Printed on recycled paper U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2010–3017

Revised 2012

Climate Change and Wildlife Health: Direct and Indirect Effects

Climate change will have significant effects on the health of 

wildlife, domestic animals, and humans, according to scientists. The 

Intergovernmental Panel on Climate Change projects that unprecedented rates of climate change will result in increasing average global 

temperatures; rising sea levels; changing global precipitation patterns, 

including increasing amounts and variability; and increasing midcontinental summer drought (Intergovernmental Panel on Climate Change, 

2007). Increasing temperatures, combined with changes in rainfall and 

humidity, may have significant impacts on wildlife, domestic animal, 

and human health and diseases. When combined with expanding human 

populations, these changes could increase demand on limited water 

resources, lead to more habitat destruction, and provide yet more opportunities for infectious diseases to cross from one species to another. 

Awareness has been growing in recent years about zoonotic 

diseases— that is, diseases that are transmissible between animals and 

humans, such as Lyme disease and West Nile virus. The rise of such 

diseases results from closer relationships among wildlife, domestic 

animals, and people, allowing more contact with diseased animals, 

organisms that carry and transmit a disease from one animal to another 

(vectors), and people. Disease vectors include insects, such as mosquitoes, and arachnids, such as ticks. Thus, it is impossible to separate the 

effects of global warming on wildlife from its effects on the health of 

domestic animals or people (fig. 1). 

Climate change, habitat destruction and urbanization, the introduction of exotic and invasive species, and pollution—all affect ecosystem 

and human health. Climate change can also be viewed within the context of other physical and climate cycles, such as the El Niño Southern 

Oscillation (El Niño), the North Atlantic Oscillation, and cycles in solar 

radiation that have profound effects on the Earth’s climate. The effects 

of climate change on wildlife disease are summarized in several areas of 

scientific study discussed briefly below: geographic range and distribution of wildlife diseases, plant and animal phenology (Walther and others, 2002), and patterns of wildlife disease, community and ecosystem 

composition, and habitat degradation.

Geographic Range and Distribution of Wildlife Diseases 

In the Northern Hemisphere, global warming has likely played a 

role in geographic shifts of disease vectors and parasitic diseases that 

DISEASE

Figure 1. Ecosystem health reflects 

environmental quality, an important 

factor in the well-being of humans, 

domestic animals, and wildlife. 

Prevention of disease occurring at 

the interface between these components requires a holistic approach 

of “one health” for the benefit of all 

(Friend, 2006). (Drawing by John Evans)

have complex life cycles. For example, the black-legged tick, which 

carries and transmits Lyme disease and several other tick-borne zoonotic 

diseases in North America, has been expanding north into southern 

Ontario (fig. 2) and western Ontario and Manitoba (Ogden and others, 

2006), and, more recently, into Quebec and the Canadian Maritime 

Provinces (Ogden and others, 2005, 2009, and 2010). 

Georgian

Bay

Lake

Er

L

ie

ake Michigan

Ontario Lake

Lake Superior

Lake

Huron

Ottawa River

Duluth

Detroit

Cleveland

Buffalo

Chicago

Thunder Bay

Sault Ste. Marie OTTAWA

Toronto

Greater Sudbury /

 Grand Sudbury

C A N A D A

U N I T E D S TAT E S

Figure 2. Surveillance for the black-legged tick identified a single resident population in 1991 (yellow arrow). Between 1991 and 2003 additional 

resident populations were reported (black arrows) showing the expanding distribution of the tick in southern Ontario. The red line shows the 

approximate current temperature limits for the black-legged tick (Ogden 

and others, 2005). Adapted with permission from the Ecological Society 

of America and D.H. Ogden, Public Health Agency of Canada. 

