United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

General Technical Report

RMRS-GTR-257

June 2011

A System for Assessing 

Vulnerability of Species 

(SAVS) to Climate Change

Karen E. Bagne, Megan M. Friggens, and Deborah M. Finch
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Bagne, Karen E.; Friggens, Megan M.; and Finch, Deborah M. 2011. A System for Assessing Vulnerability 

of Species (SAVS) to Climate Change. Gen. Tech. Rep. RMRS-GTR-257. Fort Collins, CO. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 28 p.

Abstract

Sustained conservation of species requires integration of future climate change effects, but few tools exist 

to assist managers. The System for Assessing Vulnerability of Species (SAVS) identifies the relative vulnerability or resilience of vertebrate species to climate change. Designed for managers, the SAVS is an easily 

applied tool that uses a questionnaire of 22 predictive criteria to create vulnerability scores. The user scores 

species’ attributes relating to potential vulnerability or resilience associated with projections for their region. 

Six scores are produced: an overall score denoting level of vulnerability or resilience, four categorical scores 

(habitat, physiology, phenology, and biotic interactions) indicating source of vulnerability, and an uncertainty 

score, which reflects user confidence in the predicted response. The SAVS provides a framework for integrating new information into the climate change assessment process.

Keywords: climate change, vulnerability, vertebrate species, conservation, resource management

Authors

Karen E. Bagne is an ecologist and wildlife biologist for the USFS Rocky Mountain Research Station.

Megan M. Friggens is a Research Ecologist (post doctoral) within the USFS Rocky Mountain Research Station.

Deborah M. Finch is the Program Manager for the Grassland, Shrubland and Desert program of the USFS 

Rocky Mountain Research Station.

Acknowledgments

Funding for this project was provided by the U.S. Forest Service (Climate Change Initiative), the U.S. Fish 

and Wildlife Service (Middle Rio Grande Bosque Improvement Initiative), The Nature Conservancy (Santa Fe 

Office), and the Department of Defense (Legacy Program). Sharon Coe, University of Arizona and Rocky 

Mountain Research Station; Bruce Young, NatureServe; and Molly Cross, Wildlife Conservation Society, 

provided manuscript review and discussion that improved this tool. Collaborators who inspired tool 

development include Carolyn Enquist and David Gori, The Nature Conservancy; Lisa Graumlich, University 

of Arizona; and Heather Bateman, Arizona State University Polytechnic. Further support and advice was 

provided by Jack Triepke and Bryce Rickels of US Forest Service, Region 3.
Cover Photos: Clockwise from top: Cactus Ferruginous Pygmy-Owl (Glaucidium brasilianum cactorum) courtesy of National 

Park Service; Northern Prairie Skink (Eumeces septentrionalis septentrionalis); Southwestern Willow Flycatcher (Empidonax 

traillii extimus) by Jim Rorabaugh, USFWS; Canada Lynx (Lynx canadensis) by Michael Zahra; American Pika (Ochotona 

princeps) from the Canadian Rocky Mountains by sevenstar; Desert Tortoise (Gopherus agassizii) courtesy of USGS.

i

Contents

Introduction................................................................................................... 1

Development of SAVS .................................................................................... 2

Scoring Strategy.................................................................................. 2

Scoring Criteria................................................................................... 7

Habitat ................................................................................... 7

Physiology ............................................................................ 10

Phenology............................................................................. 12

Biotic Interactions................................................................. 12

Application of SAVS ..................................................................................... 13

Scoring Species................................................................................. 13

Uncertainty Scores................................................................ 13

Interpreting Scores................................................................ 15

Score Applications................................................................ 15

Discussion.................................................................................................... 16

Glossary of Terms and Concepts.................................................................. 17

Literature Cited............................................................................................ 18

Appendix 1. SAVS User Guide ..................................................................... 22

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011 1

Introduction_______________________

Global climate change is already affecting habitats and 

species worldwide (Root and others 2003; Enquist and 

Gori 2008). Yet we do not know how climate change will 

alter ecosystems because climate predictions are uncertain, global carbon and nitrogen cycling is complex, and 

our knowledge of ecological relationships is incomplete 

(Figure 1). It is clear, however, that warming trends will 

continue in the near future regardless of attempts to curtail greenhouse gas emissions (Caldeira and others 2003). 

Natural selection provides a mechanism whereby species 

can adapt to changes in their environments (Skelly and 

others 2007), but the speed with which climate is currently 

changing precludes adaptation in many species (Figure 2) 

(Janzen 1994; Visser 2008). Species unable to relocate 

or adapt to changing conditions will be at an increased 

risk of extinction. Additionally, climate projections vary 

regionally and effective strategies for conserving species 

under climate change need to integrate regional information 

on biogeography and ecology (Hannah and others 2002; 

Seavy and others 2008). The magnitude of the problem 

constitutes a major challenge for conservation practitioners. 

Despite these challenges, the potential impact on global 

biodiversity makes efforts to conserve species critically 

important.

Natural resource conservation is an iterative and 

adaptive process of identifying targets, implementing 

management actions, monitoring, and reviewing (Holling 

1978; Walters and Holling 1990). Given the magnitude of 

the threat posed by climate change, the large number of 

species at risk, and the uncertainty of future conditions, 

conserving biodiversity in the future will rely on our ability 

to accurately identify targets and focus limited resources. 

A System for Assessing Vulnerability 

of Species (SAVS) to Climate Change

Karen E. Bagne, Megan M. Friggens, and Deborah M. Finch

Figure 1. An example of one of the many consequences of climate change. This figure shows 

deviations from normal sea surface temperatures (left) and sea surface heights (right) at the 

peak of the 2009-2010 central Pacific El Niño, as measured by NOAA polar orbiting satellites 

and NASA’s Jason-1 spacecraft, respectively. The warmest temperatures and highest sea levels 

were located in the central equatorial Pacific. This represents a relatively new type of El Niño in 

which warm waters are present in the central-equatorial Pacific Ocean, rather than in the easternequatorial Pacific. This type of El Nino is becoming more common and progressively stronger 

due to recent warming trends (Tong and McPhaden 2010). Image credit: NASA/JPL-NOAA.
2 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011

Figure 2. Shepard Glacier in Glacier National Park, Montana, as seen in 1913 (left) and 2005 (right). Image 

credit: USGS.

Assessments of vulnerability or extinction risk are valuable 

tools for identifying targets and prioritizing conservation 

needs so that management actions, or adaptation strategies, can be directed in an effective and efficient manner 

(Patt and others 2009; Glick and Stein 2011). Assessments 

that also identify how species, habitats, or ecosystems are 

affected by projected changes enable managers to develop 

new protocols and assess current management practices 

in light of expected future conditions (Füssel and Klein 

2008; Glick and Stein 2011). In this paper, we describe a 

new System for Assessing Vulnerability of Species (SAVS) 

that identifies how and to what extent vertebrate species 

may be vulnerable to climate change (Table 1).

The SAVS is a simple and flexible tool designed for 

managers to assess the relative risk of individual species 

to population declines in response to projected changes in 

climate and related phenomena. The SAVS uses an easily completed questionnaire based on predictive criteria 

(Table 1) that translate response of terrestrial vertebrate 

species into scores indicating vulnerability or resilience 

to climate change. In addition to the scoring tool itself 

(Table 1), we provide worksheets for score calculations 

(Box 1), methods for calculating uncertainty (Box 1), 

detailed instructions for scoring a species (Appendix 1), 

guidelines for tool application, a glossary of terms, 

and discussion of application of scores to vulnerability 

assessments.

Development of SAVS ______________

Scoring Strategy

Our goal was to create a tool that predicts the likelihood 

and direction of population change for individual species 

under future climate scenarios. Although we focused on 

identifying vulnerable species (those with a high likelihood 

of negative population change) we also considered characteristics associated with resilience as not all species will 

respond negatively to climate change (Araújo and others 

2006). Response to climate change is estimated in SAVS 

as the cumulative value of a set of predictors of population change that represent negative or positive response 

to climate change. This cumulative score increases with 

increasing vulnerability with the range of estimated scores 

that create a standard for comparison among species. The 

SAVS is designed to be applied by the user to a targeted 

region and time period encompassing a uniform set of 

climate predictions (e.g., a single climate zone), although 

we did integrate the use of additional climate information 

for migratory species. The SAVS focuses on the effects of 

climate change rather than integrating threats from other 

sources, because current management or conservation 

plans generally cover those topics. To reduce complexity, 

this version of SAVS applies only to terrestrial vertebrate 

species.

Response of species to climate change is predicted 

from characteristics associated with exposure, sensitivity, 

or adaptive capacity (Glick and Stein 2011; IPCC 2007)

(Table 2). Exposure refers to the degree to which a species 

will experience changing climate and conditions, whereas 

sensitivity is the degree to which a species is actually affected by those conditions (Glick and Stein 2011). Adaptive 

capacity is the potential for a species to reduce exposure 

or sensitivity (Glick and Stein 2011). We used basic ecological principles and published studies linking survival 

or reproduction to climate or related phenomena (e.g., 

fire, floods, snowpack levels) to identify characteristics 

or traits indicative of sensitivity or adaptive capacity. 
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011 3

Table 1. The System for Assessing Vulnerability of Species (SAVS) (v.2.0): A Climate Change Tool 

for Resource Managers. Download from http://www.fs.fed.us/rmrs/species-vulnerability/.

Habitat 

H1. Area and distribution: breeding. Is the area or location of the associated vegetation type 

used for breeding activities by this species expected to change? Specific habitat elements 

and food resources are considered in other questions. 

a. Area used for breeding habitat expected to decline or shift from current location 

(SCORE = 1)

b. Area used for breeding habitat expected to stay the same and in approximately the 

same location (SCORE = 0)

c. Area used for breeding habitat expected to increase and include the current location 

(SCORE = -1)

H2. Area and distribution: non-breeding. Is the area or location of the associated vegetation 

type used for non-breeding activities by this species expected to change?

a Area used for non-breeding habitat expected to decline or shift from current location 

(SCORE = 1)

b. Area used for non-breeding habitat expected to stay the same in approximately the 

same location (SCORE = 0)

c. Area used for non-breeding habitat expected to increase and include the current location (SCORE = -1)

H3. Habitat components: breeding. Are specific habitat components required for breeding expected to change within the associated vegetation type? 

a. Required breeding habitat components expected to decrease (SCORE = 1)

b. Required breeding habitat components unlikely to change OR habitat components 

required for breeding unknown (SCORE = 0)

c. Required breeding habitat components expected to increase (SCORE = -1)

H4. Habitat components: non-breeding. Are other specific habitat components required for 

survival during non-breeding periods expected to change within the associated vegetation 

type? 

a. Required non-breeding habitat components expected to decrease (SCORE = 1)

b. Required non-breeding habitat components unlikely to change OR habitat components 

required for breeding unknown (SCORE = 0)

c. Required non-breeding habitat components expected to increase (SCORE = -1)

H5. Habitat quality. Within habitats occupied, are features of the habitat associated with better 

reproductive success or survival expected to change? 

a. Projected changes are likely to negatively affect habitat features associated with improved reproductive success or survival (SCORE = 1)

b. Projected changes are unlikely to affect habitat features associated with improved 

reproductive success or survival (SCORE = 0)

c. Projected changes are likely to positively affect habitat features associated with improved reproductive success or survival (SCORE = -1)

H6. Ability to colonize new areas. What is the potential for this species to disperse?

a. Low ability to disperse (SCORE = 1)

b. Mobile, but dispersal is sex-biased (only one sex disperses) (SCORE = 0)

c. Very mobile, both sexes disperse (SCORE = -1)

H7. Migratory or transitional habitats. Does this species require additional habitats during migration that are separated from breeding and non-breeding habitats?

