Decline in amphibian populations
Since the 1980s, decreases in amphibian populations, including population decline and localized mass extinctions, have been observed in locations all over the world. These declines are known as one of the most critical threats to global biodiversity.
Recent (2007) research indicates the reemergence of varieties of chytrid fungi may account for a substantial fraction of the overall decline. A more recent (2018) paper published in Science confirms this.
Several secondary causes may be involved, including other diseases, habitat destruction and modification, exploitation, pollution, pesticide use, introduced species, and ultraviolet-B radiation (UV-B). However, many of the causes of amphibian declines are still poorly understood, and the topic is currently a subject of much ongoing research. Calculations based on extinction rates suggest that the current extinction rate of amphibians could be 211 times greater than the background extinction rate and the estimate goes up to 25,000–45,000 times if endangered species are also included in the computation.
Although scientists began observing reduced populations of several European amphibian species already in the 1950s, awareness of the phenomenon as a global problem and its subsequent classification as a modern-day mass extinction only dates from the 1980s. By 1993, more than 500 species of frogs and salamanders present on all five continents were in decline.
In the past three decades, declines in populations of amphibians (the class of organisms that includes frogs, toads, salamanders, newts, and caecilians) have occurred worldwide. In 2004, the results were published of the first worldwide assessment of amphibian populations, the Global Amphibian Assessment. This found that 32% of species were globally threatened, at least 43% were experiencing some form of population decrease, and that between 9 and 122 species have become extinct since 1980. As of 2010[update], the IUCN Red List, which incorporates the Global Amphibian Assessment and subsequent updates, lists 650 amphibian species as "Critically Endangered", and 35 as "Extinct". Despite the high risk this group faces, recent evidence suggests the public is growing largely indifferent to this and other environmental problems, posing serious problems for conservationists and environmental workers alike.
Habitat loss, disease and climate change are thought to be responsible for the drastic decline in populations in recent years. Declines have been particularly intense in the western United States, Central America, South America, eastern Australia and Fiji (although cases of amphibian extinctions have appeared worldwide). While human activities are causing a loss of much of the world's biodiversity, amphibians appear to be suffering much greater effects than other classes of organism. Because amphibians generally have a two-staged life cycle consisting of both aquatic (larvae) and terrestrial (adult) phases, they are sensitive to both terrestrial and aquatic environmental effects. Because their skins are highly permeable, they may be more susceptible to toxins in the environment than other organisms such as birds or mammals. Many scientists believe that amphibians serve as "canaries in a coal mine," and that declines in amphibian populations and species indicate that other groups of animals and plants will soon be at risk.
Declines in amphibian populations were first widely recognized in the late 1980s, when a large gathering of herpetologists reported noticing declines in populations in amphibians across the globe. Among these species, the Golden toad (Bufo periglenes) endemic to Monteverde, Costa Rica, featured prominently. It was the subject of scientific research until populations suddenly crashed in 1987 and it had disappeared completely by 1989. Other species at Monteverde, including the Monteverde Harlequin Frog (Atelopus varius), also disappeared at the same time. Because these species were located in the pristine Monteverde Cloud Forest Reserve, and these extinctions could not be related to local human activities, they raised particular concern among biologists.
When amphibian declines were first presented as a conservation issue in the late 1980s, some scientists remained unconvinced of the reality and gravity of the conservation issue. Some biologists argued that populations of most organisms, amphibians included, naturally vary through time. They argued that the lack of long-term data on amphibian populations made it difficult to determine whether the anecdotal declines reported by biologists were worth the (often limited) time and money of conservation efforts.
However, since this initial skepticism, biologists have come to a consensus that declines in amphibian populations are a real and severe threat to biodiversity. This consensus emerged with an increase in the number of studies that monitored amphibian populations, direct observation of mass mortality in pristine sites that lacked apparent cause, and an awareness that declines in amphibian populations are truly global in nature.
