Abundance of African White Backed (Gyps Africanus) and Hooded Vulture (Necrosyrtes Monachus) in Wondo Genet College of Forestry and Natural Resources, Southern Ethiopia; A comparison of methods

Mebrat Teklemariam1 and Ashok Verma2

1 Samara University, Dry land Agriculture faculty, Department of Animal sciences P.O. Box 132, E-mail- furtuna1994@gmail.com

2 Hawassa University, Wondo Genet College of Forestry and Natural Resources, Department of Wildlife management and Ecotourism P.O. Box 128

ABSTRACT

A study on roosting, feeding and perching sites of African White backed (Gyps africanus)

(AWbV) and Hooded Vultures (Necrosyrtes monachus) (HV) in Wondo Genet College of

Forestry and Natural Resources, southern Ethiopia was conducted from January to March 2012

aims to estimate the abundance and population structure of vultures through different data

collection methods and suggest the best method of data collection in the study area. The mean

abundance of AWbV was estimated to be 22 (± 6.2), 35.2(± 7.2) and 41.4 (SD ± 6) at feeding,

roosting and road transects respectively. 56%, 33% and 12% of population of AWbV in March

were adults, immature and unidentified age respectively at roost count. Whereas the percentage

adults and immature of these vultures population during feeding site counts and road transect

were 67%, 33% and 66%, 34% respectively. The estimated mean abundance of HV was

60(SD±14.6), 118.4(SD±14.9) and 98 (SD±9.4) at their feeding sites, roosts and road transect

respectively. The proportion of adult to immature AWbVs and HVs in the college lied within the

range of natural populations. The number of HVs at roost count were consists of 33.2% adults,

20.2% immature and 46.6% unidentified ages. However, adult and immature percentages of HVs

were 62% and 38% as well as 65% and 35% during feeding site counts and road transect

respectively. The road transect method is appropriate for estimating abundance of AWbV

whereas roost count is for HV. Road transect may be best method for age identification of both

AWbVs and HVs. The paper discusses the reasons for such differences in the use of methods for

vultures.

Key words: abundance, comparison, Ethiopia, Gyps Africanus, Necrosyrtes Monachus

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INTRODUCTION

Vultures are nature’s most successful scavengers, having great ecological, social, cultural,

economical and medical significances for human well-being. . However, these are the most

threatened group of birds in the world. African White backed Vulture (Gyps africanus) (AWbV)

(BirdLife International, 2012) and Hooded Vulture (Necrosyrtes monachus) (HV) (BirdLife

International, 2012; Ogada and Buij 2011) are listed as Endangered species. Though vultures are

large, conspicuous birds that are easily identified, their populations remain little known and even

less is being done on the ground to ensure their survival in many African countries except

ongoing efforts in South Africa, Uganda and Kenya (Ogada, et al., 2011). This is resulted from

the lack of research, monitoring and conservation being undertaken due to lack of qualified

observers, limited funding, logistic difficulty of being able to conduct research and monitoring in

Africa and inaccessibility of some breeding sites (Anderson, 2007). The importance of selecting

the most appropriate method of abundance estimation is widely recognized, particularly when

results may be used for planning conservation strategies. Therefore the present study aims to

estimate the abundance and population structure of AWbV and HV through different data

collection methods and suggest the best method of data collection in the study area.

STUDY AREA AND METHODS

Study area

Wondo Genet College of Forestry and Natural Resources (WGCF-NR (706’N latitude and 380

37’E longitude)) is situated 263 km south of Addis Ababa and 13km south west of Shashemene

town, on the escarpment of Ethiopia rift valley in the southern nation nationalities and people

region (Mohammed, 2007) (Figure 1). The college holds about 1000 hectares of land of which

natural forests and commercial plantation forests account for 650 and 117.3 hectares,

respectively. The remaining part of the college is used for residents, offices, class rooms,

pastures, arable land, trial sites and arboretum (Haimanot, 2010).The area consists of a chain of

hills Abaro, Bachilgigisso, Gairmo, Kentere and Cheko that surround the highly populated valley

(Belayenesh, 2002). It has a bimodal rainfall pattern with the short rainy season for 3 months

(March to May) and the long rainy season for five months (June to October) with 1247 mm of

precipitation annually. The mean monthly temperature is 19.50C (Teshale, 2003).