Additional habitats required that are separated from breeding and non-breeding habitats 

 (e.g., most migratory species) (SCORE = 1)

No additional habitats required that are separated from breeding and non-breeding

 habitats (e.g., most resident species and short-distance migrants) (SCORE = 0)

Physiology

PS1. Physiological thresholds. Are limiting physiological conditions expected to change?

a. Projected changes in temperature and moisture are likely to exceed upper physiological 

thresholds (e.g., activities occur in very hot climates, amphibians in drier climates, species with narrow thermal range) (SCORE = 1) (con.)
4 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011

b. Projected changes in temperature or moisture will primarily remain within physiological 

thresholds OR species is inactive during limiting conditions (e.g., species with moderate 

thermal range, aestivators that avoid hot/dry conditions) (SCORE = 0)

c. Projected changes in temperature or moisture will decrease current incidents where 

lower thresholds are exceeded (e.g., species active in very cold climates, amphibians in 

wetter climates, species with very broad thermal range) (SCORE = -1)

PS2. Sex ratio. Is sex ratio determined by temperature?

a Yes. (SCORE = 1)

b. No. (SCORE = 0)

PS3. Exposure to weather-related disturbance. Are disturbance events (e.g., severe storms, 

fires, floods) that affect survival or reproduction expected to change?

a. Projected changes in disturbance events will likely decrease survival or reproduction 

(SCORE = 1)

b. Survival and reproduction are not strongly affected by disturbance events OR disturbance events are not expected to change (SCORE = 0)

c. Projected changes in disturbance events will likely increase survival or reproduction 

(SCORE = -1)

PS4. Limitations to daily activity period. Are projected temperature or precipitation regimes that 

influence activity period of species expected to change?

a. Duration of daily active periods likely to be reduced (e.g., heliotherms in hot climates, 

terrestrial amphibians in drier climates) (SCORE = 1)

b. Duration of daily active periods unchanged or not limited by climate (species in habitats 

buffered from extremes, nocturnal species, primarily aquatic amphibians) (SCORE = 0)

c. Duration of daily active periods likely to increase (e.g., heliotherms in cool climates, terrestrial amphibians in wetter climates) (SCORE = -1)

PS5. Survival during resource fluctuation. Does this species have flexible strategies to cope with 

variation in resources across multiple years?

a. Species has no flexible strategies to cope with variable resources across multiple years 

(SCORE = 1)

b. Species has flexible strategies to cope with variable resources across multiple years 

(e.g., alternative life forms, irruptive, explosive breeding, cooperative breeding) (SCORE 

= -1)

PS6. Energy requirements. What is this species’ metabolic rate?

a. Very high metabolic rates (e.g., shrews, hummingbirds) (SCORE = 1)

b. Moderate (e.g., most endotherms) (SCORE = 0)

c. Low (i.e. ectotherms) (SCORE = -1)

Phenology

PH1. Mismatch potential: Cues. Does this species use temperature or moisture cues to initiate 

activities related to fecundity or survival (e.g., hibernation, migration, breeding)?

a. Species primarily uses temperature or moisture cues to initiate activities (e.g., some 

hibernators, aestivators, rainfall breeders) (SCORE = 1)

b. Species does not primarily use temperature or moisture cues OR no cues to predict or 

initiate activities (e.g., photoperiod or circadian rhythms, resource levels) (SCORE = 0)

PH2. Mismatch potential: Event timing. Are activities related to species’ fecundity or survival tied 

to discrete resource peaks (e.g., food, breeding sites) that are expected to change?

a. Species’ fitness is tied to discrete resource peaks that are expected to change (SCORE 

= 1)

b. Species’ fitness is tied to discrete resource peaks that are NOT expected to change 

(SCORE = 0)

c. No temporal variation in resources or breeds year-round (SCORE = -1)

(con.)

Table 1. (continued).
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011 5

PH3. Mismatch potential: Proximity. What is the separation in time or space between cues that 

initiate activities related to survival or fecundity and discrete events that provide critical 

resources?

a. Critical resource occurs far in advance or in distant locations from cues or initiation of 

activity (SCORE = 1)

b. Critical resource does NOT occur far in advance or in distant locations from cues or 

initiation of activity (SCORE =0)

c. Species initiates activities directly from critical resource availability (e.g., opportunistic 

breeders) (SCORE = -1)

PH4. Resilience to timing mismatch. Does this species have more than one opportunity to time 

reproduction to important events?

a. Species reproduces once per year or less (SCORE = 1)

b. Species reproduces more than once per year (SCORE = -1)

Biotic Interactions

I1. Food resources. Are important food resources for this species expected to change?

a. Primary food source(s) are expected to be negatively impacted by projected changes 

(SCORE = 1)

b. Species consumes variety of prey/forage species OR primary food resource(s) not 

expected to be impacted by projected changes (SCORE =0)

c. Primary food resource(s) expected to be positively impacted by projected changes 

(SCORE = -1)

I2. Predators. Are important predator populations for this species expected to change?

a. Primary predator(s) are expected to be positively impacted by projected changes 

(SCORE = 1)

b. Preyed upon by a suite of predators OR the primary predator is not expected to be 

impacted by projected changes (SCORE = 0)

c. Species has no predators (SCORE = 0)

d. Primary predator(s) expected to be negatively impacted by projected changes (SCORE 

= -1)

I3. Symbionts. Are populations of symbiotic species expected to change?

a. Symbiotic species populations expected to be negatively impacted by projected 

changes (SCORE = 1)

b. Symbiotic species populations not expected to be impacted by projected changes 

(SCORE = 0)

c. No symbionts (SCORE =0)

d. Symbiotic species populations expected to be positively impacted by projected changes (SCORE = -1)

I4. Disease. Is prevalence of diseases known to cause widespread mortality or reproductive 

failure in this species expected to change?

a. Disease prevalence is expected to increase with projected changes (SCORE = 1)

b. No known effects of expected changes on disease prevalence (SCORE = 0)

c. Disease prevalence is expected to decrease with projected changes (SCORE = -1)

I5. Competitors. Are populations of important competing species expected to change?

a. Major competitor species are expected to be positively impacted by projected changes 

(SCORE = 1)

b. Species has a variety of competitive relationships OR no expected impacts of projected 

changes in major competitor species (SCORE = 0)

c. Competing species are expected to be negatively impacted by projected changes 

(SCORE = -1)

Table 1. (continued).
6 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011

Box 1. Computing Scores

Vulnerability

Positive values indicate vulnerability to climate change and negative scores indicate resilience. Factors are adjusted for max score per factor = 5 or -5 to aid comparison among factors. 

Overall scores are computed from all predictive criteria (i.e. the 22 questions) regardless of 

factor and adjusted for maximum score of 20 or a minimum score of -20. To calculate vulnerability scores, take the sum of positive values and the sum of negative values for each category 

and for all questions and use those values in the following equations:

Habitat Vulnerability = (Positive total x [5/7]) + (Negative total x [5/6])

Physiology Vulnerability = (Positive total x [5/6]) + (Negative total x [1])

Phenology Vulnerability = (Positive total x [5/4]) + (Negative total x [5/3])

Biotic Interaction Vulnerability = (Positive total x [1]) + (Negative total x [1])

Overall Vulnerability Score = (Positive total x [20/22]) + (Negative total x [20/19])

Uncertainty

Assuming climate change projections are correct, note the amount of information available 

for each question for assigning scores. Chose one of the following for each question:

a. Adequate information available to assign score for this species. SCORE = 0

b. Information is not adequate to confidently assign score OR conflicting predictions or 

responses make scoring difficult. SCORE = 1

Calculations are the percentage of uncertain scores for each factor and for all criteria 

(i.e., overall). Use the worksheet below to aid calculation. Calculate percent uncertainty using 

the equations below:

Percent uncertainty for Habitat = (Sum of uncertainty scores / 7)

Percent uncertainty for Physiology = (Sum of uncertainty scores / 6)

Percent uncertainty for Phenology = (Sum of uncertainty scores / 4)

Percent uncertainty for Interactions = (Sum of uncertainty scores / 5)

Percent of overall uncertainty = (Sum of uncertainty scores for all questions / 22)
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011 7

We then integrated these traits with exposure to develop 

criteria predictive of climate change response into a scoring system that is regional and species specific (Table 1). 

Thus, scores include both the predicted climate-related 

change (e.g., increased burning) and the predicted response 

of the species (e.g., fire increases preferred habitat). The 

user obtains information on exposure before scoring from 

available climate projections for the target region (Table 3).

While developing the SAVS, we considered repeatability, 

relation to quantitative values, and independence from other 

scoring criteria (Beissinger and others 2000). To increase 

repeatability, each predictive criteria or question assesses 

anticipated negative, positive, or neutral impacts, but not 

degree of vulnerability. Because knowledge of species and 

climate change is incomplete, we designed the tool to be 

flexible to new information as well as a variety of information sources including published materials, personal 

knowledge, and expert consultation.

Scoring Criteria

We considered criteria based on published species’ responses, observed or modeled, that could be used to predict 

direction, positive or negative, of climate change response. 

We identified a wide range of criteria that represent both 

direct and indirect responses to changes in temperature 

and precipitation, as well as to extreme events, which are 

important in driving population dynamics and natural 

selection (Boag and Grant 1984; Easterling and others 

2000; Parmesan and others 2000). We selected criteria 

predictive of species response to climate change from four 

broad factors or categories: habitat, physiology, phenology, 

and biotic interactions.

Habitat—Predicted changes to global temperature and 

precipitation patterns will, consequently, alter habitats 

(McCarty 2001; Hitch and Leberg 2007; Sekercioglu 

and others 2008). We identified five criteria predictive 

Table 2. Criteria used in SAVS climate change tool address one or more of the three aspects of 

vulnerability as defined by the IPCC (2007). Each criterion represents an area expected 

to experience climate-related impacts.

