Source: PACIFIC SOUTHWEST RESEARCH STATION submitted to
BIRD SPECIES ASSOCIATED WITH OLDER FORESTS AND RESPONSE TO EXTREMES IN CLIMATE
Sponsoring Institution
Forest Service/USDA
Project Status
TERMINATED
Funding Source
USDA INHOUSE
Reporting Frequency
Annual
Accession No.
0197283
Grant No.
(N/A)
Project No.
PSW-4202-3
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Feb 10, 1998
Project End Date
Feb 10, 2008
Grant Year
(N/A)
Project Director
Stine, P. A.
Recipient Organization
PACIFIC SOUTHWEST RESEARCH STATION
800 BUCHANAN STREET, WEST BLDG
ALBANY,CA 94710-0011
Performing Department
FOREST SCIENCE LAB - FRESNO, CA
Non Technical Summary
(N/A)
Animal Health Component
(N/A)
Research Effort Categories
Basic
30%
Applied
70%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1350820107050%
1350860107050%
Knowledge Area
135 - Aquatic and Terrestrial Wildlife;

Subject Of Investigation
0860 - Endangered species; 0820 - Wild birds;

Field Of Science
1070 - Ecology;
Goals / Objectives
Recent studies by this RWU have shown that the California Wildlife-Habitat Relationships database, managed by the California Department of Fish and Game, has many inaccuracies about bird-habitat relations in most or all major habitat types in the western Sierra Nevada. Two major factors are involved. First, we lack information about altitudinal shifts in breeding populations in response to annual variations in winter conditions. We also need to know whether or not permanent residents and neotropical migrants respond differently in this context. Second, we have insufficient data about the degree of dependency of certain species on mature and older forests--especially cavity nesters and species that feed primarily or exclusively on conifer seeds at least part of the year. A full understanding of these habitat relations is important to assure forest management in ways that will not jeopardize any of these bird species. A critical need remains, therefore, to identify bird species associated with attributes of older forests, and determine whether some bird species shift elevationally in response to extremes in climate. Nest sites of shrub-nesting species can be buried in snow following hard winters, but studies by this RWU have shown that males of some of these species still occupy breeding territories and sing from perches above the snow, even though nesting is not possible. Other species, such as Clark's nutcrackers and rosy finches, have nested at lower elevations where they do not normally occur during the breeding period. The extent to which such elevational movements characterize other species of breeding birds in Sierran conifer forests is unknown. Studies by this RWU are beginning to clarify details about the densities, species, states of decay, and sizes of snags most associated with use by cavity-nesting birds in the Sierra Nevada. Snag research is especially important because it will link to studies of small mammals (e.g., flying squirrels commonly den in cavities excavated by woodpeckers) and spotted owls (flying squirrels are a primary prey source for the owls; snags become fallen logs, which then decay and provide a base for hypogeous fungi--a primary food of flying squirrels and other species of small mammals). Recent studies elsewhere have shown that populations of some conifer seed specialists decline markedly in response to loss of mature and old-growth conifers in a forest. More notably, the red crossbill has been shown to consist of at least eight reproductively isolated groups in North America that behave as distinct species. These are feeding specialists on the seeds of different conifer species. This raises a distinct concern that we might unwittingly jeopardize the continued existence of one or more of these distinct crossbill types by removing most of the older members of one or more conifer species from forests in a single region, such as the Sierra Nevada.
Project Methods
Most research will be done in areas delineated for demographic studies of the spotted owl. Studies will include: 1. Annual variation in elevational distribution and abundance of Sierran land birds in relation to the intensity of winter conditions. Study whether tendencies for populations to shift elevationally are related to major assemblages (e.g., shrub nesters vs canopy nesters, or permanent residents vs neotropical migrants). 2. Nest-site selection by a subset of landbird species in relation to habitats, elevation, predation, annual variation in climate, and so on. Compare and contrast permanent residents with neotropical migrants in this regard. 3. Reproductive success of a subset of landbird species in relation to habitats, elevation, predation, annual variation in climate, and so on. Compare and contrast permanent residents with neotropical migrants in this regard. 4. Dynamics of snag abundance, snag size, and cavity-nesting birds in relation to bird species richness. Examine the role of primary cavity nesters (those that excavate nest cavities) in the dynamics of flying squirrel populations. 5. Possible impacts of a decline in density of mature and older conifers on various species of birds, especially crossbills, that are food specialists on conifer seeds. Accomplishments planned for the next 10 years:1. Relate findings under this Problem to those under Problems 1, 2, 4, 5, and 6. 2. Quantify parameters involved in nest-site selection by a subset of permanent resident and neotropical migrant birds in various forest ecosystems of the western Sierra Nevada. 3. Quantify variations in reproductive success among a subset of permanent resident and neotropical migrant birds in various forest ecosystems of the western Sierra Nevada. 4. Based on accomplishments 2 and 3 above, propose appropriate revisions in bird-habitat models (for the Statewide California WHR Database). 5. Quantify the time sequence and turnover rates in the production and maintenance of snags large enough for cavity-nesting wildlife in western Sierran red fir, mixed-conifer, and ponderosa pine forests. 6. Describe the ecological linkages among the set of factors associated with snags, primary cavity-nesting birds, nest and den cavities, flying squirrels, and spotted owls. 7. Evaluate whether or not birds that are conifer seed specialists may be severely impacted by existing forest-management practices. 8. Report all findings in annual reports, workshops, Station publications, technical journals, and symposium proceedings.

