Journal of Global Resources

Volume 3

July 2016
Page 43-51
ISSN: 2395-3160 (Print), 2455-2445 (Online)

5
BIRD DIVERSITY AND ABUNDANCE ALONG ALTITUDINAL GRADIENTS IN MOUNTHANANG FOREST RESERVE
Abraham Eustace1*, Salome Gissemoda1 and Hamad I. Dulle2
1

Wildlife Division, Ministry of Natural Resources and Tourism, Tanzania.
2

College of African Wildlife Management Mweka, Moshi, Tanzania.
*Email:abrah15@gmail.com

Abstract: Bird diversity and abundance study along altitudinal gradients was carried on April
2010 in Mount Hanang Forest Reserve in Hanang District, Tanzania. The study was
conducted purposely to observe if the altitude change have any influence to diversity andabundance of birds. Surveyed area was divided into two sites namely low altitude (15001900m.a.s.l) and high altitude (2000-2500m.a.s.l); where in all sites point count method wasused. With this method five transects with five points in each transect were established in eachsite. Ten minutes was used to count birds in each point established and at each point after
arrival five minutes were used for relaxing before starting the count and to let birds settle after
the arrival of the observer. Shannon-Weiner (H') and Simpson (D) diversity indices were used
) and Menhinick’s () indices were
to determine species diversity while Margalef’s (used to determine bird species richness. The results showed that, many bird species wererestricted in one area either low altitude or high altitude while few occurred in both sites.
Abundance differences varied significantly between low and high altitude sites (t = 3.486; df =8; P = 0.0082). Although low altitude area was having a higher diversity (H' = 2.78 and D =0.90) than high altitude area (H' = 2.10 and D = 0.82) the difference wasn’t statisticallysignificant (Shannon-Wiener: P = 0.273; Simpson: P = 0.471). Availability of food andpresence different vegetation patches were responsible for difference in abundance while
habitat heterogeneity and disturbance were dependable factors for differences in bird’s
diversity in low and high altitude areas. The results from this study plays vital role inconservation of birds in Mount Hanang Forest Reserve as it provide information since little has
been done.
Keywords: Diversity, Abundance, Richness, Point Count, Mount Hanang, Forest Reserve,
Birds, Altitude
Introduction
Biological diversity in the world is not evenly distributed; some areas tend to have a higher
biodiversity while others are having lower diversity for example, tropical region and polar
region (Gaston, 2000; Joshi et al., 2012). These variations in biodiversity have reasons and itis the target of many scholars to understand them (Stoms and Estes, 1993; Acharya et al.,2011).Biological diversity is composed by different elements; birds are one of them as they
form their own ecological niche in an ecosystem (Sekercioglu, 2006). They are found in every
corner of the earth’s surface, from desert to forest, from polar region to tropical region (Garrett,2009). Their presence in any ecosystem plays important roles such as pollination which isespecially done by nectar feeders like humming birds and sunbirds (Sekercioglu, 2006; Klein
43

