Rat composition and population in mature oil palm adjacent to paddy field

Rat is one of the main pests in an oil palm plantation, impacted at various types and stages of oil palm growth. Ungkaya estate has a historical & endemic infestation of rats, especially in several fields adjacent to paddy fields. This study aimed to find out the seasonal migration of rats from paddy fields to oil palm fields in Ungkaya Estate. Five plots were used for trapping, identifying rat species, monitoring of rat population, rat damage intensity, and rat habitat preference at each stage of the paddy season. Trapped rats were identified as Rattus tiomanicus (56.91%), Rattus argentiventer (36.17%), and Rattus tanezumi (6.91%). The intensity of rat damage to the palm was high during the vegetative phase of paddy season and the full moon phase. The regression analysis results showed that the number of trapped rats has a positive relationship to rat damage intensity for the vegetative and harvesting stage at full moon. The number of trapped R. argentiventer at vegetative stage was higher than the generative & harvesting phase of the paddy season. Moreover, there were rat footprints observed on the riverside leading to the oil palm field. The results of all observation parameters concluded that there was seasonal migration of rats between the oil palm fields and the paddy fields in Ungkaya estate. The information is pivotal in drawing up suitable mitigation measures to control and minimize rat damage to the oil palm.


Introduction
Rat is considered one of the main pests in oil palm plantations.Rats could damage various types and stages of plant growth, not only in the mature palm but also in the nursery and immature palm phases.Damage to the growing point of immature palm could cause losses of up to 80% due to casualty or stunted growth.Meanwhile, severe infestation in the mature palm can reduce FFB production by 5-10% [1].Moreover, rat attacks could also have the potential to reduce the population of pollinating weevils, Elaeidobius kamerunicus.There are three main species of rats in oil palm plantations, wood or field rats (Rattus tiomanicus), rice field rats (R. argentiventer), and house rats (R. rattus diardii) [15].
Ungkaya estate of Minamas Plantation has a historical & endemic infestation of rats.This these rat damage occurred in several fields adjacent to the local paddy field.Rice field rat R. argentiventer is main pest that is mostly found in paddy fields in South East Asia.It lives in burrows between planting seasons, and populations persist in surrounding vegetation [15].There are no data to prove that oil palm damage was caused by migrated rats from a paddy field in Ungkaya estate.Therefore, the study of rats 1308 (2024) 012015 IOP Publishing doi:10.1088/1755-1315/1308/1/012015 2 movement, migration from rice fields to oil palm fields in Ungkaya estate is very important as basic knowledge in determining the timing and effective control strategies.

Study area
The trial was conducted from March until August 2021.Observation of rat behavior and migration was carried out in mature oil palm fields, i.e., field B006 and field C004, Ungkaya estate, Central Sulawesi.Both fields B006 and C004 were flat in topography and separated by Ungkaya River from the paddy field (Figure 1).In this study, about five plots (plot A, B, C, D, and E) were used with 180 palms population for each plot.

Identification of rats and monitoring of rats population
Cage traps were installed along the boundary of the oil palm field in each plot.Loose fruits were used as bait that was set in each cage trap.Rat trapping was conducted at all stages of paddy season for 2 consecutive days fortnightly, at full moon and no full moon night.If the rat was trapped on the first day, the traps were replaced and appropriately washed with detergent to remove trap shyness.The new traps and the same type of bait were used for the next day.The trapped rats were identified using identification keys [6][9].Qualitative characteristics observed were hair texture, nose shape & body shape, dorsal & ventral body color, and also dorsal & ventral tail color.Quantitative characters measured were body weight, head & body length, tail length, earlobe width, foot length, pair of rodent teeth, and number of nipples in pairs.Monitoring of the rat population (density) has been carried out by using the capture-mark-recapture (CMR) technique.Captured rats were put into a black cloth bag, drugged, and weighed.Newly captured rats were marked by nail-clipping and painting their hind legs to give a unique identity based on the trapped location.The determination of the rat population was based on the following formula [12]:

Observation of rat damage intensity
For each plot comprising 13 x 14 palms, ten palms were selected in each rows 3, 7, and 11.In total, there were 30 palms observed for rat damage intensity and area of infestation.The damage intensity of the sample palm was conducted by counting the infested palms from the total palm sample [5].Then, damage scoring was carried out based on the cluster being infested (Table 1) [6].The area of infestation and intensity of rat damage were calculated using the formula [11].
 Area of infestation:  Rat damage intensity: Table 1.Qualitative characters of trapped rats

Observation of rat nest preference and rat footprints
Observation was carried out to find out habitat preferences during paddy season, either on the ground [15] or in the palm crowns [3].On this observation, the demolition of the rat nest was carried out after the last day of trapping.The worker's team moved progressively through the plots by breaking frond stacks in the inter-rows, pocking with sticks in palm crowns, and digging out holes in the ground.For rat footprints observation, it was conducted based on tracking of rat footprints leading to oil palm fields on river side.