Potential secondary causes
Numerous potential explanations for amphibian declines have been proposed. Most or all of these causes have been associated with some population declines, so each cause is likely to affect in certain circumstances but not others. Many of the causes of amphibian declines are well understood, and appear to affect other groups of organisms as well as amphibians. These causes include habitat modification and fragmentation, introduced predators or competitors, introduced species, pollution, pesticide use, or over-harvesting. However, many amphibian declines or extinctions have occurred in pristine habitats where the above effects are not likely to occur. The causes of these declines are complex, but many can be attributed to emerging diseases, climate change, increased ultraviolet-B radiation, or long-distance transmission of chemical contaminants by wind.
Habitat modification or destruction is one of the most dramatic issues affecting amphibian species worldwide. As amphibians generally need aquatic and terrestrial habitats to survive, threats to either habitat can affect populations. Hence, amphibians may be more vulnerable to habitat modification than organisms that only require one habitat type. Large scale climate changes may further be modifying aquatic habitats, preventing amphibians from spawning altogether.
Habitat fragmentation occurs when habitats are isolated by habitat modification, such as when a small area of forest is completely surrounded by agricultural fields. Small populations that survive within such fragments are often susceptible to inbreeding, genetic drift, or extinction due to small fluctuations in the environment. 
Pollution and chemical contaminants
There is evidence of chemical pollutants causing frog developmental deformities (extra limbs, or malformed eyes). Pollutants have varying effects on frogs. Some alter the central nervous system; others cause a disruption in the production and secretion of hormones. Experimental studies have also shown that exposure to commonly used herbicides such as glyphosate (Tradename Roundup) or insecticides such as malathion or carbaryl greatly increase mortality of tadpoles. Additional studies have indicated that terrestrial adult stages of amphibians are also susceptible to non-active ingredients in Roundup, particularly POEA, which is a surfactant. Although sex reversal in some species of frogs occur naturally in pristine environments, certain estrogen-like pollutants can forcibly induce these changes. In a study conducted in a laboratory at Uppsala University in Sweden, more than 50% of frogs exposed to levels of estrogen-like pollutants existing in natural bodies of water in Europe and the United States became females. Tadpoles exposed even to the weakest concentration of estrogen were twice as likely to become females while almost all of the control group given the heaviest dose became female.
While most pesticide effects are likely to be local and restricted to areas near agriculture, there is evidence from the Sierra Nevada mountains of the western United States that pesticides are traveling long distances into pristine areas, including Yosemite National Park in California.
Ozone depletion, ultraviolet radiation and cloud cover
Like many other organisms, increasing ultraviolet-B (UVB) radiation due to stratospheric ozone depletion and other factors may harm the DNA of amphibians, particularly their eggs. The amount of damage depends upon the life stage, the species type and other environmental parameters. Salamanders and frogs that produce less photolyase, an enzyme that counteracts DNA damage from UVB, are more susceptible to the effects of loss of the ozone layer. Exposure to ultraviolet radiation may not kill a particular species or life stage but may cause sublethal damage.
More than three dozen species of amphibians have been studied, with severe effects reported in more than 40 publications in peer-reviewed journals representing authors from North America, Europe and Australia. Experimental enclosure approaches to determine UVB effects on egg stages have been criticized; for example, egg masses were placed at water depths much shallower than is typical for natural oviposition sites. While UVB radiation is an important stressor for amphibians, its effect on the egg stage may have been overstated.
Anthropogenic climate change has likely exerted a major effect on amphibian declines. For example, in the Monteverde Cloud Forest, a series of unusually warm years led to the mass disappearances of the Monteverde Harlequin frog and the Golden Toad. An increased level of cloud cover, a result of geoengineering and global warming, which has warmed the nights and cooled daytime temperatures, has been blamed for facilitating the growth and proliferation of the fungus Batrachochytrium dendrobatidis (the causative agent of the fungal infection chytridiomycosis).
Although the immediate cause of the die offs was the chytrid, climate change played a pivotal role in the extinctions. Researchers included this subtle connection in their inclusive climate-linked epidemic hypothesis, which acknowledged climatic change as a key factor in amphibian extinctions both in Costa Rica and elsewhere.
New evidence has shown global warming to also be capable of directly degrading toads' body condition and survivorship. Additionally, the phenomenon often colludes with landscape alteration, pollution, and species invasions to effect amphibian extinctions.
