Potential roles of birds diversity in optimizing sustainable oil palm plantations at PT Gunung Tua Abadi

Indonesia has declared the green economy paradigm; as one of the strategic sectors in implementing the green economy, oil palm plantations are expected to start reducing the use of chemical fertilizers, fungicides, pesticides and etc. Additionally, oil palm plantations are expected to be able to optimize the roles of biodiversity in oil palm plantations. So, it will enhance sustainable and environmentally friendly plantation management. Therefore, there is a need for further studies on the species potential and role of birds in oil palm plantations. The study was conducted on four types of land cover at PT Gunung Tua Abadi (PT GTA) with a line transect method in the morning and afternoon with three repetitions. The number of bird species in the Young Oil Palm (YP) is as many as 20. Meanwhile, the lowest number of species was found in Medium Oil Palm (MP) and Old Oil Palm (OP), as many as 10 species. In addition, if grouped by a guild, the birds in PT GTA belong to 8 guilds. Each type of guild is thought to have its role to assist in oil palm operations, including the role of controlling insect pests (Centropus sinensis, Centropus bengalensis, Collocalia linchi); seed dispersal (Trerons vernans), and also as pest control (Tyto alba, Elanus caeruleus). Further research is needed to determine more deeply the effectiveness of the role of each bird species in oil palm plantation.


Introduction
As the country's largest foreign exchange earner, the oil industry plays a crucial role in the national economic sector (Up to $30 million-2021), fuelling the community's economic sector and absorbing labour.Oil palm plantations have been shown to stimulate economic growth and reduce poverty in Indonesia [1].The oil palm plantation sector also contributes to implementing a green economy by producing environmentally friendly biofuel sources.To realize sustainable and environmental management of oil palm plantations, one of the green economy efforts that can be implemented is to utilize biodiversity optimally.Indonesia's palm oil (CPO) production in 2021 reach 51.30 million tons [2].Although the potential for oil palm expansion is high, there are various issues that arise in oil palm plantations, one of which is connected to biodiversity impact.
One of the species affected is birds.One of the species affected is birds.However, several studies have shown that bird species diversity in oil palm plantations tends to increase over time [3,4,5], due to the ability of plantations to supply food and habitat.with this increase in species diversity.
Furthermore, oil palm plantations are projected to improve production with low waste while also optimizing biodiversity roles in oil palm plantations, especially the roles of bird diversity.So, it will improve the sustainability and environmental friendliness of plantation management.Birds can be further exploited for the control of rodents and insect pest.However, there needs to be more investigation into the potential of bird species in oil palm plantations.As a result, more research on bird species' potential and role in oil palm farms is required.

Methods
The research was carried out at the oil palm plantation of PT Gunung Tua Abadi (GTA) in Ogan Komering Ilir District (OKI), South Sumatra.The study was carried out on young oil palm plantations (YP), medium oil palm plantations (MP), old oil palm plantations (OP), and High Conservation Value areas (HCV).Data collection was carried out using the line transect method with a track length of 1 Km and a width of 50 m (Figure 1).The observer follows the transect, documenting the species and quantity of birds observed or heard, the time of encounter, and the substrate on which the bird was observed.Each land cover type path was observed simultaneously in the morning at 06.00-08.00WIB and in the afternoon at 16.00-18.00WIB, with three repetitions.After obtaining data related to bird species diversity, the role of each species in the plantation was then identified from various literature.Data related to bird species diversity was then analyzed using the following indexes: a. Shannon-Wiener Diversity Index (H') Bird species diversity was calculated using The Shannon-Wiener diversity index [6].The index formulation is as follows (1): The species richness index was calculated using the Margalef species richness index [7].The index formulation is as follows (2): However, the lowest number of bird species can be found in YP with a total of 10 species.
HCV is known to have the highest number of individuals among other land covers, but the species found in HCV areas tend to be fewer.The cave swiftlet and scooty-headed bulbul were found in almost all observation locations.It is because many species of small insects are a source of food in oil palm plantation [9].The diversity of bird species is related to the qualities of the area they occupy, according to [10].The prevalence of different bird species under different land cover is induced by changes in plant species, comfort levels, and nearby supporting habitats.The number of species and individuals is shown in Figure 2 below.In line with the high number of species found in the YP area, the area also has the highest diversity and species richness index compared to other land cover categories.This is due to the location of the YP area, which is overgrown by a variety of understorey plants that can support bird life.In addition, the location of the YP directly adjacent to a large river also affects the high diversity of bird species in that location.The least number of bird species is found in MP due to high human activities and the need for more available resources.Furthermore, harvesting activities in medium and old-growth oil palm land cover resulted in 1243 (2023) 012008 IOP Publishing doi:10.1088/1755-1315/1243/1/0120084 less dense undergrowth than in young-growth oil palm plantations.Humans frequently visit the area, so the environment has a high level of human disturbance that can affect species diversity in their habitat [11].According to [12], the quantity of bird species in a habitat is related to the fact that the area still supports bird survival and is far from human disturbance.

