Many birds species all over the world are highly sensitive to the effects of climate change. Scientists have found declines of up to 90 percent in some bird populations, as well as total and unprecedented reproductive failure in others, althought the role of any change in climate is typically not determined. Population declines generally have several associative causal factors including habitat loss, habitat fragmentation and pollution.
Specific groups that are at high risk from climate change include migratory birds, mountain birds, island birds, wetland birds, Arctic birds, Antarctic birds and seabirds. Bird species that can move easily to new habitat are expected to continue to do well; however, bird species that thrive only in a narrow environmental range can be expected to decline, and to be outcompeted by invasive species.
With a 0.8°C average of global warming having occurred in the past century, it seems that the world is in the early stages of human-caused climate change. Bird species are already demonstrating the effects of some of these changes in regions ranging from the poles to the tropics. More specifically, these changes can be tracked from the level of individual species all the way up through entire communities. This evidence shows that climate change is already impacting biodiversity. There is a general scientific consensus that climate change has already had a profound effect on biodiversity and will continue to be a primary driver in the loss of biodiversity. Significant impacts that are already occurring include changes in the distribution of species, population sizes, timing of migration or reproduction, and a greater occurrence of pests or infectious diseases. One of the most crucial factors determining the magnitude of these changes is the rate of climate warming because a faster rate of warming equates with the adaptation capacity rapidly declining. This data suggests that there will soon be an accelerated decline in biodiversity. Currently, there are 9,787 known living species of birds, 21 percent of which are currently prone to extinction due to a wide variety of threats. Habitat destruction and fragmentation are currently the greatest threats; however, it seems that if climate change continues unchecked, it will cause greater rates of extinction than habitat loss and fragmentation. Ultimately, climate change is surfacing as perhaps the greatest long-term risk to biodiversity in many, if not most, of the world’s regions in future decades.
How climate change affects birds
Similar to most plants and other animals, the distribution of birds is often limited by climate factors. Climate, in fact, is perhaps the greatest factor in determining birds’ ranges and abundance. Climate factors vary for different species of birds; for example, at high latitude, temperature is the greatest climatic influence for many species. At low-latitude regions, which generally have consistently warmer temperatures, variables related to the surrounding bodies of water seem to have the most influence. Regardless of the regions where different species are located, all species of birds appear to be very sensitive to changes in climate, and evidence seems to indicate that this sensitivity makes them primary indicators of global climate change.
For birds, a change in temperature can be one of the most threatening climate factors. Birds’ responses to temperature changes will, of course, vary from species to species, but their ability to adapt largely depends on how strongly their metabolisms react to new temperature levels. Climate change, however, will affect temperatures in regions around the world differently. Regions closer to the poles will undergo more drastic changes in temperature, with the Arctic warming almost twice the global average rate over the past three decades. Because of this, habitat loss is expected to be most severe towards the poles. Where local and regional climates tend to warm, bird species are expected to shift their distributions either towards the poles or upward in elevation in order to help maintain their optimal temperatures.
Another factor of climate that greatly impacts bird species is precipitation. Fluctuating precipitation levels are also expected to greatly influence the behavior of birds, especially the behavior of migratory bird species. Precipitation fluctuations are expected to affect species’ decisions to depart for migration by the effects on food availability. Drought in critical stopover areas along the migration routes of species also affects migratory birds’ ability to refuel on water and prey before crossing critical barriers. As a result of unpredictable precipitation fluctuations, many migratory species could see a decline in population in the coming years.
Frequency and severity of storms
Global warming is also suspected to cause greater weather extremes, which can effect the survival of both the young and adult birds in a species. Because some species of birds are pushed to their limits during migration, an increased frequency of storms may reduce some birds’ abilities to reach their breeding grounds on time, if at all.
Indirect effects of climate change
In addition to the direct effects of climate change, several predictions about the indirect effects of climate change have been made. It is expected that birds’ habitats will be altered through changes in sea level, fire, vegetation, and human land use. Coastal habitat may be altered or completely eroded away as sea levels rise and wave activity continues to increase. It is also likely that increased drought will raise habitat susceptibility to fire. Fire and additional effects of climate change are expected to cause major vegetation shifts, further reducing bird habitat. Climate change could also potentially affect land use by humans, which could result in encroachment upon previously unaffected habitat. As these direct and indirect effects accumulate, a shift in communities is likely to occur as more species push pole-ward, which may also increase competition with invasive species or cause complete displacement.
