Differential foraging of oxpeckers on impala in comparison with sympatric antelope species

Article (PDF Available)inAfrican Journal of Ecology 28(3):240 - 249 · April 2008with 313 Reads
DOI: 10.1111/j.1365-2028.1990.tb01157.x
Cite this publication
Abstract
Published data reveal a significant positive relationship between number of red-billed oxpeckers Buphagus erythrorhynchus per unit body surface area and species-typical body weight, suggesting that the larger ungulate species maintain a higher density of tick mass per unit surface area. The impala Aepyceros melampus is the smallest ungulate that oxpeckers are reported to attend. A field survey of attendance by red-billed oxpeckers on impala and 4 other sympatric antelope, 2 of which are larger than impala, revealed that only impalal were attended by oxpeckers. Oxpeckers foraged upon areas of the body that impala cannot reach with their own mouths by oral grooming. The typical behavioural response of impala to oxpecker foraging was toleration or accommodation. That impala apparently harbour a greater tick mass per unit body surface area than the other antelopes compared could reflect the fact that impala inhabit wooded areas, higher in tick density than grassland areas inhabited by the other antelopes. -from Authors
Afr.
J.
Ecol.
1990,
Volume
28,
pages
24G249
Differential foraging
of
oxpeckers on impala
in
comparison
with
sympatric antelope species
BENJAMIN L. HART, LYNETTE A. HART
and
MICHAEL
S.
MOORING
Department
of
Physiological Sciences, School
of
Veterinary Medicine, University
of
California,
Davis, Caiifornia
95616,
USA
and Department
of
Animal Physiology, University
of
Nairobi,
Nairobi, Kenya
Summary
Regression analysis performed on published observations of oxpeckers foraging
for ticks on different species of ungulates revealed a significant positive relationship
between number of red-billed oxpeckers per unit body surface area and species-
typical body weight. The relationship suggests that the larger ungulate species
maintain a higher density
of
tick mass per unit surface area. The impala is the
smallest ungulate that oxpeckers are reported to attend.
A
field survey ofattendance
by red-billed oxpeckers on impala and four other sympatric antelope (Thompson’s
gazelle, Grant’s gazelle, Coke’s hartebeest and topi), two of which are larger than
impala, revealed that only impala were attended by oxpeckers. Oxpeckers foraged
upon areas
of
the body that impala cannot reach with their own mouths by oral
grooming. The typical behavioural response of impala
to
oxpecker foraging was
toleration or accommodation. These observations suggest that impala harbour a
greater tick mass per unit body surface area than the other antelopes compared.
This could reflect the fact that impala inhabit wooded areas, reportedly higher
in
tick density than grassland areas inhabited by the other antelopes.
Key
words:
Impala, oxpecker, parasites, antelope, ticks, infestation.
Resume
Une analyse de regression exkcutee
a
partir d’observations publikes de pique-
boeufs cherchant les tiques sur diffkrentes especes d’ongults a reve1C une relation
positivement significative entre les nombres de pique-boeufs
a
bec rouge par unite
de surface corporelle et le poids corporel de l’espece. La relation siuggkre que les
plus grandes especes d’ongules abritent une plus haute densite de tiques par unite
de surface.
L’impala est le plus petit ongule sur lequel on ait rapport6 les ‘services’ des pique-
boeufs. Une etude de terrain sur la presence de pique-boeufs
a
bec rouge sur
l’impala et
4
autres antilopes sympatriques (gazelle de Thompson, gazelle de
Grant, bubale de Coke et topi), dont
2
sont plus grandes que l’impala, montre que
seul l’impala etait assist& par les pique-boeufs. Ceux-ci se nourrissent
a
des endroits
du corps que l’impala ne peut atteindre de sa propre bouche en grooming oral. Le
comportement reponse typique de l’impala
a
la presence des pique-boeufs est fait
de tolerance et d’acceptation. Ces observations suggkrent que l’impala abrite une
plus grande densite de tiques par unite de surface corporelle que les autres antilopes
de l’ktude. Ceci peut refleter le fait que l’impala habite des zones boiskes, bien
connues pour abriter une plus grande densite de tiques que les zones herbeuses
frequentkes par les autres antilopes.
