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Black Harriers – Ecology and Fitness

The Black Harrier Circus maurus is a rare southern African endemic raptor, which breeds within Fynbos and Karoo biomes. It is estimated that there are less than 1 000 breeding individuals, and the species is considered Endangered in South Africa, Namibia and Lesotho.

Carrying on the research initiated by Rob Simmons in 2000, PhD student Marie-Sophie Garcia-Heras’s main goal was to investigate how various environmental factors may affect the breeding and health of this endangered species, at both the population and individual levels. Her research focused on factors influencing Black Harrier breeding performance, in particular diet composition, prey abundance and availability, habitat quality and weather conditions (temperatures and rainfall). She also explored the effects of persistent organic pollutants such as polychlorinated biphenyls (ΣPCB) and dichlorodiphenyltrichloroethane (ΣDDT) which are suspected to be a major threat to the population. The potential sub-lethal effects of these contaminants on diverse health indicators were also investigated. Studies on movements between breeding and non-breeding areas, and levels of connectivity between subpopulations, which may influence the level of genetic mixing were also assessed. Marie-Sophie submitted her PhD thesis in January 2017.

Health status:

Laboratory analyses on organochlorine (OC) pesticides showed that both Black Harrier adults and chicks carry contaminants in their blood. PCB and DDT were detected in 79% of adult and 84% of chicks. Nestlings had significantly higher ΣPCB and p,p’-DDT concentrations than adults; adults presented higher levels of p,p’-DDE than nestlings. Levels of ΣPCB significantly increased with an index of “electric transformer density”, (a measure combining the number and power of electric transformers around nests – PCBs were used in transformers). This could be used as a useful tool for assessing this potential source of ΣPCB exposure in wildlife. Levels of p,p’-DDE significantly increased with the proportion of wetlands in the breeding territory and with the percentage of bird biomass in the diet, confirming intra-specifically the association between diet and DDT contamination. No association was found between OC levels and the protected area status of nesting sites; some of the highest levels occurred in nestlings in protected areas north of Koeberg.

We also show associations between OC levels and indicators of physiological condition. White blood cell count increased with higher p,p’-DDT levels, while the heterophil to lymphocyte ratio increased with higher ΣPCB levels, suggesting increased physiological stress and reduced immunity in contaminated individuals. Analyses on the carotenoid-based colouration of the cere and tarsi in nestlings revealed that the a disruption of yellow-orange colouration was correlated with a decrease in circulating carotenoid levels at high levels of blood p,p’-DDT. This may have implications for nestlings given the importance of the expression of carotenoid-traits for social communication. Our results suggest that OC contaminants are a threat to Black Harriers, and probably affect other predators breeding in the same area.

Highlights:

  • Field work in coastal areas along the Western Cape was contrasted with inland areas in the Northern Cape to identify differences between breeding populations. Breeding parameters were collected at 490 nests during 2000-2015.
  • Data were collected on physical and physiological condition (i.e. measurements, blood samples for contaminants and carotenoid analyses, stress hormone level) and photographs to assess skin colouration (cere and tarsi) from 90 chicks and 32 adults at 46 nests.
  • PCBs and DDTs in the blood of nestlings and adults apparently induce sub-lethal effects on indicators of health and disrupt skin colouration of nestlings.
  • We collected 954 pellets at breeding sites during 2006-2015 containing 1679 prey items. Black Harriers fed primarily on small mammals (64.4%), birds (19.2%) and lizards (16.3%). However, inland breeders consumed twice as many birds as small mammals as a result of a marked seasonal decline in the occurrence of small mammal prey.
  • Automated cameras placed at 18 nests in 2014 showed a marked reduction in small mammal provisioning rates during midday in the hotter inland regions, which did not occur in the cooler coastal regions.
  • Three satellite transmitters and six GPS/GSM transmitters fitted to adult birds during 2013-2015 provided accurate data on the foraging habitats of breeding Black Harriers, confirming the west-east-west migration routes and identifying non-breeding areas in Lesotho and the Eastern Cape.

Impact of the project

Overall, the results of Marie-Sophie’s thesis highlight the importance of multifaceted and long-term studies, when attempting to understand a species´ limiting factors. She showed the importance of the coastal region (fynbos biome) for the stability and sustainability of the overall Black Harrier population. Fynbos habitat seems to provide better conditions for breeding in terms of food availability and weather conditions, but suitable habitat is severely fragmented. Neither provincial nor private reserves offered protection against persistent chemical pollutants affecting this rare harrier. Hence the scarcity of Black Harriers may be related to a lack of optimal, i.e. un-urbanised, un-polluted, un-fragmented and food-rich areas for breeding. The preservation and protection of the fynbos should, therefore, be prioritized to insure optimal and sustainable conservation of Black Harriers in the long term, but also for the conservation of many other terrestrial species that face similar threats.

Key co-sponsors

National Research Foundation; Golden Fleece Merinos; BirdLife South Africa

Research team

Dr Rob Simmons (FIAO, UCT)
Dr Beatriz Arroyo (CSIC, Spain)
Dr Francis Mougeot (CSIC, Spain)
Dr Raphael Mateo (CSIC, Spain)
Pablo E. Camarero (CSIC, Spain)
Dr Graham Avery (Iziko Musuems)
Dr Margaret Avery (Iziko Museums)

Student: Marie-Sophie Garcia-Heras (PhD, UCT)