1 Background

The research on large wild mammals is one phase of a continuing effort to document and describe the richness and distribution of Ethiopian mammals in remote and less accessible ecosystems (Girma and Worku 2020). They are able to colonize a variety of habitat types due to their diverse morphological, physiological, and behavioral adaptations. In terms of global distribution, they are among the most common species. In spite of this, human activities have changed the composition of mammal assemblages across vast areas (Li et al. 2021; Rodríguez 2021). Compared to smaller, commensal species, anthropogenic development and activities had either negligible or favorable effects on large, endangered species (Shamoon et al. 2018). To determine the status and suggest effective conservation measures, it is essential to understand the fauna's diversity, abundance, and habitat preferences (Gonfa et al. 2015). With a thorough faunal diversity inventory, including all vertebrates in all seasons, and tight park management, the ecosystem will be capable of supporting diverse biodiversity components (Gonfa et al. 2015). “The region's with high vegetation coverage against other ecosystems that would provide ample food, cover and space to attract large numbers of mammalian species to live in” (Bakala and Mekonen 2021). Habitats with greater area tend to contain higher number of species. “The medium and large size mammals to include all species with a body mass of greater than 1 kg, thus excluding all relatively small, terrestrial mammals” (Mercês et al. 2020). For conservation efforts to succeed, mammalian species must exist to preserve their residual populations (Beca et al. 2017). In forest ecosystems, large and medium-sized mammals are crucial for managing prey populations, spreading seeds, and interacting with predators (Bogoni et al. 2017; Botelho et al. 2012). Demand for bush-meat and other animal goods will increase strain on already reduced mammal communities as the human population continues to rise and spread (Dobbins et al. 2020; Bisi et al. 2019). One of the main causes of biodiversity loss is thought to be the conversion of natural habitats towards agricultural land use (Drouilly et al. 2018; Ishige et al. 2017). Given the unprecedented threats to biodiversity posed by anthropogenic disturbance, knowledge of the occurrences of species and communities enables an efficient and quick method to evaluate the status and susceptibility of mammals (Cavada et al. 2019; Woodgate et al. 2018). Understanding the diversity, abundance, and habitat preferences of the fauna is essential for determining the status and suggesting effective conservation actions (Rabira et al. 2015). The introduction of large and medium-sized mammals in this work serves as a springboard for the expansion of ecological inquiry into the consequences of habitat loss and fragmentation on the mammal community in the Tirba Lake region. In the Tirba lake, there is no any scientific study about large and medium mammals. Therefore the present study aims to the composition, relative abundance, and diversity of medium and large mammals in Tirba Lake Awi Zone, Ethiopia. This study also provides as a baseline for researchers planning similar ecological studies and for managers of the area to make successful conservation decisions.

2 Materials and Methods

2.1 Study Area Description

The study area is found in the Awi zone, the Amhara region of Ethiopia. The administrative center of the Awi zone is Injibara town. Agew Awi is one of the zones in the Amhara Region of Ethiopia. It is named for the Awi sub-group of the Agaw people, some of whom live in this zone. Agew Awi zone is bordered on the west by Benishangul-Gumuz Region, on the north by Semien Gondar zone, and on the east by Mirab Gojjam. According to Awi zone department of agriculture, 2018 report, most part of Awi zone is Woyena Dega (72%) followed by Dega (17%) and Kolla (11%). The area ranges from 700 to 2900 m.asl in altitude and the area having better annual rainfall distribution (800 to 2700 mm/year) in Amhara region (Kassaye et al. 2022). The temperature of the area ranges from 15 to 24 oC. From the total area of zone (8,935,520 ha) of land 297,133 ha (33.25%) is used for farm practices. However, most of the area in Awi zone 34.02% (76,554 ha plantation, 277,842 ha natural forest) covered with forest area. Range land and grazing land covers 24.3% (217,138 ha) area of land from total area and other land uses like infrastructure and settlement covers 8.38% (74,853 ha) area land (Kassaye et al. 2022; Derebe et al. 2022). The plant species like Acacia decurrens, Juniperus procera, Cupressus lusitanica, Pinus radiata, and Eucalyptus globulus were some of the frequently observed plant species in the study area. The area is also home to a variety of wild animals’ that include amphibians, reptiles, birds, and mammals. Papio anubis, Crocuta crocuta, Canis aureus, Panthera pardus, Felisserval, Sus scrosa and Colobus guereza, are some of the frequently observed animals in the study areas. Like in every other community in the nation's highlands, farming and livestock raising are the main sources of income. Tirba Lake is found in Ankasha woredas in the Awi zone. It is geographically located between 10˚49′30'' N to 11˚50′ 15'' N and 36˚ 50′ 15''E to 36˚ 51′ 15''E (Fig. 1).