Oxpecker Foraging on Impala
24
1
Introduction
Two species of tick birds are found in Africa: the red-billed oxpecker
Buphagus
erythrorhynchus
(Stanley), and the yellow-billed oxpecker
B.
africuna
(Linnaeus).
The yellow-billed oxpecker, with a broad heavy bill, feeds with a pecking or
plucking action to remove adult ticks and seems to prefer buffalo
(Syncerus cafler
(Sparrman)), black and white rhinoceros
(Diceros bicornis
(Linnaeus) and
Ceratotherium sirnum
(Burchell)), zebra
(Equus
spp.), eland
(Trugelaphus oryx
(Pallas)) and giraffe
(Girafu camelopardalis
Linnaeus), which generally have
moderate to heavy tick loads and large feeding surface areas (Attwell, 1966;
Grobler
&
Charsley, 1978; Hustler, 1987). The red-billed oxpecker, on the other
hand, has a narrower bill that is used in a scissoring action to grasp larval and
nymphal ticks in addition to plucking adult ticks and is typically seen on a wider
range of host species, including the more densely-furred, medium-sized antelope
such as greater kudu
(Tragelaphus strepsiceros
(Pallas)), sable antelope
(Hippotragus niger
Harris), roan antelope
(Hippotragus equinus
(Desmarest))
and the smaller impala
(Aepyceros melampus
(Lichtenstein)) (Atwell, 1966;
Bezuidenhout
&
Stutterheim, 1980; Buskirk, 1975; Mundy, 1983).
Oxpeckers depend on the presence of ticks on domestic and wild ungulates for
the mainstay of their diet (Attwell, 1966; Bezuidenhout
&
Stutterheim, 1980).
Stomach analyses of free-living oxpeckers by Bezuidenhout
&
Stutterheim
(
1980)
revealed that the average bird had approximately
400
ticks in its stomach, and that
captive oxpeckers can consume as many as
7000
larval or 60 adult ticks in 24 hr.
When cattle were experimentally infested with larval ticks, foraging by red-billed
oxpeckers was found to reduce the number
of
ticks by twenty to 99%, depending
on the developmental stage
of
ticks that the birds were allowed to feed upon. The
greatest reduction in ticks occurred when the oxpeckers were allowed to feed on
adult ticks (Bezuidenhout
&
Stutterheim, 1980).
For oxpeckers to continuously associate with an ungulate species the foraging
must be cost effective, that is, there must be enough ticks on the typical host to
support the energy expenditure of first finding the host animal and then searching
for ticks. Several factors would be expected to influence the economic feasibility of
exploiting a given host species. One major influence is host size. Larger ungulates,
which are reported to harbour a larger proportion of adult ixodid ticks than
smaller ungulates (Horak, 1982; Horak
et al.,
1983), would be expected to be more
commonly frequented by oxpeckers than smaller ungulates, which harbour more
larval and nymphal stage ticks. Larger ungulates could attract more oxpeckers per
animal either because they support a greater tick mass per unit body surface area
than smaller ungulates, or because they possess a greater absolute surface area to
forage upon. In addition to host size, ungulate species that inhabit regions of high
tick density where individuals are likely to pick up many ticks should be more
preferred by oxpeckers than ungulates living in a lower tick-density habitat.
Finally, whether an animal tolerates or rejects a tick bird’s foraging actions would
also influence whether animals are attended by tick birds. Members of an ungulate
species that are not customarily attended by tick birds may be intolerant of
a
bird
alighting on them. Assuming that removal of ticks contributes to an animal’s
fitness, one would expect a species whose members typically harbour large
numbers
of
ticks to have evolved behaviour accommodating or facilitating the
foraging patterns of the birds.
242
Table
1.
Body weight and
observed oxpeckers on
ungulates
B.
L.
Hart,
L.
A.
Hart and
M.
S.