Factor & Criteria Vulnerability Component

Habitat

H1. Breeding habitat area and distribution Exposure, Sensitivity

H1. Non-breeding habitat area and distribution Exposure, Sensitivity

H1. Habitat components required for breeding Exposure, Sensitivity

H1. Habitat components required outside breeding Exposure, Sensitivity

H1. Habitat quality Exposure, Sensitivity

H1. Ability to colonize new areas Adaptive Capacity

H1. Reliance on migratory or transitional habitats Sensitivity

Physiology

PS1. Physiological thresholds Sensitivity, Adaptive Capacity

PS1. Sex ratio related to temperature Sensitivity

PS1. Exposure to weather-related disturbance Sensitivity, Exposure

PS1. Changes to daily activity period Sensitivity, Adaptive Capacity

PS1. Survival during resource fluctuation Adaptive Capacity

PS1. Energy requirements Sensitivity

Phenology

PH1. Mismatch potential: Cues Sensitivity

PH1. Mismatch potential: Event timing Sensitivity

PH1. Mismatch potential: Proximity Sensitivity

PH1. Resilience to timing mismatch Sensitivity, Adaptive Capacity

Biotic Interactions

I1. Food resources Exposure, Sensitivity

I2. Predators Exposure, Sensitivity

I3. Symbionts Exposure, Sensitivity

I4. Disease Exposure, Sensitivity

I5. Competitors Exposure, Sensitivity
8 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011

Table 3. A list of the major types of data that should be gathered for SAVS. The questions addressed 

by the data are indicated in parentheses after the list item.

Climate Change Scenarios (all questions)

•	 Change in total annual precipitation

•	 Change in seasonal precipitation

•	 Change in average temperatures (night and day)

•	 Maximum summer temperatures

•	 Minimum winter temperatures

•	 Changes to snowpack duration, amount

•	 Change to number of frost days

•	 Projected drought duration and frequency

•	 Changes in potential, frequency and timing of flooding

•	 Changes in frequency, severity, extent or timing of fire disturbances

•	 Changes in frequency, duration, extent or timing of extreme weather events (e.g.,

storms, heat waves)

Natural History Data Needed for Species Assessments: 

Habitat

Climate projections related to vegetation type for breeding and non-breeding habitats 

including disturbance processes (All Questions)

Habitat/associated vegetation type: Breeding and nonbreeding habitats, vegetation type 

associations (Questions 1, 2)

Habitat components required for breeding or survival (Questions 3, 4) 

Any aspect of the breeding or nonbreeding habitat associated with habitat quality 

(improved breeding or survival) (Question 5) 

Dispersal ability and sex biased dispersal (Question 6)

Migration habits/requirements (Question 7)

Physiology

Threshold or sensitivity to moisture or temperature extremes (Alternative: species range 

relative to area under assessment) (Question 1) 

Sex ratio/temperature relationships (some reptiles) (Question 2) 

Potential exposure of species to extreme weather condition/Known cases of mortality of 

failed reproduction related to weather events (Question 3)

Climate or weather-mediated limitations to active periods (Question 4) 

Endothermic or exothermic (Question 5)

Variable life history strategies/Able to postpone reproductive output (Question 6)

Phenology

Temperature or moisture variables used as cues (Question 1) 

Events that need to be timed to coincide with reproduction/survival (insect emergence, 

etc.) (Question 2)

Proximity (temporal and geographical) of cues, activities, and essential resources (Question 3) 

Number of breeding attempts per year (Question 4)

Biotic Interactions

Identify primary food resources, expected changes to resources (Question 1) 

Identify primary predators and expected changes to predator populations (Question 2) 

Identify symbionts and expected changes to symbiont populations (Question 3) 

Identify significant pathogen entities, disease risk factors, and expected changes to these 

issues (Question 4) 

Identify major competitors and expected changes to competitor populations (Question 5) 
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011 9

of population change as climate affects habitats: changes 

in habitat area or location, effects on habitat elements, 

changes in habitat quality, dispersal ability, and reliance 

on additional habitats during migration. We consider 

breeding and non-breeding habitats separately in this 

assessment, because requirements or locations for these 

activities differ for many species.

Survival is typically tied to specific habitats, which in 

turn are tied to local climate conditions. Thus, populations 

are likely to be affected as changes in local conditions 

change the availability of suitable habitat. In addition to 

changes in overall area, climate changes may result in 

major shifts in distribution of associated vegetation types. 

This also affects habitat availability, because of complexities arising from species-specific plant responses 

to climate and differences in new site characteristics 

such as soil profiles, existent vegetation, topography, and 

land use (Martínez-Meyer 2005; Ibáñez and others 2008). 

Significant shifts have been predicted for many vegetation 

types, including North American forests (Iverson and 

Prasad 2001; Rehfeldt and others 2006) and European 

alpine (Dirnböck and others 2003). We have already seen 

habitat loss for range-restricted species, such as those from 

high altitudes and distributional shifts (Figure 3) consistent 

with those predicted by warmer temperatures, and these 

responses are likely to increase as temperatures continue 

to rise (Root and others 2003; Parmesan 2006).

Species may also require additional features or components within suitable vegetation types for survival or 

reproduction. Climate changes can affect the availability 

of key ephemeral resources and critical habitat features. 

For example, the hydroperiod of amphibian breeding ponds is a critical component directly affected by 

changes in precipitation patterns (Paton and Crouch 2002). 

Populations of cavity-nesting birds are often affected by 

the availability of cavities (reviewed by Newton 1994) 

components potentially altered by climate change.

We can expect climate-induced changes to habitat quality 

when climate alters the structure or composition of habitat 

components that affect rates of survival or reproduction 

(Figure 4). For example, precipitation is closely associated 

with plant biomass, an important element of habitat quality 

for herbivores (Chase and others 2000). Habitat changes 

may also be related to snowpack and ice formation or sea 

level rise. Deeper snowpack is expected to hinder grazing 

animals in winter (Post and Stenseth 1999). Conversely, a 

smaller snowpack is expected to negatively affect species, 

such as lemmings and pikas that rely on snow for protection (Lindström 1994; Coulson and Malo 2008).

As habitats change, dispersal strategies and mobility 

of organisms become important indicators of how a species could cope with shifting habitats (Thomas and 

others 2004; Araújo and others 2006; Jiguet and others 

2007). Species that are able to travel long distances have 

a greater chance of finding and colonizing new habitat 

patches. Conversely, some long distance dispersers are at 

an increased risk for negative habitat effects if they rely on 

multiple habitats that are likely to be exposed to disparate 

climate change effects (Visser and others 2008).

Figure 3. Over the last few decades the range of the Red Fox (right) has expanded northward and upward, 

displacing the Arctic Fox (left) in North American Tundra Habitat (Hersteinsson and MacDonald 1992). Boundary 

changes were related to warming trends, which increased food availability for the competitively superior Red 

Fox. In the context of the criteria used in the SAVS, warming is effectively increasing the area of suitable habitat 

for the Red Fox, a positive habitat effect, but increasing competitive pressure for the Arctic Fox, a negative 

interaction effect. Image credit: USGS and John Sarvis, USFWS.
10 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011

Physiology—Species exhibit physiological requirements and limitations related to temperature and moisture 

(McCain 2007), which can help predict future impacts 

(Helmuth and others 2005). We identified six predictive 

criteria related to physiology: physiological thresholds, 

temperature-dependent sex ratios, exposure to extreme 

climate or disturbance events, energetics related to activity 

patterns, adaptations to cope with resource fluctuations, 

and capacity to moderate metabolic expenditure.

The range of temperature and moisture tolerances exhibited by species is important in predicting direct impacts 

of climate (Beever and others 2003; Humphries and others 

2004; Bernardo and Spotila 2006). For birds in France, 

species that had a lower tolerance for high temperatures 

were more likely to have experienced recent declines 

(Jiguet et al. 2007). Additionally, nocturnal reptiles and 

small mammals generally have lower tolerances for high 

temperatures than diurnal species (Cowles 1940). A comparison of metabolic stress in montane salamanders along 

an elevational gradient indicated that species that adapted 

to cool temperatures were physiologically intolerant of 

increasing temperatures (Bernardo and Spotila 2006). 

Conversely, species that tolerate extremely warm or dry 

conditions are not necessarily more tolerant of climate 

change, but rather may be vulnerable to temperature increases if they are already near their physiological limits 

(Figure 5) (Hargrove 2010).

Some reptiles have temperature-sensitive sex determination and will be vulnerable to skewed sex ratios 

that ultimately affect population viability (Janzen 1994; 

Mitchell and others 2008). For example, mean temperature increases of 4 °C are projected to eliminate males in 

painted turtle populations (Janzen 1994).

Disturbance and extreme conditions affect species’ 

distributions and drive natural selection (Boag and Grant 

1984; Parmesan and others 2000). Changes in climaterelated disturbance events, such as fire, flooding, or 

freeze events are expected to affect species survival and 

reproduction (Westerling and others 2006; Hamlet and 

Lettenmaier 2007). Some bird species are exposed to 

storms and hurricanes during migration and could be 

affected if these events intensify or become more frequent 

(Butler 2000; Frederiksen and others 2008). Breeding 

success of Humboldt penguins, which nest in burrows or 

on the ground, is negatively impacted by flooding caused 

by events such as the heavy rains associated with El Niño 

events (Simeone and others 2002). Response to disturbance events, however, can vary depending on a species’ 

sensitivity (Pike and Stiner 2007). For example, some bird 

species are adapted to take advantage of post-fire habitats, 

while others favor habitats in later stages of succession 

(Hutto 2008; Bagne and Purcell 2009).

In addition to physiological thresholds, energetic 

constraints linked with climate will play an important 

role in species’ response. Population variations and 

reproductive output are often associated with energetic tradeoffs related to climate (Franklin and others 

2000). Even moderate changes to daily temperature or 

humidity levels can influence daily activity patterns 

and ultimately limit food intake, limit access to mates, 

or increase predation risk (Lueth 1941; Walsberg 2000; 

Sinervo and others 2010). Recent local extinctions in 

Mexican lizards were attributed to climate-induced 

changes to suitable foraging time (Sinervo and others 

2010). Alternatively, changes in limiting conditions 

may decrease restrictions for some species. Warmer 

Figure 4. Increased snowpack can reduce access to forage during winter months and result in population 

declines in large ungulate species like these Caribou (Adamczewski and others 1988; Post and Stenseth 1999). 

Image credit: USGS.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011 11

conditions in the Arctic are expected to improve energetic conditions for hibernating mammal species in 

that region (Humphries and others 2004).

Warming is expected to increase climate variability 

(IPCC 2007) and affect the availability of resources and 

habitat conditions needed for species survival and reproduction. Increasing unpredictability in weather conditions 

may favor species with life history traits that allow them to 

endure and recover from periods of drought, excessive heat, 

or other limiting conditions (Bronson 2009). Some species 

have specific adaptations or strategies that allow them to 

cope with fluctuating resources (Figure 6). For example, 

spadefoot toad tadpoles can switch between omnivore 

and carnivore morphs in response to variation in pond 

longevity and food abundance, allowing them to maximize 

recruitment under a variety of conditions (Pfennig 1992). 

