An elephant feeds as it starts to rain in Hwange National Park in Hwange, northern Zimbabwe on December 16, 2023. (Photo by ZINYANGE AUNTONY/AFP via Getty Images)
The dung of African savanna elephants decomposes into the soil increasing carbon capture; grazing by wildebeest reduces the risk of fires; while birds, bats and insects pollinate, disperse seeds and provide pest control.
These are just a few examples of the climate-related services that migratory species provide, but a major new report has warned that climate change is already having “catastrophic impacts” on many of these species and on their ability to provide ecosystem services to humanity.
The report of the Convention on the Conservation of Migratory Species of Wild Animals, a United Nations biodiversity treaty, said that the direct effects of climate change on many migratory species are already being seen, including poleward range shifts, changes in the timing of migration and reduced breeding success and survival.
“These negative impacts limit the capacity of migratory species to provide ecosystem services that benefit humanity.”
Some key findings
Rising temperatures, for example, are causing changes in the reproduction and survival of krill, small shrimp-looking fish, and harm marine mammals and seabirds that rely on krill as a key food source.
There is strong evidence, too, that climate change is affecting the distribution and timing of migration of migratory species, the report found. Temperature increases are driving poleward range shifts and earlier migration and breeding and in some species, such as wading birds, there is a risk that this will cause a mismatch between the timing of breeding and the time when prey species are most abundant.
It noted how changes in water availability are causing the loss of wetlands and reduced river flows, which are likely to affect the migration of fish and waterbirds particularly. Extreme climate-related events such as landslides are causing severe habitat destruction “and have already been observed at some seabird breeding sites”.
The report finds, too, that there is strong evidence that migratory seabirds and marine mammals will be affected by the changes in oceanic currents, which are likely to alter the nature and functioning of many marine and terrestrial ecosystems.
Vital to ecosystems
Migratory species face a variety of threats from climate change, including loss of suitable habitat, increased frequency of extreme weather events and wide-scale changes in ecosystem functioning.
“Many of the world’s most iconic species migrate as part of their life-cycles: whales, dolphins and marine turtles; elephants, large carnivores and antelopes; and a whole range of birds,” the report said. “Migration is key to the survival of these species; they are finely adapted to specific habitats that change with the seasons. It has been known for some time that climate change has the potential to adversely impact migratory species.”
They are integral to the ecosystems they live in and support vital ecosystem services that both mitigate the impacts of climate change and increase resilience to climatic hazards.
“Migratory species are important for ecosystem function and climate change mitigation, especially when they form a significant part of an ecosystem or aggregate in large numbers at particular times of the year.”
Many migratory species are related to the movement and dispersal of seeds and nutrients. “Large migratory species can contribute to climate change mitigation through the decomposition of their faeces, which locks carbon into the soil or seabed, as well as through more complex processes, such as maintaining trophic webs that protect forest or seagrass beds that are important for carbon sequestration.”
Migratory species can also contribute towards climate adaptation by enhancing ecosystem resilience. For example, seabird guano increases the nutrients available for coral reef growth, which, in turn, reduces coastal erosion.
‘Nature knows no borders’
The conservation of migratory species is “an important part of the answer to both the biodiversity crisis and to the climate change crisis”, the report said. There is an urgent need to identify migratory species that are vulnerable to climate change, and to “act now” to help vulnerable migratory species adapt to a changing climate.
“Comprehensive and well-connected protected area networks, that conserve and restore ecosystems, will support species in moving to new locations in response to climate change.”
More direct human interventions, such as translocating individuals to new areas, may be required for some species and importantly, robust monitoring is needed to understand the success of any interventions and to inform future actions.
Nature knows no borders. “The recovery of migratory species is dependent on collective action across migratory routes. Countries working together to protect and restore shared ecosystems can enable the recovery of migratory species, while gaining benefits from nature-based solutions for climate change mitigation and adaptation.” Cooperation and sharing of information between countries is “crucial for maximising the success of any actions”.
The report was commissioned by the government of the United Kingdom of Great Britain and Northern Ireland through the Joint Nature Conservation Committee and was prepared by the British Trust for Ornithology.
Sidebar: Climate impacts on some migratory species
Reptiles: Marine turtles and saltwater crocodiles are particularly threatened by the loss of nesting habitat because of sea level rise and increasing storm frequency and intensity, the report said. Coastal development on alternative beaches, particularly at the poleward edges of their shifting ranges, is a key threat to their ability to adapt to sea level rises and temperature increases.
“The human response to storm surges and sea level rise will also determine whether beach profiles shift inland naturally, likely maintaining suitable nesting habitat, or are lost. Temperature increases have had a significant impact on turtle and crocodile sex ratios, although currently this is likely to be beneficial to population trends,” noted the report.
Bony fish: Most migratory fish species have undergone extreme population declines over the past 50 years. The main drivers are habitat loss, disruption of migration through damming, and overfishing, but climate change is “increasingly becoming a major threat”. Its impacts on migratory fish are complex and under-researched but are likely to be detrimental to most species. Increasing temperatures, reduced river flow and, in some areas, reduced rainfall will lead to spawning habitat loss and may also impact survival rates and lead to extinctions.
Sharks and rays: Since 1970, the global abundance of oceanic sharks and rays has declined by 71%, largely because of overfishing, bycatch and coastal habitat loss, mainly from fishing activities such as trawling.
“The impacts of climate change on sharks and rays are complex, due to various physiological, behavioural and ecological changes. For most species, research on the impacts of climate change is scarce, but in general, sharks and rays are thought to be vulnerable to climate change due to low reproduction rates.”
Species dependent on coastal and inshore nursery habitats or coral reef habitats are likely to be at the highest risk from climate change. Increases in sea surface temperatures are changing food availability, and also metabolic rates. Increased ocean acidification reduces the growth of zooplankton, on which some species feed, and reduces olfactory function in sharks and rays, reducing their ability to hunt.”
Seabirds: Most are long-lived, breed colonially and spend long periods away from land. Increases in sea surface temperature generally cause reductions in food availability, which are having widespread negative effects on survival, breeding success and population abundance.
“Linked to this, reductions in sea ice extent are reducing the area of suitable habitat for polar-dwelling species, and these may be replaced by more temperate species. The breeding habitat of those [using] low-lying coastal areas is threatened by both sea level rise and a predicted increase in the frequency and severity of storms. There are already observed changes in species distribution, the timing of breeding … and, possibly, migration routes.”
Terrestrial mammals: They cover a diverse group of species, including primates, bears, elephants, carnivores and ungulates. “Migration is generally seasonally-driven by food availability, often linked to rainfall patterns. Declines in rainfall across some areas, for example over much of the Sahel region and northern Africa, will lower primary productivity.”
This reduces food availability for herbivores, also reducing the food available for carnivores, “indicating the interlinked nature” of climate-induced changes. Population trends vary between species and regions, but declines are most common, and for many species habitat loss due to human activities is the biggest threat, which “may be compounded by human responses to climate warming”.