Mooring
No.
of
oxpeckers per animal’
Species Body wt
(kg)’
Red-billed Yellow-billed
White Rhino 4125 0.452
Black Rhino
1
I50
0,833
Buffalo 650 0,429
Giraffe 650 0.207
Eland 575
-
Sable 328
-
Zebra 27
1
0.0707
‘Body weight data are from Kudu 234 0.0322
IOxpecker tending data Nyala 104 0.0168
from
Stutterheim
(1980)
and Impala 56 0,00793
Grobler
&
Charsley (1978).
Haltenorth
&
Diller (1980). Wildebeest 214
0.01
12
0.133
0,214
0.0527
0.0677
0.0264
0,0668
0.0109
0.003 19
-
-
-
A
perusal of the literature documenting oxpecker counts on various ungulate
species indicates that larger ungulates attract oxpeckers more frequently than
smaller ungulates (Grobler
&
Charsley, 1978; Stutterheim, 1980; Stutterheim
&
Panagis, 1985). These studies further suggest that oxpeckers forage almost exclus-
ively upon large or medium size ungulates, as smaller species of gazelle
(Gazeflu
spp.), hartebeest
(Alcelaphus buselaphus
Pallas), and topi
(Damaliscus
lunatus
Burchell) are not mentioned in the reports or are mentioned as not being attended
by oxpeckers. An exception to this generalization is impala, a relatively small
antelope attended by oxpeckers in Kenya (Hart
&
Hart, 1988) as well as in Zambia,
Zimbabwe, Botswana and South Africa (Attwell,
1966;
Grobler
&
Charsley, 1978;
Stutterheim, 1980; Stutterheim
&
Panagis, 1985). If the attractiveness of an
ungulate for foraging by oxpeckers is related to body size, and impala are unusual
among smaller ungulates in being attended by oxpeckers, these findings would
suggest that impala harbour more ticks than comparably sized antelope. Heavier
tick loads could be a function of impala habitat preference, social behaviour, and/
or
foraging habits.
To
obtain a quantitative expression of the relationship between ungulate body
size, surface area and attending preference by oxpeckers we conducted an analysis
using the oxpecker density (‘preference’) values from Stutterheim (1980) for red-
billed oxpeckers and from Grobler
&
Charsley (1978) for yellow-billed oxpeckers.
Preference values (oxpeckers per animal) for various ungulate species are tabulated
in Table
1.
Data on the white rhinoceros were not included in the analysis because
its weight is four times that of the next heaviest species. Stutterheim
&
Panagis
(1985) also reported on number of oxpeckers per animal and their findings were
similar to the two studies we utilized. Published body weights from Haltenorth
&
Diller (1980) were averaged for males and females to obtain mean species mass
(Table 1).
Simple linear regression was performed separately for red-billed and yellow-
billed oxpeckers. We first plotted number of oxpeckers per animal against body
mass. Because larger body mass
is
confounded
by
greater absolute surface area
(and length) available for foraging, the preference values were adjusted to reflect
2
0.6
a,
0
a,
Q
0.4
0.2
t
0
Oxpecker Foraging on Impala
243
8
8
n
AA
8
A,
5
=o.otfi*
*
I
I
I
I
0
200
400
600
800
1000
1200
Species-typical
Mass
(kg)
Fig.
1.
Scatter plot of number
of
red-billed oxpeckers
(0)
and yellow-billed oxpeckers (A) per animal
as
a
function
of
species-typical body mass.
There
is
a
significant positive relationship for red-billed oxpeckers
(y=
-0.1
14+0.001x,
$=0.92, P=0.0002),
but
not
for
yellow-billed oxpeckers
(r’=0.46,
P=0.09).
density of oxpeckers per unit surface area. The number of oxpeckers per animal
was divided by body mass raised to the allometric exponent of
0.67
in order
to
convert mass to relative surface area (Schmidt-Nielsen, 1984). We omitted the
allometric coefficient
(w
10 for the mouse-to-elephant curve) because the calcu-
lations were for comparative purposes only. The adjusted value was then regressed
against body mass. Preference values were similarly converted to oxpeckers per
unit body length by dividing by mass raised to the
0.33
power (Economos, 1983)
and regressed against body mass.