et al., 2007).Birds make a considerable contribution to human welfare in the form of foodespecially to the poorest villagers living in the most remote areas (McNeely et al., 1990).Also;
they are cleaners of environment particularly scavenging birds (Ssemmanda and Pomeroy,2014). Their activities and presence help much to balance the ecosystem.
However, birds are common, occupying even remotest deserts, oceans, andmountains; they are the one of the most conspicuous groups in many ecosystems (Hawkins etal., 2007; Garrett, 2009) and their diversity and abundance do vary (Hawkinset al., 2007). The
variation in diversity and abundance of birds is influenced by many factors one being altitudinal
gradients. For example, in the Paramos of Venezuela, several species including birds occur
over different altitudinal gradients, some are restricted at low elevations and others occur only
above 3000 meters above sea level (msl) (Wien, 1992). Therefore, altitudinal changes play animportant role in changing diversity and abundance of birds in the ecosystem because it leads
to the variation in temperature, moisture and rainfall which in turn affect food availability(Waterhouse et al., 2002; Joshi et al., 2012). Altitudinal change controls mountain climates
which have a significance influence on the diversity and abundance of species in ecosystems(Beniston, 2002). The variation in abundance and diversity is also caused by environmental
variables like temperature, precipitation and humidity (Speight and David, 1989; Waterhouse
et al., 2002).The environmental stability states that “the more stable the climate parameters
and the more favorable the climate, the more species will be present” (Krebs, 1994).
Differences in degree of temperature in low and high altitude areas lead to the differences in
species diversity and abundance (Clarke and Gaston, 2006). High altitude area tends to have
low temperature compared to low altitude area, because as you move up
100m.a.s.ltemperatures tend to decrease by 0.6 C (Chang, 2012, p.179; Seemann et al.,2012 p. 125; Rose, 2013 p.40). Montane forests are characterized by low temperature in someseasons of the year; this may result to some bird species to move to the areas with optimum
temperature for their survival (Baker and Baker, 2002). In low altitude temperature isconducive which in turn affect availability of food hence become productive for bird species(Kahana and Malan, 2007;Garrett, 2009). Climatic condition of high altitude is extreme badwhich attract few species of birds (Blake and Rouges, 1997; Garrett, 2009). Change in floristic
composition in Usmabara Mountains, Tanzania does impact species diversity and abundance
including birds (Hamilton, 1998). Therefore altitudinal changes have impact on diversity andabundance of birds in any ecosystem. These factors might be responsible for influencing
diversity and abundance of birds in Mount Hanang Forest Reserve, but there can be otherfactors also. The causes of such variations are poorly understood but this study attempt tounderstand them.
It is known that about 15.2% of the world’s total land is covered by semi-arid(Environment Management Group, 2011). In Tanzania semi-arid areas covers about 50-80%
of land (Mbwambo, 2004). Within these semi-arid regions, there are patches of Mountain
forests within the vast semi-arid areas that offer unique conditions suitable to a number of floraand fauna. Mount Hanang Forest Reserve is among those areas that offer such conditions
necessary to a number of fauna. Despite the fact that, Mount Hanang Forest Reserve is
supporting a good number of fauna including birds; there is a little information existing about
birds. Therefore, this research adds some information about diversity and abundance of birds
in Mount Hanang Forest Reserve to the existing one.Also by understanding patterns of44

diversity and abundance and their causes along altitudinal gradients, it plays significant role inbiodiversity conservation (Paudel and Šipoš, 2014).
Generally this study aimed to assess the diversity and abundance of birds in Mount
Hanang Forest Reserve. Specifically we determined bird’s diversity and abundance in two
altitudinal levels (low and high altitudes) in Mount Hanang Forest Reserve. We assumed that
there is no significant difference in bird’s diversity and abundance between low and highaltitudes of Mount Hanang Forest reserve.
MATERIALS AND METHODS
Study Area Description
Mount Hanang Forest Reserve is one of the protected forest reserves located near Katesh
town of Hanang district in Manyara region. The forest reserve is located 200 km southwesternof Arusha region. The area was gazetted as forest reserve in 1936 and it covers 5,832
hectares. The Mount Hanang is 3,800 m high located in semi-arid environments with 600 mm
annual rainfall. The climate and soil of the area favor wheat cultivation. The low altitude area ofMount Hanang Forest Reserve (below 2000 meters above sea level (msl) is dominated byhuman settlements and different human activities are conducted. Vegetation of this area
includes scrubland, small scale farmland and some patches of forest. High altitude of thereserve is dominated by afro-montane forest and the area is highly protected but some illegal
activities such as livestock grazing, firewood collection and tree logging do exist.
Field Reconnaissance Survey
The Field reconnaissance survey was conducted before data collection. With this survey,
areas for setting transects in both altitudes were identified. Low altitude was at1500–1900 msl.
and high altitude was 2000-2500 msl. All micro habitats present in each site (low and highaltitude) were observed and recorded.
Point Count
Five transects of 1km each were established at every altitudinal level, the distance from one
transect to another was 500 m. At each transect five points separated by 200m were
established. In every point a radius was established, where the radius of 75m was used inopen habitats and radius of 25m was used in closed habitats. All points and transects werelocated by using a Garmin GPS 12 channel. Ten minutes were used to count birds in eachpoint established but after arrival five minutes were left for relaxing before starting the count.
This was necessary so as to let birds settle after the arrival of the researcher since thisapproach would have caused some disturbances. All birds observed within a determinedradius were counted. Counting was done in morning (6:30-10:30 hrs.) and evening (17:3018:30 hrs.) because at this time is when birds are active in the study area. It was assumed thatany bird present will be detected during the count and that, none slipped away as the counter
was approaching the area. Field guide book by Stevenson and Fanshawe (2002) was used for
identification and distant observation was aided by binocular (50 × 20). All birds identified wererecorded in a prepared data sheet including their habitat.