Cooperative breeding (Ligon and Burt 2004) and irruptive 

movements are also thought to be adaptations to cope with 

unstable food supplies (Newton 2006).

Ectothermic animals, which have lower resting 

metabolic rates than birds or mammals, might also have 

a survival advantage over endotherms when resources 

are restricted (Bennett and Ruben 1979).

Figure 5. Desert adapted species are also likely to be sensitive to climate change. The distribution of 28 bird species in California 

moved an average of 116 m upslope over a 26-year period corresponding to temperature increases (Hargrove 2010). While species 

like the California Quail (left) showed substantial movement up slope, others like the black throated sparrow (right) showed no 

movement despite significant reductions in breeding success at lower elevation sites relative to upland areas. Such observations 

indicate that adaption to arid conditions is not by itself an indicator of resilience to future climate changes. Image credit: Sid Mosdell 

and Elaine R. Wilson, Wikimedia Commons.

Figure 6. A Couch’s Spadefoot Toad from 

Amistad National Recreational Area, Texas. 

Like most amphibians, these toads rely on 

water for fertilization and tadpole development 

and are therefore sensitive to the availability of 

appropriate ponds. However, these species also 

have adaptations that may allow them to better 

survive future climate conditions including the 

capacity to aestivate, sometimes for several 

years, during dry periods and polymorphic 

tadpole forms (see text). Image credit: Clinton 

and Charles Robertson, Wikimedia Commons.
12 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011

Phenology—Effects of climate change on phenology 

are among the best known (McCarty 2001). Many species 

improve survival and reproduction by timing important 

biological activities like reproduction, migration, and hibernation to seasonal variations in resources and habitat 

conditions. These species initiate activities in response to 

cues that directly, or indirectly, signal favorable resource 

events or environmental conditions. We identified four 

phenological criteria: reliance on climate-related cues, 

reliance on distinctly timed resource events, proximity of 

cues to events, and the potential for synchrony of breeding 

and favorable conditions

Changes in temperature and precipitation alter the timing of life history events through altering cues, altering 

the benefits associated with the cue or both (Beebee 1995, 

Dunn and Winkler 1999). When cues become disassociated 

from their benefits, populations can be reduced (Both and 

others 2006). Earlier flowering (Bowers 2007), breeding (Millar and Herdman 2004; Parmesan 2007), and 

migration (Bradley and others 1999) have been linked to 

climate change. As different species respond to changing 

temperatures at different rates, the risk of mistiming of 

resource peaks within and across ecosystems is increased. 

For other species, mismatch occurs when unchanging 

endogenous cues lead to timed behaviors that no longer 

correspond to critical resources that track climate changes 

(Inouye and others 2000; Carey 2009). For example, timing of migration in Nearctic-Neotropical birds is primarily endogenous (Hagan and others 1991), thus increasing 

the potential for mismatches in timing with temperature 

sensitive resources on the breeding grounds (Figure 7). 

Changes in the timing of favorable sea ice conditions 

without accompanying changes to breeding timing 

have greatly reduced emperor penguin populations with 

probable extinction if penguins fail to adapt (Jenouvrier 

and others 2009). For the purpose of this assessment, we 

assumed vulnerability increases with any expected shifts 

in the timing of either cues or associated events (Root 

and others 2003), but acknowledge that synchrony may 

be maintained when timing shifts of interacting elements 

respond equally and, thus, continue to coincide.

Some species are better able to adjust to changes in the 

timing of discrete events or conditions. Opportunistic or 

eruptive breeders respond rapidly to irregular events and 

may be less prone to mistiming (Visser and others 2004). 

Similarly, species with more than one breeding attempt 

per year or that have extended breeding periods are more 

likely to experience synchrony with critical resources or 

conditions in any given year (Jiguet and others 2007).

Biotic Interactions—Climate change has the potential to indirectly affect many species where species are 

closely associated through trophic or other interactions 

(Memmott and others 2007). Climate change will have 

the most severe consequences for the stability and persistence of biotic communities when multiple or critical (e.g., 

keystone) species are negatively impacted. We selected 

five primary interactions—food, predation, symbiosis, 

disease, and competition—as the most important indicators 

of a species’ ultimate climate change response. Although 

an oversimplification of ecological relationships, these 

interactions encompass major aspects of life history that 

are feasible to include in a simple scoring tool.

Availability of food resources directly impacts survival 

and reproduction. In general, specialist species that rely on 

one or only a few other species for food are considered at 

greater risk of extinction because they are more sensitive 

to stochastic events that change food availability (Gilg and 

others 2009; Gilman and others 2010). Similarly, changes 

in the population of predators as a result of climate change 

Figure 7. The European Pied Flycatcher is a 

well known example of how climate change can 

influence populations through the mismatch of 

timed events (Both and others 2006). This long 

distance migrant has experienced populations 

declines of 90% where warmer temperatures 

have led to earlier peaks in food resources on 

breeding grounds. These declines are not seen 

for populations that migrate to areas where 

food resources continue to peak later in the 

season. Image credit: Caricata de Aelwyn, 

Wikimedia Commons.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011 13

could have striking downstream effects on prey species. 

Climate has already influenced predator-prey interactions 

through effects on both the survival (Barton and Schmitz 

2009) and hunting efficiency of predators (Schmitz and 

others 2003). Disease exposure may be altered if climate 

becomes more, or less, favorable to vectors (Figure 8) 

(Benning and others 2002; Freed and others 2005). A 

number of studies relate the recent emergence and reemergence of many wildlife diseases to the effects of 

warming trends on vector species (Githeko and others 

2000; Epstein 2001; Harvell and others 2002) as well as 

host immunity (Rohr and Raffel 2010). Climate-related 

disruptions to plant-pollinator interactions and mutualisms have profound implications for ecosystem function 

(Gilman and others 2010; Memmott and others 2007). 

Competitive interactions can also be altered as new climate 

regimes favor or hinder competitors (Brown and others 

1997; Jackson and others 2009; Gilman and others 2010). 

Many non-native invasive species are expected to have a 

competitive advantage under future climate with potential 

consequences for native species (Carroll 2007).

Application of SAVS ________________

Scoring Species

To begin scoring a species, the user selects a target region and time period for climate change projections that 

is relevant to management goals. The targeted region can 

be a management unit, an ecoregion, or the entire range 

of species, but the boundaries for a set of scores cannot 

encompass disparate climate projections (i.e., multiple 

estimates of exposure). Once selected, the user collects 

information on projected temperature and precipitation as 

well as related phenomena such as snowpack, sea level, 

and disturbance for the target area (Table 3). Additional 

projections are also collected for migratory species. Next, 

the user collects data on the species to be scored from 

literature or expert sources (Table 3). Using this data, the 

user selects among the options for each question and marks 

a value for uncertainty. Responses relating to situations 

where a species is expected to benefit from future conditions either by possessing a favorable trait or through an 

expectation for favorable conditions have a value of -1 and 

signify resilience. Responses relating to expectations of 

less favorable situations for a species because it either possesses a trait that confers greater sensitivity or is expected 

to be exposed to declining conditions have a value of +1 

and signify vulnerability. Both responses to questions 

and uncertainty values are tallied and scores calculated 

using the formulas presented in Box 1. Users can access 

a web-based version of SAVS (http://www.fs.fed.us/rmrs/

species-vulnerability/) or use the scoring worksheet in 

Table 4 and Box 1 to calculate scores by hand.

Uncertainty Scores—It is difficult to incorporate 

climate change into vulnerability assessments, because 

the strongest climate change effects have yet to manifest, 

effects are known for relatively few species, and future 

predictions are inherently complex. The complexity of ecological communities is also likely to lead to 

unpredictable changes relating to the formation of new 

species assemblages (Brown and others 1997) and novel 

ecosystems (Harris and others 2006). For this reason, 

Figure 8. Avian malaria poses a threat to many bird species endemic to Hawaii. Malaria transmission is highly 

dependent upon climate conditions and has so far been restricted to the mid elevation zones that support the 

mosquito vector. Both the Akiapola’au (left) and ‘I’iwi (right) survive in high elevation refuges on Kauai, Maui, 

and Hawaii. However, warmer temperatures would favor the expansion of mosquitoes into higher elevations 

and result in a loss of 60-90% of these high elevation refuges (Atkinson and LaPointe 2009). Temperature 

changes will also extend the season for disease transmission, potentially leaving bird populations with no period 

for recovery. Image credit: USFWS.
14 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011

Table 4. Scoring Worksheet. Mark the corresponding boxes for the selected score and for uncertainty. Use Box 1 to calculate 

scores. Shaded cells are not valid scores. Questions have been abbreviated.

Vulnerability Uncertainty

HABITAT A 

(1)

B 

(0)

C 

(-1)

A 

(yes)

B

(no)

H1. Is the area or location of the general associated vegetation type used for breeding 

activities by this species expected to change? 

H2. Is the area or location of the general associated vegetation type used for non-breeding 

activities by this species expected to change?

H3. Are specific habitat components required for breeding expected to change within 

associated vegetation type?

H4. Are specific habitat components required for survival expected to change within 

associated vegetation type?

H5. Within habitats occupied, are features of the habitat associated with better reproductive 

success or survival expected to change? 

H6. What is the potential for this species to disperse?

H7. Does this species require additional distinct habitats during migration?

Total columns Total “yes” 

Enter Here -> 

PHYSIOLOGY 1 0 -1 A

(yes)

B 

(no)

PS1. Are limiting physiological conditions expected to change?

PS2. Is sex ratio determined by temperature? 

PS3. Are disturbance events that affect survival or reproduction expected to change? 

PS4. Is activity period expected to change? 

PS5. Does this species employ adaptive strategies?

PS6. What is this species metabolic rate?

Total columns Total “yes”

Enter Here ->

PHENOLOGY 1 0 -1 A

(yes)

B

(no)

PH1. Does this species use temperature or moisture cues to initiate activities? 

PH2. Are activities tied to discrete resource peaks that are expected to change? 

PH3. What is the separation between cues/activities and discrete events/ resources?

PH4. Does this species have more than one reproduction event per year?

Total columns Total “yes”

Enter Here ->

INTERACTIONS 1 0 -1 A

(yes)

B

(no)

I1. Are important food resources for this species expected to change?

I2. Are important predator populations expected to change?

I3. Are populations of symbiotic species expected to change?

I4. Is prevalence of disease in this species expected to change? 

I5. Are populations of important competing species expected to change?