A number of diseases have been related to mass die-offs or declines in populations of amphibians, including "red-leg" disease (Aeromonas hydrophila), Ranavirus (family Iridoviridae), Anuraperkinsus, and chytridiomycosis. It is not entirely clear why these diseases have suddenly begun to affect amphibian populations, but some evidence suggests that these diseases may have been spread by humans, or may be more virulent when combined with other environmental factors.
There is considerable evidence that parasitic trematode platyhelminths (a type of fluke) have contributed to developmental abnormalities and population declines of amphibians in some regions. These trematodes of the genus Ribeiroia have a complex life cycle with three host species. The first host includes a number of species of aquatic snails. The early larval stages of the trematodes then are transmitted into aquatic tadpoles, where the metacercariae (larvae) encyst in developing limb buds. These encysted life stages produce developmental abnormalities in post-metamorphic frogs, including additional or missing limbs. These abnormalities increase frog predation by aquatic birds, the final host of the trematode.
A study showed that high levels of nutrients used in farming and ranching activities fuel parasite infections that have caused frog deformities in ponds and lakes across North America. The study showed increased levels of nitrogen and phosphorus cause sharp hikes in the abundance of trematodes, and that the parasites subsequently form cysts in the developing limbs of tadpoles causing missing limbs, extra limbs and other severe malformations including five or six extra or even no limbs.
Non-native predators and competitors have also been found to affect the viability of frogs in their habitats. The mountain yellow-legged frog which typically inhabits the Sierra Nevada lakes have seen a decline in numbers due to stocking of non-native fish (trout) for recreational fishing. The developing tadpoles and froglets fall prey to the fish in large numbers. This interference in the frog's three-year metamorphosis is causing a decline that is manifest throughout their ecosystem.
Increased noise levels
Frogs and toads are highly vocal, and their reproductive behaviour often involves the use of vocalizations. There have been suggestions that increased noise levels caused by human activities may be contributing to their declines. In a study in Thailand, increased ambient noise levels were shown to decrease calling in some species and to cause an increase in others. This has, however, not been shown to be a cause for the widespread decline.
Symptoms of stressed populations
Amphibian populations in the beginning stages of decline often exhibit a number of signs, which may potentially be used to identify at-risk segments in conservation efforts. One such sign is developmental instability, which has been proven as evidence of environmental stress. This environmental stress can potentially raise susceptibility to diseases such as chytridiomycosis, and thus lead to amphibian declines. In a study conducted in Queensland, Australia, for example, populations of two amphibian species, Litoria nannotis and Litoria genimaculata, were found to exhibit far greater levels of limb asymmetry in pre-decline years than in control years, the latter of which preceded die offs by an average of 16 years. Learning to identify such signals in the critical period before population declines occur might greatly improve conservation efforts.
The first response to reports of declining amphibian populations was the formation of the Declining Amphibian Population Task Force (DAPTF) in 1990. DAPTF led efforts for increased amphibian population monitoring in order to establish the extent of the problem, and established working groups to look at different issues. Results were communicated through the newsletter Froglog.
Much of this research went into the production of the first Global Amphibian Assessment (GAA), which was published in 2004 and assessed every known amphibian species against the IUCN Red List criteria. This found that approximately one third of amphibian species were threatened with extinction. As a result of these shocking findings an Amphibian Conservation Summit was held in 2005, because it was considered "morally irresponsible to document amphibian declines and extinctions without also designing and promoting a response to this global crisis".
Outputs from the Amphibian Conservation Summit included the first Amphibian Conservation Action Plan (ACAP) and to merge the DAPTF and the Global Amphibian Specialist Group into the IUCN SSC Amphibian Specialist Group (ASG). The ACAP established the elements required to respond to the crisis, including priority actions on a variety of thematic areas. The ASG is a global volunteer network of dedicated experts who work to provide the scientific foundation for effective amphibian conservation action around the world.
