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Morphology and Bait Preference of Black Rat (Rattus rattus) in the University Community in Nigeria: Obafemi Awolowo University as a Case Study

Aims: This study assessed the morphology and the bait preference of black rat (Rattus rattus) in Obafemi Awolowo University student hostel with the aim of controlling the population of black rat in the students’ hostels. Place and Duration of the Study: The study was carried out at Obafemi Awolowo University which is situated in Ile-Ife, an ancient city in the Southwestern Nigeria and lies between latitudes 7°28′N and 7.467°N and longitudes 4°34′E and 4.567°Ewith a landmass of 5,506 hectares between December 2017 and February 2018 Methodology: Locally made metal traps (cage traps) (Plate 1) contains baits were placed fortnightly in various sampling locations (Awolowo, Fajuyi, Angola, Akintola, Mozambique and Moremi halls of residence) for a period of 3 months between the months of December 2017 to February 2018. The traps were set around the dark corners of the sites in the evening and Original Research Article Bamidele and Kowobari; AJRIZ, 2(1): 1-12, 2019; Article no.AJRIZ.48013 2 collected the following morning (6.00am). Results: A total of 236 black rats (Rattus rattus) were caught (81 male & 155 female), with the female having the highest weight (238.30 g). Among the baits used, fried fish caught the highest number of the black rat (58%) followed by beans cake (akara) (28%) and the locust bean (14%). There was a positive correlation in the morphology of the black rat caught in all the hostels. Conclusion: The black rats in the University student hall of residence were of the same family and genus, and fried fish is the best-preferred bait.


INTRODUCTION
The black rat is one of the most widespread animal species in the world due to their adaptability to a wide range of habitats [1]. Rattus rattus is able to utilize most terrestrial habitat types on continents and islands. In urban areas, they are found around warehouses, residential buildings, and other human settlements. Roof rat (R. rattus), house rat (Mus musculus) and Norway rat (R. norvegicus) play a significant role within public health sector [2] such as carriers of many infectious and parasitic diseases that can be transmitted to a human being [3].
In urban areas, the damage caused by rodent incisor activity cannot be underestimated, most especially to power cable leading to blackout and fire in most cases [4]. At home and hostels, black rat (R. rattus) caused damage to clothes, foods, books, household materials that are stored and sometimes in use. At home, the tips of fingers and toes are biting by the black rat if they are not properly washed before going to bed [5]. If not control, rodent pests are connected to considerable economic losses and become a considerable conservation threat to life, indigenous flora, and fauna in most part of the world [2].
In various hostel and staff quarters in the Obafemi Awolowo Universities, black rat (R. rattus) has been the major rodent causing damage to both students and staff properties. The population of black rat kept increasing due to the availability of shelter, food, and water [6]. The University community has defined many means of controlling black rat (R. rattus), but no success.
In the line of the damage caused by a rodent (Black rat), continuous control of rodent population is important especially in a human populated area (Hostel) where risks to health and security are greater due to the presence of rats pests [2]. Alteration of the environment can produce substantial changes invertebrate population since they depend upon the environment for shelters, food, and water [7].
The black rat is a medium-sized, slender brownish-or grayish-black rat with a coarse fur, grayish-white under part, large eyes and ears, and whiskers around the nose which is pointed. They possess a tail that is sparsely scaly and longer than the combined length of the head and body. The total length is about 32.5-42.5 cm long, tail length about 19-24 cm long, hind foot length 3.5-3.8 cm long and weight is about 140-280g. In the other hand, Black rat (R. rattus) is an omnivore but a selective feeder and eat a wide range of foods including seeds, fruits, stems, leaves, fungi and a variety of invertebrates and vertebrates [8]. They are not specific in their preference for food, they have been observed to feed on anything ranging from stored food to cooked food, to plastic, wood and many other food sources. They are therefore called generalists [9]. However, human being often provides rodents with an abundance of food, water, shelter and microclimatic condition, which allow them to be comfortable and multiply easily [10]. The number of rats that are able to exist in any given location depends on the availability of foods, water, and shelter [11].
These factors are commonly found among students in the University where both shelter and food are being provided for black rat (R. rattus). Since rodent populations have been attributed to the risk of health in high densities of human inhabitants (such as University hostels), it is important to look for a way to control them without endangering them. Hence, this study is aimed at assessing the morphological variation of black rats (Rattus rattus) found in some locations on Obafemi Awolowo University Campus; and determine the most effective bait that can be used to capture black rats in the University community.

