Travelling through Southern Africa in October, I was excited to photograph these characters...
The weaver birds (Ploceidae) are famous for their elaborate nest construction. They mainly inhabit sub-Saharan Africa, although a few species occur in Asia too. For many of the Ploceus weavers (e.g Village and Masked weavers), the complex nest is crafted by the handsome male, who weaves strips of grass and leaves together using a similar technique to human weavers. Somehow he can complete this exquisite construction within a day or two!
Once the nest is complete, the males try to attract females by hanging upside-down underneath it and fluttering their wings whilst producing a metallic 'churring' song. If a female approves of a male's nest, she lines it before she mates with the male and lays her eggs. Afterwards, the male's attention rapidly shifts towards building more nests and attracting as many females as he can.
Female weaver birds have some battles of their own to fight. For starters, other female weavers in the colony might try to sneak their eggs into her nest! But there is a far more sinister invader about which she should be concerned. A number of these colonial breeding weaver bird species (such as Village, Masked and Cape weavers) are hosts for the brood parasitic diederik cuckoo (Chrysococcyx caprius).
Although the diederik cuckoo males are gorgeous metallic green-backed birds with vivid red eyes, their females are somewhat duller and more difficult to spot. The females have to be sneaky, so that they can slip in and deposit their own egg in a weaver bird nest the moment the opportunity arises.
Weaver birds and diederik cuckoos have provided an interesting natural experiment because weaver birds were introduced from mainland Africa to the islands of Mauritius and Hispaniola, where they live life diederik-free. Studies conducted by David Lahti suggest that the absence of diederik cuckoos on the two islands has resulted in the weavers eggs becoming less variable in appearance across females and less consistent within a given female's clutch. So without the pressure of brood-parasitism, weaver birds appear to have reduced the pigmentation that they add to their eggshells. However, the weaver birds are no less likely to reject foreign eggs than mainland birds, when the harder task of distinguishing between eggs due to the greater within-clutch variation is accounted for.
So it seems as though weaver egg appearance on mainland Africa has evolved in response to parasitism by diederik cuckoos. This has arisen via an evolutionary arms-race between cuckoos producing mimetic eggs to fool the weavers, and weavers producing eggs that minimise the risk of accepting a cuckoo egg or rejecting their own eggs by accident.
I enjoyed reflecting on these fascinating interactions between diederik cuckoos and weaver birds as I watched this male diederik relentlessly calling out to attract a female... "dee-dee-dee-dee-derik". Meanwhile, in a tree not more than 50 meters away from their foe, the weaverbird males hung upside down flapping their wings and churring to impress their own ladies, blissfully unaware of the imminent dramas that would unfold in their carefully woven nursery baskets.
I have a passion for robins. And a passion for Africa. Out of these two separate interests a quest was born! A special zoological quest that took me back to my childhood home in Zimbabwe, to marvel at one of the most elusive and rare robins on the continent...
My first independent research project as an undergraduate was to study the song of European robins in the green spaces around the City of Bristol. This left me with inordinate fondness for these confiding, beady-eyed balls of bright red fluff! On finding Terry Oatley and Graeme Arnott's delightfully illustrated "Robins of Africa", I realised it was time to return to Africa once more, but this time to visit Zimbabwe for the first time as an adult.
I left Zim when I was 8 years old, but it had a lasting impression on me and is no doubt the reason why I study the behaviour of animals. As a kid I was fascinated by the chameleons and agamas that I would find and then carry around. I stared in wonder at the big grey mammals that could destroy your tent or car, or even you if you made the wrong move, but were typically gentle giants. The big predators struck instinctive awe and fear into me, especially after one time hearing a lion roar not meters away from our tent in the dead of night. But the birds were often flitting gems that I couldn't quite capture and comprehend in the detail they deserved.
The youngest of 4 kids, I travelled in the boot of our Renault hatchback with the luggage. A benefit of this position was ready access to the field guide books that I would flick through to while away the long bumpy hours over corrugated dirt roads. In these guides, I glimpsed the beauty and variety of flora and fauna that Zim had to offer. And now, over 25 years later, I have sought to capture some of this with grown-up eyes, and lots of optical gear. So I decided that it was time to go in search of Swynnerton's robin in the Bvumba forests in the Eastern highlands of Zimbabwe.
Swynnerton's robin is interesting for two main reasons. The first lies in its name: Swynnertonia swynnertoni. The latin and common names were given to commemorate the entomologist, and Fellow of the Linnean Society, Charles Swynnerton, who tragically died en route to collect a prestigious award for his contributions to tsetse fly research. Swynnerton was a keen naturalist and his interest in cuckoos led him to suggest that host birds might paint their eggs with 'signatures' to help them detect foreign cuckoo eggs in their nests. And in time these ideas were vindicated by the work of Claire Spottiswoode on cuckoo finches. Interestingly enough, Swynnerton's robin is also recorded as an occasional host for the red-chested cuckoo.
The second reason that Swynnerton's is a particularly interesting robin is because this is the only African robin species for which the female can be readily distinguished from the male in the field based on her olive-green instead of dark grey face. The male puffs out the sharply contrasting black and white bib on his neck when he conducts his bobbing displays to the female to entice her. However, we don't yet understand why this sexual dimorphism has emerged in just this one African robin species.
So with all this in mind, it was a spectacular thrill to creep through the tangled undergrowth of the Bvumba and spy a pair of these special birds. We followed them intently as they foraged in the understory. The light environment was a photographic challenge, but then this handsome male briefly popped out into a clearing, lingering just long enough for me to take this single photograph.
A successful quest! But I am left even more curious and enchanted by the Bvumba forest and its inhabitants. Now listed as 'vulnerable' and with suitable habitat rapidly declining, this fascinating and unobtrusive forest-dweller could sadly fade away as revenue from international tourism and conservation efforts have declined in the area. This would be a real shame, not just for Swynnerton's robin, but for the many other fascinating species living in the region that deserve our appreciation and protection.
I hope that I will return to see more of these fascinating birds in the Bvumba one day!
If you are considering a trip to Madagascar ... just go!
behaviour and evolution