In Europe, a similar northward expansion of the European castor 

bean tick, which also carries and transmits Lyme disease, tick-borne 

encephalitis (TBE), and other diseases, has been reported in Norway 

(Hasle, 2009) and Sweden (Tälleklint and Jaenson, 1998; Lindgren, 

2000). On both continents, migrating birds carrying feeding ticks are 

likely the source of long-range expansion of the tick vectors (Ogden and 

others, 2008; Hasle and others, 2009; Brinckerhoff and others, 2011), 

and increasing environmental temperatures have likely permitted the 

ticks to become established in larger geographic areas (Lindgren, 2000).
Scientists also expect changes in disease distribution with changes 

in altitude. For example, climate warming may lead to year-round 

transmission of mosquito-borne avian malaria at higher elevations in the 

Hawaiian Islands, further threatening endangered native Hawaiian birds 

that have little or no resistance to the introduced disease. Currently, 

on the island of Hawai’i, avian malaria, caused by the parasite Plasmodium relictum, is limited to warmer elevations below 1,500 meters 

(or 4,920 feet; fig. 3) (Van Riper, III, and others, 1986). If the higher 

elevations become warmer as projected, mosquito activity and parasite 

development in these areas will increase. Conservationists are concerned 

that climate change may lead to increased avian malaria transmission 

throughout the year at increasingly higher elevations.

V

Native birds

ectors

Malaria parasites

ELEVATION, IN METERS

0 500 1000 1500 2000

ABUNDANCE

Figure 3 Abundance of avian malaria parasites in Hawaiian birds, 

disease-carrying mosquitoes, and native Hawaiian birds, in relation to 

elevation on the island of Hawai’i (Van Riper, III, and others, 1986).

Phenology: Effects on Wildlife Disease 

The timing of recurring seasonal biologic cycles of some plant and 

animal species has already been affected by climate change (Walther 

and others, 2002). The study of these seasonal cycles is called phenology. The timing of biological cycles, such as the arrival of a bird species 

in the spring and the availability of its preferred food source, is critical 

for successful breeding and survival. Several studies in Europe show 

that some migratory birds have changed their migration patterns in 

response to climate change by arriving earlier than records show historically (Lehikoinen and others, 2004; Jonzen and others, 2006; Thorup 

and others, 2007). Significant population declines were reported recently 

for bird species that have not responded with earlier arrival (Saino and 

others, 2011), and the population declines have been interpreted as 

indicating the magnitude, and negative effect, in mismatch between bird 

arrival time and the onset of plants emerging from dormancy in spring. 

When an earlier emergence of plants from dormancy is combined with 

a mismatch in bird arrival time, critical food sources for returning birds 

might be past the period when they are most nutritious.

Variability in the timing of these biological cycles also can lead 

to increases or decreases in the risk for infectious disease, particularly 

diseases transmitted by mosquitoes or ticks. In Europe, transmission 

of TBE to humans often increases when warmer temperatures in the 

early spring result in the overlap of feeding activity of virus-infected 

nymphal and uninfected larval European castor bean ticks. Under these 

conditions, TBE is more readily passed between ticks feeding on small 

rodents. The period of viral infection is brief in tick-infested rodents, so 

when both stages of tick feed at the same time, more larval ticks become 

infected, and the risk for human infection increases (Randolph, 2009). 

Cooler spring temperatures result in less feeding overlap of nymphal 

and larval ticks, and under these conditions, the virus-infected rodents 

have time to recover from infection and are less likely to pass the virus 

to feeding larval ticks (fig. 4). 

Warmer spring

temperatures

MONTHLY MEAN LAND SURFACE

TEMPERATURE, IN DEGREES CENTIGRADE

1 2 3 4 5 6 7 8 9 10 11 12

MONTH

10

30

20

0

Cooler spring

temperatures

Nonoverlapping

larvae

Overlapping

larvae

TICK NUMBERS

Nymphs

MONTH

1 2 3 4 5 6 7 8 9 10 11 12

300

150

0

Figure 4. Human risk for tick-borne encephalitis in Europe is heightened in some years by slightly warmer temperatures in early spring (red 

line and arrow, top figure) that are associated with overlapping feeding 

of infected nymphal ticks and uninfected larval ticks (grey and red line, 

bottom figure). A slower rise in spring temperatures (black line, top 

figure) is associated with nonoverlapping feeding (graphs provided by 

S. Randolph, 2010).

At sites in North America, the same seasonal temperature effect 

has been observed in the transmission of the bacterium Borrelia burgdorferi, the pathogen or cause of Lyme disease, from infected nymphal 

black-legged ticks to uninfected larval ticks. When larval and nymphal 

ticks feed simultaneously, this not only contributes to the successful 

transmission of the pathogen to larvae, it also results in greater genetic 

diversity in this zoonotic pathogen (Gatewood and others, 2009). Climate change, by altering seasonal weather patterns, has the potential to 

affect these natural cycles. 

