The role of birds diversity in increasing oil palm productivity at PT Permata Sawit Mandiri, West Kalimantan

The expansion of oil palm plantations has reaped many damaging accusations, namely as the leading cause of deforestation, and is responsible for the decline in biodiversity. Oil palm cultivation cannot be separated from pest attacks that affect its quality and quantity. Besides being expensive, pesticides can cause environmental damage and decrease palm oil productivity. Therefore, optimizing the utilization of biodiversity in its management is necessary. As insectivores, birds significantly control pests that attack oil palm plants and also have other beneficial roles for oil palm plantations. This study aims to identify the diversity of bird species and the role of various bird species in the oil palm plantation of PT Permata Sawit Mandiri, West Kalimantan. Data were collected using a combination of line transects, point observation methods, and vegetation analysis methods. Meanwhile, data related to the role of birds in oil palm plantations were obtained through a literature study. The total species of birds found in oil palm plantations were 38 species in 6 land cover locations. The highest number of bird species was found in Secondary Forest in block G12 land cover and based on the type of feed, most bird species also found in this land cover (20 species), which acts as natural pollinators, seed dispersers, and pest control. While the least species of birds were found in oil palm with the oldest planting year (3 species). The diversity and the role of bird species found in secondary forests and rubber forests bordering oil palm plantations have the potential to source food, pollination, and pest control for birds in oil palm plantations.


Introduction
The palm oil industry has a strategic role in the national economic sector as the country's largest foreign exchange earner, driving the community's economic sector and absorbing labour.The development of oil palm plantations has been proven to encourage economic growth and reduce poverty in Indonesia [1].Indonesia's palm oil (CPO) production in 2020 reached 44.8 million tons with an area in 2019 of 14,456.611hectares, of which 60% belonged to large private plantations, 35% to smallholder plantations, and 5% to large state plantations [2,3].The development of palm oil production in the form of CPO continues to increase, with an average growth rate of 11.13% per year.Indonesia is the world's largest palm oil exporter, exporting CPO and its derivative products, reaching 36.17 million tons throughout 2019 [3].
The high demand for palm oil requires companies to continue to increase the quantity and quality of their production.However, problems related to pests that attack oil palm plants which can cause losses 1243 (2023) 012011 IOP Publishing doi:10.1088/1755-1315/1243/1/012011 2 [4,5] are quite an obstacle in their management.The use of insecticides or pesticides as an effort to control pests that attack plants excessively in the long term can result in the accumulation of residues in the products produced [6], killing non-target plants, causing environmental damage, and endangering the animal community, including the bird population [7].The decline in bird populations is due to the accumulation of pesticides in bird tissue which causes death and loss of worms as bird feed [7].
According to [8], continuous use of pesticides kills target pests and natural enemies.This environmental issue has received a lot attention from the government and NGOs.Therefore, high standards are needed for business actors to be accountable for environmental and social problems.Sustainable and environmentally friendly plantations must implement the integrated pest control that prioritizes economic and ecological principles by empowering natural enemies and predators as pest control.
Birds are animals that have an existence in assessing biodiversity because they occupy various habitats and are close to the top of the food chain [9].Birds have an essential role in maintaining the ecosystem's balance, including acting as pollinators, dispersing seeds, and controlling pests.[10] found that insectivorous birds in oil palm plantations can contribute to the control of leaf-eating oil palm pests.The bird's contribution can provide an economic incentive for oil palm producers to make plantations more biodiversity-friendly and compliant with the RSPO standards.In addition, according to [11] the palm oil industry will benefit by maintaining biodiversity in its plantations by reducing the need for pest control.Therefore, this study aims to identify the diversity of bird species and the role of various bird species in the oil palm plantation of PT Permata Sawit Mandiri, West Kalimantan which plays an important role in increasing oil palm productivity.