Rats identification, composition, and population
Results of observation of trapped rats based on qualitative and quantitative characters were tabulated in table 2 & table 3. Three species have been identified, i.e., Rattus tiomanicus, R. argentiventer, and R. tanezumi.Both of R. tiomanicus and R. tanezumi have almost the same qualitative character (figure 2).But the difference between these rats species is the ventral body color, which is white for R. tiomanicus and black-gray for R. tanezumi.Meanwhile.R. argentiver has brownish yellow for dorsal body color and white to brownish white for ventral body color.The results of rat trapping in oil palm fields adjacent to the paddy fields was quite diverse, with compositions including R. tiomanicus (56.91%),R. argentiventer (36.17%), and R. tanezumi (6.91%) (Figure 3).The highest number of rats trapped, mainly R. argentiventer was observed at the vegetative phase rather than the generative and harvesting phase.The highest total number of rats trapped in the study area during the paddy-vegetative phase was related to the availability of food.About 70% of rat population will be migrated to surrounding habitats that provide food, while 30% remaining will settle down to survive by utilizing existing food sources, by the time fallow, vegetative, or paddy has been harvested [9].Among the rats identified, R. tiomanicus was the dominant species living in the study area.This dominance showed that rats have adapted well to this ecosystem.The rice field rat, R. argentiventer was also found in the oil palm fields.Four rat species attack oil palm plantations, namely R. tiomanicus, R. tanezumi, R. argentiventer, and R. exulans [7].Earlier, in the Malaysian peninsula, R. tiomanicus was the characteristic rat species of fully mature oil palms and virtually the only species found.R. argentiventer was usually found in some localities but only up to early maturity [14].Based on the study results [9], there were four species of rat in West and Central Sulawesi, R. tiomanicus, R. tanezumi, Maxomys hellwaldii, and Rattus sp.R tanezumi is a house rat with a genetic difference with R.r. diardii is 14% (genetic distance) [10].Rat population (density) for all stages of paddy season and all moon phases was undefined or indeterminate.It was due to no marked rats being re-trapped on the second day.The low recapturing of marked rats was allegedly related to the deterrence trap (trap shyness).Rats that had been trapped before and re-released became hard to recapture.This can cause bias in the population density calculation with CMR method.Therefore, the estimated rat population was based on the trap success.As compared to R. tiomanicus, R. argentiventer is more difficult to trap and more specially to re-capture [15].This can cause bias in the population density calculation with CMR method.Therefore, the estimated rat population was based on the trap's success.

Rat damage intensity
Rat damage intensity was highest in the vegetative phase with an average damage intensity of 35%.Based on the moon phase, damage intensity was higher in the full moon phase.In the full moon phase, rat damage intensity was observed to be high in Plot A, D & E (table 4).2018).In addition, the condition of the river that separates field B010 from paddy fields has a steeper river bane and broader than the river conditions in field C014 (Figure 4).These may be the factors that trigger rat population and potential for rat migration higher in plots D & E compared to plots A, B, and C.

Relationship between and rat population and rat damage intensity
Rat damage intensity to oil palm due to rat attacks was strongly influenced by the abundance of the rat population.The higher the rat population, the higher the rat damage intensity.The regression analysis results showed that the number of trapped rats has a positive relationship to rat damage intensity for vegetative and harvest stages at full moon, while the poorer correlation with other stages of the paddy cycle.
The results of linear regression analysis between rat population and rat damage intensity for the harvesting stage at full moon R 2 = 94.4% which means that every addition of 1 individual rat will increase the intensity of the damage by 1.28% (Figure 5).This aligns with [8] findings between damage and rat population.The results showed that rats were observed dominantly in palm crowns.R. tiomanicus was species that was mostly found in palm crowns.The rats went into the palm crowns to feed on the oil palm fruit.This finding was in line with [3], where the rat's shelter was the majority in palm crowns, frond stacking, and vegetation.Another rat nest observed was in the ground hole or burrow.R. argentiventer is rat species that usually make a burrow in paddy fields or edges of waterways.Rat's nest burrows have been studied that during periods of unavailability of food or floods, the rat's nest burrow is left and when food is available in the vicinity, the hole is re-occupied [13].The results of a study by [2] in Pinrang showed that a few weeks after harvesting, only 10% of active burrows were found in paddy fields not far from plantations and villages.More active holes are found in irrigation canals, farm roads, and at the edges of cocoa and oil palm plantations [4].Another observation of this study was the tracking of rats' footprints.The presence of rats' footprints was observed on the riverside on oil palm and paddy fields.The result showed that rats' footprints were majority leading to oil palm fields compared to paddy fields.

