Population density of the (Pycnonotus goiavier) Yellow Vented Bulbul in Bacolod City National High School, Bacolod City, Negros Occidental


AuthorsXenon Jay G. Relota, Nino Dale P. Depasucat, Rammela Ashanty G. Arenas, Joshua Raul H. Barbas, Art Joseph P. Suarez, Phillip Raymund R. De Oca, Andrew Ross Tse Reintar, Philip Godfrey C. Jakosalem
Volume2
Date Published December 18, 2023
Date UpdatedMay 16, 2024


Abstract

The Yellow-vented bulbul Pycnonotus goiavier is a fruit-eating endemic bird in the Philippines that can be found in almost all habitats including urban areas. Its presence and population density can be used as an index in measuring the health of green spaces in highly urbanized cities like Bacolod City. In this study, P. goiavier’s population density at Bacolod City National High School was estimated. Via point count method at five plot points two hundred to five hundred meters apart, distance sampling approach was employed in a span of 26 days. Using Distance 7.5 software, their population was analyzed, where thirty eight detections were filtered from 51 incidences within the school. Results show that the uniform cosine model had the lowest Akaike’s Information Criterion (AIC = 117.75; % CV= 33), thus, it is best fit as a detection probability function model. The model also showed that P. goiavier’s population density was at 2.0 individuals per hectare. Hence, the estimated population of P. goiavier at BCNHS, a ten hectare school, is 20. The index value indicates that the school can be a potential green space. Likewise, since P. goiavier is abundant within the school, more trees and plants should be restored not only to comply with the national greening program of DepEd but also for the future biodiversity management interventions.



Introduction

The Philippines is known for its vast forests and abundance of wildlife and being one of the 18 mega biodiversity countries[1][2] . With a vast majority of wildlife sanctuary, it makes up two thirds of the world's biodiversity[2] . With the country's urbanization expansion many forests and green spaces were removed[3] . The Philippines currently has a 47.98% urbanization rate[4] . It lost over 63,728 trees per hectare in 2020[5] . In developing cities, urbanization is a rising problem[6] .

Bacolod City is the most urbanized city in Negros[7] . It had an estimated area of 160.71km2 with a total population of more than 600,000[7] .Due to continued population growth[8] , many forests and green spaces were removed to build houses and buildings[9] . In May 4, 2017 Bacolod City and DENR ink agreement was established for a 5 year greening program, the objective for this program is to recover or improve areas that have little but no trees[10] . But in 2021, Bacolod has lost over 227 hectares of tree cover. [11][12] .

Despite issues of urbanization, the potential of green spaces was recently recognized.[13] Green spaces are man-made sites that promote diversity, like birds, and can be found around cities including parks and schools[11][14] . Birds dwell in the cities due to green spaces for food, nesting spots and cover from predators.[15] They provide many ecological services such as environmental sustainability and biodiversity protection as well as human health and well being. Because of this green spaces are becoming a crucial aspect to urban growth[16] . Studies from Vallejo et al., Ong et al., and Banzon et al. Shows that the Yellow Vented Bulbul is one of the most abundant species in the research site[17][18][19] .

The Yellow-vented Bulbul, also known as Pycnonotus goiavier, is Southeast Asia’s most common urban bulbul[20] . They have a wide range and are a common bird that seems to thrive in the urban areas[21] . They can be found in towns, parks, and plantations, as well as open forests, edges, and secondary growth. Brown on top and whitish on the bottom, with a brilliant yellow vent and a broad black line connecting the bill and the eye [20] . Males and females are similar in appearance, Although females are somewhat smaller than males[22] . They eat berries and tiny fruits, they also drink nectar, eat young shoots, and catch insects[23] . They are residential birds and labeled as Least Concerned in both IUCN and DENR checklists.[20]

Though ecology of the P. goiavier Yellow Vented Bulbul is known, data has been limited to populations in General South East Asia (including the Philippines). Its population trend appears to be increasing, so the species does not meet the vulnerable criteria (greater than 30% drop over a decade or a total of three generations)[24] . Also, since it is a native bird in the Philippines that can be found in almost all habitats including urban areas, its presence and population density can be used as an index in measuring the health of green spaces in highly urbanized cities[11] .

As birds are bioindicators of environmental health, their population must be assessed. Since no information about the P. goiavier Yellow Vented Bulbul population density in the city is available, and their profile is vital for compliance of the Phillippine Biodiversity Action Plan, this study aims to present information on distribution of the population density and conservation status of the species on Negros Occidental is proposed. And to determine the population density of the Yellow Vented Bulbul in Bacolod City National High. School using distance analysis software. The site was chosen due to the school being a greenspace, with a large area of vegetation, a high number of Yellow Vented Bulbul, and a large population of insects and fruit bearing trees. The study may provide information that The Yellow-Vented Bulbul is an indicator for green spaces health[25] .



