Female Black Harrier at the nest in South Africa's Western Cape:females like this were captured and
fitted with a satellite transmitters to follow their routes northwards.
South Africa's black harrier (Circus maurus) is a rare near-endemic that has been the subject of a long-term project based at the FitzPatrick Institute in Cape Town. Students and staff have focused mainly on breeding and foraging ecology. 138 nest sites and 9 years later we know a good deal about the limits to success of this species. What remains unstudied, and may be limiting the global population to under 2000 birds, is the wintering ecology of this species.
Odette Curtis and Sabelo Lindani hold a male
Black Harrier shortly before release with a
conventional VHF tail-mounted transmitter.
Sightings indicate that black harriers head north into the scrublands and deserts of northern South Africa and Namibia, where they may feed mainly on passerine birds. With technology finally allowing satellite transmitters small enough to put on birds as light as harriers, Rob and Natural Research have teamed up to buy 3 transmitters that were deployed on harriers as they finished breeding. Rob monitored their movements to determine where they roost (possibly communally), how far they range in their winter quarters and what they feed on. Given that those pairs that feed mainly on birds during breeding fare poorly in relation to those that feed mainly on small mammals, we expect that capture success and prey yield will be low for wintering birds existing on birds.
In 2009 three breeding harriers - one male and two females - were followed in South Africa using satellite tagging. Two were caught and followed around the core of the species' breeding range in the West Coast National Park, while a third female was caught farther north in the mountains about 5 h north of Cape Town.
The first female "Charlize" showed very little movement around her nest and successfully reared young and then moved north about 100 km in the non-breeding time. The third female also moved into this area following a long move south, suggesting the Cape Columbine region on the west coast of South Africa may be an important wintering area for harriers. The male "Motlanthe" also completed breeding successfully and the tagging indicated foraging movements up to 20 km from his nest. This foraging area later became his over-wintering area. Both tags stopped functioning just before the start of the next breeding season (June 2009) and one was recovered. The third female neatly undid all of our pre-conceptions about harrier movements. She too completed breeding successfully, headed south to the Cape west coast but then after 2 months headed east directly across the Karoo basin, covering 1000 km in 4 days. She headed north through the mountain kingdom of Lesotho and emerged into the grasslands of the Free State where she was died near powerlines 1600 km from her home. She had covered in one trip the entire range of the Black Harrier in 23 days.
This and apparent nocturnal movements prove that satellite tagging is an invaluable tool in Black Harrier conservation and further funding is required for additional tags.
Climate change is bringing drier weather to western parts of South Africa and Namibia and if birds (and small mammals) are negatively influenced by the lower rainfall, this may reduce numbers of available prey, just as dry spells in Africa's Sahel decrease the number of grasshoppers available to migratory Pallid and Montagu's Harriers. This study is therefore expected to shed light on what may limit these birds, and which factors are most important in keeping them as a globally Vulnerable species.
Hawk Mountain Sanctuary and The Dogwood Fund provide additional support to this project.
Photos: Top: A. Jenkins Bottom: R.Simmons