Total columns Total “yes”

Enter Here ->
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011 15

SAVS includes uncertainty scores to identify specific 

areas where scoring was complicated by multiple effects, 

predictions, interactions, or a general lack of data. An 

uncertainty score is calculated for each criterion or question and used to assess overall confidence in the predicted 

species’ response (Box 1). Uncertainty is quantified as 

the percentage of criterion scored where either the direction of change could not be predicted because of lack of 

information or the predicted response was comprised of 

both negative and positive aspects.

Interpreting Scores—The scoring system outputs four 

factor scores and an overall score for a species within the 

targeted region and time period. Overall scores and factor 

scores are calculated differently and are used for different 

purposes as detailed in the next section. The number of 

criteria is unequal among the four factors (Table 1). Thus, 

to facilitate comparison among factors, we adjusted these 

scores by the number of questions present in that factor. 

Calculations for the overall score treat all criteria as equal 

predictors of vulnerability or resilience and, therefore, are 

not simply the sum of the factor scores.

When the scores associated with each response are 

tallied, the cumulative value of scoring criteria reflects the 

balance of the positive (vulnerable) and negative (resilient) 

impacts of climate on a species, with 0 representing a 

neutral effect. The magnitude of the scores reflects the 

relative balance of the number of vulnerable and resilient 

traits possessed by the species for that set of criteria. The 

overall vulnerability score is scaled to a range of -20 to 

+20 and each factor or category (habitat, physiology, phenology, biotic interaction) is scaled to a range of -5 to +5. 

Although the scoring system is based on a linear scale to 

provide a metric for multispecies comparisons, this does 

not translate to a linear biological effect of the predictors. In addition, obtaining a maximum or minimum 

score for a species is unlikely because some criteria only 

apply to some vertebrate species and traits reflect both 

resilience and vulnerability. Uncertainty scores should 

be taken into account when interpreting scores. A high 

uncertainty paired with a neutral score may indicate a 

lack of information rather than a realized neutral effect 

of climate change. Species that receive high uncertainty 

scores may also be good candidates for further research 

and monitoring.

Score Applications—Scores can be used to assess individual or multiple species within one or across several 

target(s). Overall scores can be used to rank vulnerability 

for a group of species scored for the same target and, 

along with other considerations, can aid in prioritization, 

selecting targets for management actions, and planning 

for climate change. Resilient species can also be targets 

for management actions. Multiple scores may also be 

calculated for a single species at several locations, and 

across disparate climate projections, to assess relative 

vulnerability to changes across a broad landscape.

Factor scores highlight the relative contribution of 

each group of species’ attributes (i.e., habitat, physiology, 

phenology, or interactions) to the vulnerability of one 

or multiple species to climate change. By highlighting 

specific areas of concern, factor scores suggest effective 

areas to target for management actions either by directing 

management towards an expected source of vulnerability 

or by identifying common areas of vulnerability for a 

group of species (Table 5). A strength of SAVS lies in 

its capacity to identify specific variables relevant to the 

potential response of individual species to climate change. 

Table 5. Examples of management actions that correspond 

to each of the scoring factors. Many actions can 

address multiple issues.

Factor Management Action 

Habitat Manage fire

Thin forests

Stabilize stream banks

Install nest boxes and bat roosts

Create or enhance corridors

Translocate individuals or populations

Physiology Install artificial waters

Install flood control features

Protect vegetation types with thermal

advantage

Plant shade plants

Breed individuals in captivity

Protect areas with favorable 

microclimates

Phenology Line or enlarge water catchments

Manage areas with different 

microclimates cooperatively

Adjust management plans to anticipate

shifts in breeding timing

Maintain important migratory stopover

habitat

Release water from dams strategically

Take advantage of limiting periods for

invasive species control

Biotic Interactions Provide supplemental food

Control or reintroduce predators

Use reintroductions/translocations to

replace keystone species

Reduce opportunities for disease 

transmission

Regulate commerce to reduce 

likelihood of disease introductions

Control invasive species
16 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011

Each question relates to a specific area of vulnerability or 

resilience and identifies a potential target for management 

action. For example, if dispersal ability is limited, creation 

of corridors or translocation of individuals might be used 

to increase a species’ resilience. Uncertainty scores play an 

important role in identifying research needs or species that 

will require a more complex assessment of vulnerability.

The application of SAVS scores is limited for some situations. For any species, a single trait or criterion, although 

equally contributing to the overall score, may represent a 

critical issue that will lead to population declines despite 

the presence or absence of other resiliencies or vulnerabilities. Additionally, the scoring system only considers 

some effects of climate change rather than all possible 

factors that impact populations. Therefore, scores should 

be considered within context of each species’ biology and 

current threats in order to gauge future population trends 

under projected scenarios.

Discussion ________________________

We identified 22 criteria predictive of species’ response to climate change that, although not an exhaustive 

list, highlight relevant species’ attributes that can be easily 

and consistently considered across diverse taxa. This 

scoring system is based on a framework that integrates the 

three primary aspects of vulnerability, exposure, sensitivity, 

and adaptive capacity, as well as a measure of uncertainty. 

Most scoring criteria regard species sensitivity, both with 

respect to inherent physiological limitations (e.g., low 

thermal tolerance) and susceptibilities related to behavior 

(e.g., habitat associations or trophic specialist) (Table 2). 

Exposure or expected future conditions for a particular 

region and time period are integrated into the scoring 

system and results are tailored to the user’s needs. A wide 

spectrum of both direct and indirect climate effects can 

be accommodated for exposure. Since use of the scoring 

system relies on the development of a climate change 

scenario, which identifies future conditions, estimation 

of exposure can vary among different users and care 

must be taken to standardize efforts when working in a 

team setting. Some criteria represent adaptive capacity 

or potential resilience (Table 2). For instance, dispersal 

ability and other physiological adaptations that maximize 

a species’ capacity to take advantage of increases in interannual resource variations directly relate to the capacity 

of species to deal with climate-related changes to habitat. 

The distinction between sensitivity, exposure, and adaptive capacity have direct relevance to decisions regarding 

management actions where identifying how a species is 

vulnerable to climate change leads naturally to strategies 

to help that species cope with expected changes or reduce 

the impact of expected changes (Glick and Stein 2011).

The SAVS was created to provide a straightforward 

prediction of direction rather than degree of response to 

reduce scoring variability and ease its use. The SAVS is 

also flexible to varied and evolving information sources 

including online natural history databases or personal 

knowledge. Users can easily recalculate scores as new 

information becomes available.

Assessments can be used to set conservation goals and 

engage stakeholders (Füssel and Klein 2008; Glick and 

Stein 2011). We have used SAVS to assess vulnerability of 

species for a variety of stakeholders and targeted groups 

of species in the southwestern United States. Using an 

earlier version (v1.0) of the tool, we assessed an entire 

suite of terrestrial vertebrates for riparian forests of the 

Middle Rio Grande, New Mexico (Friggens and others 

2010; Finch and others 2011). Results of this case study 

were designed to identify and coordinate priority actions 

across the large number of land managers that oversee this 

region. Importantly, we found that the greatest vulnerability was associated with not only rare but also relatively 

common species that generally receive little management 

attention. We focused on scoring threatened, endangered, 

rare, and species at-risk for two clearly defined management units, Fort Huachuca and the Barry M. Goldwater 

Range in Arizona, (Bagne and Finch 2010). Based on 

specific areas of expected vulnerability along with current 

threats, we also identified management options, several of 

which applied to multiple species, such as protecting and 

enhancing natural or artificial water sources (Bagne and 

others 2010). Thirty species of conservation interest in the 

Coronado National Forest, Arizona were targeted for assessment as part of the Forest Service’s efforts to integrate 

climate change into species management plans (Coe and 

others 2010). As part of this effort, researchers from the 

University of Arizona created spatially explicit occupancy 

maps for individual species integrated with vulnerability 

scores to create maps that outlined hotspots of vulnerability. 

Although most species expressed some level of resilience 

to climate change, scores from all assessments indicated 

greater overall vulnerability for the majority of species, 

supporting the prediction of challenging times ahead 

for species conservation. Results also pointed towards 

relatively large numbers of vulnerabilities in phenology 

and physiology, which unlike habitat or interactions, 

are attributes seldom targeted for management and may 

require more innovative management solutions (Bagne 

and others 2010).
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011 17

Despite uncertainties and because climate change 

impacts are likely to intensify over time, we need to take 

immediate action to identify vulnerable species to institute effective management actions and plan proactively. 

With high likelihood of increasing intensity of warming, 

even low vulnerability species may be in need of intervention. Assessment is a first step toward anticipating 

and responding to climate change and SAVS provides a 

framework for integrating new research and information 

into species conservation and management planning.

Glossary of Terms and Concepts _____

Definitions for terms and concepts as they relate to SAVS.

1. Adaptation. Adjustment or changes in behavior, 

physiology, and structure of an organism that increase 

survival or reproduction.

2. Adaptive. Exhibiting an adaptation as pertaining to 

(1) Increased survival or reproduction of an organism 

(as above) or (2) The process of changing or active 

learning as in a management decision process.

3. Adaptive capacity. The ability of an organism to 

adjust to changing conditions.

4. Biodiversity. The number of genes, species, and 

ecosystems within a particular area.

5. Carbon cycle. The flow of carbon in its various forms 

through the atmosphere, ocean, and biosphere and 

lithosphere (IPCC 2007). Carbon dioxide (CO2), a 

naturally occurring gas, is the principal greenhouse 

gas associated with anthropogenically derived 

warming trends. Sources and sinks within the carbon 

cycle, along with other greenhouse gases, will ultimately determine atmospheric CO2 concentrations 

and the degree of global warming.

6. Climate. “Average weather” patterns or trends for a 

particular region over a period of many years (NCAR 

2004).

7. Climate change. Change in the state of the climate 

that is identified by significant changes in the mean 

and/or the variability of weather parameters and that 

persist for an extended period, typically decades or 

longer (IPCC 2007).

8. Climate projections. The expected response of the 

climate system to emissions that are often based on 

simulations of various emission scenarios and climate 

models. Climate projections are made with specific 

assumptions about future emission rates given future 

socio-economic and technological developments. 

Due to these assumptions, projections are considered 

subject to substantial uncertainty (IPCC 2007).

9. Climate change scenario. Projections of climate 

and related phenomena for the particular region and 

time period selected by the user for scoring.

10. Competitive interactions. Interactions between 

species to obtain resources in which survival or 

reproduction are lowered for one species by the 

presence of another.

11. Cooperative breeding. A social system in which 

individuals care for young that are not their own at 

the expense of their own reproduction.

12. Cues. Indicator used by individuals to signal appropriate or favorable conditions for the initiation 

of activities.

13. Critical resource. Food or other element required 

for successful reproduction or survival. This may 

include the availability of certain food items or environmental conditions (rain, calm weather) during 

critical periods of a species lifecycle.

