U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3092

December 2012 Printed on recycled paper

Are Amphibians Really Declining? 

Clear evidence of major declines of amphibians in the 

United States and around the world has been established. The 

estimated rate of worldwide amphibian extinction since 1980 

is thought to be 105 times higher than the background rate 

(McCallum, 2007). These declines threaten the extinction of 30 

percent of the world’s approximately 7,000 amphibian species 

(Stuart and others, 2004). This constitutes the greatest extinction 

event since the “Pleistocene extinctions” 10,000 years ago 

(Wake and Vredenburg, 2008). 

The number of extinctions in the United States is not as 

extreme as in other parts of the world, but serious declines 

have been documented (for example, Mountain Yellow-legged 

Frog [Drost and Fellers, 1996]; Yosemite Toad [Sherman and 

Morton, 1993]; Boreal Toad [Corn and others, 1989; Muths and 

others 2003]; and Mississippi Gopher Frog [Richter and others, 

2003]). Every ranid frog species in the western United States 

is on a list of concern. To date, the most comprehensive source 

of information on declines for amphibians in the United States 

is a species by species assessment summarized by Bradford 

(2005) that suggests about 42 percent of species are threatened 

or declining. A similar approach used by Stuart and others 

(2004) to classify the status of amphibians globally, suggests 

that 21 percent of species in the United States are declining. 

These assessments were classified as “expert opinion,” which 

means that they were not necessarily based on quantitative 

data, but on the field experience and knowledge of professional 

herpetologists. Although expert opinion surveys should always 

be interpreted with caution, even the lower of these two 

estimates suggests a serious problem. The U.S. Geological 

Survey (USGS) Amphibian Research and Monitoring Initiative 

(ARMI) maintains a network of monitoring sites where the 

occurrence and abundance of amphibian populations are 

estimated statistically to provide the first strictly quantitative 

assessment of the status of select amphibians across the United 

States. The ARMI estimate is higher at 61 percent, but includes 

species exhibiting any level of decline (even a very low level). 

ARMI estimates a 3.7 percent average annual decline in the 

proportion of sites occupied by the 50 species that ARMI 

monitors. This reflects a mean annual change for all cases of 

-3.7%, although some cases increased and others decreased 

much more rapidly than the average. In mathematical terms, 

this number means that occupancy in any year was equal to the 

following equation: [(occupancy in the previous year) minus 

(0.037 times occupancy in the previous year)]. 

More than 25 years ago, scientists began to identify unexplained 

declines in amphibian populations around the world. Much has been learned since then, 

but amphibian declines have not abated and the interactions among the various threats to 

amphibians are not clear. Amphibian decline is a problem of local, national, and international 

scope that can affect ecosystem function, biodiversity, and commerce. This fact sheet provides 

a snapshot of the state of the amphibians and introduces examples to illustrate the range of 

issues in the United States. 

The State of Amphibians in the United States

Annual percent change in occupancy

Counts of time-series

0

10

30

20

40

< −20 −10 0 10 > 20

Decreasing Increasing

Distribution of trends in the rate of amphibian occupancy for monitoring 

projects conducted by the U.S. Geological Survey, Amphibian Research 

and Monitoring Initiative. Each case represents a species by site 

combination. The mean annual change for all cases was -3.7%. 

Estimates of amphibian declines. 

Amphibian 

species 

threatened or 

declining 

(percent)

Method Species and places 

considered Source

42 Expert opinion United States (all) Bradford (2005)

21 Expert opinion United States (all) Stuart and others 

(2004)

1

61 Quantitative 

monitoring

United States (nonrandom subset)ARMI monitoring 

data

1 Percentage of cases where any level of decline occurred from 2002 to 

2011. Some of these declines likely are part of natural fluctuations.
Yonahlossee Salamander, photograph 

by A. Cressler, U.S. Geological Survey.

Why are Amphibians Declining?

Habitat Destruction and Alteration 

Land-use change is a key reason for the loss of global 

biodiversity and is the most obvious cause of amphibian 

declines in the United States. Destroying habitat directly 

eliminates populations and increases the isolation of remaining 

populations in a landscape. When the space between habitat 

patches is hostile, the ability of amphibians to move across the 

landscape to find food, breed, or recolonize areas decreases. The 

effects of habitat loss are dramatic but in some ways could be 

the easiest to manage.

