Monthly Archives: June 2012

Walking with Paul : Fork -tailed Drongo – one of the most intelligent birds in the African bush ?

One of my favourite birds to see when out walking in the bush is a rather conspicuous little black bird called the fork-tailed drongo .

Fork-tailed Drongo in Lower Zambezi National Park – Zambia

The plumage is entirely black and the eye is the colour of red wine , closer inspection reveals a deeply forked tail , which is actually a result of the outer rectrices ( tail feathers ) being curved at the end . They are usually solitary and have small territories that they defend against any intruders with quite an aggressive display. This involves buzzing around the intruder and shouting at it vigorously . Even the largest of the eagles or a human passerby is not immune to this behaviour . Will also scold snakes and owls and even monitor lizards or mongooses , drawing attention to a potential predator in the area , which quite often attracts other bird species to come along and join in the mobbing behaviour . A gathering of birds of different species making a lot of noise is sure to indicate a snake , owl or some other kind of predator being scolded by the birds .

Drongos are mostly insectivorous ,but will catch small birds , kill chicks in nests and have been seen plunge diving like kingfishers to catch small fish . They will feed on nectar if it is available .They have a small hook on the end of the bill which enables them to hold their prey firmly . Sensory bristles ( called rictal bristles ) are found around the mouth and nostrils, this gives them an advantage in catching prey . Drongos will typically hawk insect prey , this is done from a perch . As an insect is spotted they will fly out and catch it and then return to the same spot to devour it . The drongos often lead bird parties( mixed –species foraging flocks ) , which involves a mixture of different bird species feeding together for increased advantage, both in terms of food availability and also for increased vigilance from predators . Often seen catching insects that are disturbed by mammals as they forage through the bush . There are records in the Kalahari of the drongo mimicking the call of the pearl -spotted owlet when foraging around suricate troops . This causes the troop to scatter for cover leaving their food behind . The drongo then kleptoparasitises the leftovers . Other species of drongos have been observed making false alarm calls that scatter the other members of the bird party they have joined and results in better access to particular food sources for themselves .

This bird is the only known host of the African cuckoo which is an intra-African migrant ( migrate within Africa moving north or south of the equator according to temperature and food availability ) and their distribution is very closely correlated in Southern Africa ( this is called sympatry ). The cuckoos are all brood parasites which means that they lay their eggs in the nests of other birds and the host female will incubate the egg and raise up the chick as her own .
Drongos are monogamous in their breeding habits and usually lay three eggs between August and January .
The African cuckoo has to mimic the pattern of the hosts eggs as close as possible in order for the single intruder egg not to be rejected by the host bird. The drongo is what is known as a discriminator , which means that she makes sure the eggs all match in the nest( some host species do not notice if the brood parasites eggs match and are called non-discriminators ) The female cuckoo may lay up to 25 eggs per season in different nests , usually one per nest, but she has to become a matcher in order for the eggs to be accepted . This is complicated by the fact that the drongo lays polymorphic eggs , each female having a different pattern . The drongo has up to six different egg patterns that it lays in order to confuse and outsmart the cuckoo . If a strange egg is detected amongst the clutch this will be removed from the clutch by the host .Statistically up to 50% of African cuckoo eggs are rejected by the host drongo . The cuckoos nesting peak is October and November , this corresponds to a time when there are hairy caterpillars around for them to eat and it correlates with the breeding period of the drongo .
The Fork tailed drongo is certainly one of the most interesting and charismatic birds in the bush , even though they have only black colouration which is caused by melanin pigments , their characters surely makes up for any lack of colour on their bodies . In Australia a person might be called a drongo which means they are an ‘idiot ‘

Be careful not to confuse the Fork Tailed Drongo with a similar looking bird , the Black Flycatcher . The flycatcher has only a slight indentation in the tail compared to distinct fork in the drongo’s tail . Drongo has a red-brown eye which shows when it catches the light , while the flycatcher has a dark brown eye . One of the ways to separate them them is whether the bird is bold and noisy , which will be the drongo or relatively quiet and unobtrusive ,which is more likely to be the flycatcher .

Image shows the conspicuous deeply forked tail

Walking with Paul – The Praying Mantis

When you are out walking in the African bush , you might be forgiven for mistaking that dry grass coloured stick for a piece of dead plant . Approach it closer and the prayer like attitude of its huge raptorial forelegs begins to unfold , you have probably come across a praying mantis .

Order Mantodea is Greek for Soothsayer , comes from an attitude of prayer that they are mostly found in when observed in the field . This attitude masks a deadly predator . The praying mantis The praying mantis is an amazing creature , they use camouflage to hide away and patiently wait for an insect to come within range , they then grab their hapless victim with a lightening quick jab of their raptorial , spiked forelegs and then administer the coup de grace with ( sideswiping crunching )the chewing mouthparts .

At night their camouflage becomes irrelevant and it has been discovered that they have a cyclopean ear on the thorax , this enables them to pick up the echo location activity of bats and enables the mantis to avoid them quite drastically by simply falling out of the sky when they detect the bats sonar emissions.

The best way to observe the micro fauna on a walking safari is to turn your binoculars upside down , which transforms them into a microscope , magnifying the subject many times .looking at a praying mantis in this way transforms them into creatures from the movie “Men in Black ” .