Methods
Data collection was carried out in a plantation area owned by PT Permata Sawit Mandiri in Nanga Tayap District, Ketapang Regency, West Kalimantan Province the study is conducted from January 2020 to April 2020.The equipment used for bird inventory includes camera traps, binoculars, meter tape, cameras, and tally sheets.Identification of bird species is also assisted by using a field guidebook for birds of Sumatra, Kalimantan, Java, and Bali by MacKinnon et al. (1998).The bird inventory was conducted using a combination of line transects and point observation methods.The line transect method is carried out by taking samples in the form of observation lines with a width of 100m and a length of 1km, while the point observation method is a predetermined point from a preliminary literature study and interviews with local residents who are suspected of having encountered with the birds and are the core area or bird habitat.The inventory of birds was carried out in 6 land covers, namely the newly planted oil palm plantations (SM), oil palm areas aged 1 year (SS), oil palm areas aged 2 years (ST), and forested areas adjacent to oil palm areas, namely rubber forests (KK) and secondary forests in block G12 (HG) & block F12 (HF).The data recorded included the time of encounter, the types of birds found, the number of individuals of each species found, and bird vocalization.Observations were made in the morning (06:00-08:00) and afternoon (15:30-17:30) for 3 repetitions.
Remarks: Xi = Animal position; D = The average visibility for observers at a given location; Pi = Observer position Figure 1.Birds observation transect illustration Data analysis includes quantitative and descriptive qualitative analysis.Descriptive analysis is used to explain the diversity of bird species in oil palm plantations which are described descriptively based on the results of a literature review.Meanwhile, quantitative analysis is carried out using the following index:

Shannon-Wiener diversity index
The Shannon-Wiener diversity index [12] is used to determine the diversity of bird species with the following formula (1): H' = Shannon-Wiener diversity index ni = number of bird species N = the number of individuals of the whole species

The Margalef species richness
The species richness index serves to determine the species richness of each species in each community encountered and can be calculated using the Margalef species richness index [13] with the following formula (2): Dmg = Species richness index (Margalef index) S = The number of bird species observed N = The number of individuals of the whole species ln = Natural logarithm

Index of evenness
According to [14], the Index of Evenness functions to determine the evenness of each species in every community encountered, can be calculated using the following (3):

E
= Evenness index H' = Shannon-Wiener diversity index S = number of bird species

Community similarity index
According to [15], to calculate the level of similarity of bird communities between each land cover, was used as the following formula (4): = the same number of species in both communities

