Population and Habitat Viability
Assessments for Golden-Cheeked Warblers
and Black-Capped Vireos: Usefulness to
Partners in Flight Conservation Planning
Carol J. Beardmore
Jeff S. Hatfield
Abstract—Golden-cheeked Warblers and Black-capped Vireos
are Neotropical migratory birds that are federally listed as
endangered. Recovery plans for both species advise the use of
viability modeling as a tool for setting specific recovery and
management targets. Population and Habitat Viability Assessment workshops were conducted to develop population targets
and conservation recommendations for these species. Results of
the workshops were based on modeling demographic and environmental factors, as well as discussions of management issues,
management options, and public outreach strategies. The approach is intended to be iterative, and to be tracked by research
and monitoring efforts. This paper discusses the consensusbuilding workshop process and how the approach could be useful
to Partners in Flight.
Population and Habitat Viability Assessments (PHVA) were
used to develop population targets and conservation recommendations for Golden-cheeked Warblers (Dendroica chrysoparia) and
Black-capped Vireos (Vireo atricapillus). This paper explains what
PHVAs are, discusses how they are conducted, describes the
general results that are produced, and suggests how Partners in
Flight (PIF) might use a similar process for bird conservation
planning. Detailed results of the assessments are not discussed
here; however they can be found elsewhere (Beardmore and others
1996a,b).
Population and Habitat Viability Assessments were considered
for Golden-cheeked Warblers and Black-capped Vireos because
they are controversial, endangered species, and the species’ recovery plans list PHVAs as tools to develop recovery recommendations.
The U.S. Fish and Wildlife Service (USFWS) realized that the data
needed to perform PHVAs for these species is limited, but that
various conservation efforts, such as the Balcones Canyonlands
Conservation Plan and other endeavors, were proceeding without
benefit of the biological summarization and guidance that a PHVA
could provide.
Function and Structure of
PHVAs_________________________
A PHVA is a tool to compile, evaluate, and synthesize data
and build a framework for conservation actions. It provides
an in-depth examination and synthesis of what is known of
a species’ life history, ecology, management, and other
factors to determine courses of action to manage for viable
populations. Assessments include consideration of model
analysis, habitat management, captive breeding (if appropriate), genetic factors (if appropriate), life history, status,
threats, geographic distribution, education and information, other conservation efforts, human demography, research, and any other component deemed necessary. In
contrast, Population Viability Analysis (PVA) refers to computer simulation modeling of biological processes that produce probabilities of extinction or survival under different
scenarios. That is, a PVA is often only one step of a PHVA.
Why Were PHVAs Conducted?
Recovery plans for both Golden-cheeked Warblers and
Black-capped Vireos list viability model development as a
task in the Narrative Outline for Recovery Actions (U.S. Fish
and Wildlife Service 1991; U.S. Fish and Wildlife Service
1992). The intent of USFWS was to initiate a process that
would result in information that could be used in determining
the population sizes, and the habitat patch size and distribution needed, to ensure viable populations (i.e., one of the
recovery criteria). Other results that were anticipated included recommendations for habitat management, research
needs, and public outreach strategies.
How Were the PHVAs Conducted?
In: Bonney, Rick; Pashley, David N.; Cooper, Robert J.; Niles, Larry,
eds. 2000. Strategies for bird conservation: The Partners in Flight planning process; Proceedings of the 3rd Partners in Flight Workshop; 1995
October 1-5; Cape May, NJ. Proceedings RMRS-P-16. Ogden, UT: U.S.
Department of Agriculture, Forest Service, Rocky Mountain Research
Station.
Carol J. Beardmore, Partners in Flight, c/o Arizona Game and Fish Dept.,
2221 W. Greenway Rd., Phoenix, AZ 85023. Jeff S. Hatfield, Patuxent Wildlife
Research Center, 11510 American Holly Dr., Laurel, MD 20708.
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A PHVA workshop, hosted by the USFWS, was held for
each species. The format of the workshop was similar to
PHVA workshops conducted by the IUCN’s Conservation
Breeding Specialist Group (CBSG 1993). The consensusbuilding, group discussion format was assisted by a trained
facilitator. A group of biologists representing federal, state,
county, and local governments; universities; consulting companies; and nongovernmental organizations was invited to
participate. These biologists had either direct research experience with the warbler or vireo in the field, direct association with managing the species’ habitat, or responsibility for
USDA Forest Service Proceedings RMRS-P-16. 2000
education programs that would benefit recovery. The group
was kept small to facilitate group discussion, but included a
representative from all groups that had conducted research
or management on these species. CBSG often includes many
stakeholders in their workshops, including private landowners involved in implementation. However, because of
the complexity of developing biological objectives for these
species, our workshops focused only on the species’ biological
needs and not on implementation. Future workshops are
planned that will involve landowners and land managers,
and that will encourage their participation in developing
and implementing recovery solutions using the biological
information developed in the first workshops.