45

Data Analysis
Data were analysed by Shannon-Wiener ( ′) and Simpson ( ) diversity indices for calculating
the species diversity while species richness was determined by Menhinick’s
andMargalef’s
indices of species richness (Davari et al., 2011). In determination ofabundance, bird individuals were summed up for each transect in one site to get theabundance of the site while in getting total abundance of the study area, bird individuals of twosites were summed up.Two-tailed t-test at 0.05 significance level was applied so as to test if
significance difference in bird’s diversity and abundance between low and high altitude exist.
Data were subjected to Kolmogorov-Smirnov normality test before undergo to t-test. We
presented the findings by using tables and graphs and analysis was assisted by MedCalc
version 12.5.0.0 and Microsoft Excel 2013software.
RESULTS
Abundance of bird species in low and high altitude
From both sites, a total of 420 individuals of birds belonging to 18 families were recorded fromten random placed transects of 1km each. Low altitide site (1500-1900 m.a.s.l)was having 330
individuals from 16 families recorded in five transects and high altitude (2000-2500 m.a.s.l)
was having 90 individuls from 10 families recorded in five transects. From 44 bird species
encountered during the survey, 30 species were encountered only in low altitude and 9
species of birds were observed only in high altitude areas while 5 species of birds wereobserved and recorded in both areas (low and high altitude) (Table 1). Low altitude wasrelatively higher in abundace (78.57%) than high altitude (21.43%) areas (Figure 1) and thisvariation was statistically significant (t = 3.486; df = 8; P = 0.0082).
Figure 1: Relative abundance of birds in low and high altitude recorded from ten randomly
placed transects of 1 km length per transect.
90

RELATIVE ABUNDANCE (%)

80
70
60
50
40
30
20
10
0

Low Altitude

High Altitude

46

Table 1 Birds observed and recorded in low and high altitude sites
#

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35

LOW ALTITUDE BIRDS
Common names
Relative
abundance (%)
Variable sunbird
3.33
Paradise whydah
0.30White bellied go0.30
away bird
Ring-necked dove
1.21
Tacazze sunbird
1.52
Spectacled weaver
0.30
Straky seed-eater
0.30
Mourning dove
1.21
Olive sunbird
0.30
African fire finch
1.21
Black-necked
0.61
weaverReichenow's weaver 2.73
Fiscal shrike
6.97
Amathyst sunbird
Speckled pigeon
Tropical bulbul
Rufoussparrow
Rough winged
swallow
House sparrow
Yellow bishop
Red bishop
Masked weaver
Rufous-naped lark
Richard pipit
Pied crow
Speckledmouse bird
Superb starling
Augur buzzard
Hunters sunbird
White-necked raven
Tawny eagle
Black kite
African wagtail
Red-billed quelea
Black headed
weaver
TOTAL

1.21
3.64
3.94
3.94
3.33

HIGH ALTITUDE BIRDS
Common names
Augur buzzard
Amani sunbird
Black rough wing swallow

Relative
abundance (%)
12.22
1.11
35.56

Tropical boubou
Tropical bulbul
Variable sunbird
Purple breasted sunbird
White-necked raven
Square-tailed drongo
Hartlaub'sturaco
Bare-faced go-away-bird

3.33
7.78
2.22
2.22
3.33
5.56
2.22
10.00

Speckled mouse bird
White headed rough wing
swallow
White-starred bush robin
TOTAL

12.22
1.11
1.11
100.00

11.52
0.30
0.91
1.82
21.82
0.30
1.21
1.52
4.55
0.30
0.30
1.21
0.30
0.61
0.61
15.15
1.21
100.00Source: Field data, 2010

Diversity and richness of birds in low and high altitude
Although low altitude site was having higher species diversity than high altitude (Low altitude
site:H' = 2.78 and D = 0.90; high altitude site:H' = 2.10 and D = 0.82), this difference wasn’t
statistically significant (Table 2).Low altitude area was richer in terms of species (= 1.92and= 5.86) than high altitude area (= 1.48 and= 2.89).Presence of diverse
47

habitats in low altitude compared to high altitude might be the factor which influence thesedifferences.
Table 2 Diversity and richness of birds in low and high altitude sites of Mt. Hanang Forest
Reserve.
Diversity
IndicesRichness
IndicesParameters
Shannon-Wiener( ′)Low altitude
2.78

High altitude
2.10

t-test P values at α = 0.05
P = 0.273

Simpson ( )