Methodology

Five sites were surveyed in our study at the Bacolod City National High School: Bacolod City National High School Field, Senior High School Oval, Behind Bacolod Arts Center, Bacolod City National High School Ecopark, and the site near the Audio Visual Room.Only 5 sites were plotted in order to prevent double counting. These sites were chosen based on the amount of vegetation and trees. The survey was done within a valid time period adherent to Wildlife Gratuitous Permit No. R6-2023-003 issued by the Office of the Regional Executive Director of DENR, Iloilo City. During this survey, we only focused on Yellow-Vented Bulbul sited within 40m sampling points. Data collection lasted for 26 days, 5 minutes were spent per site for observation.



Research Site

The grounds of Bacolod City National High School, which cover roughly 10 hectares , are thickly wooded and with a lot of food available making it a great habitat for birds. Buildings and facilities in the region are used for events and other activities. The area is near highways and a river. A boundary is set to avoid counting bird species outside Bacolod City National High School. This study focused mainly on the school; inside the parameter



The Materials Used For The Study And Plotting Survey Points

The Photographic Guide to the Birds of Negros, Panay, and Cebu, Nikon Arrow id 3000, Binoculars from Celestron, one from Coated Optics, and three from Nikon, Google Maps, Distance 7.5, and Tally Sheets



Distance 7.5

Distance 7.5 is software for designing and analyzing wildlife population distance sampling studies. This software comes in two versions: a Windows-based application and a collection of tools for the statistical programming language R. This software is rarely used in the Philippines and the only known software that can run distance analysis. Only a few publications are known for using the Distance Software.



Point Count Method

Point Count Method was used for this study due to the research site having multiple types of habitats and a limited space, making it unable to use line transect method. Point counts are one of several methods used to inventory and monitor bird populations. A point count is a tally of all birds observed by sight and sound by a single observer stationed at a specific location over a given time period [26] . The observer underwent training on bird call identification to properly identify the specific bird call.



Survey Sites

To ensure that the researchers get to clear the school grounds, the sightings of the P. goiavier Yellow Vented Bulbul is concentrated on separate locations with an estimated distance of 203-470 meters to avoid a double count of birds in bird watching. Five sample points were established to obtain data. The observation radius is 40 meters, and the estimated distance between the observation stations is 203 to 470 meters. All P. goiavier Yellow Vented Bulbul species within the radius were documented. A circular plot with a fixed radius of 40 meters has been shown to be more successful than a fixed-width transect because the quantity of individuals of species is larger [27] .



Bird Observation

Each site was visited 26 times. Each point was 203 to 470 meters away from each other. The points were marked using Google Maps. Daily observations are from 6:00 AM to 7:30 AM and using the point count method. The following were considered for each Philippine Yellow-Vented Bulbul sighting: (1) Whether the sighting record was a sighting or call, (2) The number of Yellow-Vented Bulbul seen, (3) estimated distance for point of detection and (4) and the activity of the Bulbul (i.e. feeding, calling,flying, preening, perching)[25] . The count duration for each point is five minutes. Point-to-observation perpendicular distances were also measured or estimated [28] , allowing our data to be analyzed as point transects[29] . All sightings of the Philippine Yellow-Vented Bulbul were estimated using Nikon Arrow id 3000, a distance finding tool. All recorded sightings were mapped and compared by location and time to filter any possible double counting.



Rules in Data Collection

Before the study was conducted all members of the team underwent two to three.



Results and Discussion

FIGURE 5. The Map of BCNHS of Yellow-vented Bulbul sightings

After 26 efforts (days), the total recorded sightings of the Yellow-Vented Bulbul is 51. The highest number of sightings was 18 recorded at point C, followed by 13 sightings at point B, 9 sightings at point a, 8 sightings at point D, and 3 sightings at point E. Most Yellow Vented Bulbul detections were found at densely vegetated areas and trees (Figure 5). Days of field training in bird identification and survey methods with an emphasis in distance sampling. 5 Groups were established for the 5 points. Each group had 3 members. 1 Spotter, 1 identifier, and 1 recorder. Before the group can start the survey, they must rest for 1-2 minutes so that the birds have time to go back to their normal state and can see you as a friend and not a threat. After that, each group has 5 minutes to observe and collect the data, and must be synchronized to avoid double counting any sightings.

Figure 6. Uniform cosine detection probability function model.



Detection Probability

The Detection Probability Function model ( Figure 6), presents the confidence value/probability of identifying a Yellow-Vented Bulbul by radial distance measured by in meters. Each time the distance decreases the confidence value/probability also decreases. Based on the model. 0-5 has the highest confidence value/ probability, while 30 - 40 meters has the lowest confidence value/ probability. The graph also shows that most birds were detected within 10 meters and fewer birds were detected more than 20 meters. Table 3. Comparison of models based on three detection functions



Density Estimates

All recorded sightings were grouped to calculate the density (expressed as individuals/ha) using Distance version 7.5[30] The Effective detection radius (EDR) is 19 meters,with the majority of data falling under the 0-20 m distance band, with relatively few records beyond 40 m from the observer. To remove any errors, all data were right-truncated at 50 m, outlier data were for enhanced model fit[31] . Table 3 shows the comparison of 3 models, where lowest AIC, the CV, and the accurate density value were determined for the population analysis of the Yellow Vented Bulbul. To calculate the Akaike's Information Criterion (AIC), Coefficient Value (CV), and the Density of Bacolod City National High School, Distance 7.5 software was used for the 3 models (Half-normal simple polynomial,Uniform cosine, and Hazard-rate cosine).

