Seabirds threatened by heat waves

Herring porpoises and other seabirds risk losing both eggs and young in prolonged heat waves.

In a study on Stora Karlsö, on some occasions over 47 degrees were measured in the sun.

– We saw several children who died in the heat, says Agnes Olin at SLU.

Seabirds often nest on rocks and beaches, without the cooling protection of, for example, trees. This also applies on Stora Karlsö outside Gotland, in the largest herring grizzly colony in the Baltic Sea.

The area was affected by heat waves at the end of June in both 2020 and 2022. According to a study from the Swedish University of Agriculture (SLU), it was on some occasions over 47 degrees hot in the direct sunlight on the rocks.

“Very sensitive”

It caused adult birds to seek refuge in the cooling sea – with dire consequences for chicks and eggs, which were left in the sun or risked being accidentally kicked off the rocks.

– Chicks and eggs are very sensitive if they are left alone in the sun, says Agnes Olin, who is a researcher at SLU.

– We didn’t think it would be that bad. But during the heat wave in 2020, we saw that just over a fifth of the breeding attempts that were underway then failed. So that’s a pretty significant part.

Bigger factor

The herring piglets on Stora Karlsö have otherwise had a positive development in recent decades, partly thanks to reduced threats from environmental toxins.

However, the extreme and prolonged heat waves are expected to increase in line with the ongoing climate changes. According to the researchers, this could have serious consequences for seabirds both in the Baltic Sea and elsewhere.

– A heat wave now and then is probably not a major problem for the population at large. But we know that the heat waves will come more often and be more intense, says Agnes Olin.

– So it will become a bigger and bigger factor and can absolutely affect the population going forward.

Facts

Guillemot

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