ITFC as I experienced it
back then- Phil Shaw
Stripe-breasted Tits at
Ruhija: life in the slow
lane
"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?
Initially
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." |