Remarks: YP (Young aged oil palm); MP (Medium aged oil palm); OP (Old aged oil palm); HCV (High Conservation Value)
The value of species evenness in the oil palm land cover (YP, MP, OP) is classified as having a high value because E > 0.6.This indicates that each bird species is evenly distributed in each community [9].The highest species evenness value was in the OP land cover, with a value of 0.97.In contrast, the lowest species evenness value is in the YP, which is 0.86.However, something different is seen in the low HCV area's evenness index value.This low index value is caused by the species dominating this area, namely Javan myna.
The HCV area in PT GTA has diverse bird species and index values.This type of land cover provides a more stable habitat so that it can support a high diversity of animal species [13] The higher the diversity index in an ecosystem, the more stable it is; conversely, the lower the diversity index, the less stable it is [14].Complex habitat structures can support a greater diversity of bird species [15].This finding implies that forest areas around plantations are important habitats that provide plenty of food, water, and shelter.Loss of forests can lead to the extinction of birds and other species, as the findings of Krisanti [16].

The role of birds based on guild type
Birds are found at all levels of the food chain, from mid-level consumers to top predators.Birds, like other native organisms, help maintain sustainable population levels of their prey and predator species and provide food for scavengers and decomposers after death.Many birds contribute to plant reproduction by acting as pollinators or seed dispersers [17].Birds are an example of an ecosystem service that can be used to control rodents and insect pests.The oil palm plantation is home to several endemic nocturnal and diurnal bird species that have the potential to control pests such as rats and bagworms [18,19].The role of each bird species can be further examined based on the type of food it feeds on.
Birds are classified into several groups based on the type of food they consume.[20] classifies these birds into four groups: honey-eating birds (nectivore), seed-eating birds (granivore), fruit-eating birds (frugivore), insectivorous birds (insectivore), birds that eat small mammals, herpetofauna, and fish (carnivores), and birds that eat everything (omnivores).Insectivorous bird species (including insectivore-frugivore and insectivore-granivore) are the most common and can be found at all observation sites.De Chenon and Susanto [21] state that the higher species of insectivorous birds in oil palm plantations often fluctuate in tandem with caterpillar outbreaks.In addition, insects are a food source that is abundant in nature and available all year [22].Meanwhile, nectarivores are bird species that are only found in a few locations (1 species).This is because the number of resources for this bird species is low.Figure 4 shows the composition of the bird species guild in PT GTA.Then, based on the guild, the role of bird species diversity in PT GTA can be grouped into several types.These roles include assisting natural environmental processes such as natural pollinators (pollinators) and seed dispersal (seed dispersal), assisting in environmental protection such as pest control, and assisting in environmental protection such as indicators of environmental change, indicators of seasonal changes, and indicators of environmental health [23].Table 1 shows the potential birds and their roles in various land cover types based on the type of feed.According to Table 1, insectivores birds that serve as insect pest controllers dominate all land cover.In contrast, nectarivores birds, which serve as natural pollinators, are found only in one type of land cover, YP.The dominant insectivores bird species found in almost every land cover namely are Centropus sinensis, Hirundo rustica, Acridotheres javanicus, and Collocalia linchi, These insectivorous birds act to control the number of insect pest populations by consuming them [24].
Based on [21] Parus major, may feed on many insects (nettle caterpillars) daily from 6.55 a.m. to 6.15 p.m. On the soil, Centropus sp. was observed feeding on nettle caterpillar cocoons.Pycnonotus sp. and Cosyphus sp.eat a wider variety of insects, such as small beetles, caterpillars, and ants.More giant insects are caught in flight by Halcyon sp (such as grasshoppers and beetles).Orthotomus sp., was observed only feeding on the pollinating weevil Elaeidobius kamerunicus.Even Pycnonotus aurigaster also reported to feed on the weevil [25].In this case, bird species like these may deplete the weevil population, resulting in a lower fruit set.However, because many of these insectivores birds require 1243 (2023) 012008 IOP Publishing doi:10.1088/1755-1315/1243/1/0120086 nesting holes, which are scarce in younger oil palm plantations, it appears worthwhile to establish artificial nesting boxes to increase the population of these beneficial birds in plantations [21].Furthermore [13,26] also state that intercropping and crop integration can also help some bird species establish themselves in oil palm plantations.