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Figure 1: Location of Wondo Genet College of Forestry and Natural Resources

The flora of the college includes indigenous i.e. Large-leaved cordia (Cordia africana), Podo

(Podocarpus falcatus), African wild olive (Olea africana) and exotic species such as Mexican

cypress Mexican (Cupressus lusitanica), Weeping pine (Pinus patula), Silky oak (Grevillea

robusta), Eucalyptus spp. (Hjelm, 2001). The forest harbors a variety of mammals; Bushbuck

(Tragelaphus strepsiceros), Dik-dik (Madoqua kirkii), Warthog (Phacochoerus africanus), Civet

(Civettictis civetta), Serval cat (felis serval), Leopard (panthera paradus), Spotted Hyena

(Crocuta crocuta), Aardvark (Orycteropus afer), White-tailed mongoose (Ichneumia albicauda),

Colobus monkey (Colobus guereza), Vervet monkey (Chlorocebus mitis) and Baboon (Pupio

anabus) (Tola, 2005). It is a home for 118 species of birds, of these; seven are endemic or near

endemic species (Sim, 1979).

Methods

A pilot survey was conducted on December to identify roosting, feeding and road transects of

both vulture species. Vantage points were selected to get an overview of vulture movement

during day and evening. The actual data was collected by two observers from January to March

2012 using binoculars (Bushnell 7-15 x35). Birds flying overhead were not counted during road

transect surveys to minimize the double counting of same birds (Marion and Ryder, 1975; Hiwot,

2007). Similarly at roost sites, vultures were only counted when perched in trees. Adult and

immature vultures were distinguished and recorded by differences in plumage coloration

(Ceballos and Donazar, 1990) to determine the age structure of the species during March.

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Feeding site counts

Spot surveys were conducted at feeding sites, mainly dumping grounds. Later identified vulture

feeding sites were surveyed to estimate the number of vulture species at each site via regular

visits once a week that is a total of 12 counts was made. The survey took place at suitable time of

the day (between 7:00 – 10:30 am) in which most vultures were active (Thiel, 1977; Fuller and

Mosher, 1981; Kushwaha and Kanaujia, 2010). Soni (2008) also estimated population of vultures

through feeding site counts.

Road transect counts

Road transect counts are used to calculate relative abundance and study habitat use of raptors

(Fuller and Mosher, 1981). Vultures are attracted to roads (Stolen, 2000; Bosler, 2011). The road

surveys were made in an area of 103 ha at the already identified vultures’ perching sites during

the pilot survey. In all, 12 visits, once a week, were made within and around built-up area.

Surveys were conducted during day light hours with good visibility and low wind velocity

(Marion and Ryder, 1975) from 8:00-4:30 AM. To minimize bias due to visual obstruction, the

observations were limited to vultures seen within 100 m to each sides of the road (Stolen, 2000).

Additionally, surveys were made by walking at similar average speed on foot with frequent stops

((Thiollay, 2007a, Breen and Bildstein, 2008). The survey started from the entrance of the

College and ended at the arboretum.

Roost counts

Communal roosts have been found to be as important source for counting birds in a short time

(Fuller and Mosher, 1981, Sweeney and Fraser, 1986). The communal roost sites were located by

detecting the vultures’ direction of flight an hour before sunset till half an hour after sunset

(Sykes, 1985, Sweeney and Fraser, 1986: Ssemmanda 2005). Additionally, indirect signs for

vulture presence such as white washes and molted feathers were searched.

Roost counts were made both in the morning about an hour before sunrise until all vultures had

left the roost and in the evening from 4:30 pm (i.e. before the first bird arrived at the roost site)

until all had roosted (Sykes, 1985; Thomas and James, 1986; Sweeney and Fraser, 1986; Baral et

al., 2005; Ssemmanda, 2005; McVey, 2008; Kumar, 2009). At large roosts with more than 50

birds, two observers worked together to count the roosting vultures as they entered the site

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(Ssemmanda 2005). Every roost sites were counted on its own days having nine visits (three

visits for each month) both in the evening and morning times. A total of 81 counts were carried

out in the study area. Evening count of the first day (arrived vultures) and morning count of the

next day (left vultures) being treated as one count (day average) per each roost sites.

Data analysis

The data was analyzed using SPSS version 16.0. The population size in colonies was estimated

by calculating the mean number of vultures counted during the three months censuses. The mean

abundance at each method (roost, perch and feeding site) was estimated by the formula: ∑X

i.ni/N where X i is the mean number of vultures in roost or perch or feeding site i, n i the number

of observation days at roost or perch or feeding site i, and N the total number of observation days

in all roosts or perches or feeding sites. In a given study period final population estimate for the

whole area was obtained by summing the three months means of individual roosts or perches or

feeding sites (Xirouchakis and Mylonas, 2005; Hiwot, 2007).

RESULT

Population

The abundance of vultures was estimated using feeding site counts, roost counts and road survey.