Changing Patterns of Wildlife Disease

In nature, pathogens can be transmitted directly between animals 

or indirectly through intermediate “hosts,” such as infected prey or biting insects. Indirect transmission cycles are often affected by environmental conditions such as temperature and rainfall. Higher temperatures 

associated with climate change may contribute to an increase in pathogens within intermediate hosts and vectors, or increased survival of animals that harbor disease. For example, warmer summer temperatures in 

the Arctic now allow the lung nematode larvae often found in muskoxen 

to develop to the infectious stage within the intermediate host, the marsh 

slug, at a rate that has reduced the parasite’s life cycle from 2 years to 

1 year (Kutz and others, 2005). 

Survival of another nematode, the brain worm of white-tailed 

deer, may also be increased by recently warmer temperatures and milder 
winters in the north-central United States and southern Canada. The 

parasite, which overwinters as larvae in snails and is accidentally eaten 

with plants, causes neurological disease in moose. Moose are already 

heat stressed by climate change (Lenarz and others, 2009) and may be 

more susceptible to parasitic and infectious diseases (Murray and others, 

2009), including the brain worm of white-tailed deer (fig. 5).

Changes in precipitation patterns also have a significant potential 

to affect patterns of wildlife disease through survival of disease agents 

or vectors and through effects on host parasite relationships. In the 

example of the brain worm of deer, increased precipitation also may 

result in increased survival of the snail populations, resulting in more 

exposure of deer to infected snails.

Figure 5. Healthy North American bull moose (U.S. Fish and Wildlife 

Service). Diseased North American cow moose in the final stages of a 

brain worm infection in St. Louis County, Minn. (Mike Schrage, Wildlife 

Biologist, Fond du Lac Band).

Community and Ecosystem Changes

Determining the effects of climate change on communities and 

ecosystems is difficult because the effects are likely to be highly variable, and this may be especially true for marine ecosystems. Since the 

1980s, coral reefs in the Western Atlantic have suffered massive declines 

due to disease (Porter and others, 2001). It is likely that coral mortalities 

were initially due to widespread mortality of sea urchins, which allowed 

algal overgrowth of reefs, followed by environmental degradation and 

increased coral susceptibility to disease (Lessios, 1988). Since the early 

1980s, mass “coral bleaching” has been observed worldwide, especially 

following the major 1998 El Niño event, and it has been linked to higher 

sea-surface temperatures (Hoegh-Guldberg, 1999) and to rising carbon 

dioxide levels that increase acidification of the oceans, which further 

weakens the coral structure (Kleypas and Yates, 2009). Corals are able 

to survive in nutrient-deficient waters because corals and the photosynthetic algae that live on them support each other. Corals that have lost 

these algae due to increased water temperature, changes in salinity or 

pollution may be susceptible to disease, leaving white coral skeletons, 

referred to as “coral bleaching” (fig. 6). Elevated temperatures will 

likely increase coral bleaching, which can lead to coral die-offs (Baker 

and others, 2008). Corals that fail to recover sufficiently may lead to 

loss of coral reefs and associated tropical marine life that depend on 

them for food and shelter. Coral bleaching has already been associated 

with significant declines in the diversity and population size of reef fish 

(Jones and others, 2004; Wilson and others, 2006). Coral bleaching and 

declines in the physical integrity of reef systems also are anticipated 

to lead to further reductions in the complexity of coral reef ecosystems 

(Pratchett and others, 2008). As a result, local economies that depend on 

coral reefs for sustenance or tourism could be significantly affected by 

climate change (Pandolfi and others, 2005). 

Figure 6. Extensive coral bleaching on a reef, St. John, U.S. Virgin 

Islands (Caroline S. Rogers, U.S. Geological Survey).

Questions to Ponder about Climate Change

Because of the uncertainty associated with the effects of 

climate change on the health of wildlife, domestic animals, and 

humans, we recommend four areas of study.

1. Long-term interdisciplinary projects can help determine 

climatic effects on biological factors associated with disease 

emergence, including species abundance, animal interactions 

and movements, vector populations). How might various 

physical, social, and economic factors contribute to disease 

emergence, persistence, and spread?