The workshops had several steps. Introductory material
was presented on the general intent of the workshop, an
overview of small population biology, new biological data,
the importance of informing the public of what is needed to
recover endangered species, and a demonstration of the
simulation model. Then, the group developed a set of workshop goals. The Black-capped Vireo group agreed to the
following set of goals, which were similar to those developed
in the Golden-cheeked Warbler workshop (Beardmore and
others 1996b):
• Update and describe range-wide distribution and status (breeding, wintering).
• Update information on habitat characteristics.
• Identify and rank threats.
• Describe population dynamics, conduct simulation models, and estimate extinction probabilities (range-wide,
special cases); define and estimate viable population
sizes.
• Evaluate data on critical biological parameters, review
methods and recommend standardization.
• Identify stakeholders and partners (agencies, organizations, private sector) and resources for implementing
recovery.
• Develop a cooperative urban and rural outreach strategy.
• Describe short-term and long-term consequences of
action or inaction by stakeholders.
• Specify research needs.
• Determine management needs for cowbirds, habitat
(public and private ownership); discuss cost-benefit
analyses and incentives and disincentives (Beardmore
and others 1996a).
These goals were divided among four subgroups to address:
(1) population biology and modeling, (2) habitat management
strategies, (3) outreach and partnerships, and (4) distribution, status, and threats. All subgroups identified future
research needs for their topics. Each subgroup drafted a
report that summarized information, discussions, and recommendations. After the workshop, draft reports were
compiled into chapters of a draft document and sent out for
participant review. Each species group asked to have a
subsequent one-day meeting during which comments on the
draft document were discussed and chapters modified. The
revised chapters from the one-day meetings were incorporated into final reports (Beardmore and others 1996a,b).
The reports from the PHVA workshops are intended as a
framework from which managers can develop habitat in
such a way that it will help meet the report recommendations. We were cognizant of possible misinterpretations, and
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were careful to include our assumptions and caveats. The
results represent the best direction we have with the current
state of knowledge, recognizing that we used minimal data
for some values. Further data collection and analysis and
the results of recommended conservation efforts will change
the scope of recovery needs. That is, we intend the PHVAs to
be part of an iterative process. The workshops’ participants
will meet again, both to target strategies for specific situations and to refine recommendations with new data. To
implement recommendations found in the final reports,
local workshops will be needed to involve landowners and
land managers in developing specific strategies for action at
the site level. Also, when research provides new information
about processes, threats, and/or species biology, a reassessment of the targets and recommendations may be needed.
What Resources Were Needed to Conduct
a PHVA Workshop?
The Golden-cheeked Warbler and Black-capped Vireo
PHVAs were supported by a National Biological Service
(NBS) grant and the participants’ agencies and organizations. Total expenses for one workshop were about $7,000,
including a computer simulation model, biostatistician support, and partial costs for travel and meeting facilities. This
figure does not include the field work necessary for data
gathering, but does include data synthesis.
What Data Were Needed for the PHVA?
By working through the available data in the population
biology and modeling subgroups, the participants realized
that the complexity of the simulation model that could be
used for the analysis relates directly to the adequacy of the
data available. If a substantial amount of the necessary data
is available, a customized model can be developed that
simulates important aspects of a species’ life history; if data
are limited or not appropriate for the model, a less sophisticated model can be used. For the Black-capped Vireo and
Golden-cheeked Warbler, we did not have sufficient data to
develop a customized simulation model. Instead we used a
generalized, commercial model, RAMAS/metapop (Akáakaya
1994). RAMAS/metapop, like all PVA models, required an
estimate of survivorship (from mark-recapture banding) at
the same location for more than three consecutive years (to
provide temporal variance), fecundity (number of fledglings
per adult), and dispersal rates and distances (anecdotal
information was used for the warbler and vireo from banded
individuals).
