Warming’s mixed effects on migratory animals

Global warming brent geese

Milder weather means breeding conditions have improved for Brent geese, but that nesting mothers are more likely to die. Image: Ricky Bamford via Flickr

New studies on beluga whales and Brent geese reveal that they respond to global warming in conflicting ways, making species survival hard to predict.

LONDON, 13 January, 2017 Beluga whales are responding to climate change in a rapidly warming Arctic – but only some of them. And migratory geese ought to be flourishing with milder conditions at nesting grounds in the far north – but the mother geese are at greater risk.

Both studies leave biologists guessing a bit at the response of their animal subjects to climate change. But the evidence shows that even the animals themselves may have to take a guess.

Warming Arctic

US scientists report in Global Change Biology that one population of beluga whales is taking advantage of the longer summers in the far north, while another is keeping to a calendar that pre-dates climate change.

Beluga whales, those ghostly white hunters of the northern seas, tend to winter in the Bering Sea between two continents, and then swim north as the ice melts and the Arctic seas open up.

The two populations of whales are genetically distinct – they have different ancestries – and travel as family groups, the young learning from their mothers.

Those that feed on fish and molluscs in the Beaufort Sea north of Alaska and Canada tend to leave the summer feeding grounds in autumn with the first risk of freezing. Those that hunt in the Chukchi Sea to the north and east of Alaska are delaying their response to take advantage of the longer spells of open water.

Summer sea ice has been in retreat for the last 30 years, and last autumn was an astonishing 20°C above average.

So biologists are confronted with a big question: is one population guarding against being caught by a sudden build-up of Arctic ice, while the other is consciously taking a risk but benefiting from a longer spell in richer feeding grounds?

The biggest take-home message is that belugas can respond relatively quickly to their changing environment, yet we can’t expect a uniform response across all beluga populations,” says Donna Hauser, of the University of Washington’s polar science centre in the US, who led the research.

If were trying to understand how these species are going to respond to climate change, we should expect to see variability in the response across populations and across time. That may complicate our predictions for the future.”

The polar puzzle is nothing new for biologists: creatures that migrate to the Arctic have always experienced a mix of good and bad summers.

Research like this is important because
we have to understand how animal populations
will respond to the changing climate if we want
to make decisions about protecting biodiversity”

Some Arctic predators, such as the polar bear, which depends on sea ice for a living, are imperilled by the early thaw and the late freeze. Other predators and herbivores can shift to new territories, or gain from changing climate one year and lose the next.

But as ecosystems shift dramatically in response to global warming, the tally of winners and losers becomes harder to predict.

The light-bellied Brent geese that breed each summer in northeast Canada could become a textbook example, according to a new study in the Journal of Animal Ecology.

Climate change means that nesting mothers breed more successfully in longer, warmer summers. But the latest study suggests that the same high productivity is accompanied by a higher death rate among mothers. That could be because the birds nest on the ground, stay longer in better conditions and become more vulnerable to predators.

In a bad breeding season, mothers abandon nests or do not breed – but they do survive to try again another year.

Climate change

We tend to think of climate change as being all one way, but here we’ve got a population being affected in conflicting ways,” says Ian Cleasby, of the Centre for Ecology and Conservation at the University of Exeter in the UK.

This population is sensitive to changes in adult survival, so the increased breeding may not be enough to offset the loss of more adult females.

Research like this is important because we have to understand how animal populations will respond to the changing climate if we want to make decisions about protecting biodiversity.” Climate News Network

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