2. How are threatened and endangered free-ranging wildlife 

populations currently threatened by disease? How might 

climate change affect the current situation? 

3. How will climate change play a role in the threat of wildlifeassociated water- or vector-borne diseases for free-ranging 

wildlife, other animals, and humans? 

4. How will climate change play a role in the lives of native 

peoples who are dependent upon wildlife as a major source of 

food? Will wildlife population declines or wildlife-associated 

food-borne diseases threaten native peoples?

Habitat Alteration 

Climate change has caused dramatic changes in several macro- and 

microhabitats on Earth. While wildlife species are likely to be adaptable, 

within their physiological limits, in dealing with direct impacts of climate change on temperature and precipitation, their ability to respond to 

major physical changes in their environment, short of migration, is more 

limited. Along the Antarctic Peninsula, populations of Adelie Penguins 

are declining, because coastal ice no longer persists through the winter 

in many locations. In Antarctica, the Adelie Penguin is commonly a 

coastal bird found in areas where sea ice persists throughout the winter, 

because it relies on sea ice for access to feeding areas where upwelling 

ocean currents contain many krill and fish.

Climate change is also having a detrimental effect on microhabitats. Amphibian and reptilian populations have declined in the lowland 
forests in Costa Rica in part through the effect of climate change on the 

humid leaf litter microhabitat of the forest floor (Whitfield and others, 

2007). Weather conditions also significantly affect the microclimates for 

nests and burrows. For example, in sea turtles, elevated temperatures 

may lead to altered sex ratios or loss of nesting beaches secondary to sea 

level rises. Temperatures outside the range of those that turtles can tolerate result in the death of the developing sea turtle embryos (Morreale 

and others, 1982). 

References

Baker, A.C.; Glynn, P.W.; and Riegl, B., 2008, Climate change and coral reef 

bleaching: An ecological assessment of long-term impacts, recovery trends 

and future outlook: Estuarine, Coastal and Shelf Science, v. 80, p. 435–471.

Brinckerhoff, R.J.; Folsom-O’Keefe, C.M.; Tsao, K.; and Diuk-Wasser, M.A., 

2011, Do birds affect Lyme disease risk? Range expansion of the vector-borne 

pathogen Borrelia burgdorferi: Frontiers in Ecology Environment, v. 9, no. 2, 

p. 103–110.

Friend, M., 2006, Disease emergence and resurgence: The wildlife-human connection: U.S. Geological Survey, Circular 1285, p. 400.

Gatewood, A.G.; Liebman, K.A.; Vourc’h, G.; Bunikis, J.; Hamer, S.A.; Cortinas, 

R.; Melton, F.; Cislo, P.; Kitron, U.; Tsao, J.; Barbour, A.G.; Fish, D.; and 

Diuk-Wasser, M.A., 2009, Climate and tick seasonality are predictors of Borrelia burgdorferi genotype distribution: Applied and Environmental Microbiology, v. 75, no. 8, p. 2476–2483.

Hasle, G.; Bjune, G.; Edvardsen, E.; Jakobsen, C.; Linnehol, B.; Røer, J.E.; Mehl, 

R.; Røed, K.H.; Pedersen, J.; and Leinaas, H.P., 2009, Transport of ticks by 

migratory passerine birds to Norway: Journal of Parasitology v. 95, no. 6, 

p. 1342–1351.

Hoegh-Guldberg, O., 1999, Climate change, coral bleaching and the future of the 

world’s coral reefs: Marine and Freshwater Research, v. 50, p. 839–866.

Intergovernmental Panel on Climate Change, 2007, Climate change 2007: Synthesis report: contribution of working groups I, II, and III to the fourth assessment report of the Intergovernmental Panel on Climate Change: Geneva, 

Switzerland, Intergovernmental Panel on Climate Change, 104 p.

Jonzén, N.; Lindén, A.; Ergon, T.; Knudsen, E.; Vik, J.O.; Rubolini, D.; Piacentini, D.; Brinch, C.; Spina, F.; Karlsson, L.; Stervander, M.; Andersson, A.; 

Waldenstrӧm, J.; Lehikoinen, A.; Edvardsen, E.; Solvang, R.; and Stenseth, 

N.C., 2006, Rapid advance of spring arrival dates in long-distance migratory 

birds: Science, v. 312, p. 1959–1961.