A
scatter plot of oxpeckers per host animal as a function of body mass (Fig.
1)
indicates a positive relationship for red-billed
Cy
=
-0.1
14+
O.OOlx,
r2
=
0.92,
P=
0.0002), but not for yellow-billed oxpeckers
(r2
=
0.46,
P=
0.09).
When the
adjustment was made to hold body surface area constant by dividing by rna~s~’~’,
regression revealed a significant relationship for red-billed
0,
=
-
0.0003
1
+
0-OOOOlx, r2
=0-89,
P=
0-0004; Fig. 2), but not for yellow-billed oxpeckers
(r2=
0.32,
P=
0.19). With oxpecker density adjusted for body length regressed
against body mass, again there was a significant relationship for red-billed
oxpeckers
(y
=
-
0.0085
+
O.O0007x,
r2
=
0.92,
P=
0.0002) but not for yellow-billed
oxpeckers
(r2
=
0.41,
P=
0.12). We conclude that red-billed oxpeckers prefer larger
host species, and that this preference is over and above the factor of greater surface
area and length.
Because
of
this robust relationship between body mass and red-billed oxpecker
attendance, with impala being the smallest antelope species attended, we were
interested in determining if impala were unique among smaller antelope in attract-
ing oxpeckers.
A
field study was conducted to compare oxpecker attending of
impala with other small or medium sized antelope in the same area. Two of the
species, topi and Coke’s hartebeest, are larger than impala, one species, Grant’s
gazelle
(Gazella granti
Brooke), is about the same size, and one species, Thomson’s
gazelle
(G. thomsoni
Giinther), is smaller (Table
2).
244
B.
L.
Hart,
L.
A.
Hart and
M.
S.
Mooring
,
,
,
,
,
,
0
Species-typical
Mass
(kg)
Fig.
2.
Number
of
red-billed oxpeckers per unit body surface area (number of oxpeckers divided by
masso6’)
regressed against species-typical body mass. The relationship is highly significant
01
=
-0.0003
1
+
O~OOOO~X,
f2
=
0.89.
P=0.0004).
Dashed lines indicate
95%
confidence bands. Species abbreviations are:
I,
impala.
N,
nyala;
W,
wildebeest;
K,
kudu;
Z,
zebra;
G,
giraffe;
B,
buffalo;
R,
black rhinoceros.
Materials
and
methods
The principal study took place in the Mara region (inside and outside of the Masai
Mara Reserve) and on farms in the Lake Naivasha area of Kenya. The species
observed in both areas were Thomson’s gazelle, Grant’s gazelle, impala and Coke’s
hartebeest. Topi were observed in the Masai Mara area only. Impala were also
observed in the Lake Nakuru area as a separate non-comparative project since the
comparison antelope species are not found in Nakuru National Park. Both female
groups, consisting usually of several females and one territorial male, and all-male
bachelor groups were observed for all species.
Impala inhabit open woodland areas and in this study they were observed
mostly at the interface of wooded areas and grassland meadows or plains. The
other antelope inhabit mostly grassland areas, although they were sometimes near
wooded areas. All observations were made from four-wheel-drive vehicles using
binoculars or a spotting scope. Groups
of
either female or male bachelor antelope
were observed at distances of 50-200 m for the presence
of
oxpeckers attending any
animals in the herd. Groups were observed for 5-20 min before concluding that
there were no oxpeckers. The number
of
antelope per herd and the maximum
number
of
oxpeckers seen during the observation period were recorded. Herds
were observed just once on any given day. An attempt was made to observe as
many separate herds of animals as possible in order
to
avoid pseudoreplication
(Machlis
et
al.,
1985).
