Monday, March 29, 2010

Sometimes even friends aren’t welcome...

Watching the mongooses forage today was a real joy.

You may wonder what's so appealing about small animals crunching up spiders, gnawing squealing rain frogs or licking larvae-innards from their whiskers, but at this time of the year (the close of the wet season) the mongooses are feasting on grasshoppers.
I must admit, though, that dwarf mongooses aren't the most efficient grasshopper-catchers. The insect usually manages two or three good hops before the mongoose gets its paws on it. So accompanying Halcyon group this morning was like stumbling into the middle of an acrobatics troop on speed. There were mongooses flying everywhere; erratically bounding back and forth through the grass, leaping a metre up into the air, or dangling precariously from trees and shrubs.

Amid all this frantic chaos, I noticed something strange. There were no drongos.

Fork-tailed drongo (Dicrurus adsimilis). Photo borrowed from here.

Now, dwarf mongooses usually forage in the company of birds, and their most favoured companion is the fork-tailed drongo (Dicrurus adsimilis). These black, shrike-like birds often escort mammals and ground-foraging birds, fluttering about, snatching up the insects they flush. You can see them following elephants or impala, babblers or buffalo weavers. But their relationship with mongooses seems to be two-way. Each day the mongooses go out of their way to find, and follow, the resident drongos.
Why? Well dwarf mongooses are highly vulnerable to predators. Being small (250g) and foraging by day, they're a source of culinary interest to more than 25 local raptor species. To counter this, the mongooses take turns as sentinels, climbing high up on a tree or boulder to sit and watch for predators while the group forages. They also indulge in eavesdropping. If one of their feathered companions should utter so much as a peep of alarm, the whole group races for safety. Is this why they like drongos?

Chlorophyll (HM004) on sentinel duty.

To find out if the mongooses felt safer when drongos were present, I recorded how often the groups mounted sentinels when a drongo was there, compared with when it wasn't; and a student (from Stellenbosch University) monitored how frequently individual mongooses interrupted their foraging to look around for danger. We found that the mongooses halved both these behaviours when drongos were present. But were the drongos actually causing this change? Perhaps drongos only escorted the mongooses when birds of prey were scarce and the mongooses didn't need caution.
To test this, we artificially simulated the presence of a drongo by playing recordings of its territorial calls. We also played to the mongooses recordings of the white-bellied sunbird (Cinnyris venusta). This beautiful little bird is very common at the study site, but it never accompanies the mongooses.
What happened? The mongooses didn't change their behaviour at all in response to sunbird calls, but when they heard the drongo calls, they visibly relaxed and halved their rate of vigilance. This makes it clear that they really were relying on the drongo to help detect danger.
So why weren't Halcyon foraging with drongos today? I heard the resident drongos calling in the distance, but the mongooses simply ignored them. Fork-tailed drongos, of course, are wickedly efficient at capturing insects on the wing. Once a grasshopper gets airborne in the presence of a drongo, its fate is sealed. I suppose if I was a short-legged mongoose who needed three tries to land a grasshopper, I wouldn't be too keen on having a drongo hanging about either. It just shows, there are times when even your friends aren't welcome...

White-bellied sunbird (Cinnyris venusta).
Photo by Nigel Mushet, borrowed from here.
One of the many golden orb-web spiders (Nephila senegalensis) enjoying the abundance of grasshoppers.

Sharpe, L. L., Joustra, A. S. & Cherry M. I. 2010. The presence of an avian co-forager reduces vigilance in a cooperative mammal. Biology Letters. Published online 3 February. doi: 10.1098/rsbl.2009.1016.

Friday, March 26, 2010

Come into my parlour...

At this time of year, I don't envy flying insects.
In truth, I don't envy them anytime, but now, at the end of the wet season, their lot is particularly grim. The bush is brimming with orb-web spiders.
Tier upon tier of vast, disc-like webs tremble between every tree and bush. Each web spans about 1.5 m and shimmers golden when viewed from the side. A stroll through my study site leaves me feeling like Frodo in the tunnel of Torech Ungol.
The most common species is the massive golden orb-web spider, Nephila senegalensis. The females are daunting, with a body 25-30mm long (add legs and they're larger than my spread hand). They weave a web so strong it ensnares small birds (I released a struggling blue waxbill recently). Fortunately, they're harmless to humans and flee rapidly when their web is blunderingly destroyed, so the pitter-patter of scuttling feet on one's face lasts only a second or two.

Golden orb-web spider, Nephila senegalensis.

The golden orb-web spider is named for the colour of its silk. This is the patch of silk at the centre of the web.

