SA’s national bird faces “ecological trap” in Western Cape wheatlands

South Africa’s national bird, the blue crane, isstruggling to raise chicksin parts of the Western Cape and scientists warn the region might be becoming an “ecological trap” for the species. A new study published in the ornithology journalOstrich, comparing breeding success, found that blue cranes in the Overberg and Swartland wheatlands were producing far fewer fledglings than birds in the Karoo and eastern grasslands. It was led by researchers from theFitzPatrick Institute of African Ornithologyat the University of Cape Town and theAfrican Crane Conservation Programme, a partnership between theEndangered Wildlife Trustand theInternational Crane Foundation.

The blue crane is listed as vulnerable on the International Union for Conservation of Nature Red List because its population has declined by an estimated 19% from 2011 to 2019. The researchers noted that the reasons for the recent decline were unclear. “Historically powerline collisions, poisoning and habitat transformation led to declines in the Karoo and eastern grasslands,” the study said.

“Now the decline is largely occurring in the Western Cape’s Overberg wheatlands, where blue cranes occur in intensively farmed cereal croplands and planted pastures.” Nonetheless, the Overberg wheatlands were “a stronghold for the species, with the highest densities of blue crane occurring in this artificial habitat, as opposed to natural habitats in the Karoo and grasslands. There are concerns that the Western Cape may be Breeding productivity, which is measured by how many chicks survive per nesting attempt, was almost twice as high in the Karoo and grasslands as in the Western Cape’s intensive agricultural areas. In the grasslands, cranes produced an average of 0.95 fledglings per attempt and in the Karoo about one chick per attempt.

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In contrast, productivity in the Overberg was just 0.55 fledglings per attempt and even lower in the Swartland, at 0.48. The proportion of breeding pairs that managed to raise at least one chick also sharply differed. In the grasslands and Karoo, about two-thirds of pairs successfully fledged chicks each year.

However, in Overberg and Swartland, the figure dropped to about 40%. The study also found worrying signs in winter flocks. Between 2019 and 2021, juveniles made up only 4% of cranes in winter flocks in the Overberg and 3.6% in the Swartland.

That is roughly half the proportion recorded in the Overberg 30 years ago. Historically, blue cranes were drawn to agricultural habitats. However, modern farming practices might be undermining breeding success.

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