William M. Block

Modeling the effects of environmental disturbance on wildlife communities: avian responses to prescribed fire

Prescribed fire is a management tool used to reduce fuel loads on public lands in forested areas in the western United States. Identifying the impacts of prescribed fire on bird communities in ponderosa pine (Pinus ponderosa) forests is necessary for providing land management agencies with information regarding the effects of fuel reduction on sensitive, threatened, and migratory bird species. Recent developments in occupancy modeling have established a framework for quantifying the impacts of management practices on wildlife community dynamics. We describe a Bayesian hierarchical model of multi-species occupancy accounting for detection probability, and we demonstrate the models usefulness for identifying effects of habitat disturbances on wildlife communities. Advantages to using the model include the ability to estimate the effects of environmental impacts on rare or elusive species, the intuitive nature of the modeling, the incorporation of detection probability, the estimation of parameter uncertainty, the flexibility of the model to suit a variety of experimental designs, and the composite estimate of the response that applies to the collection of observed species as opposed to merely a small subset of common species. Our modeling of the impacts of prescribed fire on avian communities in a ponderosa pine forest in Washington indicate that prescribed fire treatments result in increased occupancy rates for several bark-insectivore, cavity-nesting species including a management species of interest, Black-backed Woodpeckers (Picoides arcticus). Three aerial insectivore species, and the ground insectivore, American Robin (Turdus migratorius), also responded positively to prescribed fire, whereas three foliage insectivores and two seed specialists, Clarks Nutcracker (Nucifraga columbiana) and the Pine Siskin (Carduelis pinus), declined following treatments. Land management agencies interested in determining the effects of habitat manipulations on wildlife communities can use these methods to provide guidance for future management activities.

Hairy woodpecker winter ecology in ponderosa pine forests representing different ages since wildfire

Abstract We investigated how changes in vegetation structure and prey resources following wildfire affected the winter ecology of hairy woodpeckers (Picoides villosus) in ponderosa pine (Pinus ponderosa) forests of northern Arizona, USA. Using point-counts, radiotelemetry, and focal bird observation, we assessed the relative abundance, home range size and composition, and habitat use by foraging hairy woodpeckers in 3 stands that had experienced wildfire in 1996, 2000, or 2002. Because we conducted the study over 2 years, we used the 1996 fire to represent 6 and 7 years after fire, while we used the 2000 fire to represent 2 and 3 years after fire in a space-for-time substitution chronosequence analysis. We also assessed bark beetle and woodborer density by x-raying bark samples collected from a subset of trees within burned areas. We detected significantly greater hairy woodpecker relative abundance in burned forests representing 1 and 2 years after fire, and bark beetle and woodborer density was highest in these stands as well. Woodpecker home range size increased across stands representing increasing time since fire. Within a burn, hairy woodpeckers used high-severity burned areas more than moderate-severity burned areas representing 2 and 3 years after fire, but not in areas representing 6 and 7 years after fire. Bark beetle and woodborer densities were also higher in high-severity burned stands representing 2 and 3 years after fire. Hairy woodpeckers used edges of high-severity burned areas more than the interior. We hypothesize that an initial increase in bark beetle and woodborer density following fire allowed for higher woodpecker abundance and smaller home ranges, but as burned forests aged, bark beetle and woodborer density within trees decreased, killed trees fell, and, in response, hairy woodpecker relative abundance decreased and home range size increased. These patterns suggest that high-severity burned areas provide important but ephemeral resources to this dominant primary cavity-nester. The higher bark beetle and woodborer densities and greater use of edges of high-severity burned areas by woodpeckers suggests that salvage logging of these areas could remove potential prey and preferred foraging areas for hairy woodpeckers, especially when trees are removed along severely burned edges.

Prey ecology of Mexican spotted owls in pine-oak forests of northern Arizona

Abstract We studied Mexican spotted owl (Strix occidentalis lucida) diets and the relative abundance and habitat associations of major prey species in a ponderosa pine (Pinus ponderosa)–Gambel oak (Quercus gambelii) forest in north-central Arizona, USA, from 1990 to 1993. The owls diet was comprised of 94% mammals by biomass and consisted of primarily the deer mouse (Peromyscus maniculatus), brush mouse (P. boylii), Mexican woodrat (Neotoma mexicana), and Mexican vole (Microtus mexicanus). Spotted owl prey in our study area were smaller on average than prey in other locations, and the total biomass of potential prey was less than that reported in other areas within the owls geographic range. Although all prey populations exhibited seasonal fluctuations in relative abundance, only the deer mouse exhibited significant temporal variation in population abundance. The general pattern was for prey populations to rise during spring, peak during summer, decline in fall, and reach a winter low. Deer mice exhibited the greatest amplitude in population change as evidenced by the shift from a high of 12.2 mice/ha (SE = 2.3) during summer 1991 to a low of 3.3 mice/ha (SE = 0.7) during winter 1991–1992. Woodrats and brush mice used areas on slopes >20°with relatively more rocks and shrub cover than found in other areas. In contrast, deer mice were found in forests with relatively open understories and little Gambel oak. Conservation measures for the Mexican spotted owl must include management directed at sustaining or increasing prey numbers rather than assuming that managing for owl nesting and roosting habitat will provide favorable conditions for the prey as well. Management practices that increase and sustain shrub and herbaceous vegetation should receive the highest priority. This can be accomplished by thinning small diameter trees, using prescribed fire, and managing grazing pressures.

