El Niño–Southern Oscillation is a large-scale, cyclical climate fluctuation in the Pacific Ocean. The warming phase of the sea surface temperature is known as El Niño and the cooling phase as La Niña, with neutral periods in between – and they can have dramatic effects on ocean ecosystem productivity.
Many mobile species which breed in temperate or higher latitudes migrate long-distance – even across the globe. This allows them to escape the extremes of seasonal climate variation. However, we don’t fully understand how they deal with and are affected by these longer, phased climate fluctuations. While El Niño and La Niña are a natural cycle, climate change is expected to intensify their effects. Researchers have now investigated how the Manx shearwater (Puffinus puffinus), a long-lived migratory species, responds to this kind of environmental change by collecting and analysing 13 years of data.
They discovered that in El Niño years, non-breeding birds were at more northerly latitudes than in La Niña years: a response attributable to individual flexibility in migratory destinations. In parallel with this latitudinal shift, birds foraged less in El Niño years.
They also found that in El Niño years, in their next breeding period – a hemisphere away – the birds foraged for less time and provided less for their chicks: and this was not because of conditions at their breeding grounds in the North Atlantic. Individuals may therefore adjust to fluctuating non-breeding conditions, but still experience cascading effects on later behaviour. Lead author Dr Katrina Siddiqi-Davies said:
“On an individual level, animals can adjust their migratory behaviour between years and are not completely fixed in their strategy. It gives me hope that individuals can adapt to climate change, but there are still consequences as they are likely in worse physical condition and not raising their young as effectively. For me, the results highlight the importance of investigating the entire annual cycle.”
Understanding how migratory animals might respond to climate change is a key challenge – one which is becoming more feasible to investigate as datasets accumulate years and become increasingly long term. Geolocation data for individual animals allows researchers to look at the whole annual cycle and get a fuller picture of what is going on for individuals over several years. Katrina added:
“The data we have now allows us to ask interesting questions about how an animal might respond to their environment when it changes, and how this affects them across their annual cycle. This is particularly interesting in a long distant migrant like the Manx shearwater, which experiences a completely different set of weather conditions in the breeding and non-breeding grounds – which are hemispheres apart.”
The researchers plan to continue to work on shearwater movement, understanding more fundamental parts of their life history, and how they might be affected by human modifications to the offshore environment such as offshore wind farms.
To read more about this research, published in Proceedings of the Royal Society B Biological Sciences, visit: https://doi.org/10.1098/rspb.2024.1944