The ACAP (Gascon et al 2007), concerned that time and capability were short, recommended that all relevant species be immediately incorporated into ex situ breeding programs. On 16 February 2007, scientists worldwide met in Atlanta, U.S., to form a group called the Amphibian Ark to help save more than 6,000 species of amphibians from disappearing by starting captive breeding programmes. Overall between the call to action in 2007 and 2019 there has been a 57% increase in number of breeding programs, or 77 additional species.
Areas with noticed frog extinctions, like Australia, have few policies that have been created to prevent the extinction of these species. However, local initiatives have been placed where conscious efforts to decrease global warming will also turn into a conscious effort towards saving the frogs. In South America, where there is also an increased decline of amphibian populations, there is no set policy to try to save frogs. Some suggestions would include getting entire governments to place a set of rules and institutions as a source of guidelines that local governments have to abide by.
A critical issue is how to design protected areas for amphibians which will provide suitable conditions for their survival. Conservation efforts through the use of protected areas have shown to generally be a temporary solution to population decline and extinction because the amphibians become inbred. It is crucial for most amphibians to maintain a high level of genetic variation through large and more diverse environments.
Education of local people to protect amphibians is crucial, along with legislation for local protection and limiting the use of toxic chemicals, including some fertilizers and pesticides in sensitive amphibian areas.
- Effects of pesticides on amphibians
- Holocene extinction
- Colony collapse disorder
- Decline in insect populations
- White nose syndrome
- The Sixth Extinction (book)
- Racing Extinction (film)
- Kriger, Kerry M.; Hero, Jean‐Marc (26 July 2007). "The chytrid fungus Batrachochytrium dendrobatidis is non‐randomly distributed across amphibian breeding habitats". Diversity and Distributions. 13 (6): 781–788. doi:10.1111/j.1472-4642.2007.00394.x. S2CID 85857635.
Batrachochytrium dendrobatidis has been implicated as the causative agent of mass moralities, population declines, and the extinctions of stream‐breeding amphibian species worldwide.
- Retallick, Richard W. R.; Miera, Verma (2007). "Strain differences in the amphibian chytrid Batrachochytrium dendrobatidis and non-permanent, sub-lethal effects of infection" (PDF). Diseases of Aquatic Organisms. 75 (3): 201–207. doi:10.3354/dao075201. PMID 17629114.
The chytrid fungus Batrachochytrium dendrobatidis (Bd) is likely the cause of numerous recent amphibian population declines worldwide.
- O’Hanlon, Simon J; et al. (2018). "Recent Asian origin of chytrid fungi causing global amphibian declines". Science. 360 (6389): 621–627. Bibcode:2018Sci...360..621O. doi:10.1126/science.aar1965. PMC 6311102. PMID 29748278.
- McCallum, M. L. (2007). "Amphibian Decline or Extinction? Current Declines Dwarf Background Extinction Rate" (PDF). Journal of Herpetology. 41 (3): 483–491. doi:10.1670/0022-1511(2007)41[483:ADOECD]2.0.CO;2. S2CID 30162903. Archived from the original (PDF) on 2008-12-17.
- Stuart, Simon N.; Chanson, Janice S.; Cox, Neil A.; Young, Bruce E.; Rodrigues, Ana S. L.; Fischman, Debra L.; Waller, Robert W. (3 December 2004). "Status and Trends of Amphibian Declines and Extinctions Worldwide". Science. 306 (5702): 1783–1786. Bibcode:2004Sci...306.1783S. CiteSeerX 10.1.1.225.9620. doi:10.1126/science.1103538. PMID 15486254. S2CID 86238651.
- "IUCN Red List - Search Results". IUCN Red List of Threatened Species. Version 2010.3. IUCN. Retrieved September 8, 2010.
- McCallum, M.L.; Bury, G.W. (2013). "Google search patterns suggest declining interest in the environment". Biodiversity and Conservation. 22 (6–7): 1355–1367. doi:10.1007/s10531-013-0476-6. S2CID 15593201.
- "Conservation International - Amphibians". Retrieved 8 August 2012.
- Science Daily (October 15, 2004), Amphibians in dramatic decline: Study finds nearly one third of species threatened with extinction. Sciencedaily.com. Retrieved on September 18, 2007.
