Phil Shaw

Back in 1995 Derek Pomeroy from Makerere and Chris Perrins from Oxford University arranged for 25 nestboxes to be erected in the vicinity of Ruhija. Their aim was to shed light on the breeding biology of a small songbird endemic to the Albertine Rift: the Stripe-breasted Tit. What sets this species apart from most other Albertine Rift endemics is that it is closely related to some of the world’s most intensively studied birds; species like the Great Tit and Blue Tit (in Europe), and the chickadees of North America. Many of these species will readily take to nest-boxes, enabling researchers to monitor their breeding success, and to catch and ring (or ‘band’) the parents and chicks.

About 20% of the world’s birds live in the north temperate zone, where high winter mortality and a super-abundance of food in the spring have a marked effect on population dynamics and brood sizes. So, while many European and North American songbirds are known to be short-lived fast breeders, capable of rearing large broods of chicks, their counterparts in more ‘benign’ tropical habitats are usually characterised as long-lived, slow breeders. So much so that - as one Australian researcher has quipped - tropical birds seem to approach reproduction as if it’s really just a spare-time interest. So why do they appear to live life in the slow lane?

nestbox.jpgInitially the 25 nest-boxes were inspected monthly, by Robert Bitariho. But it was not until 1996 that the first two Stripe-breasted Tit nests were discovered. This was before the advent of internet access at Ruhija, and these discoveries were passed on to Derek Pomeroy by letter, or by e-mail from Kabale. Over the next few years, nest-box inspections were sporadic, and very little information was gleaned from the few nests discovered. Accordingly, Derek Pomeroy and Chris Perrins placed a short note in the Bulletin of the African Bird Club, inviting anyone interested to visit Ruhija to help monitor subsequent breeding attempts.

In response to their article I contacted Derek and arranged to visit Ruhija in October 1998, reasoning that (as throughout much of Africa) breeding activity was likely to coincide with a seasonal peak in rainfall, September and October being the two wettest months at Bwindi. Unfortunately, although it was not hard to find Stripe-breasted Tits around Ruhija, none seemed to be stimulated by the vast quantities of water tipping down every day. My accommodation (a room in the Education Centre) was comfortable and waterproof, but offered limited scope for drying out sodden rain gear each night. Convinced that this was little more than bad luck, I returned in October 1999 to witness first-hand a similar absence of breeding activity. We now know that Stripe-breasted Tits generally breed in the driest months of the year.

In January 2000 a clutch of four Stripe-breasted Tit eggs was discovered by Narsensius Owoyesigire and the Godfrey Myooba, two Field Assistants at ITFC. When the eggs eventually hatched they recorded the frequency with which parent Stripe-breasted Tits brought food to the nestbox, showing that their ‘provisioning rate’ was much slower than is typical of European tit species, even allowing for the smaller brood size. A second brood, 18 months later, provided an opportunity to double our sample size, and also revealed the presence of helpers, confirming that Stripe-breasted Tits sometimes breed cooperatively. Thanks to colour-ringing it has since emerged that most pairs have between one and three helpers, who are usually sons from earlier attempts.

In the early years, much of the fieldwork was undertaken by Godfrey and Narsensius. But since 2000 Narsensius has carried out most of the nestbox inspections, observation sessions, ringing and weighing of chicks, often assisted by Savio Ngabirano and, more recently, by Lawrence Tumugabirwe and Margaret Kobusingye. In 2004 Narsensius and Savio were joined for a few months by a volunteer from the UK, David Ebbutt, who helped them to record incubation and provisioning rates. 

Early in 2003 a student, Jane Yatuha, followed the outcome of three breeding attempts for her MSc project, one of these being in a nestbox close to the Director’s House. At that time the director’s house accommodated the ITFC library, providing Jane with a dry and suitably academic setting from which to make her observations.

In the course of Jane’s study some of the adults and chicks were given colour rings, to help identify them later. Since 2004, Narsensius and I have colour ringed virtually all breeding adults, their helpers and offspring, allowing us to monitor their subsequent survival, movements, breeding attempts and divorces. It is clear that Stripe-breasted Tits are indeed ‘slow’ breeders, in the sense that their annual fecundity is much lower than that of their European and North American relatives. Now, nine years since ringing was begun, there are also sufficient data to determine whether Stripe-breasted Tits live correspondingly longer.

There remains the question of why Stripe-breasted Tits choose to breed during the drier months of the year. Routine meteorological data collected at ITFC should help to piece together the relationship between rainfall patterns and breeding activity. A more promising line of enquiry lies in linking breeding activity with leaf production in local tree species, since tender young leaves nurture fat, juicy caterpillars, which in turn sustain healthy chicks. Fortunately, since 2008, leaf phenology data have been collected each month from a sample of trees around Ruhija, as part of the long-term Mountain Gorilla study. These data may enable us to explore the link between rainfall, leaf production and Stripe-breasted Tit breeding success, perhaps providing an insight into the likely impacts of changing rainfall patterns on one of the Albertine Rift’s endemic songbirds.

To date, much of the cost of the Field Assistants’ time has been borne by ITFC. Without this initial boost, and the support provided by Alastair McNeilage, Douglas Sheil and Miriam van Heist, it would not have been possible to sustain this study over its 17 years."