Progress 02/10/98 to 02/10/08

Outputs
OUTPUTS: The activities under this problem area includes participation as a co-chair of the Consortium for Integrated Climate Research in Western Mountains. Two workshops targeting resource managers and climate impacts were conducted, technical sessions, and a full lenget conference. PROJECT MODIFICATIONS: This problem has been closed and terminated.

Impacts
The work under this area successfully assisted in the launch and development of the Consortium for Integrated Climate Research in the Western Mountains. This focused on bringing technical climate science knowledge to bear on forest and water resources management and policy throughout the mountain regions of western North America.

Publications


    Progress 10/01/04 to 09/30/05

    Outputs
    Our study on forest responses to 20th century climate change in the Sierra Nevada documents strong effects of climate and non-equilibrium, individualistic nature of ecological behavior. Independent sub-studies investigated invasion by conifers into montane meadows, invasion by conifers into former snowfield openings, shift in subalpine tree forms (from shrubform to upright), and changes in stem growth at upper treeline over the 20th century. We found that 20th century climate was significantly correlated with changes in each trait, with no significant influences from local land-use practices. Responses were individualistic, with some responding directionally to long-term temperature increases (invasion into snowfields and growth increases) while others (meadow invasion and crown form) responded to multi-decadal climate phases correlated with the Pacific Decadal Oscillation. Abrupt and reversible effects occurred in each study. In another study, we document abrupt changes at centennial scale in historic climate and associated unexpected changes in forest composition and structure. Mountaintops in the Sierra Nevada currently above treeline comprised mixed conifer forests of fast-growing upright trees during the Medieval period (650-1100 years ago). Species composition of this forest assemblage is not analogous to anything at present in the Sierra, and the six species that grew together during the Medieval period currently inhabit five different forest types from diverse elevations. One species does not currently exist in the region. We modeled Medieval climate at this site to be up to 3 degrees C warmer than present, and 20mm drier, similar to projections for California by the end of the 21th century. A synthesis analysis of these studies above and two others previously published was developed that underlines the complex and diverse responses of subalpine forests in upper elevations to warming climates. In global and regional climate-modeling scenarios, these forest types have been assumed to shift directionally uphill as temperature increased. Combined results as we have produced show this is not the case, rather that responses can include regional and local extirpations; regional and local invasions; populations shifts in aspect, species composition, growth forms, and structure; individualistic range shifts, which may be up- or downhill; and reversible and episodic responses. As founding member and co-chair of the Consortium for Integrated Climate Research in Western Mountains, our progress in reaching regional climate goals has vastly improved. Five new GLORIA alpine plant monitoring sites for climate change were installed, 8 new high-elevation longterm climate monitoring stations installed, two workshops targeting resource managers and climate impacts conducted, 3 technical sessions, and one full-length conference. Six Work Groups were established, focused on climate monitoring, hydrologic monitoring, GLORIA plant monitoring, ecosystem responses, international relations, and paleoclimatic archives for managers. A new website was developed to coordinate these activities: http://www.fs.fed.us/psw/cirmount/

