Global warming: Not as bad as we thought?

Global warming has gained a bad rap, as it is causing the polar ice caps to melt and sea levels to rise. It is disrupting the habitats of various species and bringing about longer, more intense heat waves, but there is some yang to its yin

Before I dive into this controversial conversation, I’d first like to bid thee farewell. A wonderful job opportunity is luring me to Namibia, so this will be my last SHEQ Sound Off – unfortunately.

It has been an amazing ride and I hope you’ve enjoyed reading this series. Thankfully, I have one last opportunity to dive into this beloved acronym – in true Sound Off style, of course …

With their noisy banter and untidy nests, crows can be inconvenient for people, but people are convenient for crows, a scientific study has found.

Across much of South Africa the pied crow benefits from modern infrastructure – in particular electricity pylons – and warming temperatures caused by climate change, according to a study by the Percy FitzPatrick Institute of African Ornithology, at the University of Cape Town.

Electricity pylons have provided useful nesting sites in South Africa’s steadily warming western scrubland where traditional tree nest sites are a scarce commodity – much to the crow’s satisfaction. The net result is an increase in the regional pied crow population, says the study originally published in the international journal: Diversity and Distributions.

“Pied crow numbers have increased in response to climate warming, with their spread facilitated by electrical infrastructure in south-western South Africa,” the study says.

Significantly, the study shows that it is the combined effect of climate change and electrical infrastructure that has fuelled the increase and not any single factor.

Findings were based on an analysis comparing two bird atlas surveys, conducted 20 years apart, which were then matched with geographic and climate data. The method produced some intriguing results:

• While there has been an increase in pied crow populations in the warmer south-west, there has been a decrease in the cooler north-east. There is a strong relationship between temperature warming in the period between the two surveys and crow population changes.

• By contrast, there is no relationship between changes to crow populations and current levels of urbanisation or power-line density. However, in the south-west, where numbers have increased, there is “a significant relationship between increases in pied crow reporting rates and the density of power lines”.

Susie Cunningham, co-lead author of the study, says results show how human infrastructure has allowed crows to track a “preferred climate bubble”, into the south-west, as this area of the country has warmed under climate change.

“They’ve been enabled to move into the treeless Karoo by our provision of power pylons on which to nest. As climate change progresses, we expect to see more and more synergies of this kind allowing species to change their distributions in the landscape,” Cunningham says.

The range expansion is partly due to the crow’s high intelligence and adaptability – qualities that sometimes irk mankind, according to co-lead author Chrissie Madden: “Being generalists, they are not constrained by a specific diet or nesting requirements. With power lines being suitable nest sites, and road-kill a constant supply of food, we are providing perfect crow habitats in the south-west,” Madden says.

The new study also provides valuable insight into how species respond to patterns of change: one anthropogenic (human driven) factor, like climate change, might have a different impact on a particular species when combined with another anthropogenic factor, or several other factors.

In the case of the pied crow, although the impact of climate change alone explains some of the increase in pied crow populations between the two surveys, these increases can be better explained when looking at the combined effect of climate change and power-line density.

“In light of this, we caution that other studies exploring climate-related distribution changes should take into account observed patterns of climate change within the study region, as well as explicitly investigating potential non-climatic drivers,” the report says.

The study provides “a clear example of compound influence of multiple global change drivers promoting a significant change in a species range and reporting rate”.

Cunningham says the study is important since it links crow population changes with anthropogenic landscape transformation (pylons) and climate change. “We are altering the environment, and, naturally, there will be some losers and some winners. Pied crows are currently winning,” Cunningham points out.