Diversity of the bird species
The observation managed to find 38 species from 26 families and a total of 141 individuals in 6 land cover locations.Most bird species can be found in PT.PSM is on HG land cover, with a total of 20 bird species and 32 individual birds.In comparison, the lowest species that can be found is only 3 species and 10 individual birds on ST land cover.The most common bird species found were the Hirundo rustica or the barn swallow (17 individuals), Collocalia linchi or the cave swiftlet (14 individuals) and Anthracoceros malayanus or the black hornbill (10 individuals).Hirundo rustica was found in almost all observation locations because there are many species of small insects that are a source of food in that location.According to [16], the diversity of bird species is related to the characteristics of the habitat they occupy.The existence of differences in the presence of bird species in various land cover is caused by differences in plant species, comfort levels, and adjacent supporting habitats.In [17] research it even says that differences in the presence of understory vegetation alone will affect the decrease in bird species richness, it reinforces that differences in vegetation greatly affect the diversity of existing bird species.
The bird diversity index value in PT.PSM varies as shown in table 1 below.The highest species diversity index was found in HG land cover, with a value of 2.79.while the lowest index is on land cover ST with a value of 1.03.According to [18], the factors that affect the value of diversity are environmental conditions, the number of species, and the distribution of individuals in each species.Further elaboration for the number of species, total individuals, and diversity of bird species in PT.PSM are presented in the following table 1.The high number of bird species in HG is due to the lack of human activity and the large number of vegetation used as a bird habitat.This is in accordance with [19] statement that the number of bird species in a habitat is due to the fact that the habitat still supports the survival of birds and is far from human disturbance.
The highest species richness index (Dmg > 4.0) in bird observations at PT. PSM was on non-oil palm land cover, namely HG, with a species richness index of 5.48.Meanwhile, PT.PSM's oil palm plantations have a species richness index classified from moderate (SS) to low (SM, ST).This is in line with the opinion of [20,21,22], which state that changing land cover to plantations will lead to a minimum reduction of 60% of bird species richness.
The value of species evenness in the six land covers is classified as having a high value because E > 0.6.This indicates that each bird species is evenly distributed in each community.The highest species evenness value was in the ST land cover, which has a value of 0.94.While the lowest species evenness value is in the SM and HF land cover, which is 0.90.This value shows a value close to 1, which means that the bird species that are found in the ST land cover even though there are only 3 species namely the Centropus sinensis, Amaurornis phoenicurus, and Trichastoma rostratum but all three are evenly distributed, with no dominated species, and the community is stable because the number of individuals between species is almost balanced [23].
The community similarity index between each land cover in PT PSM's oil palm plantations varied from 0 -0.61.The highest similarity of bird communities was found between HF and HG land cover, which was 0.61 or 61%.This figure indicates that bird communities in HF and HG land cover have the same species composition of 61% of the total bird species in both habitats.HF and HG land cover are secondary forests with similar compositions of vegetation and habitats and both are close, thus, allowing birds to move from one place to another more easily in the search for feed and other resources to support their survival.This is in accordance with the research conducted by [24].The bird community similarity index in PT PSM is further presented in table 3 below.Meanwhile, the smallest bird community similarity index value was found between KK and company palm oil (SM and ST) land cover, which has a value of 0%, which means that there is no similarity at all or dissimilar.The low similarity or the different of the community can be caused by the different habitat characteristics and vegetation in each land cover.PT PSM's oil palm plantation has a habitat type that is more open and hotter, where the palm crown that grows is still short so that the intensity of light entering is higher, and there are fewer ground plants on the estate floor.This is different from the condition of the community estate around the company, which are not only overgrown with rubber trees but also cocoa, coffee, nutmeg, etc.These differences in conditions cause birds to be unable to move so that species differences are evident [25].In accordance with the opinion of [26] that the similarity values are very different indicating that the environmental conditions at each location compared are relatively heterogeneous, so that the presence of bird species at each location has quite distinctive characteristics.Because there are real differences between the two habitat conditions, then birds tend not to be able to move in search of food from one place to another because the available resources are also different to be used as feed sources.
Based on the results of observations made on 6 land covers in the oil palm plantation of PT.PSM there were 26 bird families observed.The family composition of each bird species is presented in Figure 2 below.

Figure 2. Family composition of each bird species
Figure 2 shows that the bird families found in 6 land covers in the oil palm plantation of PT.PSM is dominated by the Pycnonotidae family, with a total of 4 bird species.The Pycnonotidae family is a group of fruit-eating birds or frugivores that help in the dispersal of plant seeds, as well as being able to accelerate the germination process of plant seeds, which contributes to maintaining the forest regeneration process [27,28].