14. Disease. Refers to infectious condition that can be 

transmitted from one organism to another by direct 

contact or environmental contamination. Diseases 

may be caused by viral, bacterial, or fungal organisms. Endo- and ectoparasites may also have the 

potential to cause mortalities in a population under 

certain conditions. Climate can affect pathogen and 

vector population growth, mortality rates, suitable 

range, and winter survival (Dazak and others 2000; 

Harvell and others 2002).

15. Ecosystem. A system of interacting organisms 

living in their physical environment.

16. Endotherm. Organisms that control body temperature primarily through physiological mechanisms 

and typically maintain a constant temperature.

17. Exotherm. Organisms that control body temperature 

primarily through external means and generally 

experience fluctuation in body temperature.

18. Explosive breeding. A sudden, concentrated burst 

of breeding activity that is typically initiated in response to the appearance of some critical resource. 

This type of breeding is seen in some amphibian 

species in response to rain events (Wells 2007).

19. Exposure. The degree to which a species will experience changing climate and conditions, which will 

be a function of local climate as well as biology of 

the species.
18 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011

20. Greenhouse gas. Atmospheric gases (e.g., CO2, 

N2O, CH4, O3) that absorb and emit radiation, reflecting heat back to the earth’s surface.

21. Habitat. The environment naturally occupied by 

individuals of a species. For scores within the Habitat 

factor we are referring to habitat type, the particular 

type of vegetation or aquatic or lithic subtrate a species occupies (Morrison and others 1998).

22. Habitat components. Discrete physical elements 

that must be present for a species to reproduce or 

survive. A habitat component is usually selected 

by a species at a relatively small scale within the 

broader habitat type.

23. Habitat quality. Feature of occupied habitat that 

affects rates of reproduction or survival.

24. Irruptive species. Species that undergo dramatic, 

irregular movements (often birds) to areas where 

they are typically not found.

25. Management area. Specific geographical areas 

administered within a set of defined objectives, 

generally under a single management entity (e.g., a 

National Forest, a city preserve).

26. Microclimate. Conditions or variations in climate 

within a small localized area or atmospheric zone. 

Microclimates are usually influenced by topography, 

vegetation, structures, or proximity to water and 

can vary substantially from the general climate of 

an area.

27. Mismatch potential. The risk that a species initiates an activity that is mistimed with an expected or 

required resource or condition. Climate change can 

increase the risk of mismatch through three primary 

mechanisms: (1) changes to a cue upon which a species relies to initiate important biological activities; 

(2) changes to timing of critical pulses or weather 

conditions upon which a species relies for successful 

reproduction and survival; and (3) unequal changes 

to the timing of cues and resources.

28. Natural selection. Differential reproduction or 

success among groups of phenotypically different 

individuals (Futuyma 2009).

29. Nitrogen cycle. The flow of nitrogen in its various 

forms through the atmosphere, ocean, and biosphere 

and lithosphere (IPCC 2007). Nitrogen oxides (NOx) 

released as a result of soil cultivation practices are 

powerful greenhouse gases.

30. Opportunistic breeder. Species that breed whenever environmental conditions are favorable. 

Opportunistic breeders depend on short-term factors (cues) such as rainfall, food abundance, and 

temperature to initiate breeding.

31. Phenology. The study of recurring plant and animal 

life cycle stages (phenophases) such as the leafing and 

flowering of plants, maturation of crops, emergence 

of insect, breeding activities, and migration.

32. Physiological threshold. Physical conditions 

beyond which an individual will experience physiological stress that, if sustained, results in death.

33. Resilience. The ability to tolerate changing 

conditions.

34. Resiliency traits. Characteristics of species that 

are expected to increase or not change survival and 

reproduction, fundamentally or relative to other species. Resiliency is not simply a lack of vulnerability.

35. Sensitivity. The degree to which a species is physiologically or behaviorally affected by a particular 

set of conditions.

36. Symbionts. A species that uses an interaction with 

another species to survive or reproduce. A symbiotic relationship may be mutualistic (benefits both 

species), parasitic (benefits one species at the cost 

of another), or commensal (one party benefits and 

the other is neither harmed or helped). Symbiotic 

relationships may be obligate (required for the survival of one species) or facultative (beneficial but 

not required for survival).

37. Vulnerability. The state of having increased probability of population decline.

38. Vulnerability traits. Characteristics of species that 

are expected to decrease survival and reproduction, 

fundamentally or relative to other species

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Appendix 1. SAVS User Guide _______

This is a guide to applying the scoring system developed 

by the Rocky Mountain Research Station for assessing the 

vulnerability of individual vertebrate species to climate 

change (v.2.0). Specifically, these sections provide direction 

for the inclusion or exclusion of data during the scoring 

process. We also list suggested sources of information 

and the type of data that might be helpful for selecting an 

appropriate response. Reference to literature and italicized 

terms can be found in the literature cited and glossary 

sections of the primary document. We recommend documenting sources of information used for scoring as well as 

explanation of specific score choices. This will aid future 

edits. Additionally, scores for uncertainty should be noted 

during the scoring process. Users should make an effort 

to obtain information for every question, but if response 

is unknown then assign a score of 0 with uncertainty 1.

Information on projected climate changes for your area 

of interest should be gathered before scoring species. IPCC 

(Intergovernmental Panel on Climate Change) reports 

and Climate Wizard (www.climatewizard.org) are two 

good starting points for future climate projections. Also 

consider impacts beyond temperature and precipitation 

such as flooding, droughts, timing of frosts, wildfire frequency, and changes to snowpack that may affect target 

species (Table 2). Choose a time period for scoring from 

available projections that will be relevant to the scope of 

management planning or conservation needs.

Habitat

H1. Area and distribution: breeding. Is the area or 

location of the associated vegetation type used 

for breeding activities by this species expected 

to change?

Change in area or distribution of suitable habitat has 

a direct impact on populations. Hall and others 1997 

defines habitat as “the resources and conditions present 

in an area that produce occupancy—including survival 

and reproduction—by a given organism.” By this definition, habitat extends beyond the vegetation and resources 

available to an animal. However, for Questions 1 and 2 we 

are specifically concerned with the resources that provide 

cover for a species (other aspects of habitat are covered 

elsewhere) and thus are referring to what may be called 

habitat type: an area supporting a particular type of vegetation or aquatic or lithic substrate (Morrison and others 

1998). Consider whether the overall area of the vegetation 

association for this species’ breeding habitat is going to 

shrink, expand, or move from your targeted area. This 

question does not require a comprehensive account of all 

documented breeding locations for an individual species, 

but the answer should consider all primary vegetation 

associations collectively where more than one is used 

regularly. A species is vulnerable to climate change if 

projections indicate a loss or shift of associated vegetation 

and resilience to climate change where climate effects are 

likely to increase the area of a species’ associated vegetation type. For geographical shifts, consider your target 

time period as well as shifts large enough to result in a 

significant population change (e.g., a shift of >50% from 

the former range by 2050). There are numerous vegetation classification systems, but most guides and species 

accounts will report broad biome classifications or biotic 

communities, which are the most appropriate resolution for 

this tool. More specific habitat components and resources 

are considered in other questions.

Relevant data and suggested sources: Information on 

vegetation associations along with species range is available 

from most field guides and online species accounts (e.g., 

NatureServe, BISON-M, Birds of North America Online, 

AmphibiaWeb). For endangered species, the USFWS 

recovery plans contain good reviews of available natural 

history information.

H2. Area and distribution: non-breeding. Is the area 

or location of the associated vegetation type 

used for non-breeding activities by this species 

expected to change?

Species will be impacted by climate-related changes in 

the area or location of required habitat. Consider vegetation types and habitat associations for the species outside 

of the breeding season, generally those used in winter. 

As above, consider geographic shifts within the context 

of your target time period as well as shifts large enough 

to result in a significant population change (e.g., a shift 

of >50% from the former range by 2050). For resident or 

sedentary species, associations considered here may be 

identical to those scored in Question 1, in which case the 

species will receive identical scores for both questions. 

Stopover or other transitional habitats between breeding 

and non-breeding habitats are considered in Question 7.

Relevant data and suggested sources: Same as Question1.

H3. Habitat components: breeding. Are specific habitat components required for breeding expected 

to change within the associated vegetation type?

Climate change may affect the availability of critical 

habitat components within primary vegetation types that 

are required for breeding. Species are vulnerable when 
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011 23

climate effects will result in a loss of components and, 

consequentially, a loss in breeding opportunity. Only 

specific components or features of the habitat necessary 

for breeding should be considered (i.e., breeding does 

not occur without this component). Only components 

influenced by climate should be considered. Consider 

whether a required component will become more or less 

prevalent with changes in climate or related aspects such 

as disturbance. Examples of habitat elements commonly 

required for breeding include snags, caves, ponds, rocky 

terrain (crevices), ice, snowpack, etc. Variation in breeding 

success associated with a component or habitat characteristic is covered in Question 5.

Relevant data and suggested sources: Field guides or 

natural history accounts should contain information on 

required components, if present.

H4. Habitat components: non-breeding. Are specific 

habitat components required for survival during 

non-breeding periods expected to change within 

the associated vegetation type?

Climate change may affect the availability of critical 

habitat components that are required for survival rather than 

reproduction as in Question 3. Only specific components or 

features of the habitat necessary for survival during nonbreeding periods should be considered here. Components 

may be a physical feature, such as a cave for hibernation 

or may be directly related to climate, such as snowpack, 

but components must be required elements for species’ 

occurrence rather than to improve survival (Question 5). 

Other examples of habitat components necessary for survival include flowing water, subnivean space (Coulson and 

Malo 2008), and anything that provides protection from 

harsh weather conditions and is absolutely required for 

species survival. Consider whether a required component 

will become more or less prevalent with changes in climate 

or related aspects such as disturbance.

Relevant data and suggested sources: Information 

regarding habitat components, if present, is readily available in most species’ natural history accounts or online 

species accounts.

H5. Habitat quality. Within the habitats occupied, 

are features of the habitat associated with better reproductive success or survival expected to 

change?

Habitat features associated with quality are those that 

incur variation in survival or reproduction. These can be 

aspects of habitat components (Question 3 and 4). Consider 

aspects of the habitat (e.g., vegetative cover, snow depth) 

that directly lead to differential breeding or survival success in the focal species and that will ultimately affect 

populations. Do not consider changes in overall habitat 

availability (area), the presence or absence of critical 

habitat components, or direct impacts to food resource 

availability. Examples of habitat features sometimes related to quality include: ash deposition in water sources or 

increased erosion from increased fire activity (associated 

with lower quality), less forage due to reduced ground 

cover (lower quality), shrub density, water temperature of 

ephemeral ponds, and presence of forest mosaics (versus 

homogenous stands) (see Johnson 2007 for discussion). 

Consider whether projected changes in climate conditions will increase, decrease, or not affect habitat quality. 

