Transcript Feeding Ecology of Giraffe (Giraffa camelopardalis) in a

Feeding Ecology of Giraffe
in a Fenced Game Reserve
in North-Central Namibia
Katherine Forsythe
&
Laurie Marker
Large Herbivores & Habitat

Large herbivores can alter habitat rapidly,
especially in savannah ecosystems

Need to understand interactions to
effectively manage landscapes

Even more important in small and/or
enclosed systems
Game fencing & Giraffe

In Namibia game fenced farms are
common and can stop movement of
wildlife
On small fenced game
reserves, giraffe may be
the largest herbivore
present

Implications of Game Fences

Population level
◦ Decreased genetic flow

Individual level
◦ Not enough forage, variety in forage or
preferred species

Habitat level
◦ Change in vegetation type/structure
Aims

Within a small game fenced reserve
◦ Determine what the giraffe are eating within
the reserve
◦ Is their feeding behaviour typical of giraffe in
other areas?
◦ Do the giraffe have preferences for certain
species?
METHODS
Study Site

Bellebenno Reserve
◦
◦
◦
◦
4000 ha
Game fenced
North-Central Namibia
Encroached semi-arid
thornbush savannah
dominated by Acacia spp.
◦ Main herbivore species
include giraffe, eland,
kudu, zebra and oryx
Methods

Individuals were identified and monitored
using spot patterns from photos collected
over 4 years
At time of study the
population consists
of 33 individuals

Methods

Focal follows were conducted on all
adults and sub adults during late dry
season (Sept-Oct)

Focals lasted for 15 mins feeding time

Started once the giraffe started eating
from a new tree/shrub
Methods

Recorded:
◦
◦
◦
◦
◦
◦
Tree species
Tree height
Distance between trees
Time spent per tree
Group size & composition
Identity of closest 5 trees
to first tree and whether or not eaten
subsequently
Methods

Relative abundances of dominant
tree/shrub species within the reserve
previously determined using circular plots
(n = 186)

Preferences on fine and broad scale
established using Jacob’s Index (-1 to +1)
RESULTS &
DISCUSSION
Group size & sex differences

Males browsed taller trees than females (3.9m vs.
2.7m) (t-test, p < 0.05)

No difference in distance moved between trees
(av. 36.4 m) or time spent per tree (av. 191 sec)
(t-tests, p > 0.05)

Av. groups size 4-5 individuals

More solitary adults male giraffe observed than
solitary adult female giraffe (χ2 test, p < 0.05)
Group size & sex differences

Similar to other studies where males
were found to browse higher than
females (e.g. Ciofolo & Le Pendu 2002)

Similar groups size to other areas (e.g.Van der
Jeugd & Prins 2000)

Typical in terms of males being more
solitary (e.g.Van der Jeugd & Prins 2000)
Tree species eaten

Giraffe recorded eating six plant species
A.Tortillis
4%
A.
Reficieus
24%

Most commonly eaten species
◦ A. erioloba, A. reficiens and A. fleckii
A.
Mellifera
15%
A.
Hebeclada
4%

A.
Erioloba
31%
A. Fleckii
22%
Most time spent eating
◦ A. erioloba (30%), A. fleckii (25%) and A. mellifera (18%)
Tree species eaten

Typical acacia dominated diet, though often
recorded to eat many more species (e.g. 45 spp.
Ciofolo & Le Pendu 2002 and 26 spp. Sauer et al. 1977)

Often seasonal differences in diet, with
lower numbers at certain times (e.g. only 5 spp. in
Dec, Ciofolo & Le Pendu 2002)

May use other species at different times of
the year (e.g. T. camphoratus in March/April but not winter, Parker
et al. 2003)
Fine vs. Broad scale habitat choice

Compare the tree species in areas in
which the giraffe foraged, with trees/shrub
species within entire camp

Giraffe chose to feed in areas with more
A. erioloba, A. fleckii, A. reficiens and lower
A. mellifera and T. camphoratus
Browse Preferences
A. erioloba
A. fleckii A. hebeclada A. mellifera A. reficiens
A.tortillis
1.00
Jacobs Index
0.50
Fine
0.00
-0.50
-1.00
Broad
Browse Preferences

Scale dependent

Strong preference for A. hebeclada, A.
erioloba & A. tortilis
Low availability of
A. hebeclada (<1%)
and A. tortilis (<4%)

Browse Preferences

Unlike our study, previous studies have
shown giraffe have preference for over
85% of important species eaten (Parker et al.
2003) or eat mostly in order of availability
(Parker & Bernard 2006)

Our study, only one of the four most
important species was preferred on a fine
scale
Acacia Browsing

High hydrolysable tannins
◦ = toxicity

And/or elevated condensed tannins
◦ = reduced dietary uptake

Made up all observations in our study

Potential long term effects?
Condensed tanin
content
Preferences & Tannin
-1

Fine scale
preference
1.5
Broad scale
preference
1
0.5
0
-0.5
0
0.5
Preference (Jacob's Index)
1
No correlation between preference and
tannin content
Summary of Results

Acacia dominated diet, but lower than
typical number of species being eaten

Typical group size and intersex differences
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Foraging habitat not same composition as
larger habitat = selecting foraging patches
Summary of Results

Selective browsing of less abundant but
preferred species
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Not related to published tannin results
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Up to 61% of the diet comes from nonpreferred species

Highly preferred species only accounts for
27% of available vegetation across reserve
Potential Implications

Species dependent response to browsing
◦ Decrease fruit production (Young and Augustine 2007)
◦ Reduce canopy & height (Dharani et al. 2008)
◦ Decrease growth rate and more susceptible to
drought (Birkett & Stevens-Wood 2005)
◦ Stimulate tannin production (Furstenburg & Van Hoven
1994)

Browsing selected species could rapidly
change habitat and could become more
unfavorable for giraffe
Conclusions

Preferences should be established on the
scale of foraging habitat

Small game fenced reserves, giraffe may be
forced to continuously browse nonpreferred species, which could have
detrimental effects on the animal

Selective browsing of less abundant
species could alter habitat
Future Directions

Seasonal changes in diet & preferences

Changes to habitat type over time

Monitoring health and breeding of population
Tannin contents
of continuously
browsed species

Acknowledgements

Aymeric Houstin, Ryan Sucaet and James
Slade for help in the field
CCF Volunteers and Interns for
help with data collection and
data entry
References
Birkett & Stevens-Wood 2005 Afr. J. Ecol. 41, 123-130
 Ciofolo & Le Pendu 2002 Mammalia 66, 183-194
 Dharani et al. 2008 Afr. J. Ecol. 47, 184-191
 Furstenburg & van Hoven 1994 Comp. Biochem. Physiol.
107, 425-431
 Parker & Bernard 2006J. Wild. Mgmt. 70, 1477-1480
 Parker et al. 2003 Afr. J. Ecol 41, 245-253
 Sauer et al. 1977 S. Afr. J. wildl. Res. 7, 53-59
 Young & Augustine 2007 Biotropica 39, 559-561
 Van der Jeugd & Prins 2000 J. Zool. Lond. 251, 15-21