Fig. 1
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The research area's map

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2.2 Methodology

Prior to the real study, a pilot survey was carried out to collect broad details via direct observation and interview regarding the forest area, accessibility, and animal type present in the study area. Setting a baseline for a species' long-term monitoring at a specific place requires an understanding of its range, abundance, and habit needs (de Jong et al. 2015). Therefore this study were collected in both the rain (we season) and dry seasons. December through April was regarded as the dry season and May through November as the rainy season, respectively, based on the area's rainfall distribution.

2.3 Study Structure and Data Gathering Strategy

Based on land cover characteristics, satellite pictures, and a preliminary survey, the area was stratified into homogeneous habitat types for this study. These habitat categories included cliff location, open forest, deep forest, and shrubland. In regions with uniform vegetation that were representational of each habitat type, line transects were routinely built. Data collection took place in the four sampled habitats using the line transect survey method (Gonfa et al. 2015; Diriba et al. 2020). Along the line transect, direct observations were made, softly observing up to a distance of 100 m on either side (Diriba et al. 2020). To reduce animal disturbance caused by odours, the transect was oriented in the opposite direction from the wind. Thirty points were taken in Tirba Lake along eight transect lines used in the study. Depending on the scale of each habitat, different numbers of transects were used: at Tirba Lake, there were 2 transects for the dense forest, 3 for the open forest, and 3 for the shrub lands. Transect sizes varied according to habitat type: the longest measured 250 m in the open forest, while the shortest measured 100 m in the dense forest. There are 8 points on dense forest transects, 12 points on open forest transects, and 10 points on shrub transects, depending on habitat size and type. A line transect cannot be drawn in the cliff, however, point counting was used in caves beneath it. In the cliffs, one point was counted in each cliff, there were three cliffs. According to the area covered by each habitat, 40 transect lines were built, including 18 for wetland, 12 for woodland, 7 for riverine, and 6 for grassland habitats (Gonfa et al. 2015). Each transect's beginning and ending points were GPS tracked. Direct observations were used to identify animals and count their numbers, assisted by binoculars and mammal identification guides (Diriba et al. 2020). Fecal droppings, feed markings, foot prints, calls, and other indirect evidences were also documented in addition to direct observation (Rocha et al. 2019). To survey mammals, both direct and indirect methods can be used (Lyra-jorge et al. 2008). However, because the species identified from the data were subsets of the species seen during the normal survey, they were not included in the data analysis (Sutherland 2006). Each point was counted six times, three times during the wet season and three times during the dry season. Throughout the study period, four visits to each transect were made (Diriba et al. 2020). When observing an animal in the wild, the animal's English, native, and scientific names have been recorded. Date, time, habitat type, species name, number of individuals for each species, and GPS location are the data that were recorded. Two people were allocated to each transect and the transects were visited twice in a single day. Surveys were conducted between 6:00 and 10:00 a.m. and between 15:00 and 18:00 p.m., when it is believed that most animals are most active (Gonfa et al. 2015). To prevent competition, the activity patterns show a temporal partition of the species that coexist in the same area (Oliveira et al. 2019). A prepared datasheet was used to record all of the animal species that were seen. Both the locals and a field reference book were used to identify the species of mammals. Using simultaneous counting and thorough observation of the feeding and sleeping locations of animals, especially in the cliffs, double-counting of the same species or individual animals at a time during the animal survey was prevented. To gather precise data, knowledgeable researchers with experience working with wild animals were recruited. Prior to undertaking animal counting and identifications, all observers got introductory training on how to use the methodology and utilization of field supplies and tools. Body weight was a criterion employed in the study to divide participants into medium-sized and large-sized groups. As a result, mammals weighing between 2 and 7 kg were classified as medium size, and everything above that was considered giant (Gonfa et al. 2015).

