For many visitors the first thing that comes to mind when thinking about the West Coast National Park (WCNP) is the allure of its impressive beaches and the Langebaan Lagoon. But many don’t know that the park is also a safe haven for a scarce bird of prey, the black harrier.
By studying and observing the populations of these harriers in the park, which is one of their core breeding areas, researchers are hoping to determine which factors influence their breeding success. Once this is known, researchers might have a better understanding of their low numbers.
Marie-Sophie Garcia-Heras collaborated with the Percy FitzPatrick Institute of African Ornithology, studying these birds as part of her PhD. Garcia-Heras is focusing on various aspects of their ecology which includes breeding parameters, habitat use, diet, and even pollutants present in their blood.
So far, her team has found that birds seem to breed less well when the winter rainfall preceding the breeding months is low, as was the case in 2011 and 2015. In fact, not a single pair in WCNP was successful in breeding during these two years. “When rain is less, breeding pairs decrease. This is a trend across their range. Pairs that tried to breed failed,” says Garcia-Heras.
Black harriers are endemic to southern Africa but have a very restricted distribution range. Approximately 1000 breeding birds are found in South Africa, Lesotho, and Namibia, where the species has recently been classified as endangered.
After tagging 12 birds with satellite transmitters, the researchers learnt that the harriers migrate once fledglings are able to fend for themselves. Breeding season starts in winter and last until between September and December, depending on location. Harriers along the coast start breeding around June/July and may last until November/December if conditions are good. Those breeding in the mountainous areas start as late as October and finish around November.
The reason for their migration might be to leave the scorching summer weather of the West Coast and Northern Cape behind. They then move towards Lesotho and the north of the Eastern Cape, usually to areas with grassland plains and lots of mice. There are still some unanswered questions. “It is still unclear if the adults migrate with their juveniles, or if everyone leaves by themselves.” There is also no information available on what these birds do during the non-breeding season.
Apart from studying their migration patterns, Garcia-Heras is also trying to find other factors that could cause low numbers. “Surely habitat fragmentation during the last 50 years contributed to a reduction of breeding and hunting sites for black harriers, which is not helping the population,” she says. Black harriers nest on the ground, unlike the large majority of other raptors.
Another aspect that Garcia-Heras is looking at is the pollutants in the harriers’s blood, but unfortunately results for this are not available yet. “I am looking at the effects of Organochlorine Compounds (DDTs and PCBs) on the health of nestlings and adults.”
Another black harrier expert from the Percy FitzPatrick Institute, Dr Rob Simmons, has been studying these birds for the past 16 years. “The decline worries me and Garcia-Heras’s research will reveal more on why they are rare,” he says. Simmons suspects that they might always remain rare, but at least there is suitable habitat for them in protected areas such as the WCNP.
Learn more about the project by visiting http://blackharrierspace.blogspot.com.es/
Written by René de Klerk – SANParks Times Reporter
Pictures: Francois Mougeot, Davide Gaglio and Gareth Tate
Content courtesy of SANParks Times: www.sanparkstimes.co.za