The mean abundance of AWbVs were 25.3 (±7.1), 18 (±5.6) and 21.5 (±6.2) at feeding site

counts, 36.4 (±6.8), 36 (±6.9) and 33.7 (±8.1) during roost counts and 38 (±5.6), 45 (± 6.9) and

41.3 (±5.4) at road transect in January, February and March respectively (Figure 2). Accordingly,

a mean of 22 (±6.2), 35.5 (±7.2) and 41.4 (±6) AWbVs were recorded at the feeding site counts,

roost counts and road transect respectively. The age identification of both species was done

during March. Accordingly, there were total of 101, 91 and 167 AWbVs during roosting, feeding

sites and road transect respectively. Of these the number of adults, immature and unidentified

age of AWbVs were 56 (55.5%), 33 (32.7%) and 12 (11.8%) respectively. The age composition

of individual adult and immature of these vultures was 61 (67%) and 30 (33%) throughout

feeding site counts and 110 (66%) and 57 (34%) during road transect counts .

The mean abundance of HVs in January, February and March were 49 (±9.9), 56 (±13) and 75

(±19); 105 (±10.4), 100.8 (±10.7) and 149.5 (±21) as well as 89.3 (±7), 84 (±8.5) and 121

5

(±11.8) at feeding counts, roosting counts and road transect counts respectively (Figure 3). As a

result, the college was supported a mean of 118.4 (±14.9), 60 (±14.6) and 98 (±9.4) HVs at

roosting, feeding and road transect counts respectively. There were total of 446 HVs at roost

counts, of these the number of adults were 148 (33.2%), immature 90 (20.2%) and unidentified

age 208 (46.6%) individuals of HVs. The number of HVs at feeding site counts was 299 (186

(62%) adult and 113 (38%) immature) and 501 (326 (65%) adult and 175 (35%) immature)

individuals during road transect counts.

January Febraury March0

5

10

15

20

25

30

35

40

45

50Feeding site Roost site Road transect

Mea

n A

bund

ance

of A

WbV

Figure 2: A comparison of mean (±SD) population size of AWbV through feeding and roost

counts and road survey in WGCF-NR, Southern Ethiopia, January -March 2012.

6

January Febraury March0

20406080

100120140160

Feeding site Roost site Road transectM

ean

Abu

ndan

ce o

f H

V

Figure 3: A comparison of mean (±SD) population size of HV through road survey, feeding site

counts and roost counts in WGCF-NR, Southern Ethiopia, January -March 2012

DISCUSSION

Population

There were variations in the abundance of AWbVs and HVs between estimation methods as seen

in previous study (Sweeney and Fraser, 1986) between roost counts and road transect. Both

vultures recorded during feeding site counts were less than road transect and roost counts. The

relatively less number of vultures recorded during feeding site counts may be due to the presence

of food sources of vultures other than the three feeding sites. Mostly AWbVs were not seen

feeding on the refuse damping areas rather observed feeding slaughter house leftovers during

periods of slaughtering animals. As a result, relatively more AWbVs were seen perched on large

trees in and around the settlements of the college. This is supported by the opinion of Routledge

(2006), vultures do not expected to eat every day as carcasses may not be available since they

have distensible crops and gizzards and can hold enough food to last for several days. Yet, HVs

scattered throughout the college for searching food in addition to food sources from the three

feeding sites. Consequently, relatively high numbers of these vultures observed during roost

counts when they returned back and congregate at their roosts in the evening. Therefore, the

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highest number of AWbVs and HVs recorded during road transect and roost site counts

respectively.

All vultures recorded during feeding counts and road transect could be identified to their age

classes (immature and adult), but it was difficult during roost counts. Probably different counting

time affected the result. Due to poor visibility during late evening hours age of all arriving

vultures could not be ascertained. Also factors such as gregarious roosting behavior, and dense

foliage of the roost trees were also responsible for inaccurate identification of the vultures. This

finding is in line with the previous studies that dense foliage roosts (Sweeney and Fraser, 1986)

and darkness (Ceballos and Donazar 1990, Donazar et al. 1996) affects the accuracy in

identification of vultures at roosts.

The proportion of immature to adult ratio of AWbVs and HVs was not equal at each method of

data collection. In both vultures, adults were numerous than immature. This may happen due to

the life history of vultures having delayed maturity, low productivity and relatively high pre

adult survival ship. This is consistent with the suggestions of Xirouchakis and Mylonas (2005),

Michele (2010) and Ogada et al. (2011), vultures have long life cycles and low fecundity

enabling them to invest considerable time to their offspring. Moreover, HV (Routledge, 2006,

Michele, 2010; BirdLife International, 2012) and AWbVs (Anderson and Hohne, 2007) lay one

egg annually that contributes for their low reproduction rate. Donazar, et al. (2002) in their study

reported that the stability of the population depends on the high pre adult survival of the species.

