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In this Issue - Part 1
Road Names in Raptor's View - Derek Solomon
In the previous issue we discussed Pygmy Falcon road; two roads branch off this road, the first being Fish Eagle. This is certainly the best known and loved raptor in South Africa and as I write one is calling loudly over our home on Martial Eagle road.
The scientific name of the African Fish Eagle is Haliaeetus vocifer. Halieous is a Greek term for a fisherman and aetos an eagle. Vocifer is Latin for vociferous and refers to its loud, yelping call that is so well-known to everyone. World-wide there are 10 species of fish or sea eagles, our African Fish Eagle being the only representative in Africa occurring throughout sub-Saharan Africa. The closest relative is the Madagascar Fish Eagle Haliaeetus vociferoides which is restricted to the western coast of the island and is regarded as endangered. It also gives a loud yelping call with a toss of the head.
The white head and breast of the African Fish Eagle is very obvious even from some distance, the breast patch of the female being broader but only useful when both sexes are perched side by side. The female is about 10% larger. The underparts and shoulder are a deep chestnut as are the wing coverts when seen in flight and the upperparts are dark brown or black.
While identification of the adults is easy, the juvenile is confusing and variable – mainly dark brown, streaked with black and white. After the first year the plumage starts to change but it is only in the third year that it starts to show some adult features and adult plumage only attained in the fifth year.
Juvenile (up to a year of age)
It spends up to 90-95% of the day perched in trees, more often than not in pairs. The loud yelping calls may be given both when perched or in flight, often with the head tossed back and often in duet with that of the female being deeper. The rest of the time is spent soaring, displaying, chasing off intruders and fishing, the latter as activity taking up little more time than 1% of the day. The Fish Eagle is an active pirate chasing other birds and harassing them until they drop their prey. In addition to fish, it also hunts other birds including waterbirds, Guineafowl and queleas at breeding colonies. Monitor lizards, crocodile hatchlings and terrapins are also on its menu.
The height of the breeding season in our area is between March and August and we hope that any active nest sites will be reported to the editors for further observation. Nests are usually built in tall trees particularly Acacias and sometimes even large Euphorbias and may be used in consecutive years.
Self defence in plants - Thorns and thorny structures - Dave & Bernie Spencer
Many plants have developed good defence strategies to limit browsing and grazing particularly in the early stages of growth. Good examples easily visible (or more painfully felt) on RV are thorns and thorn like structures. Plenty of species on the estate are armed with either spines or prickles, sometimes both. These are adaptations of the stem, often in pairs but not exclusively so. As trees grow the need for thorns diminishes as mature plants are more able to withstand a fair amount of browsing.
The well armed trunk of a young Vachellia nigrescens, Knob Thorn.
The trunk of a mature Vachellia nigrescens with no obvious thorns.
Thorns may assist in plant identification especially during the dry months when leaves and flowers are are often absent. Here are some good examples to look out for around your home and along the trails.
The distinctive paired spines and recurved thorns of Vachellia tortilis, Umbrella Thorn.
Senegalia senegal, Three-Hook Thorn with three curved prickles at a node.
Ziziphus mucronata, Buffalo Thorn with one hooked spine pointing backward and one straight spine pointing forwards.
Other thorn-like structures may be seen on species such as Ximenia , Sourplums and Dichrostachys cinerea, Sickle Bush. These plants have single, straight spine-tipped branchlets often with leaves, flowers or fruit on the same branchlet.
Ximenia caffra, Blue Sourplum with a leaf on the spine tipped branchlet
Dichrostachys cinerea, Sickle Bush with leaves and fruit on the same spine tipped structure. (Plus a tiny spider! )
RV’s two Helmetshrikes – Steve Benbow
Helmetshrikes are highly sociable bushshrikes characterised by stiff, bristle-like feathers protruding from the forehead. Usually seen as family groups moving through the veld and staying in touch with each other by contact calling. They are also prone to window tapping which is thought to be a territorial action against the bird’s reflection in the glass. On Raptors View we get two species of Helmetshrikes; the White-crested Helmetshrike and Retz’s Helmetshrike – there is a third species, the Chestnut-fronted Helmetshrike which is found further to the north east in Mozambique and the south-east corner of Zimbabwe.
White-crested Helmetshrike (Withelmlaksman in Afrikaans).
