1. Introduction
Waterbirds live on or around water. Some of these birds are more terrestrial while others are more aquatic. Their adaptations will vary depending on their environment. Waterbirds play key functional roles in many aquatic ecosystems, including predators, herbivores, vectors of seeds, invertebrates, and nutrients, although these roles have often been overlooked. Waterbirds can maintain the diversity of other organisms, control pests, be effective bioindicators of ecological conditions, and act as sentinels of potential disease outbreaks. They also provide important provisioning (meat, feather, egg, etc.) and cultural services to both indigenous and Westernized societies [1] .
For the purposes of the International Waterbird Census (IWC), all species in the following thirty-three (33) families are considered by Wetlands International to be waterbirds: Gaviidae, Podicipedidae, Pelecanidae, Phalacrocoracidae, Anhingidae, Ardeidae, Scopidae, Ciconiidae, Balaenicipitidae, Threskiornithidae, Phoenicopteridae, Anhimidae, Anatidae, Gruidae, Aramidae, Rallidae, Heliornithidae, Eurypygidae, Jacanidae, Rostratulidae, Dromadidae, Haematopodidae, Recurvirostridae, Burhinidae, Glareolidae, Charadriidae, Scolopacidae, Pedionomidae, Thinocoridae, Laridae, Sternidae, and Rynchopidae. Only a few wetland birds are excluded by considering entire families in this way. Conversely, the inclusion of whole families results in the waterbird list containing a few non-wetland species such as some coursers and thick knees. These rather minor anomalies are thought to be outweighed by the convenience of a whole-family approach to the definition of the term “waterbird” and considering the complications that arise from applying the definition rigidly to every species. The Ramsar Convention on Wetlands recently widened its approach to include more families traditionally regarded as seabirds, as well as certain raptors and passerines, and it is possible that a small number of additions will be made in the coming years to the families and species included in the IEC [2] .
The wetlands of Casiguran are primarily the source of livelihood for most of the coastal communities of the area, however, this also serves as a feeding ground for many of the migratory and resident waterbirds. There are waterbird species occurring in the area that need protection but only a few studies of these species exist. This study would therefore provide a database for the future management regimes of the waterbirds in the wetlands. This paper, therefore, is aimed to census and identify the waterbirds present in the study site, determine the conservation status and index of abundance of identified waterbirds, and describe their habitat association.
2. Materials and Methods
2.1. Data Gathering Instruments
The following instruments were used for the conduct of the study: guide/reference books for proper identification of the waterbirds, a digital single-lense reflex (DLSR) camera with a 600 mm zoom lens used to capture good photographs of the waterbirds for the identification process, tripod as a base of the camera and binoculars to avoid blurring of the photos, binoculars to locate the waterbirds in the areas, a global positioning system (GPS) to record the coordinates of the waterbirds for mapping purposes, and record book to list down relevant information in the conduct of the study.
2.2. Location of the Study Site
The study was conducted from February to March 2019 at the wetlands of the following barangays: Cozo, Calangcuasan, Lual, Marikit, and Tinib, Casiguran, Aurora as seen in Figure 1. The study site was selected by the researcher considering the area of the wetlands, size of the mudflats and presence of waterbirds in the mentioned Barangays. Furthermore, there are few numbers of study with regard to the waterbirds of these barangays.
2.3. Data Gathering Procedure
Before the conduct of this study, a courtesy call to the barangay Chairperson was done. Upon approval, the researcher hired four residents as guides and porters. The person who is knowledgeable enough about the areas with more knowledge where the birds are found was considered. The identification of the waterbirds was done twice a day, during the early morning (6:00-9:00) and late afternoon (3:00-6:00). The waterbirds were documented using the DSLR camera and binoculars for the later identification process. Waterbirds were identified using
guidebooks and for the unfamiliar birds, proper consultation with the experts was done. The researcher conducted reconnaissance in the area where the birds are located to identify the habitat association of each species. Coordinates using GPS were recorded for the mapping of waterbirds distributions.