Description of Study Area
The study was carried out at Obafemi Awolowo University which is situated in Ile-Ife, an ancient city in the Southwestern Nigeria and lies between latitudes 7°28′N and 7.467°N and longitudes 4°34′E and 4.567°Ewith a landmass of 5,506 hectares and altitude of 300m above sea level (Encyclopedia Britannica, 2014).
The climate of the area is humid tropical with distinct dry and wet seasons. The wet season starts from around mid-March to late October and the rainfall pattern is bi-modal with peak periods in July and September. The dry season runs from November to March but a short spell usually occurs in August. The mean annual rainfall is about 1400mm. The mean ambient temperature ranges from 20°C to 30°C with a mean temperature of 26°C.

Sampling Sites
The location of the survey includes three male halls of residence and three female halls of residence on Obafemi Awolowo University Campus. These sites were chosen in order to note and record the food consumed and mostly preferred by the black rats in the halls of residence. Three traps were used for one week interchangeably to ensure random sampling of the captured rats. The trapping activities were carried out during the months of December 2017 to February 2018. The various hall of residence includes.

Awolowo hall
This is a male hall and is known to be the most populated hall in Obafemi Awolowo University with a maximum capacity of 2,032 legal occupants (students). Trees and bushes of varying sizes are found around this hall of residence. It consists of 8 blocks of 42 rooms each, and annex of 8 blocks with 10 rooms each.

Fajuyi hall
This is a male hostel and 2 nd most populated hall in Obafemi Awolowo University with a maximum capacity of 1,788 legal occupants (Students). It is very close to a female hostel known as the Akintola hall. It consists of 5 main blocks with 60 rooms each and annex of 10 blocks with 10 rooms each.

Angola hall
This is a male hall which is close to Awolowo hall and far from the academic environment. It has a maximum capacity of 1,320 legal occupants (Students). The hall consists of 11 blocks with 10 rooms each.

Moremi hall
This is the female hall of residence. It has a maximum capacity of 1,228 legal occupants. The hall is divided into two parts altogether containing 8 blocks with 30 or 33 rooms each.

Ladoke Akintola hall
This is the female hostel which is very close to Fajuyi hall of residence. It has a maximum capacity of 640 students. This hall of residence consists of 4 blocks with 30 rooms each.

Mozambique Hall
This is a female hall located adjacently to Angola hall. It has a maximum capacity of 1,722 legal occupants (students). It consists of 14 blocks with 10 rooms each and 2annexes at the lower part of the hall. There are a lot of small grasses and bushes around it.

Sampling method
Locally made metal traps (cage traps) (Plate 1) contains baits which are the locust beans, beans cake and fried fish hooked to an iron rod attached to it in order to attract the rats were placed fortnightly in various sampling locations (Awolowo, Fajuyi, Angola, Akintola, Mozambique and Moremi halls of residence) for a period of 3 months between the months of December, 2017 to February, 2018. The traps were set around the dark corners of the sites in the evening and collected the following morning (6.00am). The trapped black rats (R. rattus) were taken to the laboratory for measurement and further analysis.

Data collection
The captured rats were anesthetized in a closed jar containing chloroform, tagged, and weighed on a scout weighing balance (Plate 2) and placed on the measuring board (Plate 3) for morphometric determination. The tag carried the specimen number along with other information which included place of collection, date of capture and sex of the rat which was determined by checking the scrotal sacs (only males have scrotal sacs) were documented.
The morphometric parameters such as the Body length (BL), Tail length (TL), Ear length (EL), Sex, Hind-foot length (HL) and the Body weight (BW) were recorded. The body length was taken by measuring from the tip of the mouth to the tip where the tail attaches to the body. The tail length is measured from where the tail attaches to the body. The ear length is measured from the tip where the ear attaches itself to the head to the longest end of the ear. The hind length is measured from its point of attachment to the leg to the tip of the longest toe.

Data analysis
One-way analysis of variance (ANOVA) was used to determine the significant difference between the means, while the significant mean was separated at p ≤ 0.05 using Least Significant Difference (LSD) test from System Analysis Software (SAS Institute, 1997). Principal Component Analysis (PCA) was carried out with PAST version.