- Blaustein, A.R.; Wake, D.B. (1990). "Declining amphibian populations: a global phenomenon?". Trends in Ecology and Evolution. 5 (7): 203–204. doi:10.1016/0169-5347(90)90129-2.
- Crump, M.L.; Hensley, F.R.; Clark, K.I. (1992). "Apparent decline of the golden toad: Underground or extinct?". Copeia. 1992 (2): 413–420. doi:10.2307/1446201. JSTOR 1446201.
- J. Alan Pounds; Martha L. Crump (1994). "Amphibian Declines and Climate Disturbance: The Case of the Golden Toad and the Harlequin Frog". Conservation Biology. 8 (1): 72–85. doi:10.1046/j.1523-1739.1994.08010072.x. S2CID 53330451.
- Pechmann, J.H.K.; Scott, D.E.; Semlitsch, R.D.; Caldwell, J.P.; Vitt, L.J.; Gibbons, J.W. (1991). "Declining amphibian populations: the problem of separating human impacts from natural fluctuations". Science. 253 (5022): 892–895. Bibcode:1991Sci...253..892P. doi:10.1126/science.253.5022.892. PMID 17751826. S2CID 27171692.
- Houlahan, J.E.; Findlay, C.S.; Schmidt, B.R.; Meyer, A.H.; Kuzmin, S.L. (2000). "Quantitative evidence for global amphibian population declines". Nature. 404 (6779): 752–758. Bibcode:2000Natur.404..752H. doi:10.1038/35008052. PMID 10783886. S2CID 4393392.
- Eisenbeis, G., 2006. Artificial night lighting and insects: Attraction of insects to streetlamps in a rural setting in Germany. In C. Rich & T. Longcore (eds), Ecological Consequences of Artificial Night Lighting. Island Press: 281-304.
- Baker, B.J.; Richardson, J.M.L. (2006). "The effect of artificial light on male breeding-season behaviour in green frogs, Rana clamitans melanota". Canadian Journal of Zoology. 84 (10): 1528–1532. doi:10.1139/z06-142.
- "Climate link to amphibian decline". BBC News. 2008-10-27. Retrieved 2010-05-01.
- Knozowski, P.; Górski, A.; Stawicka, A. M.; Nowakowski, J. J. (2022-12-31). "Long-term changes in the diversity of amphibian communities inhabiting small water bodies in the urban area of Olsztyn (NE Poland)". The European Zoological Journal. 89 (1): 791–812. doi:10.1080/24750263.2022.2087773.
- Blaustein, Andrew R; Pieter TJ Johnson (2003). "The complexity of deformed amphibians" (PDF). Front. Ecol. Environ. 1 (2): 87–94. doi:10.1890/1540-9295(2003)001[0087:TCODA]2.0.CO;2. ISSN 1540-9295. Archived from the original (PDF) on 2013-10-29.
- Burkhart, James G.; Gerald Ankley; Heidi Bell; Hillary Carpenter; Douglas Fort; David Gardiner; Henry Gardner; Robert Hale; Judy C. Helgen; Paul Jepson; Douglas Johnson; Michael Lannoo; David Lee; Joseph Lary; Rick Levey; Joseph Magner; Carol Meteyer; Michael D. Shelby; George Lucier (2000). "Strategies for assessing the implications of malformed frogs for environmental health". Environmental Health Perspectives. 108 (1): 83–90. doi:10.2307/3454299. JSTOR 3454299. PMC 1637865. PMID 10620528.[dead link]
- Relyea, R.A. (2004). "The impact of insecticides and herbicides on the biodiversity and productivity of aquatic communities". Ecological Applications. 15 (2): 618–627. doi:10.1890/03-5342.
- Relyea, R.A. (2005). "The lethal impact of Roundup on aquatic and terrestrial amphibians". Ecological Applications. 15 (4): 1118–1124. doi:10.1890/04-1291.
- "Healthy frogs can mysteriously reverse their sex". National Geographic.
- "Pollutants change 'he' frogs into 'she' frogs". Yahoo! News. 2007. Archived from the original on March 2, 2007. Retrieved 2007-03-01.
