Changing Landscapes and Declining Populations Of
Total Page：16
File Type：pdf, Size：1020Kb
Research Article Tropical Conservation Science Volume 11: 1–17 Changing Landscapes and Declining ! The Author(s) 2018 Reprints and permissions: Populations of Resident Waterbirds: sagepub.com/journalsPermissions.nav DOI: 10.1177/1940082917750839 A 12-Year Study in Bung Boraphet journals.sagepub.com/home/trc Wetland, Thailand Rehan Ul Haq1, Krairat Eiam-Ampai2, Dusit Ngoprasert3, Nophea Sasaki1, and Rajendra P Shrestha1 Abstract Changes in wetland environments can alter the dynamics of waterbird populations. We investigated the effects of hydro- logical and landscape variables on the abundance of resident waterbirds (ducks, fish-eaters, large waders, small waders, and vegetation gleaners) from 2003 to 2014 in Bung Boraphet, Thailand’s largest freshwater wetland. Generalized linear mixed models were used to determine the effects of environmental variables on waterbird numbers, and generalized additive mixed models were used to identify the threshold for each effect. The results revealed that the population of all waterbirds declined by 27% from 2003 to 2014 with highest decline of 56% in ducks. Increasing water depth was negatively correlated with the abundance of small waders and vegetation gleaners. Higher concentrations of dissolved oxygen in the water increased the abundance of fish-eaters, while marshy areas were positively associated with the abundance of ducks, large waders, and vegetation gleaners. The abundance of fish-eaters, large waders, and small waders were negatively associated with the spatial area of waterbodies. Expanding human settlements decreased the abundance of vegetation gleaners, while vegetation infested by Mimosa pigra decreased the abundance of large waders. The study concludes that the maintenance of an optimal water depth and quality, preservation of critical marsh habitats, eradication of invasive species, and restrictions on new human settlements adjacent to wetlands are all necessary to conserve resident waterbird populations. Validating these findings in additional research sites is recommended before applying it to a broader landscape level. Keywords Bueng Boraphet, dissolved oxygen, feeding guilds, land-use, mixed modeling, resident waterbirds, waterbird conservation, water depth Introduction Waterbird populations are declining globally (Hansen, Menkhorst, Moloney, & Loyn, 2015; Z. Ma et al., 2014; 1School of Environment, Resources, and Development, Asian Institute of W. Wang, Fraser, & Chen, 2017). The decline is particu- Technology, Khlong Luang, Pathumthani, Thailand 2 larly alarming in Asia where 50% of known populations Department of National Park, Wildlife, and Plant Conservation, Ministry of Natural Resources and Environment, Bangkok, Thailand were found to be in decline (Wetlands International, 3Conservation Ecology Program, King Mongkut’s University of Technology 2012). Waterbirds, an important component of wetland Thonburi, Bangkok, Thailand ecosystems, are sensitive to changes in the wetland envir- Received 16 September 2017; Accepted 2 December 2017 onment; they either disperse or aggregate in response to such changes (Brandolin & Blendinger, 2016; Henry & Corresponding Author: Rehan Ul Haq, School of Environment, Resources, and Development, Asian Cumming, 2016). However, in some regions, the environ- Institute of Technology, P.O. Box 4, Khlong Luang, Pathumthani 12120, mental variables affecting waterbird abundance are not Thailand. yet clearly understood due to the complexity of the Email: [email protected] Creative Commons Non Commercial CC BY-NC: This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 License (http://www.creativecommons.org/licenses/by-nc/4.0/) which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages (https://us.sagepub.com/en-us/nam/open-access-at-sage). 2 Tropical Conservation Science wetland environmental systems and differences in the Pratincole Glareola maldivarum, by Chaiyarat and composition and structure of avian communities. Eiam-Ampai (2014), but no recent studies were found Several studies have demonstrated that environmental on resident waterbirds. Resident waterbirds might be at variables such as wetland hydrology and landscape can greater risk due to the rapidly changing local landscape alter waterbird abundance in different ways (Alexander & and hydrology as they select a particular territory for a Hepp, 2014; Brandolin & Blendinger, 2016; Tavares, lifetime (West, Goss-Custard, dit Durell, & Stillman, Guadagnin, de Moura, Siciliano, & Merico, 2015; Wen, 2005). Undesirable environmental changes reduce habitat Rogers, Saintilan, & Ling, 2011). For example, fluctu- availability (Orians & Wittenberger, 