    Impacts
    Responses of high-elevation subalpine conifer forests to climate variability and change indicates that diverse, complex, and abrupt behaviors will be far more common in the future than simple shifts of plant communities uphill. If such results are not incorporated into global and regional climate modeling, projections of future vegetation conditions will lead to wrong conclusions, and resource- and conservation-planning for mitigation and adaptation will be address the wrong conditions. By incorporating complex behavior into models, however, a more accurate view of future conditions is likely to pertain. Traditionally, restoration goals have used historical, pre-disturbance conditions as targets or reference conditions for restoration. Such historic conditions make inappropriate targets both to present and to future conditions. USFS slogans such as "we must make the forests of the future look more like the forests of the past", if seriously followed, may lead to forests that are ecologically ill-prepared for present, let alone future, conditions. Our work to successfully launch and develop the Consortium for Integrated Climate Research in Western Mountains, focuses on bringing technical climate science knowledge to bear on forest and water resource management and policy throughout the mountain regions of western North America. Our consortium is first in the world to do this successfully, has been endorsed as a pilot by three international science programs, and has been used as a model in initiation of two new international science networks.

    Publications

    • Millar, C.I. 2004. The consortium for integrated climate research in western mountains. In: Lee, C. and Schaaf, T., eds. Global change research in mountain biosphere reserves. Proceedings of the international launching workshop; 2003 November 10-13; Entlebuch Biosphere Reserve, UNESCO. Paris, France: Man and The Biosphere Program; 154-158.
    • Millar, C.I. 2004. Session overview: Climate and landscape change over time. In: Murphy, D.D.; Stine, P.A., eds. Proceedings of the Sierra Nevada science symposium, science for management and conservation; 2002 Oct. 8-10; Kings Beach, CA. Gen. Tech. Rep. PSW-GTR-193. Albany CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 25-31.
    • Millar, C.I. 2005. The Consortium for integrated climate research in western mountains: A new national research network. Mountain Forum Bulletin 5(1): 18-19.
    • Millar, C.I.; Delany, D.; Westfall, R.; King, J. 2004. Climate change as an ecosystem architect: Examples from high-elevation pine forests. Abstract. In: Murphy, D.D.; Stine, P.A., eds. Proceedings of the Sierra Nevada science symposium, science for management and conservation; 2002 Oct. 8-10; Kings Beach, CA. Gen. Tech. Rep. PSW-GTR-193. Albany CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 234.
    • Millar, C.I; Greenwood, G. 2005. The Consortium for integrated climate research; The role of regional integration in global studies. Mountain Research and Development 25(1): 80-81.
    • Millar, C.I.; Safford, H. 2004. Research natural Aaeas in the Sierra Nevada bioregion: Contribution to biodiversity conservation and opportunities for research. In: Murphy, D.D.; Stine, P.A., eds. Proceedings of the Sierra Nevada science symposium, science for management and conservation; 2002 Oct. 8-10; Kings Beach, CA. Gen. Tech. Rep. PSW-GTR-193. Albany CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 277.
    • Millar, C.I.; Westfall, R.D.; Delany,D.L.; King, J.C.; Graumlich, L.J. 2004. Response of subalpine conifers in the Sierra Nevada, California USA to 20th-century warming and decadal climate variability. Arctic, Antarctic, and Alpine Research 36 (2): 181-200.