An altogether more clinging species, is the black and yellow garden orb-web spider (catchy name, huh). It is also very large (25mm body) but is a bit less common.

 Black and yellow garden orb-web spider, Argiope australis.

You can see the zig-zags of white silk (called stabilimenta) that span its web, forming a cross at the centre where the spider hangs. The function of stabilimenta is still hotly debated, but these decorations may camouflage the spider, breaking up its outline, attract insects by imitating the ultraviolet runways of flower petals, or warn blundering vertebrates of the presence of a web.

From my point of view, the little (8 mm) yellow and black kite spider
is relatively inoffensive because it usually strings its web a couple of metres above the ground.

Yellow and black kite spider, Gasteracantha versicolor.

Friday, March 19, 2010

Feel the beat

While I was with the mongooses today, we came across a pair of short-snouted elephant shrews (Elephantulus brachyrhynchus).

It's only the second time I've seen these little animals, and they're breathtaking. Always nervous and poised for flight, they seem to consist of nothing but huge ears, wide, startled eyes (thanks to their distinctive white eye-ring), trembling whiskers and whiffling nose. Of course the mongooses noticed them as soon as I did, so there was no chance for a photo. The pair was instantly away, skittering wildly through the undergrowth with Spark (a Koppiekats female) in hot pursuit. But elephant shrews are amazingly fast (my mammal book describes their jinking hurtle as 'ricochetal locomotion') and they quickly lost the mongooses.

Elephant shrews (or sengis) are something of a mystery. Found only in Africa, they were believed to be Insectivores (they eat insects, after all). However, it turns out that they have the teeth and digestive tract of a herbivore (e.g. they have a relic caecum - the organ used by rabbits and horses to ferment grass). They're now thought to be a very ancient group, and they have their very own order: Macroscelidea.

Elephant shrews are diurnal (ah, I love African mammals) and they live as territorial, monogamous pairs. Apart from the usual squeaks and odorous gland secretions, they communicate using foot-drumming. They don't just stamp and vibrate their hind paws as an alarm signal (as, for example, with rabbits or phascogales), elephant shrews have incorporated drumming into their social interactions and aggressive displays too. Each species (and there are about 17) has its own unique pattern of drumming, with bouts of stomping varying consistently in length, frequency and duration. So if you're an elephant shrew expert, you can identify a species from its sense of rhythm!

This photo of a short-snouted elephant shrew was taken by Martine van Rooyen and borrowed from here.

Wednesday, March 17, 2010

A star by name and nature

I just realised that I haven't written about mongooses yet; most remiss!

My inaugural mongoose post is about the 'cover-mongoose' of this blog site (the bigger animal on the left of the blog-title photo). Orion (or KM002, to give him his proper title) is the dominant male of Koppiekats group, and I've been working with him for the last four years.

Dwarf mongooses are Africa's smallest carnivore (I like saying that – it somehow puts them on a par with lions, etc.). They live in close-knit groups of around 6-20 individuals, and are a highly cooperative lot (not toward me unfortunately, just each other) with everyone helping to rear the group's pups and protect one another from predators and rivals. Orion, like all alpha males, takes his social responsibilities very seriously. It's Orion who intervenes when the youngsters' spats grow too rough; Orion who leads the group away when someone scents a black mamba; Orion who spends hours perched high in a tree, or teetering atop a boulder, scanning for predators while everyone else forages.
Of course, he's got reason for such dedication: dominant male dwarf mongooses father about 80% of the group's pups, so Koppiekats is comprised, almost entirely, of his progeny. Still, there are times when he seems to go above-and-beyond the call of duty.

During my first summer, I was watching Koppiekats move their two-week-old pups between refuges (disused termite mounds). This is a noisy, protracted affair with everyone calling and dashing back and forth excitedly. The pups curl themselves into black, walnut-sized balls, and hang placidly from the adult's mouths as they are hauled over rocks and through thickets of grass and thorns. In the midst of all the confusion, a piercing alarm call rang out. Everyone madly dashed for cover as an African hawk eagle (their most feared predator) swooped overhead. Amethyst – Koppiekat's dominant female – was crossing a huge open rock face, and she instantly dropped the pup she was carrying and fled to cover. For a moment or two, there was complete silence; everyone was hidden. The eagle cruised low. The pup, lying exposed, way out in the open, started looking about groggily and was beginning to realise that it was on its own. It hadn't even opened its mouth to begin to wail, when a black streak came dashing out of the vegetation about 30m away. It raced at full gallop right across the group, hurtled over the open rock face, snatched up the pup as it raced by, and then disappeared back to safety. Naturally, it was Orion.

Koppiekats are named after the koppies on which they live. 