Introduced Species 

Many species of plants and animals around the world are 

now found in areas outside their natural range. Some of these 

introduced (or invasive) species cause harm to native species. 

For example, the introduction of sport fish to formerly fishless 

habitats is a major concern for amphibians in the western United 

States (Knapp and Matthews, 2000), and the American Bullfrog 

is a widely introduced species that, among other things, can act 

as a vector for disease (Daszak and others, 2004; Schloegel and 

others, 2010). American Bullfrogs are associated with declines 

of some native amphibians in the United States (Bury and 

Whelan, 1984). 

Contaminants 

Contamination of the environment can have direct and 

indirect effects on amphibians. Some contaminants, like 

acid rain, can kill tadpoles outright, while others such as 

pesticides, can disrupt hormonal systems and interfere with 

reproduction (Hayes and others, 2002). Anatomical deformities 

and behavioral changes related to pollutants lower the life 

expectancy and breeding potential of amphibians.

Disease

Emerging infectious diseases, especially rana virus 

and the amphibian chytrid fungus (Batrachochytrium 

dendrobatidis, Bd) are contributing to amphibian declines 

(Daszak and others, 1999; Briggs and others, 2005; Gray and 

others, 2009). Evidence suggests that Bd is a dominant factor in 

some of the more puzzling amphibian declines around the world 

and has affected species in the United States. The long-term 

effects of Bd on amphibian populations in the United States are 

poorly understood. 

Cross section of amphibian 

epidermis infected and thickened 

by the amphibian chytrid fungus, 

photograph by D.E. Green, U.S. 

Geological Survey.

The Amphibian Research and Monitoring Initiative

The Amphibian Chytrid Fungus 

(Batrachochytrium dendrobatidis, Bd)

The amphibian chytrid 

fungus causes a disease 

called chytridiomycosis 

that is lethal to many 

amphibians. Well-known 

examples of populationlevel extirpations related 

to chytrid fungus include 

those in California 

(Vredenburg and others, 

2005, Central America 

(Lips and others, 2006), 

and Australia (Skerratt 

and others, 2007). The 

amphibian chytrid fungus 

appears to be widespread 

in the United States 

(Fellers and others, 

2001; Longcore and others, 2007; Rothermel and others, 

2008; Muths and others, 2008; Adams and others, 2010; 

Hossack and others, 2010). The fungus is present in 

species that are candidates for federal listing, such as 

the Oregon Spotted Frog, species that are apparently 

common, such as the Pacific Tree Frog, and in invasive 

species, such as the American Bullfrog that can act 

as a reservoir and vector for this disease. Although 

extirpations have been linked to chytrid fungus infections 

in the United States, there also is evidence for the 

persistence of some populations despite the presence 

of this fungus (Briggs and others, 2005; Grant and others, 

2008; Pilliod and others, 2010). 

The USGS established ARMI 

in 2000 to monitor the status 

of amphibians and study the 

causes of decline on public 

lands in the United States. This 

was in response to a direct 

request from the Secretary of 

the Interior. ARMI scientists 

estimate abundance or 

occupancy across a network 

of amphibian populations 

at regular intervals and develop research to address 

hypotheses about the causes of decline. Monitoring is 

accomplished in partnership with other Department of 

the Interior agencies and is designed in a way that not 

only provides information on status, but also informs 

management decisions. This is possible because ARMI 

produces statistically unbiased estimates that, over time, 

can be related to potential causal factors. This program is 

among the first of its kind to use interdisciplinary tools at 

broad scales to examine a biological phenomenon.

California Tree Frog, 

photograph by C.W. Brown, 

U.S. Geological Survey.
Examples—Classifying Amphibian Problems 

The following examples illustrate the continuum of categories that describe the plight of some amphibians and highlight 

insights gained from recent research. 

Impacted by Invasives—Invasive fish can curtail breeding in Long-toed 

Salamanders (Pilliod and others, 2011) and can exacerbate negative interactions 

between invasive American Bullfrogs and native amphibians (Adams and others, 2003). 

For example, Chiricahua Leopard Frogs and Arroyo Toads are impacted by American 

Bullfrogs because this invasive species carries disease and preys on the native species 

(Daszak and others, 2004).