    Progress 10/01/03 to 09/30/04

    Outputs
    Bird censusing at the San Joaquin Experimental Range continued, completing 20 years of data collection. A manuscript that examines the use of count data to analyze trends in abundance and to test for differences among treatments, and recommends optimal study designs and sample sizes, is in review. Population trends and the effects of climate change on bird populations are being analyzed. We are currently assessing the population health of a wide range of bird species across several forest types. Low-elevation ponderosa pine forests had the highest species diversity and the greatest number of unique species. We have found a preference for certain tree species, with hardwood tree species used proportionately more than expected by a wide variety of bird species for nesting. We also completed an analysis of source-sink population modeling, the role of brood parasitism, and habitat associations of warbling vireos over an elevational gradient. Work on the effects of prescribed fire in the spring on birds and salamanders continued. Preliminary results suggest that most species did not respond strongly to low-intensity prescribed fire. Primary cavity nesters and species that nest in snags increased following prescribed fire, while species that nest in the canopy showed short-term aversion to burn sites. Bird work continues at both the Blacks Mountain and Goosenest ecological experiments through cooperators at Humboldt State University and the Wildlife Conservation Society. We are seeing increases on the less vegetated plots in species, such as Mountain Bluebird, associated with more open forests. Our interest is in the trajectories of the responses of birds to the regrowth of the forests following treatment. An investigation of the effects of habitat loss, fragmentation, and human disturbance on biological diversity, including songbirds and woodpeckers, in forested ecosystems subject to development in the urbanzing environment of the Lake Tahoe basin was continued in 2004. An investigation of the effects of off-highway vehicles on songbirds, woodpeckers, accipiters, and owls (discussed in problem 1) was continued through the winter of 2004. A national strategy for monitoring animal populations and habitat conditions (Multiple Species Inventory and Monitoring Protocol), including birds, on National Forest System lands was drafted and received national review. When finalized in 2005, it will be published as a GTR and will serve as a technical guide to be used by all National Forests. Effects of Off-Highway Vehicles (OHVs) on the Northern Goshawk addresses the effects of snowmobiles, ATVs and hikers on the behavior, reproductive success and survival of northern goshawks. It is a collaborative effort with PSW and Humboldt State University and is being conducted on the Plumas and Lassen National Forests. Twenty-five nests were monitored in 2004 and work focused on assessing OHV effects during the breeding season.

    Impacts
    Our research is providing important recommendations for study design and required sample sizes for monitoring trends and detecting the effects of land management activities on birds. It highlights the importance of lower Westside hardwoods to birds. We recommend the use of forest management practices that retain mature oaks and encourage the recruitment of oaks. Experimental responses of birds through time are rare in the literature and this work on long-term trajectories of birds related to vegetation trajectories following thinnings and fire is novel and unique. The results of the study of urbanization on forest biological diversity will be used to identify indicators of forest integrity in the revision of the Lake Tahoe regional plan. The pilot test of the off-highway vehicle area monitoring led to the development of a monitoring protocol for evaluating wildlife populations and habitats in off-highway vehicle use areas on National Forest System lands. Great Gray Owl results from 2004 indicate that existing inventory and monitoring protocols can be improved with a resulting significant savings in money, time and personnel to management agencies. West Nile Virus is known to significantly affect birds of prey such as owls and hawks.

    Publications

    • Manley, P. N.; Zielinski, W. J.; Schlesinger, M. D.; Mori, S. R. 2004. Evaluation of a multiple-species approach to monitoring species and ecosystem conditions at the ecoregional scale. Ecological Applications 14(1): 296-310.
    • Anderson, D.E.; DeStefano, S.; Goldstein, M.I.; Titus, K.; Crocker-Bedford, C.; Keane, J.J.; Anthony, R.G.; Rosenfield, R.N. 2004. The status of northern goshawks in the western United States. Wildlife Society Technical Review 04-1. The Wildlife Society, Betheseda, MD; 24 p.
    • Farris, K.L.; Huss, M.J.; Zack, S. 2004. The role of foraging woodpeckers in the decomposition of Ponderosa pine snags. Condor 106:50-59.
    • Lawler, J.J.; O'Connor, R.J.; Hunsaker, C.T.; Jones, K.B.; Loveland, T.R.; White, D. 2004. The effects of habitat resolution on models of avian diversity and distributions: a comparison of two land-cover classifications. Landscape Ecology 19:515-530.
    • Manley, P.N. 2004. Pilot test of programmatic approach to monitoring conditions and trends of wildlife populations and habitats in off-highway use areas on National Forests in California: Winter 2002-2003 pilot test. Unpublished report provided to U.S. Department of Agriculture, Forest Service, Pacific Southwest Region, Vallejo, CA; 38 p.
    • Manley, P.N.; Murphy, D.D. 2004. The role of urban forests in conserving and restoring biological diversity in the Lake Tahoe basin. Interim report on the progress of the urban biodiversity project provided to Lake Tahoe Basin Management Unit, Tahoe Regional Planning Agency, and Nevada Division of State Lands; South Lake Tahoe, CA; 63 p.
    • Manley, P.N.; Murphy, D. D.; Campbell, L. A.; Heckmann, K. E.; Merideth, S.; Sanford, M.; Schlesinger, M. D. 2004. Biological diversity along a gradient of human development and disturbance: a case study in the Lake Tahoe Basin. Ecological Society of America annual meeting, August 2004, Portand, OR - Poster presentation.
    • Manley, P. N.; Thayer, T. C.; Craig, D.; Mick, K.; Weston, D. 2004. Monitoring wildlife and their habitats in off-highway vehicle use areas: The Lake Tahoe pilot test of California's programmatic approach. Lake Tahoe Science Symposium 2004, Lake Tahoe - Published abstract of poster presentation.
    • Manley. P. N.; Thayer, T. C.; McIntyre, K. K.; Roth, J. K.; Weston, D.; Hartwig, J. 2004. Pilot test of the effects of off-highway vehicle use on wildlife populations and habitats: research and programmatic monitoring approaches. Unpublished final report provided to U.S. Department of Agriculture, Forest Service, Pacific Southwest Region, Vallejo, CA; 93 p.


