I have spent the last 3 summers monitoring cuckoos and their reed warbler hosts at Wicken Fen Nature Reserve, guided by the vast wisdom of Nick Davies: a master cuckoo whisperer. What an immense privilege it has been to learn about this fascinating system and landscape first-hand! If you also want to immerse yourself in the intricacies of life as a cuckoo on Wicken fen, then read Nick's exquisite book 'Cuckoo: cheating by nature'. To see the fen and it's inhabitants through Nick's eyes is to unlock a secret world. And this little world has firmly etched a place in my heart.
When I first started out on this project, it was a massive sensory adjustment for me to be surrounded by water and lush greenery after 6 years of Kalahari desert and red dust. I can't help but identify with the reed warblers and cuckoos who excitedly sing with the arrival of spring, and then pack up in search of Africa before the autumn seeps in. Late September every year I experience my own 'Zugunruhe', and dream about filling a backpack for African migration. But in summertime, I have begun to feel quite at home amongst the reeds.
This season's cuckoo highlights have been....
Watching a reed warbler build a nest insulated with sheep's wool and then discovering that a cuckoo had been watching too! She certainly laid her egg in the cosiest of nests that was available in mid-May. I thought to myself, that's where I'd put my egg if I had one! But of course, cuckoos lay lots of eggs, so not all of the nests that she used were so superb.
Observing the fascinating deimatic behaviour of cuckoo chicks. Cuckoos remain dependent in the nest for much longer than the reed warbler's own young. Presumably the reed warbler nestlings leave as soon as they can in order to avoid predation, since the longer they spend in one spot and the bigger and noisier they get, the greater the risk of being discovered and eaten. The cuckoo takes longer to fledge and uses a different strategy - any predator approaching the nest by this stage will presumably be as surprised as I am to see a flash of flame red and a lunging, snapping mouth, rearing up out of the nest! It definitely doesn't evoke the impression of a delicious baby bird.
As this season draws to a close, although slightly weary and worn from fieldwork, I am already missing the sneaky cuckoos and the gentle reed warblers. The ephemeral nature of this habitat makes it feel as though it might have all been a dream - one day a peacock butterfly can be feeding on lush blossoms as swifts scream above, but soon enough the same scene might feature only the rustle of dry yellow reeds and a sullen sky.
Even though there will be no chance of cuckoos, the pink skies and starling murmurations will entice me to return to visit the fen over the winter. Or perhaps because absence truly makes the heart grow fonder, I will simply visit the winter fens to mourn the summer, with regret for any day that I took for granted amidst the hustle and bustle of busy data collection.
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.
The biennial meeting of the International Society for Behavioural Ecology in Exeter was exciting, inspiring and quite exhausting! Lots of brilliant talks, catching up with old colleagues and friends, and of course meeting some new folk, kept me very busy for the week! I chaired a fascinating session on brood parasites and presented a poster on my work on testosterone and song, which led to lots of interesting chats with people.
Can't wait for the next one in 2018!
behaviour and evolution