Potentially of R. argentiventer seasonal migration from paddy field to oil palm field
From all observations conducted at all stages of paddy season, there were rats migration from the paddy field to the oil palm field.Several data and facts that lead to seasonal migration were an increase in number of trapped R. argentiventer and rat damage intensity in oil palm fields at fallow land and vegetative stages compared to generative and harvesting stages.This was also strengthened by the discovery of R. argentiventer nest in ground holes or burrows.It was also followed by rats' footprints found from the paddy fields to the oil palm fields.
According to [9], R. argentiventer responds to rapid environmental changes in paddy cultivation activities by adapting and implementing strategies to survive.One of the strategies is by migrating from paddy fields to surrounding habitats (plantations, residential areas, and warehouses) at the beginning of the planting season (vegetative).This migration was caused by the reduced availability of feed and shelter, as well as the disturbance of rat habitat due to paddy cultivation activities.
An increase in the number of rat population, followed with the high rat damage intensity in the oil palm field during the vegetative phase, could be used as the basis for integrated rat pest control.Therefore, there were several recommendations derived based on this study result.First, field upkeep is to be conducted regularly to reduce the rat's habitat.A census of rat damage is to be conducted on a monthly basis.More concern is also to be laid out on the fields along the Ungkaya River.Sustainable rat control is to be carried out by developing barn owl Tyto alba.Moreover, the development barn owl box (BOB) ratio should be according to barn owl occupation, and BOB to be placed according to the affected areas of rat attack.Chemical control by rat baiting campaign is only conducted for areas where rat damage is high.Rat bait to be used is first-generation bait, such as Warfarin and Coumatetralyl.

Conclusion
Rats species and composition in oil palm fields of Ungkaya estate were R. tiomanicus (56.91%),R. argentiventer (36.17%) and R. tanezumi (6.91%).The rat population for all stages of paddy season based on the Lincoln Index was undefined or indeterminate, due to no marked rats being re-trapped.Rat damage intensity in oil palm fields was high in the vegetative phase of paddy season and full moon phase as well.The number of rats showed a positive relationship to damage intensity for vegetative and harvest stages at full moon.Rats footprints were observed on the riverside both on oil palm fields and paddy fields.From all observations conducted at all stages of paddy season, it concluded that there were rats migration from paddy fields to oil palm fields.

Figure 1 .
Figure 1.Five trial plots (A, B, C, D, E) located in Ungkaya estate population size of rat N1: Number of rats captured on the first day N2: Number of rats captured on the second day R : Number of marked rat in the sample recaptured on the second day 1308 (2024) 012015 IOP Publishing doi:10.1088/1755-1315/1308/1/0120153 of infestation n : The number of palm showing symptoms of being infested by rats N : Total number of palms observed n number of palms belonging to an attack category Vi : Score in each category of attack N : number of palms observed Z : score for the heaviest attack category IOP Publishing doi:10.1088/1755-1315/1308/1/0120154

Figure 3 .
Figure 3. Result of trapped rats in oil palm, Ungkaya estate refer to stage of paddy season

6 Table 4 .
Rat damage intensity on all stages of paddy season & moon phasePlots A, B, and C were located in field B010 (2014) with palm circle and inter-row good upkeep conditions than plots D and E in field C004 (

Figure 4 .
Figure 4. (a) River condition in plot A, B, and C (32 m width); (b) and river condition in plot D and E (28 m width)

Figure 5 .
Figure 5.A positive relationship between rat population and rat damage intensity at full moon; (a) Vegetative stage, and (b) Harvesting stage3.4.Observation of rat nest preference and footprint trackingObservation of rat nest preference was based on the phase of paddy season (vegetative, generative, and harvesting).The results showed that rats were observed dominantly in palm crowns.R. tiomanicus was species that was mostly found in palm crowns.The rats went into the palm crowns to feed on the oil palm fruit.This finding was in line with[3], where the rat's shelter was the majority in palm crowns, frond stacking, and vegetation.Another rat nest observed was in the ground hole or burrow.R. argentiventer is rat species that usually make a burrow in paddy fields or edges of waterways.Rat's nest burrows have been studied that during periods of unavailability of food or floods, the rat's nest burrow is left and when food is available in the vicinity, the hole is re-occupied[13].The results of a study by[2] in Pinrang showed that a few weeks after harvesting, only 10% of active burrows were found in paddy fields not far from plantations and villages.More active holes are found in irrigation canals, farm roads, and at the edges of cocoa and oil palm plantations[4].

Figure 6 .
Figure 6.Observation of rat shelter

Table 2 .
Qualitative characteristics of trapped rats

Table 3 .
Qualitative characteristics of trapped rats