    Progress 10/01/02 to 09/30/03

    Outputs
    We completed data collection for a study examining the effects of prescribed fire on birds and salamanders in ponderosa pine forests. We censused birds, monitored nests, and surveyed for salamanders at nine sites, consisting of three replicates each of first entry and second entry prescribed fire, and controls. Two second-entry sites were burned in 2003. Study sites for a study examining the effects of uneven-aged forest management and prescribed fire were established. Work on examining patterns of abundance and productivity of forest birds over an elevational gradient continued. Preliminary results suggest lower elevation forests provide important habitat for a wide variety of bird species, although many species have higher nesting success at higher elevations. An inverse correlation of abundance and productivity for two abundant species suggests that birds are not able to correctly assess the probability of successful nesting. Low elevation hardwood tree species were used as nest substrates significantly more than expected. Bird censusing at the San Joaquin Experimental Range continued, completing a total of 19 years of data collection. These data were used in 2003 in power analyses and simulation models to develop guidelines for the design of bird monitoring programs using point counts. We are in the process of analyzing population trends for all species breeding at the Range. Research on past and present fire regimes in California oak woodlands described changes in habitat over time related to anthropogenic fire, activities of Euro-American settlers, fire suppression, and present-day prescribed fire activities. These changes were used to model habitat responses of birds to fire and fire suppression. Bird work continues at both the Blacks Mountain and Goosenest ecological experiments through cooperators at Humboldt State University and the Wildlife Conservation Society. The treatments have been installed at each experimental area and responses to the treatments are being evaluated. We are seeing increases on the less vegetated plots in species, such as Mountain Bluebird, associated with more open forests. Our interest is in the trajectories of the responses of birds to the regrowth of the forests following treatment.

    Impacts
    Research into the fisher habitat relations will provide insights into the management of forests to permit maintaining fisher populations. Knowledge of other small mammal ecologies is necessary to provide appropriate habitat to support their populations for their own persistence and to provide food for species of concern such as fishers, Northern goshawks and California spotted owls.