2.4 Calculation of Species Diversity

The Shannon diversity index was calculated using the formula below.

$$H^{\prime} = - \sum {pi} *\ln (pi)$$
(1)

Pi is calculated as ni/N, where ni is the percentage of the total population of the ith species and N = − ∑ni, and H' is the Shannon–wiener index. This lessens the consequences of the order-of-magnitude gap in bird numbers between species using percent rather than absolute abundance estimates. This index provides a measure of `evenness' in the proportion of each species occurring within squares.

$$J^{\prime} = H^{\prime}/ln(S)$$
(2)

where J’ is the Evenness index, H’ is the Shannon–wiener index and used formula one and S is species richness.

The similarity among and between the habitats concerning the composition of species was computed using Sorenson’s similarity index (SI):

$$(SI) = C2/S1 + S2$$
(3)

S1 is the total number of species found in habitat 1, S2 is the total number of species found in habitat 2, and C is the number of species shared between the two habitats.

$${\text{Relative abundance }}\left( {{\text{RA}}} \right) \, \left( \% \right) = n/N \times {1}00$$
(4)

where N is the total number of individuals in the species and n is the number of individuals of the particular species that have been counted.

2.5 Data Analysis

During the study period, a table with a summary of all the data by season and habitat type was created. The Shannon–Wiener Diversity Index was used to calculate the distribution, abundance, and evenness of species between the wet and dry seasons as well as among different types of habitat, and SPSS version 20 was used to analyze the data. Excel 2016 was used to generate the relative abundance and species diversity index using prepared formulas. R studio also used for make graphs.

3 Results

3.1 Species Composition

11 mammalian species and 330 individuals were counted throughout this study. There are four orders and six families of those mammals (Table 1). Carnivora and Artiodactyla had two families in each and four species in Carnivora and three species in Artiodactyla. Carnivora was the largest order that included 2 families with 4 species. The more mammalian population was recorded in the order of Primate, only one family, Cercopitheci (Three specie, 53%, 176 individuals), followed by Hyaenidae (18%, 60 individuals), Suidae (11%, 34 individuals), and Felidae (10%, 32 individuals); each with two species. The remaining families, Hystricidae (6%, 20 individuals) and Bovidae (2%, 8 individuals) were represented by single species (Fig. 2). The species composition of the wild mammalian population varies seasonally, according to observations (Fig. 3). The average numbers of animal species abundance among different habitat types with seasons were also observed (Table 2). There was a statistically significant difference in the mean seasonal variation in wild animal abundance (df=1, P=\(\le\) 0.001). Wild mammal populations totaled 330 ± 26.2, of which 180 ± 11 (or 55%) were spotted during the rainy season and 150 ± 6.5 (or 45%) during the dry (Table 3).

Table 1 Animal species found in the Tirba Lake Awi zone, Ethiopia
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Fig. 2
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Numbers of species among family in percents

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Fig. 3
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Seasonal change in wild animal species composition and abundance in Tirba Lake, Ethiopia

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Table 2 Seasonal averages of wild animal abundance in various habitat types in Tirba Lake
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Table 3 The population statistics of wild mammals during the rainy and dry seasons in Tirba Lake
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3.2 Relative Abundance

Among the 11 species of mammalians, the most prevalent baboon was the Olive baboon (Papio Anubis), comprising 30.61% with 101 individuals, Vervet monkey came in second (Cercopithecus aethiops), 16.67% with 55 individuals (Table 4). Although Leopard (Panthera pardus) and Warthog (Phacochoerus Africanus) contributed only 4.24% each, the least contributor was Common Bushbuck (Tragelaphus scriptus) 2.42% of the total recorded individuals (Table 5). The least numerous species in the research area included the Common Bushbuck, Leopard, and Warthog. Among the various habitat types, there was a statistically significant difference in the number of animal populations (df = 3, P=\(\le\) 0.001) (Table 6). Among the four habitat type shrub land carry's higher mammalian populations followed by cliff site and open forest (Fig. 4).