Effects on ecological synchrony
One of the greatest effects on ecological synchrony caused by climate change is that birds’ seasonal responses are shifting. As weather patterns continue to shift and global temperatures change, a shift in seasonal weather may push birds out of sync with the ecosystems and the communities of which they are a part. If birds are unable to adapt to changes in the surrounding ecosystem, it may be detrimental for the species.
There is also strong evidence that climate change is causing birds to lay their eggs earlier. This may potentially have several implications for the reproductive success and the survival rate for a species
The timing of migration is also being significantly impacted by climate change. The spring migration of birds is generally considered to be more important than autumn migration because spring migration determines their arrival timing at breeding grounds, which is crucial for mating and territory choice. The number of successful spring migrants also directly affects the breeding population size. In general, research is indicating that birds are migrating earlier in the spring in conjunction with the warming climate trends. In some regions, however, it is becoming apparent that climate change is causing individuals of some species to fail to migrate all together.
Climate change is seemingly causing a general mismatch between behavior and environment as many bird species’ migratory and reproductive behavior continues to shift along with climate change. There is concern among the scientific community that some bird species may not be able to alter their behavior enough to match the availability of important food sources. A timing mismatch between predator and prey could also cause a significant decline in species for both predator and prey. Because of the delicate complexity of food webs, it is likely that more and more problems among species will arise as climate changes worsen.
Although migratory species, in general, seem to be in danger as a result of climate change, it seems to be the long-distance migratory species that are in the most danger. Long-distance migratory bird species do not seem to be responding to climate change as readily as short-distance migratory bird species. Because long-distance migratory species seem to determine migration times by an internal clock, they are more likely to suffer from a mismatch with their ecosystems than short-distance migratory species are. It is argued that this has resulted because past selection pressure could have promoted a very stable timing of migration as a result of the severe reproductive consequences of arriving either too early or too late at spring breeding grounds. Genetically speaking, this means that long-distance migrants could lack the ability to change the timing of migration.
Shifting ranges and disrupting communities
In general, when the climate changes, it may force a shift in distributions for both plants and animals. When the climate boundaries change significantly enough, bird distributions are expected to shift. As mentioned before, if local and regional climates follow global trends in warming, bird species are expected to shift either upward in elevation or pole-ward to track their optimum temperatures.
When the species that make up a community respond to climate changes, they do so by shifting their ranges. Entire communities, however, do not shift intact, but rather the rate and distance at which each species shifts depends on their sensitivity to climate change, as well as their mobility, lifespan, and the availability of food sources. Consequently, the makeup of communities will change as different species shift into new areas. These disrupted ecological communities may mean that birds may also face new competitors, predators, prey, and parasites to which they are not adapted. Range shifts also make it likely that many “optimal” habitats for species will disappear, but as old habitats disappear and as new habitats emerge, the consequences of these changes are largely unknown and greatly unpredictable.
Another threat to distribution shifts is that of human barriers to migration. Human development is increasingly fragmenting birds’ habitats. Consequently, climatically-induced migrations will be obstructed by highways, farms, cities, and other human barriers in addition to the natural barriers that are already in place, such as mountain ranges or large bodies of water. Human-caused fragmentation can also make possible the introduction of invasive species into other species’ native habitat regions.
These distributional shifts are of great concern to bird conservation efforts, which in the past have mainly focused on areas with high numbers of endemic and threatened species, which are often located within protected areas. As the climate continues to change, many bird species will begin shifting their distribution patterns, possibly out of protected areas and into areas with human development or conflicting land use. Eventually, climate change is expected to cause significant contractions in range-size for many birds species as climatically suitable areas shrink or disappear all together. All of these aforementioned factors are feared to be detrimental inhibitors to conservation efforts.
Effects on population characteristics
Population dynamics are affected because local weather and regional climate patterns have a strong influence on the behavior of birds in both breeding and non-breeding seasons. Since the size of a bird population depends on both the survival through the breeding and non-breeding seasons and on breeding success, the ultimate impact of climate change will include the success rates for both of these factors. So far, research indicates that for birds whose offspring are highly dependent, known as altricial species, climate changes during the non-breeding seasons will have the most impact on the specie’s survival rate. For bird species with more independent young, known as a nidifugous species, and for birds that breed in arid environments, the effects of climate change during the breeding season is most important. An increased frequency of weather extremes will affect population characteristics by negatively impacting both adult birds and their young in the summers and winters. Overall, more extreme weather patterns can greatly reduce bird populations, and a population’s recovery can be very slow.