    Publications

    • Anderson, D.E.; DeStefano, S.; Goldstein, M.I.; Titus, K.; Crocker-Bedford, C.; Keane, J.J.; Anthony, R.G.; Rosenfield, R.N. 2003. Technical review of the status of the northern goshawk in western North America. Report of the Wildlife Society; 47 p.
    • Farris, K.L.; Garton, E.O.; Heglund, P.J.; Zack, S.; Shea, P.J. 2002. Woodpecker foraging and the successional decay of ponderosa pine. In: Laudenslayer, Jr., W. F.; Shea, P. J.; Valentine, B.; Weatherspoon, C. P.; Lisle, T. E., tech. coords. Proceedings of the symposium on the ecology and management of dead wood in western forests. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 237-246.
    • Laudenslayer, W.F., Jr. 2002. Cavity-nesting bird use of snags in eastside pine forests of northeastern California. In: Laudenslayer, Jr., W. F.; Shea, P. J.; Valentine, B.; Weatherspoon, C. P.; Lisle, T. E., tech. coords. Proceedings of the symposium on the ecology and management of dead wood in western forests. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 223-236.
    • Purcell, K.L. 2002. Abundance and productivity of birds over an elevational gradient. In: Verner, Jared, tech. editor. Proceedings of a symposium on the Kings River sustainable forest ecosystems project: Progress and current status. Gen. Tech. Rep. PSW-GTR-183. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 121-132.
    • Purcell, K.L.; Stephens, S.L. 2003. (In Press). Potential impacts on the avifauna of California's oak woodlands from changing fire regimes and livestock grazing. Gen. Tech. Rep. PSW-GTR. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture.
    • Zack, S.; George, T.L.; Laudenslayer, Jr., W.F. 2002. Are there snags in the system? Comparing cavity use among nesting birds in 'snag-rich' and 'snag-poor' eastside pine forests. In: Laudenslayer, Jr., W. F.; Shea, P. J.; Valentine, B.; Weatherspoon, C. P.; Lisle, T. E., tech. coords. Proceedings of the symposium on the ecology and management of dead wood in western forests. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 179-191.


    Progress 10/01/01 to 09/30/02

    Outputs
    We completed the eighth and final year of data collection to assess abundance and productivity of native bird species and to examine elevation shifts and annual variability in reproductive success. Study sites, 40 ha, cover an elevational gradient in four forest types. We completed bird censuses for 16 sites in 2002 and monitored over 600 nests, to a total of over 4000 nests of 69 species. Preliminary results: species richness and numbers of birds decrease with increased elevation, although higher elevations appear to be important for cavity-nesting birds. We censused birds and monitored nests to examine the effects of prescribed fire on birds and salamanders in ponderosa pine forests. These nine sites consist of three replicates each of first-entry and second-entry prescribed fire and controls. The three first entry sites were burned in spring 2002. Bird censusing at the San Joaquin Experimental Range continued, completing 18 years of data. We completed analysis of population trends and factors related to the abundance of European starlings. Starlings were more abundant following years with cool summers and warm, wet winters. Starling presence was related to level, open woodlands with fairly well-developed, accessible soil. A study to assess interspecific competition for nest cavities between starlings and native cavity nesters documented aggressive interactions between starlings and western bluebirds and acorn woodpeckers. Work continued on development of survey and monitoring protocols for California spotted owls and northern goshawks. A workshop was held in 2002 (about 75 attendees) for training on a number of goshawks survey techniques and ecology. Work continued on distributional databases for a number of goshawks and other species. Presentations were made on two methods to identify potential habitat for the endangered willow flycatcher population in the Sierra Nevada and on willow flycatcher population status and risk factors.

    Impacts
    (N/A)

    Publications

    • Standiford, R.B.; McCreary, D.D.; Purcell, K.L., technical coordinators. 2002. Proceedings of the fifth symposium on oak woodlands: Oaks in California's changing landscape; 2001 October 22-25; San Diego, California. Gen. Tech. Rep. PSW-GTR-184. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 846 p.
    • Purcell, K.L.; Verner, J.; Mori, S. 2002. Factors affecting the abundance and distribution of European starlings (Sturnus vulgaris) at the San Joaquin Experimental Range. In: Standiford, R.B.; McCreary, D.; Purcell, K.L., technical coordinators. Proceedings of the fifth symposium on oak woodlands: Oaks in California's changing landscape; 2001 October 22-25; San Diego, California. Gen. Tech. Rep. PSW-GTR-184. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 305-322.
    • Kunzman, M.R.; Ellison, K.; Purcell, K.L.; Johnson, R.R.; Haight, L.T. 2002. California Towhee (Pipilo crissalis). In: Poole, A.; Gill, F., editors. The birds of North America. No. 632. Philadelphia and Washington, DC: The Academy of Natural Sciences and The American Ornithologists' Union.
    • Liebezeit, J.R.; 2001. Nest predators and nesting success of the dusky flycatcher in a managed ponderosa pine forest. Arcata, CA: California State University, Humboldt; 68 p. M.S. thesis.
    • Liebezeit, J.R.; Luke, G.T. 2001. Nest predators, nest-site selection, and nesting success of the dusky flycatcher in a managed ponderosa pine forest. Condor 104: 507-517.