If
oxpeckers were present, some animals were chosen for
focal observations and the total time spent on the antelope
by
the bird and the body
parts foraged upon were recorded. Any immediate rejection of an oxpecker that
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    Grooming is among the most commonly performed parasite defence behaviour patterns and is effective in removing ticks. Because both tick infestation and grooming activity have a cost, natural selection should favour individuals that match the current level of tick threat with an appropriate level of tick-defence grooming effort. To test this notion, the relationship between seasonal tick challenge and grooming rate by wild, free-ranging impala, Aepyceros melampus, was investigated in Zimbabwe. Adult ticks in the vegetation showed a dramatic decrease from the warm/wet season to the hot/dry season, declining from 2·4 ticks per drag sample and 58 ticks per removal plot to virtually nil. This decline was mirrored by an associated decline in grooming rate by all impala in which self-oral and scratch grooming bouts per h decreased 30–45%. Allogrooming encounters per h (corrected for lying-down time) and total allogrooming delivered, as measured by bouts or episodes delivered per h, decreased for males but did not change for females. Overall percentage of time spent in all forms of grooming declined 37–57%. Multiple regression analysis revealed that, with the seasonal effects of temperature and rainfall held constant, self-grooming rates were significantly and positively correlated with adult tick challenge, indicating that impala adjusted self grooming to seasonal fluctuations in adult tick threat. Allogrooming delivered was influenced by nymphal tick challenge; because the larvae and nymphs of the most abundant tick species favour the ear and neck region (where allogrooming is concentrated), allogroom-ing appears to function to remove immature ticks from body regions inaccessible to self-oral grooming. These results are what would be expected if grooming serves to remove ticks before they can attach and engorge, and supports the view that grooming is an evolved response to the threat of excessive tick burden in the impala's natural environment.
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    Roosting behaviour and host preferences of oxpeckers were investigated In Moremi and eastern Caprivi. Redbilled oxpeckers were found on six mammal species in Moremi and two in Caprivi. Yellowbilled oxpeckers were found on two host species in Moremi and one in Caprivi. Redbilled oxpecker roosts were located in palm trees in Moremi, while yellowbilled oxpeckers roosted on their host species. Roosting by yellowbilled oxpeckers on their hosts is thought to be the result of their more limited choice of host species. Slaapgewoontes en gasheervoorkeure van renostervoëls is in Moremi en oos Caprivi ondersoek. Rooibekrenostervoëls is op ses soogdierspesies in Moremi en twee in Caprivi gevind. Geelbekrenostervoëls is op twee gasheerspesies in Moremi en een in Caprivi gevind. Rooibekrenostervoëls slaap in palmbome in Moremi, terwyl geelbekrenostervoëls op hui c gasheerspesies slaap. Dit word aanvaar dat die aanpassing ? van geelbekrenostervoëls om op hul gashere te slaap 'n gevolg is van hul meer beperkte keuse van gasheerspesies.•
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    Infestations of Boophilus microplus (Canestrini) were established by applying single batches of larvae to individually stalled cattle, and the percentage yields of engorged female ticks from animals kept in harness to impede licking were compared with those from animals allowed to lick freely. In the harness trials, 33 per cent. of female ticks survived to fall as engorged adults from the host; in individual infestations this survival ranged from 5 to 69 per cent. In the trials without harness the corresponding survival was 9 per cent., ranging from 0.1 to 32 per cent. Statistical analysis showed a highly significant effect of harness in promoting survival of ticks. Licking (and other forms of host behaviour, e.g. kicking and rubbing, which produce tick mortality by mechanical means) must be considered in any study of natural mechanisms regulating cattle tick populations.
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    Abstract The seasonal activity of the adults of 13 tick species was studied on cattle herds in the Central Province of Zambia from 1969 to 1972. The six main species, Boophilus decoloratus (Koch), Hyalomma marginatum rufipes Koch, H. truncatum Koch, Amblyomma variegatum (F.), Rhipicephalus appendiculatus Neum., and R. evertsi Neum. behaved as previously described for the Southern Province. R. compositus Neum. appeared from August, with peak numbers in September–October. R. simus Koch and R. tricuspis Dön. appeared from October, for seven months and three months respectively. R. supertritus Neum. and Ixodes cavipalpus Nutt. & Warb. had a brief activity season from November to January, and R. pravus gp. and R. sanguineus gp. were active from December to July. The distribution of ticks over the body of cattle was determined by fractionised collections, which gave reliable quantitative information for nine of the species. A limited number of collections from sheep, goats and dogs are analysed in relation to season. Collections from 127 wild animals, mainly along the escarpment and riverine bush of the Zambesi, are recorded.
