Bird deaths and climate link questioned

Fresh analysis has called into question the conclusions of a 2018 study that linked climate change with increasing predation on birds in the Arctic.

The initial study, led by ecologist Vojtech Kubelka of Charles University in Prague, Czech Republic, and published in the journal Science, found that nest predation among shorebird populations in the high northern latitudes had increased substantially over the past 70 years.

“In shorebirds, at least, predation rates on nests are now higher in the Arctic than in the tropics,” the researchers wrote.

They concluded that “This increased nest predation is consistent with climate-induced shifts in predator-prey relationships.”

However, a new analysis used by Kubelka’s team has reached different conclusions, dismissing the initial results as an “artefact” of data-gathering methods. {%recommended 6587%}

Also published in Science, the work is written by a large cohort researchers led by Martin Bulla of the Max Planck Institute for Ornithology in Germany.

The researchers question several aspects of the approaches used in the original paper, including the way predation rates were correlated with geographical areas and time periods.

They also strongly challenge the way in which Kubelka and colleagues drew conclusions about nests in the various bird populations they included. 

Predation rates were calculated by dividing the number of days nests were observed by the number of times predation occurred. However, Bulla and colleagues note that “59% of the 237 populations they used lacked information on exposure” and rates thus had to be estimated using other methods.

Similarly, assumptions about what point in the breeding cycles nests were first observed are also challenged. The method used to estimate how long eggs had been incubated, they point out, “remains subjective”.

Finally, research and observation methods used in tracking shorebird populations have improved substantially since the 1950s, when the first figures were gathered, leading to a possible trend distortion due to better data.

“Given these issues, the main result – the apparent increase in daily nest predation rate over time, especially in the Arctic – may simply be an artefact,” Bulla and colleagues write.

The fresh analysis, they continue, “lead us to conclude that there is no robust evidence for a global disruption of nest predation rates due to climate change”.