Xirouchakis and Mylonas (2005) noted that the age structure of Griffon Vultures is stable when

the adult birds making up 65–70% of the total population. Accordingly, the range of stability for

both species could not be noted at roost counts, due to the uncertainty with ages of the rest

unidentified vultures of each species. Nevertheless, in accordance with the suggestion of

Xirouchakis and Mylonas (2005), the age structure of AWbVs and HVs may be stable depending

on the results from feeding site counts and road transect except HVs at feeding site counts. In

comparison with the respective ratios provided in other studies of vultures; for instance, low rate

of reproduction in the population of Turkey Vultures (84:16) Breen and Bildstein (2008) and

Cape Vultures (75:25) Robertson (1984) in addition to stable population of Bearded Vulture

(63:37) Brown (1997) Griffon Vultures (63:37) Xirouchakis and Mylonas (2005) the proportion

of adult to immature AWbVs and HVs in the college lied within the range of natural populations.

8

The importance of selecting the most appropriate method of abundance estimation is widely

recognized, particularly when results may be used for planning conservation strategies. Hence,

the study was conducted in a specific site (in and around the settlements of the college) at

favorable time and weather condition for each method to minimize influences of the vultures’

visibility. In addition to this, the vulture’s large size (Louis, 2011), gregarious feeding and

roosting behavior (Mundy et al., 1992; Louis, 2011), attracted to roads (Stolen, 2000), and

accessible landscape to counts in all methods, there was no difficulty in detectability of the

vultures in all abundance estimation methods. Therefore, comparison in the abundance of these

species among the estimation methods might be possible, as the detectability criterion is fulfilled

in line with the suggestion of Fuller and Mosher (1981). They have been suggested that methods

among comparisons should standardize and comparisons should be made only when detectability

is similar or when correction factors can be applied by the biologists. Therefore, it may be better

to estimate the population of AWbVs through road transect on their perching sites and HVs in

their roosts. In selecting the best method for population structure of these vultures, comparisons

was made between road transect and feeding site counts, since roost counts was fail to fulfill

either of the criterion stated by Fuller and Mosher (1981). Hence, road transect may be best

method for age identification of AWbVs and HVs. This may probably count of more number of

both vulture species in road transect than feeding site counts.

There is an argument between using road transect counts and roost site counts to study

abundance of vultures in the previous studies. Sweeny and Fraser (1986) and Fraser and

Coleman (1990), suggested that roost site counting is better than the road transect counts due to

low number of vultures observed on the road transect as vegetation and mountains obscured

some vultures. On the contrary, Stolen (2000) believed that road transect is well suited to

assessing populations of vultures in a given area, because vultures are good candidates for road

transect and they are easy to perform then relatively inexpensive. Consequently, the present

study agreed with these two arguments. Roost counts are well suited to estimate the abundance

of HVs whereas road transect count for AWbVs.

CONCLUSION

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The study revealed that WGCF-NR, which is found in the central rift valley of Ethiopia, is an

important area as roosting, perching and feeding ground for AWbVs and HVs. The site contains

high number of HVs than AWbVs. However, both vulture species showed varied numbers when

counted by different methods at different sites. Accordingly, the range of stability for both

species could not be noted at roost counts, due to the uncertainty with ages of the rest

unidentified vultures of each species. 56%, 33% and 12% of population of AWbV in March were

adults, immature and unidentified age respectively at roost count. Whereas the percentage adults

and immature of these vultures population during feeding site counts and road transect were

67%, 33% and 66%, 34% respectively. The number of HVs at roost count were consists of

33.2% adults, 20.2% immature and 46.6% unidentified ages. However, adult and immature

percentages of HVs were 62% and 38% as well as 65% and 35% during feeding site counts and

road transect count respectively. Nevertheless, the age structure of AWbVs and HVs may be

stable depending on the results from feeding site counts and road transect except HVs at feeding

site counts. The proportion of adult to immature AWbVs and HVs in the college lied within the

range of natural populations. The mean sightings of AWbVs were 22 (SD± 6.2), 35.2 (SD±7.2)

and 41.4 (SD±6) at feeding site, roosts and along road transect respectively. The mean

population of HVs at feeding site, roosts and along road transect were 60 (SD±14.6), 118.4

(SD±14.9) and 98 (SD±9.4) respectively. In studying the abundance of AWbV, the suggested

data collection method is road transect count, while roost counts for HV. Road transect count

may be best method for age identification of AWbVs and HVs

ACKNOWLEDGMENT

The authors acknowledge the Norway Agricultural Development Project for funding this

research. Thanks are due to Kahsu Gebru, Genene Asefa and Habitamu Taddesse, Fanta Yakob,

Daniel Ashako and Firehiwot Mequanint for moral and logistical supports, and the Library staffs,

academic staffs, community of college for sharing vulture information and others.

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