Little Tern (Sternula albifrons): vulnerability to climate change
Evidence for exposure
Potential changes in breeding habitat suitability:
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Current breeding area that is likely to become less suitable (3% of current range)
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Current breeding area that is likely to remain suitable (37%)
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Current breeding area that is likely to become more suitable (59%)
Current impacts to Little Terns attributed to climate change:
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Neutral Impact: Little terns are migrating and arriving at breeding sites earlier
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Negative Impact: Changes in prey availability have resulted in lower breeding success
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Negative Impact: Little tern nests are frequently washed away by tidal surges, such events are becoming more frequent or extensive due to rising sea levels
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Negative Impact: Higher sea temperatures correlate with lower breeding success. Mechanism unknown, but likely mediated through prey availability
Predicted changes in key prey species:
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Key prey species are likely to decline in abundance in southern Portugal, along the southern coast of England, the coasts of Belgium and the Netherlands and around North Denmark.
Sensitivity
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Little terns have a varied diet, but many colonies rely on one or a few prey species. Sensitivity to changes in prey is likely to vary across its range.
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Coastal populations breed commonly on flat beaches, which are prone to flooding due to storms, tidal surges or sea level rise. A rise in extreme weather events would likely impact breeding success of little terns.
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Little terns are primarily surface feeders and have a limited foraging range during the breeding season. This increases their sensitivity to changes in prey availability, and they would likely be heavily impacted if climate change results in prolonged stormy weather, or extended heatwaves drive prey species into deeper water.
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Little terns face high levels of predation threat, notably in the in Baltic, and several of their key predators (e.g. minks and foxes) are becoming more abundant and spreading, in part due to climate change. So far this has not heavily impacted little tern populations, but continued climate change may result in declines due to predation.
Adaptive capacity
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Little terns in some areas have flexible laying dates, so although climate change has changed their migration patterns their laying date is set more by local weather and conditions, maximising breeding success.
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Little terns often display low site fidelity and will change breeding site from year to year, especially in response to disturbance. This is likely to be adaptive in terms of climate change, as it seems highly likely little terns will redistribute to more suitable areas if available.