From the three models in (table 3), the Uniform Cosine model had the lowest Akaike's Information Criterion (AIC) (AIC = 117.75; % CV=0. 33), with normal staircase pattern and decreasing motion in the Detection Probability Graph. Hence, best fit as detection probability function model.

The model was supported by the Kolmogorov–Smirnov goodness-of-fit test and was also recommended by the AI. using the model, the population density of the P. goiavier can be solved.

Table 4: Bacolod City National High School Population Estimate

Table 4. presents the values from the uniform cosine model. The estimated population density of the P. goiavier Yellow-Vented Bulbul per hectare at Bacolod City National High School was at D =2 individuals, While the entire school campus with a 10 hectare size has a projected population of N =20 individuals respectfully . The population estimate has a coefficient of variation of 33.00. But with the UCL (upper confidence limit) and the LCL( lower confidence limit). The density can be increased by ±3.914 or decreased by ±1.032.

The result confirms density of the P. goiavier, making it an indicator of green space health at Bacolod City National High School. Based on previous studies, Birds live in an environment that fluctuates on a regular and irregular basis, and bird populations respond to these changes in predictable ways. The cause-and-effect relationship between environmental change and birds is obvious and straightforward[32] .

With their density in the school, efforts from the campus administrators should be increased to help improve vegetation and tree growth within the campus to increase their population.

H With their density in school, efforts from the campus administrators should be increased and the improvement of vegetation so their population increases.



Discussion

After 26 efforts, the total sightings of the Yellow Vented Bulbul is 51. Out of the 5 points, point C had the highest sightings with 18, due to having a closed area with minimal noise pollution and human activity, it also has a large vegetation and tree cover.

Most Yellow Vented Bulbul sightings were found within 10 meters of each site and fewer birds were detected more than 20 meters. Some studies reported that birds are curious about a presence in their habitats, possibly investigating who and what is in their habitat.

Based on the survey of the Bacolod City National High School, the total Yellow-Vented Bulbul sightings is 51, but based on Distance analysis it is significantly different than the survey. The total density calculated by the software is 2 individuals per hectare and a total of 20 for the entire campus, but with the presence of the LCL (±1.032) and UCL(±3.914), the density can still be increase or decrease due to the confidence interval of the mean if it's true or not. With the total density of the Yellow-Vented Bulbul, Bacolod City National High School is not only a green space but also a habitat for other bird species. Due to that the Yellow-Vented Bulbul needs trees and vegetation to live. The large density of the Yellow-Vented Bulbul shows that the school has a healthy green space.



Conclusion

The estimated population per hectare and in the entire school of P. goiavier are 2 and an estimated 20 individuals for the entire campus. Given the estimated population, Bacolod City National High School is a potential Green space that can host not only the Yellow-Vented Bulbul, but also other bird species. As confirmed by other studies, green spaces within urbanized cities can be habitats for bird diversity. Bacolod City National High School, which supports the national greening program and instills the Makakalikasan core value of the Department of Education has strategies to regularly monitor its green space. The support of the school and the population estimate of the Yellow-Vented Bulbul makes the campus and its green space a potential habitat that must be maintained.



Recommendation

Based on the results, the study recommends the conduct of this investigation in a wider ground to further validate the results. The study also recommends reinstatement of trees and the upgrading of green spaces in schools and other urban area wildlife hotspots that can foster a variety of bird species. At the government level, the data will be shared with the Bacolod City local government unit with the aim of supporting its biodiversity conservation initiatives and projects, particularly on birds and urban wildlife. Using the population density of the Yellow Vented Bulbul, the community may be educated that their presence can be associated with the health of urban wildlife, so they can collectively participate in their conservation. Furthermore, the findings shall advocate for environmental protection in urban areas on a larger scale, and provide the groundwork for a deeper understanding of bird diversity.



Acknowledgment

This project is made possible with the support of the research unit of Bacolod City National High School and its school Principal Dr. Richard M. Gelangre. The team would also like to acknowledge the unwavering commitment of Ms. Lisa Paguntalan and the Philippines Biodiversity Conservation Foundation Inc., the support of experts and the equipment they lent made a big difference in the completion of this research. Appreciation also goes Rose Marie Getida, Jonna Mae Chua, Dwynn Leo Baranco, Jewel Jamera, Athena De Leon, Eia Nasel V. Tillana, Dave Mundaza Barrera, Emmanuel Santillian, Froilan Audriel Delima, Mae Ar Villanueva, and Aliza Gargar for providing assistance in their data collection. Lastly the group would also like to thank the Department of Environment and Natural Resources - Region VI, headed by Mr. Livino B. Duran for approving the Wildlife Gratuitous Permit of this research.



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