The possibility of extinction
Extinction is the most serious consequence of climate change for bird species as a whole. With further changes in climate likely, both globally and locally, it is likely that bird species that are even considered to have a safe conservation status currently could eventually be at risk. The key threat to climate change is the rate at which it is occurring, leaving little time for species to adapt. Species in northern latitudes will be forced to adapt even more quickly, as northern regions continue to warm at rates several times higher than those of the mid-latitudinal regions. When climate change is put into perspective, it becomes apparent that these scenarios are expected to produce even greater extinction rates than habitat loss, the current greatest threat to biodiversity. In terms of migratory species, there is concern that climate change will cause an increase in the distances between birds’ breeding and non-breeding grounds. When longer migratory distances are coupled with the continued loss of habitat, the results for migratory species could be catastrophic and eventually lead to the extinction of many species.
Ultimately, climate change is expected to interact with other human interferences such as habitat loss and fragmentation, which will cause a cascade of effects that will eventually eliminate entire species. Scientists are now beginning to use the term “extinction spasm” to describe the pending situation of climate change combined with habitat loss and destruction. When all these scenarios are considered together, these factors explain why bird species are responding more strongly than originally expected from the 0.8°C increase that has occurred during the past century. Unless efforts are made in the near future to reverse these trends, the biodiversity of the planet will receive a severe blow as bird species begin to disappear at alarming rates.
Image by Luc Viatour
References and Further Reading
- Arctic Climate Impact Assessment (ACIA). 2004. Impacts of Warming Arctic. Cambridge University Press, Cambridge, UK.
- Arnott, S.A. and Ruxton, G.D. 2002. Sandeel recruitment in the North Sea; demographic, climatic and trophic effects. Marine Ecological Progress Series 238:199.
- BirdLife International. 2004. State of the world’s birds 2004: indicators for our changing world.
- Both, C. and Visser, M.E. 2001. Adjustment to climate change is constrained by arrival date in a long-distance migrant bird. Nature 411:296.
- Both, C., Bouwhuis, S., Lessells, C.M. and Visser, M.E. 2006. Climate change and population declines in a long-distance migratory bird. Nature 441:81.
- British Trust for Ornithology (BTO). 2002. The Effect of Climate Change on Birds. Information page by David Leech.
- British Trust for Ornithology (BTO). 2005. Climate Change and Migratory Species (PDF).
- British Trust for Ornithology (BTO). 2005. Looking for lazy birds.
- Chamber, L.E. 2005. Migration dates at Eyre Bird Observatory: links with climate change? Climate Research 29(2):157.
- Coppack, T. and Both, C. 2002. Predicting life-cycle adaptation of migratory birds to global climate change. Ardea 90:369.
- Crick, H.Q.P. 2004. The impact of climate change on birds. Ibis 146(1):48.
- Davis, A.J., Jenkinson, L.S, Lawton, J.H., Shorrocks, B. and Wood, S. 1998. Making mistakes when predicting shifts in species range in response to global warming. Nature 391:783.
- Fraser, W.R. and Hofmann, E.E. 2003. A predator’s perspective on causal links between climate change, physical forcing and ecosystem response. Marine Ecology Progress Series 265:1.
- Gaston, A.J., Hipfner, J.M. and Campbell, D. 2002. Heat and mosquitoes cause breeding failures and adult mortality in an Arctic-nesting seabird. Ibis 144(2):185.
- Giles, J. 2006. US posts sensitive climate report for public comment. Nature 441:6.
- Gordo, O., Brotons, L., Ferrer, X. and Comas, P. 2005. Do changes in climate patterns in wintering areas affect the timing of the spring arrival of trans-Saharan migrant birds? Global Change Biology 11(1):12.
- Lanchbery, J. 2005. Ecosystem loss and its implications for greenhouse gas concentration stabilization. Presented at: Avoiding Dangerous Climate Change Conference, Exeter, UK, 1 February.
- Leemans, R. and Eickhout, B. 2004. Another reason for concern: Regional and global impacts on ecosystems for different levels of climate change. Global Environmental Change 14:219.
- World Wildlife Fund (WWF). Climate Change: The Problem.
This article was partially researched by a student at Texas Tech University participating in the Encyclopedia of Earth's (EoE) Student Science Communication Project. The project encourages students in undergraduate and graduate programs to write about timely scientific issues under close faculty guidance. All articles have been reviewed by internal EoE editors, and by independent experts on each topic.