The role of birds by ecological type
Based on the type of their feed, birds are divided into several groups, [29] explains groups of birds based on the type of feed, including groups of honey-eating birds (nectarivore), 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).The groups of birds, based on the type of feed, provide a role for the existing ecosystem.These roles include assisting natural processes that occur in the environment, such as natural pollinators (pollinators) and seed dispersal (seed dispersal), helping to protect the environment based on food webs, such as pest control, and assisting in protecting the environment such as indicators of environmental change, indicators of seasonal changes, and as indicators of environmental health [30].Table 3 below is the elaboration of the potential birds and their role in various land cover based on the type of feed, observed from field observations and literacy studies.Table 3 shows that in the study area, it was found 2 species of birds that act as natural pollinators, 10 species as seed dispersers, 14 species as insect pest controllers, 3 species as macrofauna pest control, and 9 species as both pest control and seed disperser.Insectivore feed type of birds that act as insect pest control dominates all land cover.In contrast, nectarivore birds, which act as natural pollinators, are only found 2 species namely in KK and SS land cover.Insectivorous birds were more abundant in HG land cover than in other land covers because the food sources in the location were relatively abundant.The dominant insectivore bird species found in almost every land cover namely are Centropus sinensis, Hirundo rustica, Cacomantis merulinus, and Collocalia linchi.Such as Hirundo rustica is most likely to choose the Formicidae family insect from the order Hymenoptera as their feed [31].Insectivore birds are more dominant to be found because there is their favorite feed in oil palm plantations ecosystem in the form of destructive insect pests such as fire caterpillars (Thosea asigna, Setora nitens, Darna trima, and Thosea bisura), bagworms (Metisa plana and Mahasena corbetti), beetles (Oryctes rhinoceros), and grasshoppers (Valanga nigricornis).These destructive insect pests are consumed by insectivore birds such as Lanius schach, and Centropus sinensis that act as pest control agents and control the number of insect pest populations [32,33].In accordance with [34] and [35] statement, which states that Oryctes rhinoceros is one of the main pests of oil palm plantations that can kill plant shoots because it attacks the point of growth so that it can reduce the quality and quantity of oil palm production.Such as Pycnonotus goiavier consume this type of pest.In addition, caterpillar pests attack oil palm leaves from nurseries, immature plants, and mature plants.Caterpillars are more commonly found in oil palm trees less than three years old.The impact of caterpillar attacks is a decrease in production to 69% in the first year and 27% in the second year after the attack; in fact, oil palm plants cannot bear fruit for 1-2 years if the attack is heavy [36].According to [37] in [38] a caterpillar consumes a leaf area of 300-500 cm².[39] explained that the more species of birds that eat insects in an ecosystem, the more effective it will be in pest control efforts.This is because the birds that eat about a third of their body weight can eat.
According to observations, nectarivore birds were found in the SS and KK areas.This is because SS is an area that has vegetation between old and young ages with fast-growing vegetation understorey.Nectarivore birds can generally help natural pollination or are called pollinator agents [40].The Arachnothera longirostra species found in SS land cover has a role in helping pollinate shrubs and understorey species such as mucuna (Mucuna bracteata), which is deliberately planted to reduce weeds in plantation areas.Meanwhile, the Aethopyga siparaja species found in KK land cover play a role in pollinating trees such as rubber and coffee through their feeding activities [41].
Pycnonotus atriceps, one of the frugivore birds found in the land cover of the KK, plays a role in the distribution of dominant plant seeds in the KK, such as coffee, through eating activities and the feces releases.Anthracoceros malayanus, commonly found in HG and HF, which are secondary land cover areas overgrown by various types of plants, has a role in the distribution of existing plant species, for example, Vitex pinnata, which is a commercial wood species.Anthracoceros malayanus is a fruit-eating bird whose one of its favourite feed species is Ficus sp. and Vitex pinnata [42].Birds with the granivore type of feed that consume grain and seeds can be found in HG, KK, SM, and SS land cover.Apart from being seed dispersers, several species of granivore and frugivore birds also have a role in controlling weeds in the oil palm ecosystem [43].The presence of weeds can reduce the quantity and quality of plants and causing plant growth disturbances and increasing pests and diseases.Birds control weeds by damaging the body parts of weeds; for example, Lonchura fuscans found in KK land cover use grass or weed parts to make nests.[44] explained that munias birds use grass as the primary material for making nests.The part of the grass's body that was damaged by the bird resulted in the grass's ability to reproduce being disturbed.KK land cover, which tends to be a monoculture, is dominated by rubber, spreading destructive pest attacks faster than land cover with various types.
In addition to acting as insect pest controllers, birds also act as natural predators for plantation pests of macrofauna, such as rats.[45] explained that pests that often attack oil palm plantations and can cause oil palm production losses are rats (Rattus sp.).One of the bird species that play a role in controlling macrofauna animal pests is predatory bird species, one of which is rats through the food chain.Bird species such as Elanus caeruleus found in the study site with a land cover of SM help control rat pests that can cause losses in oil palm plantations.[46] explained that rats are among the leading food types of Elanus caeruleus.Rats are a very influential pest in oil palm plantations.[47] explained that rats are pests that are detrimental to oil palm plantations because they can cause production loss of up to 10-15% and cause damage to fresh fruit bunches, causing a 25% decrease in production.The high rate of rat pest attacks is because the palm fruit part is the preferred food for rats, and in a bushy environment, there are many weeds which are a living place for the rats' habitat for shelter, foraging, and reproducing.The bushy plantation area makes it easier for rat pests to nest [47].Rat attack also causes a decrease in the production of fresh fruit bunches by 21.6 tons/ha/year.Another study by [48] stated that rats eat weeds on immature plants (TBM) until the plants die, while in mature plants (TM), rats eat fruit and flowers so that it can reduce oil palm production.
Birds of the omnivorous group are birds that eat various types of food ranging from plants and insectivores to small mammals.[49] explained that omnivorous birds are birds that eat more than two types of food or are often called all-eating birds.Each omnivorous bird in an ecosystem's ecology can have various roles which the main thing in this ecosystem is to be pest control and seed disperser.Pycnonotus goiavier is an omnivorous bird species because this bird eats seeds, fruits, and insects.This kind of birds can be found in SS, and KK land cover.Pycnonotus goiavier likes open places such as shrubs, roadsides, and plantations.The main food of this bird is insects from the order Coleoptera and Homoptera.In addition to preying on insects, Pycnonotus goiavier likes oil palm fruit fibers.
Similar research was also conducted by [50] on smallholder oil palm plantations in Riau province.In this study, 22 bird species from 15 different families were identified from 8 locations.The species richness index value at the location of the smallholder oil palm plantations is in the medium category (2.5 < Dmg ≤ 4) while the species evenness ranges from 0.90 -1.00 which means the community is very stable (0.75 <  ≤ 1).The same bird species found between this study and the study of Santosa et al (2018) are Streptopelia chinensis, Pycnonotus aurigaster, Pycnonotus goiavier, Centropus sinensis and Corvus enca.[50] also stated that the existence of secondary forests among oil palm plantations is important for the birds in it to find food.Although it does not explain the ecological role of birds, in [50]'s research it can also be proven that oil palm plantations still have the potential to become a habitat that provides a source of food for birds based on the findings in the field, there are various types of birds with various types of feed.