Habitat quality may not be relevant for many species and 

habitats (particularly ephemeral habitats such as early 

serial stages of vegetation) where differences in structure 

or element composition are of minimal importance to the 

perpetuation of a species. Where relationship of habitat 

quality with climate projections is unclear, score as 0 with 

a 1 for uncertainty. Food resources should be considered 

under Biotic Interactions.

Relevant data and suggested sources: Habitat quality 

is often discussed in reference to locations with variable 

fitness or in reference to habitat selection. Additionally, 

references may refer to sources and sinks: source populations are locations where recruitment exceeds mortality 

and sinks are where recruitment does not exceed mortality. Indicators of habitat quality include (1) the rate of 

species survival and reproduction, (2) species fecundity, 

and (3) length of time a habitat is suitable for residence 

by a species (Morrison and others 1998). Information on 

quality of habitats is sometimes listed as part of natural 

history information, but more often it needs to be checked 

within the wider scientific literature. Research related to 

quality will not be found for all species. Aspects related 

to quality may also be included as part of conservation 

strategies for the species. Try a query including “quality” 

or “habitat selection” and the species name in a scientific 

database (e.g., Google Scholar, BIOSIS). Also try a query 

using species name and “winter” or “mortality.”

H6. Ability to colonize new areas. What is the potential 

for this species to disperse?

Species that are able to readily disperse are likely to 

be able to travel to new locations if needed and, thus, are 

considered more resilient to potential habitat changes. 

Consider species’ capacity to move to new habitats or favorable microclimates both within the context of the selected 

time period of climate projections and the magnitude of 
24 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011

the changes. Species that only move long distances over 

several generations may not have the capacity to respond 

to rapid climate-mediated changes in habitat. Sex-biased 

dispersal (i.e., dispersal by only one sex) or strong site 

fidelity will counter some of the benefits of mobility. Site 

fidelity or territoriality restricted to the breeding season 

would not constitute inability to disperse for this question as its effect is only temporary. Dispersal may also 

be limited by barriers, including those that are physical, 

behavioral, or physiological, that effectively decrease the 

realized dispersal of a species. When movement to alternative suitable habitats is likely inhibited by one or more 

such barriers, then dispersal should be considered limited 

and the species vulnerable. In other instances, barriers 

may neither hinder nor help dispersal and the user should 

score the species according to its innate capacity to move 

long distances.

Relevant data and suggested sources: If species’ mobility is not known, data on species’ range, average dispersal 

distances, presence of sex-biased dispersal, maximum 

known dispersal, or homing capacity are useful. Studies 

of the effect of habitat fragmentation may provide useful 

to assess a species’ capacity to move to new locations. 

Look for information in species accounts and life history 

papers. NatureServe often provides further discussion 

regarding dispersal abilities and barriers in its species 

accounts. Knowledge of the geographic features of the 

focal scoring area is useful to judge whether geographic 

barriers may be an issue. Finally, information regarding 

the expected shift in habitat (e.g., 300 m upslope in 50 yrs) 

may be useful for providing a measure by which to assess 

species’ dispersal capacity.

H7. Migratory or transitional habitats. Does this 

species require additional habitats during migration that are separated from breeding and 

non-breeding habitats?

Species that require additional habitats beyond breeding and non-breeding (e.g., wintering grounds) sites may 

be more vulnerable to climate effects, because we cannot expect parallel changes in all these habitats. Good 

examples of species with additional habitat requirements 

are long distance migratory birds that require stopover 

sites to replenish resources as they move between breeding and wintering sites. Some mammal species also migrate across long distances through transitional habitats. 

Whenever additional habitats are geographically distinct 

and subject to different climatic changes or comprised of 

different vegetation types a species should be considered 

vulnerable. Distance alone, however, may not determine 

whether a species uses transitional habitats. Species 

that move through transitional habitats without resource 

utilization such as long distance migratory birds that have 

non-stop flights or elevational migrants that shift flexibly 

over relatively short distances, are not considered vulnerable to this effect.

Relevant data and suggested sources: Basic natural history information should contain migratory information. 

Specific stopover information, which is often unknown, 

is not required for scoring. A basic climate projection map 

or vegetation map should indicate if transitional habitats 

are separate from breeding and non-breeding habitats.

Physiology

PS1. Physiological thresholds. Are limiting physiological conditions expected to change?

Species often exist near their physiological limits with 

respect to temperature or moisture tolerances. If projected 

future conditions increase the likelihood that a species will 

experience limiting conditions (high heat, desiccation), then 

the species will be vulnerable to climate-related population 

declines as habitat becomes unsuitable for species survival. 

Alternately, some species may benefit (exhibit increased 

resilience) when projected changes predict a move away 

from currently limiting thresholds as might be found for a 

cold sensitive species under a warming scenario. Consider 

both minimum and maximum thresholds of the focal 

species and, when both are likely to be influenced with 

distinct outcomes, select the variable that is most limiting 

for survival when scoring. For instance, in cases where 

a species may be limited by temperature maximums but 

benefit by changes in temperature minima, base the score 

on the limiting effect; here it is the maximum temperature. 

Species that have moderate thermal range tolerances that 

are rarely exceeded under future scenarios or are able to 

avoid limiting conditions (e.g., aestivators) are not considered physiologically vulnerable to climate changes and are 

given a neutral score (option b) unless that species is also 

expected to experience a decline in the incidence of lower 

thresholds, in which case option c should be selected. In 

general, species that currently tolerate very hot conditions 

along with those known to be intolerant of high temperatures may be vulnerable (Bernardo and Spotila 2006; Jiguet 

and others 2007). Species that require moist conditions 

and are prone to drying (e.g., many amphibians) will be 

vulnerable to both temperature and precipitation changes.

Relevant data and suggested sources: Information 

may be limited to laboratory experiments, which do not 

directly correspond to survival in the field. If not directly 
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011 25

reported, a number of substitutes may be used to infer 

whether a species exists near its temperature or moisture 

threshold. Demonstrations of recent population shifts or 

records of die-offs during extreme weather may indicate 

physiological limits. Range boundaries available in basic 

species accounts often indicate a climatically driven 

limitation and thus species living along the boundary of 

their range are likely near their physiological limits. Also, 

location of species within its distribution (e.g., populations 

of interest at southern limit of range or only occur in moist 

microsites), or the range of thermal conditions (e.g., species that occupy areas of limited variability or that occupy 

extreme environments may have narrow tolerances), may 

be informative for predicting species distribution. If no 

prediction can be made, score as 0 but also uncertain.

PS2. Sex ratio. Is sex ratio determined by temperature?

Some reptile species are known to have temperaturedetermined sex ratios. Consider the effect of temperature 

on sex determination and whether future climate conditions may favor one sex over another. Although there 

have been some examples in other taxonomic groups 

with differential survival of embryos with temperature, 

this effect has generally not been well studied. There is 

some evidence that temperature can influence sex ratio 

in other taxa, such as birds and mammals, though this is 

not due to temperature-dependent sex determination but 

to other effects such as differential mortality or hormonal 

changes (Goth and Booth 2005). Differential mortality in 

young through temperature dependent mechanisms can 

lead to population declines if the effect is strong enough 

(Eiby and others 2008). If temperature has a sex-biased 

effect on survival of offspring, only consider situations 

where this effect is likely to result in strongly skewed sex 

ratios across populations.

Relevant data and suggested sources: This trait can 

usually be found in natural history profiles, field guides, 

or species accounts.

PS3. Exposure to weather related disturbance. Are 

disturbance events (e.g., severe storms, fires, 

floods, etc.) that affect survival or reproduction 

expected to change?

This question regards mortalities caused by disturbance 

events. Extreme weather events that may change under future scenarios and are known to cause massive population 

declines in a variety of taxa include droughts, unusually 

low or high temperatures, freeze/thaw events, false springs, 

storms (rain, ice, snow), heavy snowfall, and heat waves 

(Parmesan and others 2000; Easterling and others 2000). 

To be considered vulnerable, a species’ population should 

experience significant mortality as a direct result of the 

disturbance event and those events should be projected to 

increase. Do not include indirect effects of these events on 

resources (see Biotic Interactions) or habitat (see Habitat). 

Do consider the frequency, timing, and duration of these 

events when choosing a response. Consider the impact 

of disturbances for both breeding and non-breeding periods and again choose the most limiting condition when 

multiple effects are expected. For migrants, breeding and 

non-breeding may be in separate regions and have different 

projections. For non-migratory species, differences may 

simply be seasonal. Evidence of past response to extreme 

weather conditions relating to heat waves and drought are 

better used to inform decisions regarding physiological 

thresholds (Question 1) rather than this question.

Relevant data and suggested sources: Gather information 

on species habitat from natural history accounts or field 

guides and consider it in relation to your climate projection 

information. Population studies may be additionally helpful as they consider events related to mortality. Look for 

observed cases of mass mortality related to disturbances, as 

these are often unusual enough to inspire documentation.

PS4. Limitations to daily activity period. Are projected temperature or precipitation regimes that 

influence activity period of species expected to 

change?

Activities important for survival or reproduction may be 

limited by environmental conditions and result in increased 

species’ vulnerability. Often limitations are associated with 

high temperatures or dry conditions, but they can also be 

limited by cold or snow. Specifically consider whether the 

projected changes will lead to increases or decreases in 

activity periods that have the potential to affect survival 

or fecundity. Diurnal species may be exposed to greater 

temperature extremes, but nocturnal species may be less 

tolerant of extremes. Crepuscular species may already 

be restrained in an active period and unable to shift to 

nocturnal or diurnal activities. Ectotherms may be more 

vulnerable, because they rely more on behavior to adjust 

to changes in ambient conditions (Kearny and others 2009; 

Sinervo and others 2010).

Relevant data and suggested sources: Some useful information should be available in general natural history 

information. Look for information on limiting conditions 

for activity and timing of active periods and consider how 

these conditions may be altered. Most information on 

activity will be available on foraging or resting behaviors, 

but consider if these have the potential to affect fitness.
26 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011

PS5. Survival during resource fluctuations. Does 

this species have alternative life history pathways to cope with variable resources or climate 

conditions?

Some species have alternative life history pathways or 

employ strategies that allow them to maximize reproduction and survival under variable conditions, which is likely 

to confer resilience to expected climate changes. Focus 

should be on issues related to expected increases in climate 

variability, thus interannual, rather than intrannual, variation. Beneficial traits may be morphological or behavioral 

and can include the ability to take advantage of years with 

good conditions or the ability to cope during years with 

poor conditions. Species that undergo irruptive migrations, undergo explosive breeding events, use cooperative 

breeding systems, or can employ alternate phenotypes 

(e.g., neotony, carnivorous phenotypes) are examples of 

animals that have coping strategies which allow them to 

deal with resource variation and shortages. Species that 

are able to delay breeding altogether (prudent parent)

(see Forcada and others 2008), fertilization (e.g., some 

snakes, insects, others), or implantation (e.g., marsupials, 

some mammals) may also have an advantage if the trait 

improves long-term productivity. Conversely, a species 

without flexible strategies or with strategies that are not 

expected to increase its ability to survive during periods 

of low resource levels is considered vulnerable.