RESULTS
A total of two hundred and thirty six (236) black rats belonging to the family Muridae, order Rodentia was caught from the various sampled halls of residence (Table 1). Of the total caught, 23.31 % (55) was recorded in Moremi hall, which was the highest while the lowest percentage was recorded in Awolowo Hall with 12.71 % (30). The highest number of the male black rat (R. rattus) [20] was caught in Moremi Hall, while the least number of 10 each was caught in both Angola and Akintola respectively. The highest number of the female black rat (R. rattus) (35) was caught in each Moremi and Mozambique Hall, while the least number of the female black rat [21] was caught in Akintola Hall. Irrespective of the sampling point, higher percentage (65.68%) of female black rats was collected during the period of study when compared with male (34.32%).
The morphometric parameter of the female black rat specimens is shown in Table 2. The statistical analyses in the table revealed that the mean Hind-foot length (HL) and Ear length (EL) of the female black rats collected from Mozambique and Angola were statistically different (p≤ 0.05) from that of the female black rat specimens collected from other halls of residence.
The Hind-foot length of the female black rats collected from halls of residence on OAU Campus ranged from 2.10 cm (Mozambique) to 4.70 cm (Moremi) and the highest mean Hindfoot length value of 3.64 ±0.18 cm recorded in the female black rat's specimen collected from Moremi hall. This was closely followed by the specimens collected from Awolowo hall with a length value of 3.62 ±0.16 cm while the lowest mean Hind-foot length was recorded in the female black rat collected from Mozambique hall with a value of 2.70 ±0.60 cm ( Table 2).
The Ear length (EL) of the female black rat specimens which ranged between 1.70 cm (Mozambique) and 3.50 cm (Akintola) was reported to have highest mean Ear length value of 2.89 ±0.09 cm (Moremi) and a lowest mean Ear length value of 2.35 ±0.65 cm (Mozambique).
The statistical analyses, however, revealed a significant difference (P≤0.05) in the Ear length of the female black rat specimens collected from the various hall of residence ( Table 2).
The female black rat specimens collected from Moremi hall had the highest range (13.90 cm -  Table 2).
The morphometric parameters of the collected male black rats in halls of residence on Obafemi Awolowo University is shown in Table 3 Similar to the values recorded in the hind-foot length of the male black rats collected from various halls of residence, highest ear length (2.98 ±0.14 cm), mean body length (21.14 ±1.32 cm) and mean tail length (23.82 ±0.88 cm) was recorded in the male black rats specimens collected from Moremi hall while the least value of these parameters 2.35 ±0.55 cm; 14.95 ±3.75 cm and 17.65 ±5.75 cm respectively were recorded in the specimens caught in Angola hall. Statistical analyses showed that there were no significant differences (P≥0.05) in all the values recorded for these parameters (Table 3).
Male black rat specimens collected from Moremi hall had the highest mean body weight value of 160 ±3.77g which was closely followed by the specimens caught in Fajuyi hall with a value of 150 ±8.96 cm. The lowest mean body weight value (83.17 ±6.58 g) of the male black rat specimens was recorded in Mozambique hall.  Comparative analyses however showed that the mean body weight of the male specimens collected from Moremi was significantly different (P≤0.05) from the mean body weight of the rat specimens collected from Mozambique 83.17 ± 6.58 g and Angola 84.50 ±6.10 g which was not statistically different (P≥0.05) from each other ( Table 3).
Morphometric parameters subjected to a Principal Component Analysis (PCA) showed correlations and variance occurred among the six halls of residence where the specimens were captured. The Principal Component divided the specimen into five components namely the PC [1, 2, 3, 4, and 5] representing (BW, TL, BL, EL, and HL) respectively which have an Eigenvalue each and percentage variance in Table 4a. From this table, only PC1 (BW) of Eigenvalue 3040.6 and percentage variance of 99.69 had the most significant being higher than the Joliffe cut-off of 4.27.  Fig. 1 showed clearly the variance that occurred. A scatter plot diagram in Fig. 1 showed a cluster eclipse of all the halls of residence (Akintola, Moremi, Mozambique, Awolowo, Angola, and Fajuyi) represented with a different color such as (Red, Blue, Purple, Deep Green, Green, and Indigo) respectively. The plotting showed that all the black rats in the six different hall of residence belong to the same homogeneous population, though there might be a very little variation which is statistically insignificant.
The black rat preferences for the bait used in this study is shown in Fig. 2. In the figure, preference for bait showed that most of the catches were from the trap baited with fried fish (58%), followed by beans cake (28%). The trap baited with locust beans recorded the least number of catch (14%). Fig. 3A showed that the frequency of male caught by bait in halls of residence had traps with fried fish with a total of 41, followed by beans cake which caught 27 and locust beans which caught 13. Fig. 3B also showed that 95 female rats were caught by fried fish, followed by Beans cake which caught a total of 40 and locust beans with a total of 20.