Monday, March 15, 2010

It's not PC, but I don't like snakes

The python came in again last night.

I think it's determined to eat a cat.

Like a genuine nature-blogger, I actually took some photos of it.

I tried to think of some way of frightening/disconcerting it, so it wouldn't want to come back, but apparently I'm not entirely over my snake phobia, which limited me a bit.

I tried tossing pillows at it (no effect), and hurling marulas at it (also no effect).
It accurately perceives me as a gutless wonder.
It slid back out the window after about an hour of me calling it names.
Fortunately, none of the pets noticed it, as their neuroses are bad enough already.
Maybe I should make fly-screens for the windows?
I'm hoping it will hibernate for winter....

I just realised things could be worse: check out this news item from Townsville, Queensland. Click here.

Wednesday, March 10, 2010

My hero

Snakes continue to complicate my life, but today I received help from an unexpected quarter.

Magic was deeply traumatized by our last encounter with the python; it was two weeks before she'd even risk sleeping on the floor at night.
Last week I noticed the python's track on the road by my house. That night it tried to take Wobbly Cat. She often sleeps outside on warm nights, and I found her in the morning standing stiffly on the drive, staring constantly around her with saucer eyes. She had a patch of dried saliva across her shoulders and, although seemingly unhurt, she would not move. Her legs trembled for the next four hours. I put her on my bed, and she's stayed there, continuously scanning the door, window and floor, for the last four days.

To exacerbate the trauma, yet another Mozambique spitting cobra (Naja mossambica) has moved into my house. These charmers can spit venom up to 1.5 metres and although their venom is relatively dilute (better for spitting) they're still lethal. The summer before last, a local ranger died after being bitten on the wrist by a youngster he was removing from a nearby lodge.

The cobras come into my house to hunt the frogs, who come in to catch the bugs, who come in to batter themselves against the lights (I felt like Dr Zuess there). My latest house guest spat in Magic's eyes twice on Saturday and although the dogs and cats are convinced its still in the house, I haven't been able to find where it's lurking (I found the last one nestled under the mattress on the bed in my spare room).

Anyway, today as I was working on my computer I heard a kafuffle on the back doorstep. Dashing out, I was startled to find a large Nile monitor (Varanus niloticus) happily scoffing down the spitting cobra. I'd missed seeing him actually kill the unfortunate creature, but he consumed it in less than 5 seconds. Nile monitors are Africa's largest lizard (growing up to 2 metres long) and this particular one (a modest 1.5 m) is a regular visitor. He licks out the dogs' food bowls and bathes in my dish of tadpoles. But until today, I had not realised what a wonderful asset he was!

Monday, March 1, 2010

Season of... yellow fruitfulness

The marulas are fruiting.

Everywhere the bush is carpeted with fallen yellow fruits.

Along the highway, troops of baboons sprawl beneath the roadside marula trees, lounging and banqueting like families on a Sunday picnic. Herds of impala gather in the trees' shade, tails flicking and cheeks bulging with the tell-tale lumps. They patiently grind the flesh away from the woody nut for about five minutes before suddenly expelling the nut like a champion cherry-pit spitter.

Wobbly Cat among marula fruits

Marula fruits are about the size of a small plum. They have a tough skin over a litchi or grape-like flesh that clings tenaciously to the rock-hard nut. The fruits fall when they're still green and sour, but after a couple of days they ripen to yellow and fill with a delicious juice. Biting into a ripe marula is like gulping a shot of very sweet liquor. The taste is mostly just sweet, but also acidic - not surprising considering that they contain four times as much ascorbic acid (vitamin C) as an orange.
Female marula flowers
Marulas (Sclerocarya birrea) are one of the dominant tree species at my study site so my long-suffering mongooses have to cope with my constant slurping and munching as I follow them around. A single tree can produce more than 500kg of fruit each year. As the fruiting period only lasts around 3 weeks, it's impossible for the wildlife to consume so much fruit and most of it simply rots beneath the tree. When I first came to the lowveld, I was appalled at this profligate waste, and felt guilty that I wasn't busily cooking up marula jam or marula jelly or marula wine... But come my first winter dry season, I realised that the fruit wasn't wasted after all. When everything is dry and desolate, and all the vegetation has lost its leaves, the protein and oil-rich nuts are a life-saving staple for wildlife. When the baboons or wart hogs are feasting upon old nuts, you can hear the gunshot-like sound of cracking nuts more than 100m away.
The tree squirrels simply gnaw out the nut's kernel, through 2 or 3 'eye holes'. And they leave behind middens of empty husks that look disturbingly like someone has slaughtered a whole posse of small animals.

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