- Grossi, Mark (24 July 2001). "Sierra Frogs Fall Silent". The Fresno Bee. Archived from the original on June 18, 2007. Retrieved 2008-10-02.
- Dohm, M.R.; et al. (2005). "Effects of ozone exposure on nonspecific phagocytic capacity of pulmonary macrophages from an amphibian, Bufo marinus". Environmental Toxicology and Chemistry. 24 (1): 205–210. doi:10.1897/04-040r.1. PMID 15683185. S2CID 6574504.
- Andrew R. Blaustein; Joseph M. Kiesecker; Douglas P. Chivers; Robert G. Anthony (November 1995). "Ambient UV-B radiation causes deformities in amphibian embryos". PNAS. Vol. 92. pp. 11049–11052. doi:10.1073/pnas.92.24.11049. PMID 9391095.
- Belden, Lisa K.; Blaustein, Andrew R. (2002). "Population differences in sensitivity to UV-b radiation for larval long-toed salamanders" (PDF). Ecology. 83 (6): 1586–1590. doi:10.1890/0012-9658(2002)083[1586:PDISTU]2.0.CO;2. ISSN 0012-9658.
- Bancroft, B.A.; et al. (2007). "Effects of UVB radiation on marine and freshwater organisms: a synthesis through meta-analysis". Ecology Letters. 10 (4): 332–345. doi:10.1111/j.1461-0248.2007.01022.x. PMID 17355571.
- Licht, LE (2003). "Shedding Light on Ultraviolet Radiation and Amphibian Embryos". BioScience. 53 (6): 551–561. doi:10.1641/0006-3568(2003)053[0551:sloura]2.0.co;2.
- Alan Pounds, J.; Bustamante, Martín R.; Coloma, Luis A.; Consuegra, Jamie A.; Fogden, Michael P. L.; Foster, Pru N.; La Marca, Enrique; Masters, Karen L.; Merino-Viteri, Andrés; Puschendorf, Robert; Ron, Santiago R.; Sánchez-Azofeifa, G. Arturo; Still, Christopher J.; Young, Bruce E. (2006). "Widespread amphibian extinctions from epidemic disease driven by global warming" (PDF). Nature. 439 (7073): 161–167. Bibcode:2006Natur.439..161A. doi:10.1038/nature04246. PMID 16407945. S2CID 4430672.
- Messenger, Stephen (2016-09-30). "Last Frog Of His Kind Dies Alone". The Dodo. Retrieved 30 September 2016.
- Zoo Atlanta (February 17, 2012). "It's Leap Year. Remember the Rabbs' tree frog". Atlanta Fulton County Zoo. Archived from the original on May 24, 2012. Retrieved March 12, 2012.
- Pounds, J. Alan; Bustamante, Martín R.; Coloma, Luis A.; Consuegra, Jamie A.; Fogden, Michael P. L.; Foster, Pru N.; La Marca, Enrique; Masters, Karen L.; Merino-Viteri, Andrés; Puschendorf, Robert; Ron, Santiago R.; Sánchez-Azofeifa, G. Arturo; Still, Christopher J.; Young, Bruce E. (2007). "Global warming and amphibian losses; The proximate cause of frog declines? (Reply)". Nature. 447 (7144): E5–E6. Bibcode:2007Natur.447....5P. doi:10.1038/nature05942. S2CID 4372607.
- Reading, C. J. (2006). "Linking global warming to amphibian declines through its effects on female body condition and survivorship" (PDF). Oecologia. 151 (1): 125–131. doi:10.1007/s00442-006-0558-1. PMID 17024381. S2CID 24832716. Archived from the original (PDF) on 2014-02-02. Retrieved 2014-01-21.
- Pounds, J. Alan; Puschendorf, Robert (2004). "Ecology: Clouded Futures (News & Views)". Nature. 427 (6970): 107–109. doi:10.1038/427107a. PMID 14712258. S2CID 877425.
- Daszak, Peter; Lee Berger; Andrew A. Cunningham; Alex D. Hyatt; D. Earl Green; Rick Speare (1999). "Emerging Infectious Diseases and Amphibian Population Declines". Emerging Infectious Diseases. 5 (6): 735–48. doi:10.3201/eid0506.990601. PMC 2640803. PMID 10603206.