Table 4 Population mean of each species
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Table 5 Mammal species documented across habitats, along with their relative abundance in Tirba Lake, Ethiopia
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Table 6 Populations of mammals by habitat types
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Fig. 4
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Number of mammalian population among habitat types

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3.3 Mammal Diversity Indices in the Four Types of Habitat

Shrub land contains the most diverse array of mammalian species out of the four habitat types (Hʹ = 1) followed by Open forest (Hʹ = 0.8). Dense forest was the lowest diversity among habitat type (Hʹ = 0.5). Shrub land (J = 0.5) had the highest species evenness, and the other habitat types were fairly balanced (J = 0.4) for each (Table 7).

Table 7 Indices of wild animal diversity in various habitat types of Tirba Lake
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3.3.1 Species Similarity Index

The wild animal species' total Sorensen species similarity index across the four Tirba Lake habitat types was 1 (Table 8). Out of the four habitat categories, open forest and shrubland (SL = 0.8), showed the greatest degree of mammalian species similarity, and shrubland and cliff site was (SI = 0.7). Open forest with cliff site was (SI = 0.3) and cliff site with the dense forest was (SI = 0.25). The resemblance was minimal in Open forest with Dense forest and shrubland with dense forest (SI = 0.2) in each (Table 8).

Table 8 Wild animal species' similarity indices across various habitat types of Tirba Lake
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4 Discussion

Tirba Lake has unique ecosystems; the Lake is surrounded by vegetation and also cliffs with mountains. The Lake is approximately surrounded by 60–100 m sloppy cliffs. The water in the Lake never flows like rivers, it is always stationary just like a cup of tea. And also the Lake is a source of water for different wild mammalians that live around it. Large and medium mammals thrive in dense forests, open forests, shrubland, and cliff sites. However, as compared to other studies in Ethiopia, the overall number of mammalian species recorded during the present study (11 species) was comparatively low. For instance (Gonfa et al. 2015) reviewed “28 species in Dati wolel national park” and (Girma and Worku 2020) reviewed “16 species in Geremba Mountain”. Additionally, 1391 observations of 12 species of medium- and large-sized mammals from seven families and five orders were made in Wabe forest remnants in the Gurage zone of Ethiopia (Legese et al. 2019). Thirteen species of large and medium mammals, representing ten families and seven orders, were identified (Oliveira et al. 2019). However, a survey of big and medium-sized mammals in Wabe forest fragments, Gurage zone, Ethiopia is nearly identical to this study; a total of 12 mammal species from seven orders and seven families were documented there (Legese et al. 2019). Because not all mammalian species are listed, particularly medium-sized animals, which can be neglected and for which no different approach is used, the likelihood of the mammalian diversity appears to be lower (Gonfa et al. 2015; Pillco Huarcaya et al. 2020). Several scholars (Matias et al. 2011; Pires Mesquita et al. 2018) demonstrated a favorable relationship between animal species diversity and habitat heterogeneity. Out of the four habitat types in the research area, shrubland and open forest had the highest documented diversity of mammals due to the varied plant species assemblage that was present there. (Gonfa et al. 2015) mentioned Woodland and Riverine woodland as having a high diversity and even distribution of medium- and large-sized mammals. Contrarily, riverine woodland has the lowest composition and number of small mammals, according to (Meseret and Solomon 2014). The presence of water, food, and cover is frequently connected with the distribution and habitat association of animals (Yaba et al. 2011; Gonfa et al. 2015). Landscape level, fundamental biodiversity surveys are necessary to comprehend how climate change and land alteration may affect the distribution and richness of wildlife species (Woodgate et al. 2018). Land-use change had by far the biggest effects on large mammal communities, with areas of extensive livestock grazing and large wildlife exclusion attempts (Ferreira et al. 2020; Graham et al. 2019). In Tirba lake, there were different land use types mainly, crop land, grazing lands so it leads to distract the wild mammal population habitats, this is the main observational challenges. Given the unprecedented threats to biodiversity posed by anthropogenic disturbance, knowledge of the occurrences of species and communities enables an efficient and quick method of assessing their status and susceptibility (Cavada et al. 2019; Harvey et al. 2020). These variables may be to blame for the high abundance of animal species found in shrub-land (8 species) in our study. However, species richness alone cannot determine how much of the species pool is realized within local communities or the various effects of a species' loss on the communities due to its varying role in ecosystem functioning (Wen et al. 2019). Because the vegetation in the two habitats is so similar, the highest species similarity record between open forest and shrub-land may be the result of this. (Gonfa et al. 2015) reported a similar outcome in Ethiopia's Dati Wolel National Park. The dominating mammalian species among the 11 species was the Olive baboon (Papio Anubis), followed by the Vervet Monkey (Chlorocebus aethiops).