Jones, G.P.; McCormick, M.I.; Srinivasan, M.; and Eagle, J.V., 2004, Coral 

decline threatens fish biodiversity in marine reserves: Proceedings of the 

National Academy of Sciences, v. 101, no. 21, p. 8251–8253.

Kleypas, J.A.; and Yate, K.K., 2009, Coral reefs and ocean acidification: Oceanography, v. 22, no. 4, p. 108–117.

Kutz, S.J.; Hoberg, E.P.; Polley, L.; and Jenkins, E.J., 2005, Global warming is 

changing the dynamics of Arctic host-parasite systems: Proceedings of the 

Royal Society B, v. 272, no. 1581, p. 2571–2576.

Lehikoinen, E.; Sparks , T.H.; and Zalakevicius, M., 2004, Arrival dates and 

departure times: Advances in Ecological Research, v. 35, p. 1–28.

Lenarz, M.S.; Nelson, M.E.; Schrage, M.W.; and Edwards, A.J., 2009, Temperature mediated moose survival in northeastern Minnesota: Journal of Wildlife 

Management, v. 73, no. 4, p. 503–510.

Lessios, H.A., 1988, Mass mortality of Diadema antillarum in the Caribbean: 

What have we learned?: Annual Review of Ecology and Systematics, v. 19, 

p. 371–393.

Lindgren, E.; Tälleklint, L.; and Polfeldt, T., 2000, Impact of climatic change on 

the northern latitude limit and population density of the disease-transmitting 

European tick Ixodes ricinus: Environmental Health Perspectives, v. 108, 

no. 2, p. 119–123.

Morreale, S.J.; Ruiz, G.J.; and others, 1982, Temperature-dependent sex determination—Current practices threaten conservation of sea turtles: Science, v. 216, 

no. 4551, p. 1245–1247.

Murray, D.L.; Cox, E.W.; Ballard, W.B.; Whitlaw, H.A.; Lenarz, M.S.; Custer, 

T.W.; Barnett, T.; and Fuller, T.K., 2009, Pathogens, nutritional deficiency, and 

climate influences on a declining moose population: Wildlife Monographs, 

v. 166, p. 1–30.

Ogden, N.H.; Bigras-Poulin, M.; and O’Callaghan, C.J., 2005, A dynamic 

population model to investigate effects of climate on geographic range and 

seasonality of the tick Ixodes scapularis: International Journal for Parasitology, v. 35, no. 4, p. 375–389.

Ogden, N.H.; Trudel, L.; Artsob, H.; Barker, I.K.; Beauchamp, G.; Charron, 

D.F.; Drebot, M.A.; Galloway, T.D.; O’Handley, R.; Thompson, R.A.; and 

Lindsay, L.R. , 2006, Ixodes scapularis ticks collected by passive surveillance in Canada: Analysis of geographic distribution and infection with Lyme 

Borreliosis agent Borrelia burgdorferi: Journal of Medical Entomology, v. 43, 

no. 3, p. 600–609. 

Ogden, N.H.; Lindsay, L.R.; Hanincová, K.; Barker, I.K.; Bigras-Poulin, M.; 

Charron, D.F.; Heagy, A.; Francis, C.M.; O’Callaghan, C.J.; Schwartz, I.; and 

Thompson, R.A., 2008, Role of migratory birds in introduction and range 

expansion of Ixodes scapularis ticks and of Borrelia burgdorferi and Anaplasma phagocytophilum in Canada: Applied and Environmental Microbiology v. 74, no. 6, p. 1780–1790.

Ogden, N.H.; Lindsay, L.R.; Morshed, M.; Sockett, P.N.; and Artsob, H., 2009, 

The emergence of Lyme disease in Canada: Canadian Medical Association 

Journal, v. 180, no. 12, p. 1221–1224.

 Ogden, N. H.; Bouchard, C.; Kurtenbach, K.; Margos, G.; Lindsay, L.R.; Trudel, 

L.; Nguon, S.; and Milord, F., 2010, Active and passive surveillance and 

phylogenetic analysis of Borrelia burgdorferi elucidate the process of Lyme 

disease risk emergence in Canada: Environmental Health Perspectives, v. 118, 

p. 909–914.

