(This article originally appeared in the 100th edition of “The Kite”, the official newsletter of the Tygerberg Bird Club and is loaded here with the permission of its Editor. - Ed.)
If you should go walking through the woods today and you hear a noisy bird it could quite possibly be the mating call of a Black Sparrowhawk, Accipiter melanoleucus, as it’s that time of year.
The breeding season of these normally silent raptors is from April to October. Males are known to make loud “keeyp” sounds while females make short “kek” sounds.
Dr Arjun Amar of UCT’s Percy Fitzpatrick Institute recently gave a presentation, titled “Investigating polymorphism in the Black Sparrowhawk”, on his findings to volunteers and scientists at SANParks Cape Research Centre in Tokai. “Colour polymorphism is a subject that has fascinated scientists since the time of Darwin,” Dr Amar told the Bulletin, explaining that polymorphism refers to an animal species occurring in two or more colour varieties.
The Black Sparrowhawk Project was started in 2001 by Odette Curtis to monitor these birds on the Cape Peninsula (“Nature’s serial killers on the loose”, Bulletin, July 24 2008).
She continued working on the project until leaving at the end of 2006 to pursue a career in the Overberg. By that time a small but enthusiastic group of raptorphiles had formed, donating time and energy to the project, so monitoring has been continued to the present. Although, none of the volunteers are scientists, their data is used by students and scientists at the Percy Fitzpatrick Institute to expand the little that is known about Black Sparrowhawks.
Dr Amar said polymorphism occurs in about 3.5% of bird species, although its occurrence is not distributed equally across bird families or genera. Raptors, or birds of prey, show a disproportionately high frequency of polymorphism and it is particularly common among hawks.
Dr Amar said these birds occur throughout South Africa but this project’s study area is centred on the southern suburbs, from UCT to Tokai. From the 1950s Black Sparrowhawks have been expanding their range towards the Cape Peninsula where they are now common. He said Sparrowhawks on the peninsula are darker than the species found in the rest of the country. Statistics show that about 80% of birds show dark plumage in the Western Cape with 25% in the Eastern Cape and 15% in the north east of the country. Dr Amar said that climate plays a part in this with the Western Cape having more rainfall and a cooler climate.
He said they have also found that darker birds have a higher resistance to parasites and this might explain why they are more common in this region.
Plumstead resident, Ann Koeslag, was also at the presentation and is one of the raptorphile volunteers. Since she got involved in 2001 the population on the Peninsula has grown from 13 to 49 pairs. During this time, Ms Koeslag and other volunteers have ringed 180 chicks and 100 adult birds and this means that 75% of breeding adults have coloured rings.
Dr Amar said part of the study is to photograph the Sparrowhawks. Through this they have found that the plumage patterns of individuals remains constant with age. “Using information on the offspring of the young produced, and the plumage colouration of their parents, this project has identified that the species plumage colour is inherited and can describe the patterns of the genes involved,” said Dr Amar. He said current research is delving even deeper and trying to identify the specific gene responsible. This involves lots of high tech lab work and is being carried out by UCT Master’s student, Gareth Tate.
Dr Amar describes Black Sparrowhawks as charismatic birds and much prized as a hunter. “They lead quite complicated personal lives, some seeming to bond for life, although divorce and infidelity are not unknown,” laughed Dr Amar.
Although the volunteers have been watching these birds and their antics for many years they are still surprised from time to time by what they see. “During the last breeding season a booted eagle was seen trying to take a Black Sparrowhawk chick from the nest. The ensuing action from the mother of the chicks sent the eagle flying for cover until they were lost to sight. None of us were sure that the eagle would survive,” said Ms Koeslag.
Dr Amar said this project relies heavily on the public’s observations, so if you should see one of these birds contact Ann Koeslag by email at firstname.lastname@example.org or call 072 357 0909.
If you want to read more about these wonderful birds and the project visit http://blackspar1.wordpress.com/.
Black Sparrowhawks often nest in the fork of tall pine and eucalyptus trees. Sparrowhawk chicks have enormously long toes and this illustrates that they are hunters. The male weighs less than the female, 550g to 980g.
Their predators are crows and humans, but Egyptian geese cause these birds the most distress by taking over their nests to lay their own eggs in them.
The birds prey on pigeons and doves but females have been known to catch guinea fowl.
Karen Watkins - Bulletin - Thursday, February 28, 2013