Quantifying the multi-scale response of avifauna to prescribed fire experiments in the southwest United States

Landscape-scale disturbance events, including ecological restoration and fuel reduction activities, can modify habitat and affect relationships between species and their environment. To reduce the risk of uncharacteristic stand-replacing fires in the southwestern United States, land managers are implementing restoration and fuels treatments (e.g., mechanical thinning, prescribed fire) in progressively larger stands of dry, lower elevation ponderosa pine (Pinus ponderosa) forest. We used a Before-After/Control-Impact experimental design to quantify the multi-scale response of avifauna to large (approximately 250-400 ha) prescribed fire treatments on four sites in Arizona and New Mexico dominated by ponderosa pine. Using distance sampling and an information-theoretic approach, we estimated changes in density for 14 bird species detected before (May-June 2002-2003) and after (May-June 2004-2005) prescribed fire treatments. We observed few site-level differences in pre- and posttreatment density, and no species responded strongly to treatment on all four sites. Point-level spatial models of individual species response to treatment, habitat variables, and fire severity revealed ecological relationships that were more easily interpreted. At this scale, pretreatment forest structure and patch characteristics were important predictors of posttreatment differences in bird species density. Five species (Pygmy Nuthatch [Sitta pygmaea], Western Bluebird [Sialia mexicana], Stellers Jay [Cyanocitta stelleri], American Robin [Turdus migratorius], and Hairy Woodpecker [Picoides villosus]) exhibited a strong treatment response, and two of these species (American Robin and Hairy Woodpecker) could be associated with meaningful fire severity response functions. The avifaunal response patterns that we observed were not always consistent with those reported by more common studies of wildland fire events. Our results suggest that, in the short-term, the distribution and abundance of common members of the breeding bird community in Southwestern ponderosa pine forests appear to be tolerant of low- to moderate-intensity prescribed fire treatments at multiple spatial scales and across multiple geographic locations.

The Role of Old-growth Forests in Frequent-fire Landscapes

Classic ecological concepts and forestry language regarding old growth are not well suited to frequent-fire landscapes. In frequent-fire, old-growth landscapes, there is a symbiotic relationship between the trees, the understory graminoids, and fire that results in a healthy ecosystem. Patches of old growth interspersed with younger growth and open, grassy areas provide a wide variety of habitats for animals, and have a higher level of biodiversity. Fire suppression is detrimental to these forests, and eventually destroys all old growth. The reintroduction of fire into degraded frequent-fire, old-growth forests, accompanied by appropriate thinning, can restore a balance to these ecosystems. Several areas require further research and study: 1) the ability of the understory to respond to restoration treatments, 2) the rate of ecosystem recovery following wildfires whose level of severity is beyond the historic or natural range of variation, 3) the effects of climate change, and 4) the role of the microbial community. In addition, it is important to recognize that much of our knowledge about these old-growth systems comes from a few frequent-fire forest types.

HOME RANGE, HABITAT USE, SURVIVAL, AND FECUNDITY OF MEXICAN SPOTTED OWLS IN THE SACRAMENTO MOUNTAINS, NEW MEXICO

Abstract We studied home range, habitat use, and vital rates of radio-marked Mexican spotted owls (Strix occidentalis lucida) in 2 study areas in the Sacramento Mountains, New Mexico. One study area (mesic) was dominated by mixed-conifer forest, the other (xeric) by ponderosa pine (Pinus ponderosa) forest and piñon (P. edulis)-juniper (Juniperus) woodland. Based on existing knowledge of relative use of forest types by Mexican spotted owls, we predicted that the mesic area would provide habitat of higher quality for spotted owls. Results generally supported this prediction. Median home-range size for owls in the mesic area was approximately half that of owls in the xeric area during both the breeding and non-breeding seasons (n = 6 owls in each area). Despite their reduced size, however, mesic-area home ranges contained twice as much mixed-conifer forest as xeric-area ranges. Owls roosted primarily (>80% of roosting locations in both seasons) in mixed-conifer forest in both study areas, and home-range size was inversely related to relative amount of mixed-conifer forest within the home range during both seasons. Both survival and fecundity rates were higher in the mesic than in the xeric area. Estimates of population trend based on observed vital rates suggested that the population in the mesic area was self-sustaining or nearly so during the period of study (1992 through 1994), but the population in the xeric area was not. Collectively, our findings suggest that habitat quality for spotted owls was higher in the mesic area than in the xeric area, and that the xeric area might function as an ecological sink. These results support the need for data linking demographic performance to habitat conditions in development of strategies for recovering threatened and endangered species.