A complete census of the waterbirds was conducted by means of manual counting. Egrets were counted using the block method. This method involves counting or estimating a “block” of birds within a flock. Depending on the overall flock size, a “block” can be 10, 20, or 50 birds. The “block” is then used as a model to measure the remainder of the flock.
Three members of the team were tasked to count specific species of birds to avoid duplication of counts. Using binoculars, all waterbirds seen within the point of observation (location of the researchers) were documented using DLSR camera with zoom lens to produce a good image for later identification.
The data gathered in this study include the identification of waterbirds in terms of local name, common name, scientific name, and family name; habitat description, threats; and map of their distribution. Complete census of the waterbirds was employed to obtain unbiased estimate of abundance of the species.
2.4. Data Analysis
A total enumeration of the species was gathered within the barangays of Cozo, Calangcuasan, Lual, Marikit, and Tinib, Casiguran, Aurora. Relative abundance per species was computed using the formula:
(1)
where:
D = population density per species;
∑D = the sum total of all population densities of all species.
3. Results
3.1. Waterbird Species and Their Conservation Status
A total of 18 waterbird species in five families were recorded in Casiguran wetlands (Table 1). Family Ardeidae had six representative species: Chinese Egret (Egretta eulophotes), Great Egret (Egretta alba), Intermediate Egret (Egretta intermedia), Little Egret (Egretta garzetta), Grey Heron (Ardea cinerea), and Purple Heron (Ardea purpurea). The Family Charadriidae had five representative species: Pacific Golden Plover (Pluvialis fulva), Greater Sand Plover (Charandrius leschenaultia), Grey Plover (Pluvialis squatarola), Kentish Plover (Charandrius alexandrines), and Lesser Sand Plover (Charandrius mongolus). The Family Scolopacidae had five representative species: Bristle-thighed Curlew (Numerius tahitiensis), Common Redshank (Tringa tetanus), Common Sandpiper (Actitis hypoleucos), Far Eastern Curlew (Numerius madagacariensis), and Ruddy Turnstone (Arenaria interpres). Only one species represents the Family Anatidae,
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Table 1. Waterbird species in Casiguran Wetlands and their conservation status.
The standard IUCN Red List Categories (2017) are used as follows: Extinct (EX), Ex-tinct in the Wild (EW), Critically Endangered (CR), Endangered (EN), Vulnerable (VU), Near Threatened (NT), Least Concern (LC), Data Deficient (DD), and Not Eva-luated (NE).
the Philippine Duck (Anas luzonica). Similarly, Family Rallidae is also represented by a single species which is the White-Browned Crake (Porzana cinerea).
3.2. Species Relative Abundance
Table 2 revealed Intermediate Egret (Egretta intermedia) to be the most abundant (94.68%) waterbirds. This was followed by Little Egret (Egretta garzetta), Kentish Plover (Charandrius alexandrines), Lesser Sand Plover (Charandrius mongolus), Greater Sand Plover (Charandrius leschenaultia) with a relative abundance of 1.62%, 1.16%, 1.14%, and 0.33%, respectively.
3.3. Habitat Description of Waterbirds
Table 3 showed the habitat description of identified waterbirds in the study site. Philippine Duck (Anas luzonica) and White-Browned Crake (Porzana cinerea) were observed in coastal marshes. The Chinese Egret (Egretta eulophotes), Great Egret (Egretta alba), Intermediate Egret (Egretta intermedia), Little Egret (Egretta garzetta), and Grey Heron (Ardea cinerea) were observed in mangrove forest, mudflats, and rice fields during the survey. These migratory birds usually forage
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Table 2. Species relative abundance.
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Table 3. Habitat description of waterbirds.
in open situations in marshes, ponds, shores, and mudflats. The Pacific Golden Plover (Pluvialis fulva), Greater Sand Plover (Charandrius leschenaultia), Grey Plover (Pluvialis squatarola), Kentish Plover (Charandrius alexandrines), Lesser Sand Plover (Charandrius mongolus), Bristle-Thighed Curlew (Numerius tahitiensis), Common Redshank (Tringa tetanus), Common Sandpiper (Actitis hypoleucos), Far Eastern Curlew (Numerius madagascariensis), and Ruddy Turnstone (Arenaria interpres) were observed in exposed mudflats in all study sites.