In the other hand, birds are ineffective caterpillar predators when compared to arthropods and lizards.It is because birds prefer brown caterpillars over the green and grey caterpillars, meanwhile arthropods and lizards prefer all the caterpillar types.The diversity of small birds operating in the understory layer of plantations is critical for pest and weed control in coffee [27].Furthermore, some scientist which demonstrated the functional importance of birds and bats in the suppression of arthropod densities and an associated increase of cacao crop yield in tropical agroforestry landscapes.However, [28] found that oil palm yield was not associated with the occurrence of ants, birds and bats in oil palm smallholdings in Sumatra, Indonesia.Based on the statements above, the effectiveness and ecological functions of birds in oil palm plantations still need to be studied further.
Birds are perhaps plants' most dependable friends regarding seed dispersal because of their ability to travel long distances in short periods.Plants use colour and size to attract birds to their seeds, providing bright fruits or large nuts as a food source.The seeds are then dispersed in a variety of ways by the birds.Some ways birds disperse seeds are during feeding, in transit, through droppings, on their bodies, etc. Frugivores vertebrates (particularly birds) often play a major role in the seed dispersal of plants, especially as the passage of seeds through their gut sometimes increases germination and seeds are dispersed further from the parent plant [29].Frugivores birds (and other frugivores in general) disperse seeds by ingestion of fruit pulp and defecation (or regurgitation) of intact, viable seeds [30].Once consumed, seeds can be subjected to both chemical and mechanical digestion [31], influencing both the percentage of germinated seeds and the rate of germination [32].The main ways that frugivory can affect germination rates are seed coat abrasion and pulp removal [33].The retention time of seeds in the gut may also influence the degree of seed coat abrasion [34].Fruit-eating birds such as Treron vernans and Pycnonotus goiavier disperse seeds by burying them.
Granivores and frugivores birds also have a role in controlling weeds in the oil palm ecosystem.Weeds in oil palm plantations are normally controlled by chemical herbicides.The presence of weeds can reduce the quantity and quality of plants and causing plant growth disturbances and increase pests and diseases.Grain-eating birds can help reduce weeds.Judd [35] states that no less than 50 birds act as weedkillers.It is even known that birds often consume many seeds, even in a single meal.One sparrow's stomach contained 1000 pigweed seeds, while two other birds had taken 300 and 700 seeds of different types.Certain grain-eating species, like sparrows, tend to eat the seeds from weeds before they have a chance to spread around.While this weed control method might not kill existing weeds, it can help reduce the number of weeds that need to be addressed later.
Nevertheless, granivores bird are sometimes considered as pests in oil palm plantation, when the number of this granivorous bird is too large.In this situation, predatory bird species play a significant role in restricting granivores bird population increase.Furthermore, the presence of predatory bird functions as a top predator in the ecosystem, assisting in the management of other pests such as rats, which are frequently seen in oil palm plantations [37].Bird species such as Elanus caeruleus found in the study site with a land cover of HCV help control rat pests that can cause losses in oil palm plantations [38].
Despite all the benefits of birds in oil palm plantations, the presence of birds in oil palm plantations is currently under threat.In oil palm plantations, there are two major threats to birds.The first comes from the use of pesticides.Salim et al. [38] discovered that a population of 40 barn owls was reduced to two within 30 months.Many were discovered dead with bleeding from the nostrils, a symptom of anticoagulant rodenticide poisoning.He also suggested that rodenticides can cause compromised or stunted growth.The birds are also under threat from hunting activities.Long-tailed Parakeet (Psittacula longicauda), and Yellow-vented Bulbul (Pycnonotus aurigaster), are sought after as pets.At the same time these birds perform critical ecosystem functions such as pest control, pollination, and seed dispersal.

Conclusions
Insectivores birds, which reduce insect infestations, dominate the avian variety at PT GTA.This study shows that birds have the potential to play a role in oil palm plantations.To enable long-term agricultural management, the diversity and number of bird predators should be preserved by tolerating understory vegetation and limiting pesticide application.While further research is needed to determine the effectiveness of birds in the oil palm plantation.So that in the future, oil palm plantations can optimize the role and function of birds in oil palm plantations

Figure 2 .
Figure 2. Number of species, total individuals of bird species in PT GTA

Figure 3 .
Figure 3.Comparison of diversity, richness, and eveness value index in each land cover type

Figure 4 .
Figure 4. Bird guild in PT GTA The current focus is to assess what is happening 1243 (2023) 012008 Diversity of the bird speciesThe total number of bird species in the study location was 32.These 32 species belonged to 20 different families with a total of 424 individuals in 4 land cover types.Species that can be found in all types of land cover include Pycnonotus aurigaster, Centropus sinensis, Orthotomus sericeus, and Halcyon smyrnensis.Most bird species can be found on YP, comprising 20 bird species and 75 individual birds.

Table 1 .
Bird's ecological role in oil palm plantation