An unmistakable helmetshrike which is black and white with grey hind crown, broad white collar, yellow eye-wattles and orange legs. In adult plumage it has distinctive white wing bars. It is a locally common resident and occurs in broad-leaved and mixed-acacia woodland, particularly along drainage lines. As seen from the photographs, the juvenile is duller than the adult, has buffy underparts and lacks the distinctive eye-wattle. As members of the shrike family, White-crested Helmetshrikes feed on insects, spiders and small lizards.
Retz’s Helmetshrike (Swarthelmlaksman in Afrikaans) Named after Anders Adolf Retzius, a Swedish anatomist of the early 19th century, Retz’s Helmetshrike can hardly be mistaken for its White-crested cousin. Larger and darker, it is has a black forehead and crest and orange-red eye-wattle.
It shares the same habitat as the White-crested Helmetshrike and also moves around in family groups which can be as large as 30 individuals. Often interspersed with other species of birds to form ‘mixed-species bird parties’, Retz’s Helmetshrike competes with the White-crested Helmetshrike for prey.
Believed to be monogamous, the dominant pair of Retz’s Helmetshrikes build their nest in the upper branches of trees with help from other group members who also help to brood, guard, feed and attend the nestlings; the breeding behaviour of the other Helmetshrikes is similar.
Euphorbia Mania - Derek Solomon
May/June is the flowering time for the many large Euphorbia cooperi, Bushveld Candelabra Euphorbia, on the estate. The little yellow-green flowers, called cyathia, must produce copious amounts of nectar based on the huge variety and numbers of insects they attract including butterflies, wasps, bees and flies as well as predators such as spiders and geckos.
We have a large specimen growing in the front of our house on Martial Eagle, and this season we have already photographed 50 different insect species, 5 spiders and a Cape Dwarf Gecko. See some of this season’s visitors below.
This plant has milky latex highly poisonous to humans and animals and it is said to be one of the most poisonous of the Euphorbia species. Any contact with the skin, eyes and mouth causes severe pain, blisters or even blindness if it gets into the eyes. It may produce a burning sensation in the throat when standing next to bleeding plants.
The latex is used as a bird lime. It is drained from the branches, heated and boiled and the resulting sticky substance is painted on twigs and branches where birds perch to trap them. It is also used as a fish poison, generally prepared by soaking a bundle of grass in the latex, tying it to a stone and throwing it into the water. After about 15 minutes paralysed fish rise to the surface, are easily caught and eaten with impunity.
Crab Spiders (male on top of female) with huge prey
Jumping Spider Salticidae species – again with prey
Painted Bee Fly
What was of particular interest to us was the complete absence of honeybees attracted to our tree until two days before we started preparing this article (June 5). This prompted a search through the literature, and we were surprised to find several references to a product called Noors honey produced when bees collect nectar and pollen from various species of Euphorbia. Consumption apparently causes a burning sensation in the mouth, which is intensified by drinking water and lasts for several hours accompanied by nausea. This was particularly prevalent in the Sundays River Valley in the Eastern Cape in the 1920’s. In those early days the name Noorsdoring was applied to the various species of Euphorbia.
RV resident Chris Hines and I have been monitoring our home Euphorbias and he experienced the same lack of bees until the last few days of his observations, and he suggests that because Euphorbias produce some pretty unpleasant chemical products (terpenes etc.) that suppress feeding (the technical term for this is antifeedant) it may be that it is only when these are at low levels in the nectar that the bees come in. Many of the early arrivals on the flowers are after pollen or have whopping great jaws (many of the wasps) and they bite into the nectaries to access the nectar. Maybe the bees have to wait for a more available flow of nectar? But then why are the short mouth flies on the flowers so early? Lots to think about.
Interestingly plants containing pyrrolizidine alkaloids such as rhododendrons, oleander and azaleas (Ericaceae family) are also sources of poisonous honey. These alkaloids on their own are not highly poisonous, but our livers metabolize them into substances that are toxic (Winston, 2002).
Through the Office Window - Derek & Sarah Solomon
We are lucky to have one of the best ‘through the office window’ views we know; and are constantly distracted by the comings and goings of our local wildlife.
Arrow-marked Babblers usually signal their arrival with raucous calling before some vigorous bathing.
An old version of Newman’s rather aptly describes the call as “a noisy, excitable whirring started by one bird and taken up by the the others until its resembles hysterical giggling”.