0.90

0.82

P = 0.471

Margalef’s

5.86

2.89

P = 0.002

Menhinick’s

1.92

1.48

P = 0.119

Source: Field data, 2010

DISCUSSION
Birds’ abundance in study sites
In the study sites 30 bird species occurred in low altitude only while 9 bird species occurred inhigh altitude only (Table 1), this was influenced by the availability of abundant and variety offood materials and favorable habitat which was present in one altitudinal area. Also behavior
of individual species contributes to the species availability to one area than another, forexample house sparrow does nest on overhanging of buildings (MacLean, 1993). Human
settlements provide suitable habitat for their nest since the area was available in low altitude
area and absent in high altitude area. There were 5 bird species which recorded in both low
and high altitude sites (Table 1). Their behavior of conquering varieties of habitats was thefactor for their commonness. Therefore in study area most species are habitat specialists whileothers did conquer variety of vegetation zones.
Low altitude site was relatively higher in abundance than high altitude site and thedifference was statistically significant (Figure 1). Higher abundance in low altitude site was
influenced by presence of variety of habitats which include human settlements, farmland,
scrubland and forest patches. These habitats have different food materials like fruits, seeds,
insects; nectarine flowers hence make the area to harbor abundant birds. Lower abundance inhigh altitude site (Figure 1), might be influenced by unfavorable climate of the area because as
move up 100m.a.s.ltemperature tends to decrease by 0.6 C (Chang, 2012, p.179; Seemann etal., 2012 p. 125; Rose, 2013 p.40). Bad weather condition in high altitude favors low
abundance (Blake and Rouges, 1997; Garrett, 2009; Baniya et al., 2010; Acharya et al., 2011;
Wu et al., 2013; Paudel and Šipoš, 2014).
Birds’ diversity and richness in low and high altitudes
Diversity and richness of birds in Mt. Hanang Forest Reserve was higher in low altitude than inhigh altitude, this difference wasn’t statistically significant, but biologically it plays big role
(Table 2). Species diversity in the tropics is not similar; diversity can decrease, increase or
remain constant as elevation changes (Newmark, 2002).Habitat heterogeneity was
responsible for higher diversity of bird species in low altitude as compared to high altitude
area. Low altitude area was having different micro habitats including human settlement,
cultivation area, scrubland and some patches of forest while the high altitude washomogenous montane forest. Increase in habitat heterogeneity leads to an increase in species48

diversity and richness (Krebs, 1994; van Rensburget al., 2003; Acharya et al., 2011).
Presence of different habitats gives the chance to species to adapt in different feeding habits
such as seed eaters, insect eaters, fruit eaters and nectar consumers hence higher diversity.
The high structural diversity of the habitat leads to high diversity of food materials hence
higher species diversity (Aslam, 2009).
Disturbances resulted from different human activities contributed much to the higher diversityof birds in low altitude area than in high altitude area. Human activities like cultivation andestablishment of settlements were common disturbances in low altitude area. Anthropogenic
habitat disturbance is one of the most important drivers of biodiversity differences (Tylianakisetal., 2005, 2006). Disturbance significantly influences the diversity of communities (Molles,
1999); disturbed habitats had significantly higher species richness and diversity thanundisturbed habitats (Quintero et al., 2009). In both very large and very small spatial scales,
birds diversity tends to increase resulted from disturbance (Dumbrell et al. 2008). Therefore,
the low altitude area being influenced by human activities leads to higher diversity andrichness of bird species than in high altitude which is highly protected for conservation ofmountain forests.
Conclusion and Recommendations
Bird’s diversity and abundance in two altitudinal levels of Mt. Hanang forest differs greatly.
There was a higher abundance of birds in low altitude than in high altitude areas due to thepresence of abundant food, favorable climatic conditions and different vegetation patches.
Habitat heterogeneity and disturbances influence high diversity and richness of birds in low
altitude area of Mount Hanang Forest Reserve. These results suggest that bird’s conservation
is important in low altitude of Mount Hanang Forest Reserve as it harbors a variety of species
in higher numbers. We recommend the study of birds to be conducted into more than two
altitudinal zones across different seasons of the year in order to determine other underlying
factors for diversity and abundance differences. Other than birds, there are species of reptiles,
mammals, invertebrates and variety of plants in the surveyed area; therefore more studies areneeded in Mount Hanang Forest Reserve so as to discover more phenomena.
Acknowledgements
We thank College of African Wildlife Management Mwekafor their support and Mount Hanang
Forest Reserve management for the permission conduct research. Thanks to Mr. J. Masatu
and Mr. Adayo who helped much during all the processes of acquiring permit also Mr. J.
Shushu and Mr. E. Mangu for their assistance during data collection. Finally, an honorable
mention goes to all who participate in all stages of this research.
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