Tuesday, 11 October 2016

Verreaux's eagle ranging behaviour

We caught and GPS tagged the first Verreaux’s eagle for this project back in 2012. It was a breakthrough at the time and watching the first data download onto our base station filled me with excitement for what we would find out.

Here it is. Our first paper “Ranging behaviour of Verreaux’s eagles during the pre-breeding period determined through the use of high temporal resolution tracking”, published by PlosOne today. PlosOne is an open access journal, meaning it is free for anyone to click on the link and download the paper.

One of the great surprises for me was the relatively small home range that these eagles maintained. Considering the inter-nest distances, these small home ranges are expected. But considering the wingspan and soaring abilities of these birds the optimistic dreamer in me had expected soaring over vast expanses. Another surprise was the lack of any obvious difference in the distance and duration of trips away from the nest between the eagles in the natural Cederberg area and those in the agriculturally transformed Sandveld area. Verreaux’s eagles in the Sandveld were also found to be selecting for near-natural and degraded habitats over natural or fully transformed habitats, suggesting that eagles benefitted from some of the agricultural development in this region.

Although this paper is based on a small sample size of eagles, it is the first of it’s kind using high-resolution GPS tracking technology. I am extremely grateful to the UvA-BiTS team for their dedication to developing these tags and I look forward to continuing to use them in our future research on Verreaux’s eagles.

Thursday, 11 February 2016

Eagles and agriculture coexist

The first scientific peer-reviewed paper coming from research by the Black Eagle Project has been released. Here's what its all about:
To biologists’ surprise, an eagle population living in a South African landscape dominated by agriculture appears to be thriving, according to a new paper in The Condor: Ornithological Applications—even out-performing their neighbours in undeveloped mountain habitat.

Verreaux’s Eagles (Aquila verreauxii), an apex predator in southern Africa, are in decline, and Megan Murgatroyd of the University of Cape Town and her colleagues wanted to determine if habitat loss due to intensifying agriculture could be the culprit. Instead, when they compared the breeding productivity of eagles in South Africa’s heavily farmed Sandveld region to that of the smaller population of eagles in the nearby Cederberg Mountains, they found that the Sandveld population’s breeding success was actually the highest of any Verreaux’s Eagle population ever studied.

Mugatroyd and her co-authors speculate that the eagles’ prey base could be more available and diverse in the Sandveld, and that the gentler terrain could take less energy to navigate. However, the researchers caution that there may be a threshold of agricultural transformation beyond which the Sandveld region’s population would begin to struggle. They recommend that management in the Sandveld region should focus on identifying and eliminating any potential sources of eagle mortality, such as wind energy development.
Murgatroyd and her colleagues monitored eagle nest sites in the two areas over four years, visiting them every two to three weeks during the breeding season. “It has been a huge privilege to undertake fieldwork in this part of South Africa,” says Murgatroyd. “The Cederberg is a beautiful natural wilderness area, so we were surprised when it became apparent that the Verreaux’s Eagles breeding there are far less productive than those in the Sandveld, which has been extensively converted for agriculture since the 1980s. This comparison has highlighted the potential importance of an agricultural landscape to Verreaux’s Eagles, but further research, in particular with a focus on adult and subadult survival rates, is still needed for a better understanding of the long-term persistence of these populations.”
The influence of agricultural transformation on the breeding performance of a top predator: Verreaux’s Eagles in contrasting land-use areas is available at:
About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology. It began in 1899 as the journal of the Cooper Ornithological Club, a group of ornithologists in California that became the Cooper Ornithological Society.