat, could increase avian diversity contributions of existing forest without creation of additional forest habitat. Our prediction was that herbaceous field buffers would increase bird richness in adjacent forest, and we evaluated four potential mechanisms. 2. We used bird count data from a conservation buffer monitoring programme and hierarchical community models to estimate species richness of forest generalist, forest interior and shrubland (edge) species near forest edges with and without adjacent herbaceous field buffers. We accounted for heterogeneity in detection probabilities and forest cover in surrounding landscapes when estimating species- and guild-level responses. 3. Consistent with the drift fence hypothesis, adjacent herbaceous buffers were associated with a modest increase in richness of forest interior birds in woody corridors, but not in forest blocks. Consistent with resource complementation, adjacent herbaceous buffers were associated with modest increases in richness of shrubland (edge) birds in both woody corridors and forest blocks. 4. Across all species and guilds, adjacent buffers were generally associated with greater abundance (e.g. 28 of 39 species), but these increases were also relatively small and highly variable (i.e. overlapping 95% credible intervals). Corroborating existing research, effects of adjacent herbaceous buffers are likely real, but neither pervasive nor strong. 5. Synthesis and applications. Conservation practices targeted to grassland species often produce measurable conservation benefits for target species. However, biodiversity return for investment would be further increased if targeted practices could be deployed in ways that also produce benefits for non-target species in adjacent habitats. Our results suggest that additional benefits for non-target species using adjacent forest habitat are likely to be modest, so conservation planning should focus on species targeted by the conservation practices and avoidance of potential negative impacts on those species when positive benefits to adjacent habitat are weak or lacking.

Effects of managing semi-natural grassland buffers on butterflies

Butterflies are important components of biodiversity in grassland ecosystems and provide ecosystem services such as pollination. Although agricultural intensification has led to a scarcity of native grassland habitats within most agricultural landscapes of North America, fragmented remnants and semi-natural habitats may support diverse communities, including butterflies, as long as vital resources such as host plants are available. The United States Department of Agriculture’s (USDA) Conservation Reserve Program practice CP33 Habitat Buffers for Upland Birds (USDA 2004) provides semi-natural grassland habitat in agricultural landscapes, but a knowledge gap exists about impacts of prescribed disturbance (e.g. burning or disking) on butterflies. We monitored butterfly habitat and butterfly communities on experimentally manipulated CP33 grassland buffers in Clay County, Mississippi from 2007 to 2009. Disturbance guild butterfly species richness did not differ among treatments. However, disturbance guild abundance was positively affected by disking in both the first and second growing seasons following disking, and the magnitude of this response varied between years. Effects of burning on disturbance guild abundance did not differ from the control treatment. There were no treatment differences for grassland guild butterfly abundance and species richness suggesting that periodic disturbance does not unduly impact grassland-associated butterflies in the southeastern US. Our results support current USDA practice standards that require periodic disturbance during the 10-year contract, but restrict the disturbance to 1/3 or 1/4 of grassland buffer area in a given year.

Provisioning of Nestling Dickcissels in Native Warm-Season Grass Field Buffers

Abstract We used video cameras in 2008–2009 to record provisioning activities at Dickcissel (Spiza americana) nests in and around Conservation Reserve Program field buffers in north-central Mississippi, USA. We simultaneously observed foraging flight distances of parents. Provisioning rate (P  =  0.412), biomass (P  =  0.161), and foraging distance (P  =  0.159) did not increase with nestling age. Parents delivered larger items to meet demand associated with older nestlings (P  =  0.010–0.001). This suggests energetic costs of changes in prey selection were less than costs of increasing the number or distance of provisioning trips. Presence of male helpers increased provisioning rate (P < 0.001) but not biomass (P  =  0.992) because males brought smaller prey items (P  =  0.001–0.021). Presence of observers 30 m from the nest reduced provisioning rates (P  =  0.005) and biomass delivered (P  =  0.066). Lack of habitat effects for any aspect of provisioning suggests grass field buffers provided nestling food resources similar to surrounding habitats. Use of continuous video monitoring of nest activity allows well-concealed activities including provisioning and male helping to be directly observed and better quantified.