1991) and when ations in water depth influence the physical condition such changes go beyond certain limits, they can lead to of waterbird habitats (e.g., the establishment of mud- extinction of local populations (Peters & Otis, 2006). flats), affect food availability, and prey vulnerability Therefore, a better understanding of the effects of chan- (Bellio & Kingsford, 2013; Lantz, Gawlik, & Cook, ging hydrology and landscapes on the population trends 2011; Timmermans, Badzinski, & Ingram, 2008; and seasonal fluctuations of different functional groups Y. Wang et al., 2013; Zhang et al., 2016), which are char- of resident waterbirds would improve our in-depth know- acteristics that define habitat use by waterbirds ledge of habitat use and enable the implementation of (Jedlikowski, Chibowski, Karasek, & Brambilla, 2016). effective conservation measures. Likewise, the conversion of wetlands into agricultural This study was designed to investigate the effects of areas and human settlements poses a significant threat hydrological and landscape variables on waterbird abun- to waterbirds. Other than direct habitat loss, such dance in BBP. To achieve this objective, we (a) assessed change in the wetland landscape also affects hydrological the long-term trends and seasonal variations in waterbird systems (Harrison & Whitehouse, 2012), and conse- abundance in BBP from 2003 to 2014, (b) studied hydro- quently, habitat use by the waterbirds (Cintra, 2015; logical and land-use changes in BBP, and (c) examined Tavares et al., 2015). Therefore, understanding how dif- the effect of hydrological and landscape variables on the ferent environmental variables affect waterbirds is abundance of resident waterbirds. Specifically, we tested important for the effective conservation of waterbirds the hypothesis that each of the five functional groups of and the management of their habitats. However, as dif- resident waterbirds (ducks, fish-eaters, large waders, ferent functional groups of waterbird respond differently small waders, and vegetation gleaners) would show spe- to changes in environmental variables due to of varying cific responses to changes in four hydrological variables habitat requirements, the relationship between waterbird (dissolved oxygen levels in the water, turbidity, water abundance and environmental variables is complicated depth, and water temperature) and eight landscape vari- (Tavares et al., 2015). For instance, low concentrations ables (cover of fish farms, human settlements, landfills, of dissolved oxygen may affect waterbird species that use marshes, mixed crops, paddy fields, vegetation infested lake resources for foraging such as fish-eaters (Sulai et al., by Mimosa pigra, and waterbodies). Finally, we proposed 2015), whereas similar changes may not affect species that recommendations for the conservation of resident water- use waterbodies solely as daytime roosts such as ducks. birds and their habitats in BBP. Some landscapes such as paddy fields may cause an increase in waterbird species that prefer shallow water for foraging (Acosta et al., 2010), but they are not a pre- Methods ferred habitat for the larger and more sensitive waterbird Study Site species like Black-headed Ibis Threskiornis melanocepha- lus (Sundar, 2006). This study was conducted in Bung Boraphet Wetland Bung Boraphet (BBP) in Central Thailand, a wetland (BBP), Nakhon Sawan Province, Central Thailand of international importance proposed as a Ramsar site, (between latitude 15 40’N and 15 45’N and longitude provides an important habitat for both resident and 100 10’E and 100 23’E; Figure 1). BBP is the largest migratory waterbirds (Office of Environmental Policy freshwater wetland on the floodplain of the Chao Planning, 2002). It is reported that BBP is under threat Phraya River, with a total area of approximately and increasing pressure due to hydrological and land- 212 km2. It was developed in 1927 by the damming of a scape changes such as water shortage, invasion of freshwater swamp to enhance fisheries (Sriwongsitanon Mimosa pigra, and an increase in the area of land con- et al., 2009). In 1937, this area was designated as a verted for agricultural use and human settlements ‘‘Conservation Zone’’ to prevent human encroachment (Chaichana & Choowaew, 2013; Sriwongsitanon, and settlement in the area. Nevertheless, by 2015, more Surakit, & Hawkins, 2009). However, little research has than 32,000 people were living inside that zone been conducted on waterbirds and their environmental (Department of Provincial Administration, 2015) and associations in BBP. There has been one study on the were making use of its natural resources such as fish nest-site selection of a breeding visitor, Oriental and wetland