Surveys of Fruit Bats in Miag-ao
The second bat population count survey for the current year 2023 was conducted last May 19, 2023. It was done with the technical support of Unit head Wildlife Regulatory and Permitting Unit (WRPU)/Protected Area Management Biodiversity and Conservation Unit (PAMBCU)/Forester I, Ms. Jojie P. Gereza; Forest Technician (FT) II, Ms. Lore Calapardo; Database Management Staff, Cylyn Caguimbay; and Data Encoder, Allaine Celica Gavilla, all from the Community Environment and Natural Resources Office (CENRO) – Guimbal. We were also joined by EMS II/Designated MENR Officer, Mr. Isidro Mosura, Jr., and MENRO-Miag-ao staff, Ms. Cindy Cabudlay.
Right: CENRO and MENRO staff helping with the bat population count.
Visual method was used and based on the count last January 2023 (click here to learn the January 2023 survey results), there were thirty-seven (37) individual trees recorded, with fifteen (15) species. This second trimester, there are forty-four (44) individual trees roosted on by the island flying foxes, with still fifteen (15) species. There was an 18.92% increase in the number of their roosting sites and there was no change in the number of species recorded, compared to last January’s data.
The fifteen (15) species of trees are Agoho (Casuarina equisetifolia), Bubog (Sterculia foetida), Caimito (Chrysophyllum cainito), Coconut (Cocos nucifera), Gmelina (Gmelina arborea), Lanete (Wrightia pubescens), Mahogany (Swietenia macrophylla), Mango (Mangifera indica), Narra (Pterocarpus indicus), Neem Tree (Azidirachta indica), Palawan Cherry (Cassia nodosa), Sambag (Tamarindus indica), Santol (Sandoricum koetjape), Talisay (Terminalia catappa), and Tipolo (Artocarpus blancoi). There are additional seven (7) additional roosting trees.
Below are images of island flying foxes resting on Narra trees.
Last January, the total bat population count was six thousand five hundred thirty-one (6,531) individuals with nine hundred eighty-six (986) counts on an acacia tree as the highest count per tree and the least count was fourteen (14) in a coconut tree. This May, the total count was six thousand one hundred one (6,101) individuals with eight hundred fifty-seven (857) as the highest count on a mango tree and the least count was two (2) on a talisay tree.
Table 1. Distribution of the Bat Population among different trees around Miag-ao town plaza (as of May 2023).
|Tree #||Count||Tree Species||Condition (1 lowest and 5 highest)|
*Rating of the damage to the trees:
1 = 81% – 100% damage 2 = 61% – 80% damage 3 = 41% – 60% damage 4 = 21% – 40% damage 5 = 0% – 20% damage
Nine (9) out of the forty-four (44) roosting trees are gmelina, followed by seven (7) mahogany trees, five (5) caimito, four (4) narra trees, three (3) mango trees, two (2) each of agoho, bubog, coconut, lanete, santol and tipolo and one (1) each of the remaining trees.
The highest total average count per tree species is of the mango tree with four hundred ninety-one (491) count, followed by narra tree with two hundred seventy-three (273) count, gmelina tree with one hundred forty-one (141) bats, sambag tree with one hundred thirty (130) bats, mahogany trees and tipolo tree with one hundred twenty-six (126) bats, caimito trees with one hundred seventeen (117) bats, agoho trees with fifty-six (56) bats, palawan cherry tree with fifty-one (51) bats, bubog trees with forty-eight (48) bats, lanete trees with thirty-three (33) bats, santol trees with twenty-five (25) bats, neem tree with twenty-three (23) bats, coconut trees with eleven (11) bats, and talisay tree with two (2) bats.
The bat count population decreased by 6.58% compared with the last January count.
Comparing the results
Figure 1 below shows the total number of bats per trimester that the count was conducted.
The count last August 2021 was seven thousand three hundred ninety-two (7,392). Last January 2022 totaled to three thousand five hundred ninety-three (3,593), then last May, it went up to five thousand nine hundred eighty-nine (5,989) and this September, it just went down a bit to five thousand three hundred fifty-five (5,355). This January 2023 count, the bat population increased to six thousand five hundred thirty-one(6,531) and decrease a bit last May, which was six thousand one hundred one (6,101).
Throughout the survey, we noticed that they keep changing their roosting sites aside from those trees with maximum damage. The difference in the count might be due to human error since there is only 6.58% decrease and since the method used was visual counting. Their movements, tree cover, foliage and line of sight could affect the result of the count.
The next bat count will be on September 2023.
Written by: Senior Science Officer, Norielle Diamante (See profile)