Optimizing study design for multi‐species avian monitoring programmes

Summary 1. Many monitoring programmes are successful at monitoring common species, whereas rare species, which are often of highest conservation concern, may be detected infrequently. Study designs that increase the probability of detecting rare species at least once over the study period, while collecting adequate data on common species, strengthen programme ability to address community-wide hypotheses about how an ecosystem functions or responds to management actions. Study design guidelines exist for single-species occupancy models, but practical guidance for monitoring species communities is needed. Single-species population-level designs are necessarily optimal for targeted species, whereas community study designs may be optimal for the assemblage of species, but not for every species within the community. Our objective was to provide a general optimization tool for multi-species models and to illustrate this tool using data from two avian community studies. 2. We conducted a simulation study with a Bayesian hierarchical model to explore design and cost trade-offs for avian community monitoring programmes. We parameterized models using two long-term avian studies from Arizona, USA and evaluated bias and accuracy for different combinations of species in the regional species pool and sampling design combinations of number of sites and sampling occasions. We optimized for maximum accuracy of species richness, detection probability and occupancy probability of rare species, given a fixed budget. 3. Statistical properties for species richness and detection probability of species within the community were driven more by sampling occasions, whereas rare species occupancy probability was influenced more by percentage of area sampled. These results are consistent with results from single-species models, suggesting some similarities between community-level and single-species models with occupancy and detection. 4. Synthesis and applications. Study designs must be cost-efficient while providing reliable knowledge. Researchers and managers have limited funds for collecting data. Our template can be used by researchers and managers to evaluate trade-offs and efficiencies for allocating samples between the number of occasions and sites in multi-species studies, and allow them to identify the optimal study design in order to achieve specific study objectives.

Birds and burns of the interior West: descriptions, habitats, and management in western forests.

This publication provides information about prescribed fire effects on habitats and populations of birds of the interior West and a synthesis of existing information on bird responses to fire across North America. Our literature synthesis indicated that aerial, ground, and bark insectivores favored recently burned habitats, whereas foliage gleaners preferred unburned habitats.

Prescribed Fire Effects on Wintering, Bark‐Foraging Birds in Northern Arizona

Abstract We examined effects of prescribed fire on 3 wintering, bark-foraging birds, hairy woodpeckers (Picoides villosus), pygmy nuthatches (Sitta pygmaea), and white-breasted nuthatches (S. carolinensis), in ponderosa pine (Pinus ponderosa) forests of northern Arizona, USA. During winters of 2004–2006, we compared bird density, foraging behavior, and bark beetle activity among burned treatment and unburned control units. Hairy woodpecker density was 5 times greater in burn units, whereas white-breasted nuthatches and pygmy nuthatches had similar densities between treatments. Compared to available trees, trees used by foraging hairy woodpeckers had 9 times greater odds of having bark beetles in control units and 12 times greater odds in burn units. Tree diameter appeared to be the main factor bark-foraging birds used in selecting winter foraging trees. Our results suggest that forest managers can use prescribed fire treatments without detrimental effects to wintering nuthatches, while providing additional food to hairy woodpeckers.

Occupancy and Habitat Associations of Four Species of Sciurids in Ponderosa Pine-Gambel Oak (Pinus ponderosa-Quercus gambelii) Forests in Northern Arizona

Abstract In ponderosa pine-Gambel oak (Pinus ponderosa-Quercus gambelii) forests of north-central Arizona, we examined occupancy and habitats of four species of sciurids (rock squirrel Spermophilus variegatus, golden-mantled ground squirrel S. lateralis, gray-collared chipmunk Tamias cinereicollis, cliff chipmunk T. dorsalis). Numbers of captures were highly variable, suggesting a patchy distribution of species. All four species co-occurred on only one of the study sites. Gray-collared chipmunks and golden-mantled ground squirrels were relatively common on one site only. Golden-mantled ground squirrels were associated with mature forests with high canopy cover and low basal area, whereas gray-collared chipmunks were in locations with large numbers of logs and shallow litter. The two species of chipmunks appeared to be separated in space; gray-collared chipmunks were more common where cliff chipmunks were least common. Rock squirrels were relatively ubiquitous. There was evidence for an association of rock squirrels with increasing rocky cover and decreasing canopy cover, whereas cliff chipmunks occupied rocky areas with high canopy cover and numerous shrubs.