4. Discussion
In this study, two waterbird species observed (Anas luzonica and Egretta eulophotes) were listed by the International Union for Conservation of Nature (IUCN) as vulnerable [3] . This species, Egretta eulophotes, was first recorded in mainland northern Luzon [4] in 2002 in the wetlands of Cagayan Valley. Another species, Numerius madagascariensis, was listed as endangered. These results are not uncommon since even in Manila Bay, the 90 species of waterbirds present in that area include species threatened with global extinction [5] . In addition, although the rest of the waterbird species observed in the study site were classified by IUCN as of least concern, this still means that these species need conservation efforts to protect their habitat and yet, there is no official protected status of Casiguran wetlands. According to BirdLife International in their publication titled “Philippine Wetlands” [6] , large areas of natural freshwater wetland in the Philippines have been converted for cultivation, either through drainage or wet agriculture. The coastal wetlands have been greatly affected by conversion for aquaculture and cutting of mangroves for firewood, with the area of mangroves estimated to have declined by 67% in the past 60 years. This loss of habitat is one of the main reasons for the decline and extinction of waterbird populations, but hunting and human disturbance are also likely to have been important factors.
In terms of habitat, the White-Browned Crake (Porzona cinerea) species usually frequents freshwater and saltwater habitats, including mangroves, open sea, and watercourses inside forests [6] . The presence of waterbirds in this study could be attributed to the abundance of food availability in the area. Waterbirds are known to feed on bivalves and gastropods, aside from fish, which are abundant in the study sites [7] [8] [9] . Similarly, in Talabong Mangrove Forest in Bais City, Negros Oriental, Philippines, migratory birds showed a higher presence in the intertidal area since most of them are waders [10] . It is also noted that many of the waterbirds occurring in the ASEAN region are migratory [2] . A resident waterbird species, Purple Heron (Ardea purpurea) was observed in mudflats and rice fields where egrets were found. The presence of waterbirds in specific habitats in this study is related to a study that used canonical correspondence analysis (CCA) where waterbirds were divided into four categories based on their habitat preference: synanthropic (wintering gulls), special habitat (shorebirds), semi-natural (wintering coots and ducks and disturbance-tolerant (resident) species [11] .
5. Conclusion
Based on the results, the following conclusions are drawn: Casiguran wetlands are home to 18 waterbird species in five families: Family Ardeidae had six representative species, Family Charadriidae had five representative species, Family Scolopacidae had five representative species, only a single species represents the Family Anatidae and Family Rallidae; two waterbird species, Anas luzonica, and Egretta eulophotes were listed by the International Union for Conservation of Nature (IUCN) as vulnerable while Numerius madagascariensis was listed as endangered indicating that these species need conservation effort by protecting their habitat; and as habitat, Anas luzonica and Porzana cinerea can be observed in coastal marshes, Egretta eulophotes, Egretta alba, Egretta intermedia, Egretta garzetta, and Ardea cinerea can be observed in mangrove forest, mudflats, and rice fields while a resident waterbird species, Ardea purpurea can also be observed in mudflats and rice fields.
Recommendations
Based on the result of the study, the following are recommended: Casiguran wetlands as a home to a variety of waterbirds may be given conservation priority action through the formulation of a conservation management plan while considering the resource utilization of mangrove forest for agricultural purposes as well as the livelihood of the people in need; habitat conservation could be prioritized in areas where vulnerable and endangered species were observed since these habitats are considered as a temporary home and breeding grounds for the waterbirds species during migration; a management zonation with strict protection and multiple use zones can be designated in the wetland areas where different waterbirds were found so that these areas will remain to serve as their habitats, and a year round census and observation could be done to cover all species in the area
Acknowledgements
I would like to extend my heartfelt gratitude to the Aurora State College of Technology (ASCOT) President, Dr. Eutiquio L. Rotaquio, Jr., and to the Research and Development Office Director, Maria Cristina B. Cañada for funding the publication of this paper.