Relevant data and suggested sources: Life history/species accounts will generally list alternative life history 

pathways and often include information related to the 

advantages of these strategies. Consider your regional 

projections and how the identified alternatives may or 

may not be advantageous.

PS6. Energy requirement. What is this species’ metabolic rate?

Mark as appropriate. Ectotherms (e.g., lizards, frogs) have 

the lowest metabolic requirement, about 1/10 the energy 

of endotherms (Pough 1988). Metabolism in endotherms 

(e.g., mammals, birds) is considered moderate for this 

purpose unless known to be particularly high relative to 

other vertebrates, such as in hummingbirds or shrews.

Phenology

PH1. Mismatch potential: cues. Does this species use 

temperature or moisture cues to initiate activities 

related to fecundity or survival?

Cues may initiate activities such as migration, ovulation, 

egg laying, or emergence from hibernation. Cues can be 

exogenous (e.g., day length, lunar cycle) or endogenous 

(e.g., rise in body temperature, circadian rhythm) (Grant 

and others 2009). Exogenous cues are also often linked to 

climate conditions such as time since frost, mean minimum 

or max temperature, and the initiation of a rainy season. 

Species that rely primarily on a cue related to temperature 

or precipitation to initiate activities will be more likely to 

experience impacts related to changes in timing. Species 

that rely on endogenous rhythms or cues are not subject 

to this risk. A score indicating vulnerability should be 

reserved for those species where a change in climate leads 

to a change in the timing of a distinct cue and thereby 

the initiation of a major life stage (e.g., emergence from 

aestivation/hibernation, migration). This does not include 

smaller scale adjustments where species delay or shorten 

the timing or duration of certain activities (e.g., egg laying, 

incubation periods) in response to ongoing weather conditions, as these are unlikely to result in population change.

Relevant data and suggested sources: Life history/species 

accounts should list activities. How a species times activities is not always included in these accounts, but it should 

be available from more general information on taxonomic 

groups or on the timed activity such as migration.

PH2. Mismatch potential: event timing. Are activities 

related to species’ fecundity or survival tied to 

the availability of discrete resource peaks (e.g., 

food, breeding sites) that are expected to change?

Variation in the timing of critical resources due to climate 

change leaves species at an increased risk of mistiming 

their activities and species with such dependencies are 

considered more vulnerable. Assess if the species relies 

on a discrete resource event limited in time such as the 

emergence of insects or flowering plants. Certain weather 

conditions may also be discrete events that may be important such as calm weather for successful bird migration or 

onset of rainy season for amphibian breeding activity. If 

these periods are likely to change, then the migrating species is likely to be negatively impacted. Not all resources 

or favorable conditions will be limited to discrete time 

periods or will be affected by projected climate change.

Relevant data and suggested sources: You first need 

information on what discrete events are important for 

your species and should be available in life history/species 

accounts. You will then need to consider if the timing of 

these events is affected by climate or climate-mediated 

criteria. For this you may need additional information 

regarding resource pulses and/or biological properties 

of prey/forage species, which could be provided through 

accounts created for those species. Observations related 
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011 27

to annual variation in fitness or behaviors often hold 

clues to possible events of importance. The presence of 

a climate mediated timed event is sufficient evidence for 

vulnerability and you are not required to estimate the 

magnitude of the timing change.

PH3. Mismatch potential: proximity. What is the 

separation in time or space between cues that 

initiate activities and discrete events that provide 

critical resources?

Indicate whether a species initiates activities immediately 

in response to or in the immediate vicinity of a changing 

critical resource. The probability of a mismatch between 

initiating an activity and a critical resource increases with 

the length of time or distance between events. For instance, 

the rate and degree of climate changes are likely to differ 

between temperate and tropical zones and between upper 

and lower elevation sites, with consequences for species 

migrating between these areas (Both and Visser 2001). 

Long distance migrants may be less able to respond to 

climate changes because of the disjunct between the 

effects occurring at their breeding grounds versus nonbreeding grounds (Crick 2004; Wormworth and Mallon 

2007; Carey 2009). In some instances, there could be a 

fairly constant level of critical resources that would make 

a timing mismatch unlikely. Opportunistic breeders and 

irruptive species are good examples of animals that respond 

directly to a resource pulse. Other species are unlikely 

to respond within a short period of time to changes in 

resources, such as those whose activities are initiated in 

different latitude, time zone, elevation, or habitat type 

from critical resources.

Relevant data and suggested sources: Life history/

species accounts and information gathered for the 

previous two questions is applicable here. You may need 

additional information regarding resource pulses and how 

they are affected by climate. Timing of flowering, insect 

emergence, and temporary water sources are known to 

be influenced by climate and can be applied to scoring 

generally without more detailed information.

PH4. Resilience to timing mismatches during breeding. 

Does this species have more than one opportunity 

to time reproduction to important events?

The ability to breed multiple times a year increases the 

chances that at least one of those attempts is optimally 

timed with resources. Indicate how species’ reproductive 

period is distributed within a single year. Species need to 

breed and produce young more than once to qualify as 

resilient (i.e., a species that re-nests within a constrained 

period of time should not be considered to be resilient).

Relevant data and suggested sources: Life history/species accounts should have this information. Avoid using 

rare cases to determine score.

Biotic Interactions

The following questions require some knowledge of climate change effects on interacting species that have some 

demonstrable influence on the species under study. Strong 

interactions are relatively rare in most species and so the 

additional research required for this section will often be 

minimal. However, in the case where there is a notable or 

influential relationship between species, understanding 

how climate impacts will affect both parties is critical to 

assessing species vulnerability. Indeed, such a relationship may be one of the most important determinants of 

vulnerability.

I1. Food resources. Are important food resources 

for this species expected to change?

Consider important foods and especially any resources 

that are critical for species survival even if that resource is 

only required for a limited period. When an important resource has been identified, consider broadly how projected 

changes in climate are expected to impact this resource. 

Climate may reduce food resources by causing a shift in 

vegetation communities. Alternatively, population crashes 

of important food resources (see Parmesan and others 

2000 (insects), Stenseth and others 2002 (fish), others) due 

to climate extremes or extreme weather events (storms) 

or disturbances (disease, fire) can also occur. If the species utilizes several food sources with variable potential 

responses to climate change projections, then (b) will be 

the most appropriate selection. Consider whether food 

resources may be limited during critical periods such as 

during reproduction or migration.

Relevant data and suggested sources: Diet is most commonly reported in natural history documents although it 

is not always well documented for individual species or 

across a species’ range. A score of 0 is appropriate where 

information is absent. Most applications of this potential 

vulnerability will be those with more specialized diets, 

but some food resources may also be predicted to change 

even if comprised of multiple species. Life history and 

species accounts may provide information on potential 

direction of change for an animal species used as a resource. 

Additional information on a taxonomic group of interest 

may be found with online scholarly search engines such 

as Google Scholar or BIOSIS.
28 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-257. 2011

I2. Predators. Are important predator populations 

for this species expected to change?

Only predator species with a demonstrable impact on 

populations should be considered. If there are several 

predators with varying expected responses to climate 

change projections, then we assume that overall predation 

effects will remain unchanged. Climate could also affect 

the intensity or impact of predation without changes in the 

size of predator populations (e.g., loss of cover). When this 

impact has a strong potential to affect a species’ population, it is appropriate to count this as a predator-related 

vulnerability. No prediction is made if mortality from 

predation is low.

Relevant data and suggested sources: Life history/species accounts. A general understanding of the potential 

response of predator species to projected climate changes 

is required. This will likely involve reviewing the natural 

history of the predator or doing a literature search.

I3. Symbionts. Are populations of symbiotic species 

expected to change?

We define symbiotic relationships to include any type 

of required interaction with another organism(s). Consider 

species that are part of an obligatory mutualism (required 

for survival or breeding), commensalism, or parasitism (i.e., 

the focal species is parasitic). If the symbiotic species is 

only a food resource and already considered in Question 1, 

then score as 0 here unless there is some additional aspect 

to the relationship that has not been addressed.

Relevant data and suggested sources: Life history/

species accounts should list the presence of a symbiotic 

species. Knowledge of symbiont life history characteristics 

and potential response to climate change projections may 

be required (see Question 2). This question does not apply 

to hosts of parasites (see Question 4).

I4. Disease prevalence. Is prevalence of diseases known 

to cause widespread mortality or reproductive 

failure expected to change?

Consider only those pathogens or parasites that are 

known to cause substantial mortality or loss of fecundity. 

In addition to the disease-causing agent, consider how 

climate affects the incidence, spread, or virulence of the 

disease. Vector-borne diseases may be particularly prone to 

range expansions if climate projections alter range suitable 

for vector populations. For any disease or disease agent, 

vulnerability is associated with an increased mortality 

that occurs as a result of exposure to new diseases through 

introductions or range expansion or increased incidence 

and severity of diseases already affecting the species that 

may occur due to increases in vector populations. Disease 

incidence may also increase as warmer temperatures 

reduce cold related die-offs and extend activity period of 

both pathogens and their vectors. Resilience is associated 

with a decrease in mortality through any of these types of 

mechanisms. Climate changes can also indirectly affect 

disease spread through increases in crowding if resources 

become more limited (e.g., shrinking water sources) or by 

increasing host susceptibility (e.g., body condition or resistance is reduced). Consider crowding only when there is a 

demonstrable relationship between crowding and disease 

outbreak (e.g., many water borne pathogens) as well as 

mechanism where crowding is expected to increase (e.g., 

concentration of limited water sources).

Relevant data and suggested sources: Life history/species 

accounts should provide information regarding disease 

susceptibility. USGS National Wildlife Health Center is 

a good source of wildlife disease information, and a field 

manual of bird diseases is available online (http://www.

nwhc.usgs.gov/publications/field_manual/). Literature 

searches of the species name or family and “mortality” 

may also be helpful. In addition some diseases may have 

detailed projections related to climate change, particularly 

if they affect human health as well (e.g., malaria). Primary 

literature search of the specific pathogen with reference 

to climate change or range expansions is recommended. 

For any significant diseases, follow up with a search for 

transmission risk factors.

I5. Competitors. Are populations of important competing species expected to change?

Criteria: Consider the effects of climate changes on 

competing species that displace or negatively affect survival 

or reproduction in the species of interest. Specifically, note 

whether major competitors, those that are known to outcompete a species, will benefit or not by projected changes 

in climate. Consider introduced as well as native species.

Relevant data and suggested sources: Information 

on important competing species is often included with 

information on species conservation. Suggested control 

measures may indicate if certain climate conditions favor 

these species.



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