Black harrier

We saw them for the first time just outside Elands Bay. Three of them - a male, a female and a little chick.  For a few minutes they entertained us with an airshow. While two of the three rested on the telephone poles beside the road, they took turns in showing off what they could do. With their charcoal black bodies and striking white markings, they glided back and forth gracefully, took low sweeps over the coastal fields, to just suddenly shoot up in the sky and hang there - motionless.  Their long barred tails spread for balance. Totally unaware of the pleasure they gave the three humans sitting in the pickup down below, looking up completely awestruck. Of all the wonderful birds in our skies, this species is by far my favourite, the most special. The flagship of the West Coast.

Circus maurus. 

The name just appears in my head.  Black Harrier. I grew up with an almost life-sized poster of one of these birds in my room. All through my primary and high school years, it was there! I also had posters of the Black Eagle, Lanner Falcon and Black Shouldered Kite against my walls - all birds of prey that can be found at the West Coast, but the Black Harrier was the one standing out. There was something mysterious in those yellow eyes with the penetrating look out of the black head!

Circus maurus.  

Unfortunately they are one of the rarest of Southern Africa`s breeding endemics - with an estimated population of just 1500 birds. Although I have seen them a few times on the West Coast, they actually are some of the most scarce birds of prey of Africa.  Less than 100 occur in protected areas. The Black Harrier is listed as Vulnerable at a global level and at a South African level as Near Threatened.

The breeding range of the Black Harrier is limited to South Africa, and is concentrated in the coastal and montainous regions of the Western Cape.  The West Coast and in particular, the West Coast National Park is their breeding stronghold this is where I saw them the first time.  A truly exceptional moment. The poster against my wall came alive...  Even more spectacular than it ever looked against my wall. 

This species prefers coastal and mountain fynbos, highland grassland, Karoo sub-desert scrub and open plains with tall shrubs and croplands.  They prefer hunting for small mammals in open ground with low vegetation.  Mammal prey comprises mainly of rodent species such as Otomys and Rhabdomys.  Mammals, as well as reptiles and birds are caught in coastal sites, but birds (especially quail) are preferred in the diet of pairs nesting in mountain terrain.

The rarity of the species is directly linked to shrinking habitats.  Habitat transformation, by agriculture, burning of fynbos and grasslands and invasive alien plants, coupled with habitat fragmentation, pose the major threats to this species.  This trend is likely to be exacerbated in the future by factors such as climate change.  Presently more than 90% of the Cape lowlands have been transformed by agriculture and because of this the Black Harrier has lost over 50% of its breeding habitat in the last century. Harvesting of crops generally coincides with the middle of the Harrier breeding season.  The Black Harrier only nests on the ground and therefore it is doubtful that pairs breeding in wheat- or barley fields could successfully raise a significant number of young.  There is also a concern that wind turbine blades placed inappropriately might cause a serious threat to the harriers, causing significant mortalities.

While the mountainous regions are well protected as mountain catchments and provincial nature reserves, the breeding success of the species is lowest in this habitat.  In protected coastal areas with high rodent populations, the birds manage to raise on average of two young per breeding attempt, in stark contrast to mountainous terrain where more than half of all nests fail. Though the harriers do utilize the transformed landscape for foraging, they seem incapable of actively nesting in this landscape. Harriers breed close to coastal and upland marshes, damp sites, near streams with tall shrubs or reeds.  Black Harriers however do congregate in large numbers at suitable breeding grounds along the coast, especially in the West Coast National Park.

But unfortunately there is another major threat:

A study by PhD student, Sophie Garcia-Heras, suggests that the toxic PCB oils found in electrical transformers are making their way into the environment and being taken up by the harriers.  Garcia-Heras tested blood from over 100 Black Harrier adults and chicks  and confirmed that they have high levels of PCBs.  The greater the density of transformers found within 5km of harrier nests, the higher the pollutant levels in their blood - especially the nestlings - showing that PCBs are being acquired locally.  

The question arises: could PCBs be contaminating ground-water, too? 

More worrying was that DDT - banned in the Western Cape - was found in adult and nestling harriers of the Western Cape.  Those pairs with most wetlands within 5km of their nests had the highest levels of DDE. This means that DDT bio-accumulates and breaks down in local wetlands, and pollutes prey taken by the local harriers.  Most affected, are those pairs that feed on songbirds and deliver them to their brood. 

So, small-bird-prey and wetlands are dangerous for harriers as a source of DDT and, particularly, DDE. Studies show that nestling Black Harriers have the highest levels of DDT in their systems.  Are they acquiring it locally or are the females “dumping” it into their eggs and chicks?  Of concern: nestling Black Harriers have the highest of all concentrations.  

This suggests that DDT is being picked up directly by young birds, despite the ban on DDT in non-malarial areas of South Africa.

One of the consequences of high levels of PCBs is that the harrier’s immune system is compromised (gauged from white blood cell counts). This suppressed immunity could have a negative impact if harriers are exposed to natural diseases, and could affect survival or breeding success. (Black Harrier Research, Newsletter #1: April 2017)

The Black Harrier research team, lead by Dr Rob Simmons is housed at the Percy FitzPatrick Institute of African Ornithology at the University of Cape Town.  They are also the BirdLife Species Guardian for the Black Harrier under the global Preventing Extinctions Program.
  
Because of its dependence on pristine patches of indigenous vegetation, the Black Harrier can be a good indicator of the status and health of their preferred habitat.  Research has shown that presence of breeding Black Harriers indicates high mice diversity and high bird numbers.  Thus the presence of a Black Harrier on your property means it is rich in biodiversity.  Black Harriers will regulate rodent populations and in this way play an important role in maintaining community structures and ecosystems.