**2. Materials and methods**

We selected two roost-trees for the proposed studies. Of the two, one, the silk flower tree *Albizia lebbeck* (16.15 m in height, umbrella shaped crown, 1637.96 m2 in canopy area with 1.73 m in diameter) with five main branches bearing thin foliages. This tree is deciduous in nature. It is located in the village Joteghanashyam (22°31′10.0"N, 87°50′19.2″ E) of Paschim Medinipur district. The second roost-tree *Tamarindus indica* (17.67 m in height, umbrella shaped crown, 1960.79 m2 in canopy area with 3.33 m in diameter) with 14 main branches bearing thick foliages. This is evergreen in nature. It is located in the village Simla (23°22′44.20"N, 86°38′47.02′′ E) of Purulia district, 75 km west of silk flower tree; these two districts are locating in the arid zone of state of West Bengal, India.

In *A. lebbeck*, of the five main branches, the longest one was 15 m in length while the smallest one was confined to 7 m. In contrast, in *T. indica* the longest branch was 13 m and the shortest one was 3 m in length. In both cases such measurements were taken on the last sampling dates. Irrespective of roost-trees there were numerous short sub-branches at certain points along the extended parts of the main stem from the point of emergence of the main stem body.

These branches from the lower to upper part of the tree were marked as L1, L2, L3 and so on depending upon the number of branches occurring successively up to the top of the tree. Thus in case of *A. lebbeck* branches were numbered as L1 to L5 and for *T. indica* the same was ranged from L1 to L14. The lower most branch of *A. lebbeck* and *T. indica* was 5.79 m and 1.78 m above the ground respectively. We counted the number of bats hanged in respect to the marked branch including the sub-branches of the same and the data were recorded at monthly interval. We used binocular as and when necessary to locate the bats to avoid any kind of ambiguity in counting of the bats. The counting was initiated on 25 April 2011 and continued up to 30 March 2021 at Joteghanashyam, and from 19 January 2015 to 23 December 2020 at Simla.

### **3. Statistical analysis of the data**

Data collected were pooled together to estimate the average number of bat individuals selected the specific branch of the roost trees, irrespective of months of the study years as well as the standard error (SE) values. One-way ANOVA was applied to justify whether the branches have significant effect in selecting the same as roost sites by the bats. Normal probability Plot of PAST Software was used to ascertain and justify the normal distribution of the roosting bats in different branches of the roost trees. GLMM was applied to testify the proposed hypothesis by determining the overall significance levels (P<0.05).

### **4. Results**

It is revealed that the roosting abundance of *P. giganteus* varied from 73.31±6.52 to 217.19±20.88 in *A. lebbeck* at Joteghanashyam (**Figure 1**) and *Roost-Tier Preference in Roost-Trees: A Case Study in the Bats* Pteropus giganteus *DOI: http://dx.doi.org/10.5772/intechopen.99450*

*Mean (±SE) number of* P. giganteus *bats used the branches of the roost tree* A. lebbeck *daily during 2011–2021 study periods at Joteghanashyam.*

#### **Figure 2.**

*Mean (±SE) number of* P. giganteus *bats used the branches of the roost tree* T. indica *daily during 2015–2020 study periods at Simla.*

1.12±0.13 to 37.64±4.39 in *T. indica* at Simla (**Figure 2**) per roost branch. Results of ANOVA test clearly indicate that there exists significant differences in selection of the roost sites by *P. giganteus* in *A. lebbeck* (df=14, F=5.71, P=0.00, N=540) and *T. indica* (df=12, F=2.05, P=0.00, N=373). From the normality distribution plot (**Figures 3** and **4**) it is evident that there exists significant correlation between abundance of roosting bat population and the study years. GLMM studies (**Table 1**) confirmed that the roost sites occupied by *P. giganteus*, in the branches of both the roost trees (except one branch L1 in *A. lebbeck* and two branches L2 and L3 in *T. indica*) are undoubtedly preferred sites for roosting (P=0.0) depending upon the probability of availability of these sites upon their time of return to the roost tree.

*Normal probability distribution of* P. giganteus *in* A. lebbeck *roost tree during study years (2011–2021) at Joteghanashyam.*

#### **Figure 4.**

*Normal probability distribution of* P. giganteus *in* T. indica *roost tree during study years (2015–2020) at Simla.*


*Roost-Tier Preference in Roost-Trees: A Case Study in the Bats* Pteropus giganteus *DOI: http://dx.doi.org/10.5772/intechopen.99450*

#### **Table 1.**

*Results of GLMM studies on roost-tier (branch length L1=BLL1 to BLL5 in* Albizia lebbeck*; branch length L1=BLL1 to BLL14 in* Tamarindus indica *and in both sites BLL1 acts as intercept) preference in roost-trees of the bat* P. giganteus *in* A. lebbeck *at Joteghanashyam and* T. indica *at Simla, West Bengal, India.*

### **5. Discussion**

Various workers [5, 6, 8, 9, 12–14] have paid due attention on the choice and selection of trees for roosting by the bats. Though they have paid due attention on DBH, canopy nature, foliages and age of the roost trees no information in respect to preference of roosting branches is on record. From the results it is evident that the bats *P. giganteus* have preference for roost sites in a roost tree. And, from the present findings it is clear that these bats have a priority to avail the opportunity to hang in the branches occurring at the mid sector of the tree. As they are colonial in habit and all the members of a colony are habituated to use the same roost tree if and when possible, the late comers have no alternative but to hang in the branches where spaces are available, even these branches being less preferred.

The bats *P. giganteus* left the roost tree at the onset of darkness to fly to the foraging sites. Depending upon the availability of food sources some individuals being well fed at the early hours may try to return the roost tree as early as possible, perhaps to take the shelter in the preferred branches of the roost tree. This kind of behavior most probably related with the assurance of individual's safety from the effect of adverse conditions viz. the attack by the predators [19], speed of the severe cyclonic wind [20] extremely high temperature and heat being exposed directly to the sunlight, direct hit of the rain drops, extreme cold waves during cooler months and loo during summer [21].

Thus, we hypothesized that the bats *P. giganteus* have preferred roost tiers in a roost-tree to ensure self protection through the exercise of their subtle intra-specific competition.