- Johnson, P.T.J.; Chase, J.M. (2004). "Parasites in the food web: linking amphibian malformations and aquatic eutrophication". Ecology Letters. 7 (7): 521–526. doi:10.1111/j.1461-0248.2004.00610.x.
- Johnson PTJ; Jonathan M. Chase; Katherine L. Dosch; Richard B. Hartson; Jackson A. Gross; Don J. Larson; Daniel R. Sutherland; Stephen R. Carpenter (2007). "Aquatic eutrophication promotes pathogenic infection in amphibians". PNAS. 104 (40): 15781–15786. Bibcode:2007PNAS..10415781J. doi:10.1073/pnas.0707763104. PMC 2000446. PMID 17893332.
- Knapp, R. A.; Matthews, K. R. (2000). "Non-native fish introductions and the decline of the mountain yellow-legged frog from within protected areas". Conservation Biology. 14 (2): 428–438. doi:10.1046/j.1523-1739.2000.99099.x. S2CID 51734566.
- Sun, Jennifer W.C.; Narins, Peter M. (2005). "Anthropogenic sounds differentially affect amphibian call rate" (PDF). Biological Conservation. 121 (3): 419–427. doi:10.1016/j.biocon.2004.05.017.
- Alford, Ross A.; Bradfield, Kay S.; Richards, Stephen J. (2007). "Ecology: Global warming and amphibian losses" (PDF). Nature. 447 (7144): E3–E4. Bibcode:2007Natur.447....3A. doi:10.1038/nature05940. PMID 17538571. S2CID 4412404.
- P. J. Bishop, A. Angulo, J. P. Lewis, Robin D. Moore, G. B. Rabb and J. Garcia Moreno, « The Amphibian Extinction Crisis - what will it take to put the action into the Amphibian Conservation Action Plan? », S.A.P.I.EN.S [Online], 5.2 | 2012, Online since 12 August 2012, connection on 09 April 2019. URL : http://journals.openedition.org/sapiens/1406
- Alastair Campbell, ed. (1999). Declines and disappearances of Australian frogs (PDF). Environment Australia. ISBN 0-642-54656-8. OCLC 44894378. Archived from the original (PDF) on 2011-11-14.
- Stuart et al (2004) Status and Trends of Amphibian Declines and Extinctions Worldwide. Science. Vol. 306, Issue 5702, pp. 1783-1786. doi:10.1126/science.1103538
- Gascon, Claude; Collins, James P.; Moore, Robin D.; Church, Don R.; McKay, Jeanne E.; Mendelson III, Joseph R., eds. (2007). Amphibian Conservation Action Plan. Gland/Cambridge: IUCN SSC Amphibian Specialist Group. S2CID 87645483.
- Silla, Aimee J.; Byrne, Phillip G. (2019-02-15). "The Role of Reproductive Technologies in Amphibian Conservation Breeding Programs". Annual Review of Animal Biosciences. Annual Reviews. 7 (1): 499–519. doi:10.1146/annurev-animal-020518-115056. ISSN 2165-8102. PMID 30359086. S2CID 53098666.
- "Bid to save frogs from killer goes worldwide". 2007. Archived from the original on 2015-10-18. Retrieved 2007-02-22.
-  Archived December 19, 2009, at the Wayback Machine
- [dead link]
- Crump, M. (2002). Amphibians, Reptiles, and their Conservation. North Haven, CT: Linnet Books. ISBN 9780208025111.
- Halliday, Adler (2008). The New Encyclopedia of Reptiles and Amphibians (2 ed.). Online: Oxford University Press. ISBN 9780198525073.
- FrogWeb: Amphibian Declines & Malformations
- IUCN Red List - Amphibians Archived 2014-07-01 at the Wayback Machine – assesses the current status of amphibian species worldwide (incorporates the Global Amphibian Assessment)
- AmphibiaWeb – provides background information on amphibian declines.
- Reptile Amphibian & Pesticide (RAP) Database
- Weedicide induced feminization
- Photos of Sick Frogs at Queensland Frog Society