| dc.description.abstract | This thesis presents the findings of a 3-year
field study of the African Fish Eagle Haliaeetus
vocifer Daudin 1858 in Queen Elizabeth National
Park, Uganda. The primary objective of this study
was to investigate the breeding biology of the
bird with emphasis on its seasonality and nest
productivity. The study also assessed the population
distribution and its structure, the
territorial habits and diurnal activity patterns,
and the food supply of the Eagle.
Habitat variables, especially the vegetation
cover and topography, along the banks of the
water bodies influenced the Eagle's distribution
patterns. Young birds were attracted to human
settlements whereas the distribution of territorial
adults bore no significant relationship
to this habitat factor:
A pair of adults maintained a territory
of about 29 ha. from which they excluded
con specifics and other large-birds although
the Eagle sat for about O% 6f its daytime,
it continuously scanned the sky for other Fish,
Eagles and other birds intruding into their
territory. The other activities, although
taking small percentages of the Eagle's daytime,
were all keyed to its territorial way of life.
Fish comprised 99.7% of the bird's diet in
this Park. Although most of the fish was caught
by the Fish Eagle, it also pirated from neighbouring
pairs and also from wandering conspecifics.
Piracy attempts on other fish-eating birds were
common. An adult bird ate about 275 g of fish
daily, the equivalent of 10.5% of its body weight.
The Eagle took fish comparable in size to that
harvested by man. In removing only 1.04% of the
amount of fish harvested annually by man from
the Lakes Edward/George water system, the bird is
not seriously competing with man for the fisheries
resource and nor is it playing a significant role
in the nutrient cycles of the area.
In the main , study area along the Kazinga
Channel, a pair had from 0-4' nests. Both mates
participated in nest building and repairing .
Alternate and frustration nests were built and
maintained. About 15,000 kg of dry vegetative
matter was locked up in their nests in the whole
Park at anyone time.
The breeding seasonality was correlated with
a number o( environmental variables of which only
temperature and water levels significantly
influenced the observed seasonality. Despite the
lack of strong correlation between rainfall and
breeding seasonality, birds preferentially laid
during the rains. The breeding interval averaged
about 10.7 months for all successive clutches
and 12.6 months for 94 normal ones.
The Eagle laid 1-3 eggs with the 2-egg
clutch being the commonest and the 3-egg one the
rarest. The fresh egg averaged 133.3 g and it
declined in weight with progressing incubation.
The conversion efficiency of the egg materials into
the body materials of the chick averaged about 70%.
Both adults participated in incubation but the
female did so significantly more than her mate.
Eggs were incubated for 95.5% of the daytime and
at 34.8 °c, well above the 25.7 °c ambient
temperature. The incubation period is about 41
days. Because incubation started with the first
egg, chicks were also hatched,as,synchronously.
This resulted in sibling aggression in which the
first chick dominated its siblings; especially
during feedings, for the first half of the'
approximately 76-day nestling period. Chick
losses were probably largely due to vertebrate
predation and mortality decreased with age.
The nestling grew and exceeded the weight of
the adult of its respective sex. The growth
curve conformed with the sigmoid form of animal
and other bird species and was best fitted by_
the Gompertz equation (Ricklefs 1967a & _1968al.
The behaviour of the chick is described. They
The influences of brood size, hatching order and the
sex of the young on its growth rate are discussed.
The growth rates of the femur, tarsus, humerus and
the standard wing and the plumage changes during
the nestling period are described. Nestling mortality
decreased with age and was largely due to chick
disappearance, most probably due to vertebrate
predation.
included sleeping, panting, defaecation, reactions to
other animals and birds, and interactions between the
chicks, especially sibling aggression.
The nestling was brooded intensely and for
about 93% of the observation time during the first
week of its life, and for a decreasing amount of
time thereafter. Brooding stopped by the sixth
week of the nestling period. It was almost solely
undertaken by the female, the male being' released
from this ,duty in order to hunt and provide for his
expanded family. Although he caught mot of the
prey at this time, the female delivered most of them
and did most of the feeding of the brood.
The nestling period averaged 76 days and" was
not significantly influenced by brood size or the
nest site. The maiden flight was preceded by
pre-flight exercises and was made without parental
coaxing. The post-fledging young fed largely on
prey remains which , during the early post-fledging
period, were usually delivered on the nest, and
which, during the late post-fledging period, it
grabbed from the parents. The eaglet dispersed at
about 112 days after its first flight or 188 days
after hatching. Parents apparently did not drive
away their young.
Increasing clutch size significantly decreased
hatching success with the I-egg clutch achieving
100%, the 2-egg clutch 82.3%, and the 3-egg clutch
67.2% hatching successes. Egg disappearance was
the most important cause of hatching failure,
infertility/addling intermediate and egg breakage
the least important. Larger clutch sizes favoured
the production of young. Although nestling
survival was highest (75.8%,,) 'in the young brood,
intermediate (69.7%) in the 2-chick brood, and
least (66.7%) in the 3-young brood, brood size
did not significantly 'affect the annual' survival
of young " F0 0 d sh0 r tag e was apparently not
important in the survival of broods but chick
disappearance , probably due to predation was.
Annual nest success was low, averaging 31.2%
for pair-years present and 44% for active nests.
The annual production averaged 0.46 young/pair,
0.65 young/active nest, and 1.49 young/successful
pair. Increasing territory size and numbers 6f
mature trees in the territories increased, although
not significantly, the production of young.
Additionally, increasing human disturbance about
the territory affected the breeding success of the
bird by reducing the numbers of nesting attempts
made. Annually, 56.1% of the breeding attempts
failed to fledge young, 23.4% fledged l-young
broods, 19.5% fledged 2-young broods, and only
1.0% raised 3-young broods. Eaglets reared in
young broods accounted for 36.3%, those raised
in 2-young broods for 59.5%, and those in 3-young
broods made up 4.2% of the total number of young
fledged during this study. Overall, 68% of all the
pairs present during the study bred, 32% did not.
Of 202 breeding attempts made, 26 (13%) of them
were replacement clutches. | en |