A magnified view shows them to have a smallish , charactersitically triangular head , which uniquely among the insects they can swivel one hundred and eighty degrees . This allows them to turn their heads and zone in on potential prey . They have huge compound eyes that are multi- faceted and are extremely adept at detecting the slightest movement while they are in ambush mode , they could easily be mistaken for a dry grass stalk or a stick or leaf on a plant at this stage .

The male praying mantis is extremely wary of the female mantis as they have been known to engage in sexual cannabalism on occcaison . This does not happen always and a slick male can escape his partner. Some mantis species have a system of nerve ganglions that are spread through the head and thorax , if the mating female does happen to capture the male while they are mating , she might well start to feast on him while they are copulating . This sinister predatory action usually begins with the female eating the males head first , and will eat him in totality as they progress in procreation . This is the ultimate sacrifice on the part of the male to perpetuate the species . It is thought that he provides a very necessary supplement to her diet when she starts to lay her eggs, which can number up to 60 depending on species . These eggs are enclosed in a frothy mass , called an ootheca , which of course requires a lot of energy on her part .The ootheca is deposited in the darkness on a grass stalk or a small branch and is quite vulnerable to the elements .

Parasitic wasps are one of the major predators at this stage , and may incapacitate many of the eggs during their 30 days or so of metamorphosis . The small nymphs hatch out of a one way valve in the top of each cell and emerge a dark colour , quite often mimicking ants as a defence mechanism . They resemble the adults at this stage . These nymphs think nothing of cannibalizing their siblings in order to get a head start in life . They will undergo 5 or 6 moults before reaching adult hood , and usually live about 10- 12 months in the wild .

Triangular head of typical Praying mantis , note large compound eyes and huge raptorial forelegs .

EGG CASE ( OOTHECA ) OF A TYPICAL PRAYING MANTIS

Egg case ( Ootheca ) of a Praying Mantis

Walking with Paul – The Dwarf Mongoose

On a walking safari through the African bush, you might notice an old termite mound with many holes in it . These holes are quite often utilised by Africa’s smallest carnivore , the Dwarf mongoose ( Helogale parvula) . They weigh in at between 200 and 300 grams .
Active colonies will be indicated by little sausage shaped piles of dung strewn around the base of their refuge . If you were to quietly sit at a distance and wait for the sun to warm up the mound , you will be rewarded with the sight of some furry little heads popping out of these holes. This scrutiny from the safety of the mound might go on for quite some time before the alpha female , being the dominant member of the pack ,will slowly lure the other members of the pack out of their tunnels. They will play in the warm sun and scent mark one another as well as engage in social- grooming before setting off to forage , all of this behaviour is vital to maintain the social bonds of these group living ,diurnal ( day active ) ,mongooses .This is particularly relevant to male and female immigrants that join the pack from outside , as they slowly ingratiate themselves to the existing pack members and seek acceptance. Thus a fresh set of genes is introduced to the pack , and more helpers also benefit the young mongooses .
All mongooses in the pack will assist in babysitting, feeding and warming the young through their journey to adulthood .The mother , who along with the alpha male is the only breeding mongoose in this society is thus able to feed more and can therefore ensure that she lactates sufficiently for her babies survival . The alpha pair may have 2 or 3 litters in a season , they will not tolerate other pairs mating in the pack , and it is thought that they kill the offspring of other potential mothers . The alpha female will give birth to one to five babies after a gestation period of approximately 40 days . The other members of the pack are both related and unrelated to the alpha pair, but all of them will assist in feeding and caring for the babies. This altruistic behaviour ensures that the species is perpetuated, and the individuals give up their own breeding rights.The females are dominant over all males in the pack ,older animals also have higher ranking .

There may be between 2 and 32 mongooses in a pack , with 12 being the average .They are collectively called a ” business of mongooses ” .Pack size varies according to available refuge sites and local food resources .The entire pack will defend a territory of up to one square kilometre., and encounters between packs are aggressive and life threatening. Bigger packs will displace smaller packs from good refuge sites by sheer weight of numbers.

Their diet consists mostly of insects, but they will supplement this with spiders, scorpions, lizards, small snakes and birds as well as rodent’s .The adults forage for themselves and appointed babysitters look after the young.
Sentinel duty in a mongoose pack is mostly the responsibility of the subordinate males, and they will give very specific calls relating to the type of predator spotted, regarding their proximity, species etc.

In some areas the dwarf mongoose has been observed in a symbiotic relationship with various bird species, particularly the red billed hornbill and fork tailed drongo. These birds will catch insects that are disturbed by the movement of the mongooses during the course of their foraging activities. These animals have developed a mutual anti-predator relationship. It has been proven that the mongooses are far less vigilant during foraging excursions when they are in the presence of these birds. The birds will utter specific alarm calls if they detect any kind of threat , and this will be passed onto the entire mongoose troop instantaneously .The pack members will then flee for cover if it is close by or mob their attacker . The main threat that these mongooses recognize is aerial predators, such as smaller birds of prey, that will swoop in from the sky to catch any unsuspecting members of the pack . Under four months old the babies are particularly vulnerable to predation, but the adults could be taken also by raptors, snakes, storks and even monitor lizards. The new born mongooses are also small enough to be eaten by their hornbill guardians, but are not taken by them.
Cheek and anal gland secretions are used to mark objects around the nightly refuge site , they may do a handstand type balancing act to achieve this on taller objects.

Lifespan may be up to 15 years .