DISCUSSION
The abundance and composition of black rats collected in the various halls of residence, in the University, corroborates the findings and the report of several authors that black rats are cosmopolitan [12,13]. However, the sex ratio in this study was not equilibrated (81 males to 155 females) and was different from the findings of Ben Faleh et al. [14]. The reduction in the number of male black rat caught in this study may be due to competition and their territorial behavior [15].
The various variation exhibited by the black rats in the measured morphometric has been reported to be hypothetically due to climatic factors, metabolism rate, competition, and mating success [16,17]. However, differences in sizes are generally considered more liable to environmental gradients than shape [17].
Generally, a very strong positive correlation (0.97) exhibited among the determined parameters in this study corroborates the findings of morphometric characters of Albino rats by Aguha et al. [18] which showed there were satisfactory correlations between the body length and their respective parameters.

. Effects of bait preference on the percentage of black rats caught in all the halls of residen
However, there were indications that the body length and tail length may have a better link with the body weight than the rest of the parameters [18]. This study also showed that there was an increase in variation between body weight and body length when their values increased. may be due to some black rats having higher body weight but a smaller body length.
Virtually, in this study, it can be deduced from the parameters that, when compared with the body weight, had a very positive correlation coeff except in ear length which is apparently low compared to others. This was also similar to what was reported by Jimmy et al. [19] who determined the variability in body morphometric However, there were indications that the body length and tail length may have a better link with the body weight than the rest of the parameters . This study also showed that there was an increase in variation between body weight and their values increased. This having higher body weight but a smaller body length.
Virtually, in this study, it can be deduced from the parameters that, when compared with the body weight, had a very positive correlation coefficient except in ear length which is apparently low compared to others. This was also similar to what was reported by Jimmy et al. [19] who determined the variability in body morphometric measurements and relationship between body weight and other morphometric measurements in Albino rats (Rattus norvegicus). They reported a negative correlation between Body weight and Ear length, positive correlation between body weight and other parameters.
Black rat (Rattus rattus) possess the ability to select favourable food, which even displays its potential for local difference in the choice of food [6]. One food is eaten among other alternatives, based on factors such as taste; nutritional value and texture [20]. This could be one of the reasons why the black rat opt for the food used as bait in this study. Effects of bait preference on the percentage of black rats caught in all the halls of measurements and relationship between body tric measurements in ). They reported a negative correlation between Body weight and Ear length, positive correlation between body ) possess the ability to e food, which even displays its potential for local difference in the choice of food [6]. One food is eaten among other alternatives, based on factors such as taste; nutritional value and texture [20]. This could be one of the for the food used The preference for fried fish used as bait in this study by the black rats could be due to its flavour. Fishes are known to be flavoured food with high nutritional value [21]. Myers [22] reported that rats preferred food with high flavour. Also, Brooke's and Lavoie [23], Sarwar et al. [24] confirmed in their research that additives like sugar and vegetable oils at 1% to 3% concentration increases the food intakes of black rats and makes it acceptable and palatable to them. In this study, it was observed, both fried fish and beans cake (akara) had the highest rate of acceptability and preference amidst the black rats because they both contain additive like oil.

CONCLUSION
The morphology of the black rats (R. rattus) from the residence in the university are similar which means they are of the same family and genus. Fried fish out of three baits (Fried fish, beans cake & locust bean) used for the study proof efficient in catching the black rats in the hall of residences. Although it may be expensive to use, since it is the fried fish flavour that attracts the black rats. Fried fish flavour, however, can be used with other food material in catching a black rats.

ETHICAL APPROVAL
As per international standard or university standard ethical approval has been collected and preserved by the authors.