Equivocal —The Boreal Toad is clearly declining in Colorado (Corn and others, 1989), but 

evidence for decline of the same species in Oregon is less convincing (Wente and others, 2005; 

Pearl and others, 2009). Declines in this species, at least in the southern Rocky Mountains, 

appear to be related to disease (Muths and others, 2003; Carey and others, 2005). 

Apparently Robust—The Boreal Chorus Frog occupies a wide variety of 

habitats in the western United States. Although Boreal Chorus Frogs are susceptible 

to Bd, preliminary data suggest that the disease does not seriously affect survival 

and that populations studied in the Front Range of Colorado appear to be relatively 

robust (Corn and others, 1989). Some species such as the Boreal Chorus Frog may 

have an advantage in coping with stressors, but still can be vulnerable to decline. 

Pronouncing a population to be robust is particularly difficult because without 

long-term data the natural variability in amphibian reproduction and life histories 

can mask declines. 

Declining—The Mountain Yellow-legged Frog has declined dramatically in 

the Sierra Nevada of California (Vredenburg and others, 2005). Contributing 

factors include stocking non-native fish into lakes where the frogs breed (Knapp 

and Matthews, 2000), disease (Rachowicz and others, 2006), and environmental 

pollutants (Davidson, 2004).

Mountain Yellow-legged Frog, photograph 

by C.W. Brown, U.S. Geological Survey.

Boreal Toad, photograph by 

D. Herasimtschuk.

Boreal Chorus Frog, photograph by D. Patla.

Arroyo Toad, photograph by C.W. 

Brown, U.S. Geological Survey.

Insight: Multiple factors may contribute to a particular decline 

and even “pristine” locations are at risk.

Insight: One location does not provide an accurate picture 

about a species throughout its range.

Insight: Just as it is difficult to say that a species is declining, 

it is also difficult to determine that a species is robust. 

Insight: Interactions among species can play a role in declines. Negative 

interactions can be intensified when additional species are introduced.
For Additional Information Contact:

National Coordinator, Amphibian Research and Monitoring Initiative

U.S. Geological Survey

12201 Sunrise Valley Dr.

Reston, VA 20192

This fact sheet including complete literature citations can be found at 

 http://armi.usgs.gov/sota/index.php

This is contribution number 412 of the U.S. Geological Survey Amphibian 

Research and Monitoring Initiative (ARMI).

Conservation Challenges

We are faced with the potential disappearance of a 

significant proportion of an ancient group of vertebrates. 

Adding to the complexity of amphibian decline, climate 

change is an overarching process with the potential to 

interact with any of the identified causes of decline (Lacan 

and others, 2008; Seimon and others, 2007). Our challenge 

is to refine our understanding of amphibian declines by 

pinpointing causes, quantifying observed and suspected 

declines, and developing appropriate responses, which 

are the critical steps to conserve the unique amphibian 

resources of the United States.

Given the limited dispersal ability and specific habitat 

requirements of most species, developing conservation and 

management strategies is paramount for ensuring viable 

populations. Even in protected areas, populations are at 

risk from past management practices, habitat changes 

occurring along boundaries, and global threats that affect 

entire landscapes. ARMI is working with natural resource 

managers to develop strategies for effective management. 

This is especially important because many amphibians 

have restricted or fragmented distributions, which reduces 

management options. Effective strategies combine our 

understanding of population trajectories with detailed 

research into factors that are related to these trends. 

Front page photographs: Boreal Toad tadpoles and adult, photograph by D. Herasimtschuk.

 Green Salmander, by A. Cressler, U.S. Geological Survey.

Back page photograph: Boreal Chorus Frog, photograph by D. Herasimtschuk.

Northern Red-legged Frog, photograph taken by C.W. Brown, 

U.S. Geological Survey.

ARMI Principles

•	 Treat monitoring as research

•	 Maintain the flexibility to tailor projects to local needs

•	 Focus on statistically unbiased metrics that can be 

scaled up to achieve broader synthesis

 For ARMI information: http://armi.usgs.gov

Authors: E. Muths, M.J. Adams, E.H.C. Grant, D. Miller, P.S. Corn and L.C. Ball.