Pandolfi, J.M.; Jackson, B.C.; Baron, N.; Bradbury, R.H.; Guzman, H.M.; 

Hughes, T.P.; Kappel, C.V.; Micheli, F.; Ogden, J.C.; Possingham, H.P.; and 

Sala, E., 2005, Are U.S. coral reefs on the slippery slope to slime?: Science, 

v. 307, p. 1725–1726.

Porter, J.; Dustan, P.; Jaap, W.; Patterson, K.; Kosmynin, V.; Meier, O.; Patterson, 

M.; and Parsons, M., 2001, Patterns of spread of coral disease in the Florida 

keys: Hydrobiologia, v. 460, p. 1–24.

Pratchett , M.S.; Munday, P.L.; Wilson, S.K.; Graham, N.A.J.; Cinner, A.J.; 

Bellwood, D.R.; Jones, G.P.; Polunin, N.V.C.; and McClanahan, T.R., 2008, 

Effects of climate-induced coral bleaching on coral-reef fishes—Ecological and economic consequences: Oceanography and marine biology, v. 46, 

p. 251–296.

Randolph, S.E., 2009, Tick-borne disease systems emerge from the shadows: The 

beauty lies in molecular detail, the message in epidemiology: Parasitology, 

v. 136, no. 12, p. 1403–1413.

Saino, N.; Ambrosini, R.; Rubolini, D.; von Hardenberg, J.; Provenzale, A.; Hüppop, K.; Hüppop, O.; Lehikoinen, A.; Lehikoinen, E.; Rainio, K.; Roman, M.; 

and Sokolov, L., 2011, Climate warming, ecological mismatch at arrival and 

population decline in migratory birds: Proceedings of the Royal Society B, 

v. 278, p. 835–842.

Tälleklint, L.; and Jaenson, T.G.E., 1998, Increasing geographical distribution 

and density of Ixodes ricinus (Acari: Ixodidae) in central and northern Sweden: Journal of Medical Entomology, v. 35, no. 4, p. 521–526.

Thorup, K.; Tøttrup, A.P.; and Rahbek, C., 2007, Patterns of phenological 

changes in migratory birds: Oecologia, v. 151, no. 4, pp. 697–703.

Van Riper, C., III; Van Riper, S.G.; Goff, M.L.; and Laird, M., 1986, The 

epizootiology and ecological significance of malaria in Hawaiian land birds: 

Ecological Monographs, v. 56, no. 4, p. 327–344.

Walther, G.R.; Post, E.; Convey, P.; Menzel, A.; Parmesan, C.; Beebee, T.J.C.; 

Fromentin, J.M.; Hoegh-Guldberg, O.; and Bairlein, F., 2002, Ecological 

responses to recent climate change: Nature, v. 416, no. 6879, p. 389–395.

Whitfield, S.M.; Bell, K.E.; Philippi, T.; Sasa, M.; Bolanos, F.; Chaves, G.; Savage, J.M.; and Donnelly, M.A., 2007, Amphibian and reptile declines over 

35 years at La Selva, Costa Rica: Proceedings of the National Academy of 

Sciences, v. 104, no. 20, p. 8352–8356. 

Wilson, S.K.; Graham, N.A.J.; Pratchett, M.S.; Jones, J.P.; and Polunin, N.V.C., 

2006, Multiple disturbances and the global degradation of coral reefs: are reef 

fishes at risk or resilient?: Global Change Biology, v. 12, p. 2220–2234.

By Erik Hofmeister, Gail Moede Rogall, Kathy Wesenberg, Rachel Abbott, 

Thierry Work, Krysten Schuler, Jonathan Sleeman, and James Winton.

For additional information contact:

Director

USGS National Wildlife Health Center

6006 Schroeder Rd.,

Madison, WI 53711

http://www.nwhc.usgs.gov/

Banner photo credits (from left to right): Caroline S. Rogers (USGS), 

Carter Atkinson (USGS), Lawrence Igl (USGS), U.S. Fish and Wildlife Service, 

and Craig Ely (USGS).