Papio Anubis, Cercopithecus aethiops, and Crocuta crocuta were the species having the most records during the survey. During the study both medium and large in size mammalian were recorded. Large and medium-sized mammals are crucial to the health of forest ecosystems because they manage the population of prey, spread seeds, and engage in predation (Botelho et al. 2012; Guo et al. 2017; Suárez-Tangil and Rodríguez 2021; Rodríguez 2021). Due to their crucial importance in the functioning of ecosystems and vulnerability to human activity, medium- and large-bodied mammals are of interest to conservationists worldwide (Wen et al. 2019). Similar research in Wabe forest fragments in the Gurage zone of Ethiopia found the following medium and large mammals: Porcupine (Hystrix cristata), Honey badger (Mellivera capensis), Vervet monkey (Chlorocebus aethiops), Olive baboon (Papio anubis), and Colobus guereza (Colobus guereza), among the medium-sized mammals, and of the large mammals present in the research region included Spotted hyenas (Crocuta crocuta), Aardvarks (Oryctropus afer), bohor reedbucks (Redunca redunca), Oribis (Ourebia ourebi), and Common duikers (Sylvicapra grimmia) (Legese et al. 2019). In this study, the population of medium- and large-sized mammals was counted in 150 instances during the dry season and in 180 instances during the wet season. Generally speaking, summer is when there are the most mammal species and fewest mammal species in winter (Mysłajek et al. 2020). The choice of large and medium mammals for various types of forest habitat changed over time, which is tied to variations in the resources available and the environment in various forests (Zhang et al. 2019). In comparison to other studies, it is lower. For instance, 885 individuals of the species of medium and large mammals were documented during the dry season in Adaba Community Forest, West Arsi Zone, Southeast Ethiopia, whereas 1120 individuals were recorded during the wet season (Bakala and Mekonen 2021).

5 Conclusions and Recommendations

The study's conclusions show that Tirba Lake is home to numerous medium- and large-mammal species. This is the first ecological data on the variety of mammals in Tirba Lake, and it will help any organizations that are interested make wise conservation decisions as well as researchers who want to carry out effectiveness studies. To help with the creation of the management plan, studies on the population structure, spatiotemporal habitat use, and effects of human-induced actions on the park's mammals are required. These studies should be conducted in addition to tightening law enforcement efforts to reduce the current human and livestock encroachment into the area. The study region has a high biological significance, and it concentrates on the medium- and large-sized fauna in an effort to advance our understanding on a wider range of topics. In Tirba lake, there were different types of various conservation challenges like expansions of crop production, over grazing, hunting and forest degradation. To avoid the depletion of prey and the degradation of habitat, conservation activities are necessary in the research region. Therefore, responsible forest management would be the optimum activity in the buffer zones and multiple-use zones of protected areas, having significantly less of an impact and causing less conflict than alternatives like agriculture or cattle grazing while still offering economic opportunities (Tobler et al. 2018). Numerous mammals in the research region are at danger due to interacting anthropogenic causes. To protect these species, a conservation program must be implemented immediately.