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    Yellowbilled oxpeckers Buphagus africanus and redbilled oxpeckers B. erythrorhynchus occur sympatrically in Hwange National Park. Two separate areas of the park were surveyed for oxpeckers and their host preferences. Yellowbilled oxpeckers preferred buffalo Syncerus caffer, black rhinoceros Diceros bicornis and white rhinoceros Ceratotherium simum, while redbilled oxpeckers preferred sable Hippotragusniger, giraffe Giraffa camelopardalis and kudu Tragelaphus strepsiceros. Differences in oxpecker numbers, host choice and niche expansion in the absence of certain hosts are discussed. Le pique-boeuf à bee jaune (Buphagus africanus) et le pique-boeuf à bec rouge (B. erythrorhynchus) se rencontrent simultanément au P.N. Hwange. On a observé les deux espèces de pique-boeuf et leurs hǒtes préférentiels dans deux régions séparées du pare. Le pique-boeuf à bee jaune préfère le buffle (Syncerus caffer), le rhinocéros noir (Diceros bicornis) et le rhinocéros blanc (Ceratotherium simum), alors que le pique-boeuf à bee rouge préfère l'antilope Sable (Hippotragus niger), la girafe (Giraff'a camelopardalis) et le Koudou (Tragelaphus strepsiceros). On discute des différences de nombre des pique-boeuf, du choix de leur hǒte et de l'expansion de la niche écologique en l'absence de certains hǒtes.
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    and SummaryIn ethological studies it is common practice to obtain multiple observations on each individual in a sample and to Pool these observations into one data set for statistical analysis. In this paper we argue that this procedure reflects a fundamental error in the logic underlying random sampling since it implicitly assumes that the purpose of data gathering in ethology is to obtain large “samples of behaviour” rather than samples of behaviour from a large number of individuals. That is, it is assumed that the reliability of estimates of population parameters can be increased by obtaining additional observations on individuals already in the sample rather than by increasing the number of individuals observed. Using a Monte Carlo simulation we show that when such Pooled data sets are analysed statistically, the probability of rejecting a true null hypothesis is almost always substantially greater than the stated alpha level.ZusammenfassungIn ethologischen Untersuchungen ist es üblich, von jedem Individuum einer Stichprobe mehrere Meßwerte zu gewinnen und für die statistische Analyse die Werte aller Individuen zu einer einzigen Stichprobe zu vereinigen („pooling”). Diesem Verfahren liegt, wie in der vorliegenden Arbeit gezeigt wird, ein fundamentaler Irrtum bezüglich der zufälligen Stichprobenauswahl zugrunde, da implizit davon ausgegangen wird, man müsse große Stichproben der Verhaltensweisen anstatt Stichproben des Verhaltens möglichst vieler Individuen sammeln. Damit wird angenommen, daß Populationsparameter zuverlässiger geschätzt werden können, wenn man mehr Beobachtungen am bereits in der Stichprobe vertretenen Individuen macht als wenn man zusätzliche Individuen beobachtet.Mit einer Monte–Carlo–Simulation wird gezeigt, daß die statistische Analyse solcher zusammengesetzter („pooled”) Stichproben fast immer eine wesentlich großere als die angegebene Irrtumswahrscheinlichkeit für („type I error”) ergibt.
  • Resistant and susceptible cattle were infested daily with a constant number of larvae of the ixodid tick, Boophilus microplus, for a period of 13–18 weeks and restrained from self-grooming over part of the period. Tick yield increased dramatically on resistant animals from the third to the fifth week of restraint, then decreased sharply although the animals were still restricted from self-grooming. The increase in tick yield was related to the initial resistance of the animal, the most resistant showing the highest increase.