Conclusions
Bird diversity at PT Permata Sawit Mandiri consists of 38 species from 26 families and 141 individuals in 6 land cover locations.HG land cover has the highest value of species diversity (H'), species richness (Dmg), species abundance (E) and number of individual birds.In the six land covers, based on the type of feed, 5 groups of bird species were found, namely the nectarivore, granivore, frugivore, insectivore, and omnivore while the most dominant group was the insectivorous birds.Ecologically, these birds have the potential role as natural pollinators (2 species), seed dispersers (10 species), insect pest control (14 species), macrofauna pest control (3 species), and pest control and seed disperser (9 species) in palm oil plantation.The diversity and the role of bird species found around the company's palm oil (secondary forests and rubber forests) that bordering oil palm plantations have the potential to source food, pollination, and pest control for birds in oil palm plantations.
species in A community B = number of species in B community C

Table 1 .
Number of species, total individuals and diversity of bird species in PT PSM Remarks: SM (Palm with the youngest planting year); SS (Palm oil with planting year between oldest and youngest); ST (Palm with the oldest planting year); HG (Secondary Forest in block G12); HF (Secondary Forest in block F12); KK (Rubber farm); S = number of bird species; Ind = sum number of birds individual; H' = bird species diversity; E = species evenness; DMg = species richness

Table 2 .
Bird community similarity index at PT PSM

Table 3 .
Potential birds and their distribution on each land cover