PHVA Workshop Results _________
Each workshop had valuable tangible and intangible
results. The final reports have population targets and habitat recommendations that can be used by agencies, organizations, and individuals to plan, justify, and guide conservation actions. Intangible values were produced by the
interactions among participants. Each workshop capitalized on the dynamics of a group that was brought together for
a specific purpose. The participants built consensus on
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actions needed to achieve viable populations. Information,
including personal knowledge and experience which is not
found in the literature, was assembled by the participants.
Through the shared workshop experience, participants
gained appreciation for each others’ perspectives, each
others’ work, and for the workshop product. Workshop
participants realized that new and ongoing research should
focus on certain aspects of warbler and vireo biology that
previously had been addressed insufficiently. Researchers
understood how a better organized, cooperative approach
to research was needed that would generate the specific
data that could be applied to improve the simulation
models and meet other needs. Participants realized how
their work contributes, or could be modified to contribute,
to the bigger picture. In general, the workshops motivated
participants to take action when they returned to their
own work stations.
How Can PHVAs Be Useful to
Partners In Flight? ______________
The PHVA process includes the basic steps of data collection and synthesis, and building consensus about recommendations to conserve a species. The PIF process for
developing population objectives, habitat strategies, and
research and outreach recommendations should be essentially the same as the process for developing a PHVA. Often,
PHVAs are not seen as applicable to the PIF planning
process, primarily because of the perception that PHVAs are
only computer modeling exercises, not the consensus-building group process described above.
Regarding data collection and synthesis, several important recommendations are obtained from the PHVA process.
The exercise of compiling information, both for modeling and
making habitat management recommendations, is useful.
During this step, two realizations usually emerge. One is
that more information exists than is originally suspected.
Often, an important source of information is the experience
of local experts, which surfaces during group interactions
and is incorporated into recommendations. This information
is especially important because local variations can dictate
different needs and approaches even for the same species.
The other realization is identifying what data are missing or
insufficient; this is important for directing future research
priorities. In the warbler example, we learned that we had
only two banding projects that could be used to estimate
survivorship. We recommended that future banding projects
should commit to more than three years, because multiple
years of banding are needed to provide the survivorship
estimate. For the vireo, many workers were observing
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nesting success, but the methodology varied among projects.
In this case, we recommended a standardized methodology
to produce the necessary fecundity estimate.
Although simulation model analysis was used in the
warbler and vireo PHVAs, it is not a requirement of PHVAs.
A PIF group may decide whether a computer simulation is
needed. Because of the expense and length of time required
to collect survivorship, fecundity, and dispersal data, population viability analyses should be undertaken in special
cases. Factors such as vulnerability of the species to risks
and documented population declines can be considered to
determine if a computer simulation would be useful. However, the exercise of gathering the available data for high
priority PIF species—even if limited—and determining if
they could be applied to an existing model can be useful, and
quickly focuses research needs. If MAPS or BBIRD stations
are in the area, survivorship estimates (DeSante 1992a) and
fecundity estimates (Martin and others 1997) from these
programs can be considered. If data do not exist for simulation modeling, or the PIF group does not want to include
modeling in their plans, then the process of “closeting”
experts, examining what is known, and making recommendations based on the other components of PHVAs is valuable.
In the Golden-cheeked Warbler example, even with limited data we learned that relatively large, viable populations
(1,000-3,000 breeding pairs per population, depending on
rates of habitat loss) were needed to prevent an unacceptable probability of extinction (Beardmore and others 1996b).
The Black-capped Vireo modeling indicated that smaller
populations (200-1,000 breeding females) would be viable,
but only with cowbird removal (Beardmore and others 1996a).
Because multiple, viable populations are recovery criteria
for both species, the species’ ranges were subdivided based
on ecology and geography, thus giving the number of populations needed for recovery. PIF biological objectives could
also be derived from such an approach, such as:
• A viable population should have x acres of optimal
habitat that is managed to produce y pairs (e.g., for the
Golden-cheeked Warbler y = 1,000-3,000 pairs, and x
acres of optimal habitat is figured by taking a local
density, x = y pairs, X number of acres needed per pair).
• Z conservation areas should be distributed across the
range of the target species, each area consisting of a
viable population with its optimal habitat (z = number
of areas ecologically determined to be needed).
In conclusion, PHVAs should be considered as a planning
tool in bird conservation. In this process data and knowledge
can be examined and organized, deficiencies can be found,
and recommendations can be made. Computer simulations
may or may not be a part of the assessment.
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