Rice Fields Used as Feeding Habitats for Waterfowl throughout the Growing Season Author(s): Candela Marco-Méndez, Patricia Prado, Luis Miguel Ferrero- Vicente, Carles Ibáñez and José Luis Sánchez-Lizaso Source: Waterbirds, 38(3):238-251. Published By: The Waterbird Society DOI: http://dx.doi.org/10.1675/063.038.0304 URL: http://www.bioone.org/doi/full/10.1675/063.038.0304 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/ page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non- commercial use. 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Rice Fields Used as Feeding Habitats for Waterfowl throughout the Growing Season CANDELA MARCO-MÉNDEZ1,*, PATRICIA PRADO2, LUIS MIGUEL FERRERO-VICENTE1, CARLES IBÁÑEZ2 AND JOSÉ LUIS SÁNCHEZ-LIZASO1 1Department of Marine Science and Applied Biology, University of Alicante, Apartado Correos 99, 03080, Alicante, Spain 2IRTA Aquatic Ecosystems, Central Poble Nou km 5.5, Apartado Correos 200, 43540, Sant Carles de la Ràpita, Tarragona, Spain *Corresponding author; E-mail: [email protected] Abstract.—The role of rice fields as feeding habitats for the two main waterfowl herbivores, Eurasian Coot (Fulica atra) and Mallard (Anas platyrhynchos), in the Ebro Delta, a Mediterranean wetland in northeastern Spain, was investigated. Exclusion cages and tethering experiments were deployed within a rice field at the beginning of the growing season (summer 2010) and before harvest (autumn 2010). In summer, waterfowl abundances were low, but cage experiments detected rice field damage by waterfowl grazing through a significant reduction in plant biomass (although consumption was undetectable using tethers). In autumn, waterfowl abundance increased and tethering experiments detected consumption of rice plants with developed seeds, whereas cage experiments did not show grazing effects. Gut content analyses indicate that Mallards are mainly granivorous, feeding mostly on seeds of spiral ditch grass (Ruppia cirrhosa) and rice (Oryza sativa), while Eurasian Coots are herbivorous, feeding mainly on macrophyte leaves. However, stable isotope analyses and mixing model results showed that in the long term both species seem to acquire most of their dietary needs from rice plants and sago pondweed (Potamogeton pec- tinatus). Dietary analyses confirm the importance of rice in both species’ diets but also suggest that waterfowl may undergo seasonal dietary variations. These are mostly influenced by changes in the availability of food resources in the area rather than by their nutritional quality. This study confirms the ecological importance of rice fields as a complementary feeding habitat for waterfowl during the growing season in Mediterranean areas. It also highlights the importance of including these habitats in wetland management for waterfowl conservation. Received 11 December 2014, accepted 27 April 2015. Key words.—Anas platyrhynchos, Eurasian Coot, Fulica atra, grazing experiments, Mallard, rice fields, stable iso- topes. Waterbirds 38(3): 238-251, 2015 Wetlands are vital habitats for many Rice field systems, including irrigation ca- waterbird species, but human activities are nals, are used by a variety of waterbirds such greatly impacting them throughout the as waders, gulls, terns, ducks and herons, world through: 1) complete loss (e.g., drain- primarily as feeding habitats (Elphick and age for urbanization or dry cultivation); 2) Oring 1998; Bird et al. 2000). Damage to rice degradation in quality (e.g., contamination fields by birds can be caused by trampling, or alteration of hydrological regimes); or 3) which can disturb the grain or destroy seed- conversion of land to aquatic agriculture, lings, or by ingurgitation of rice seeds (Hoff- which changes the structure and function of mann and Johnson 1991). The majority of the habitat, but retains the area as wetland the studies concerning rice field damage by (Tourenq et al. 1999, 2000). In the latter situ- waterfowl have been conducted in North ation, rice (Oryza sativa) cultivation is by far and South America, Africa and Australia the most common, and 40% of the world’s (Stafford et al. 2006, 2010). In Europe, this population now depends on this food source topic has been studied primarily outside the (Fasola and Ruiz 1997). As a consequence, growing season (Tourenq et al. 2003; Ibañez in many regions natural wetlands have now et al. 2010), even though this is the period virtually disappeared, and rice fields have when rice fields become important feeding become the primary wetland habitat for win- and sheltering grounds for many species of tering (Tréca 1994; Elphick and Oring 1998) waterfowl (Pierluissi 2010). In Mediterra- or breeding (Acosta et al. 1996; Lane and Fi- nean areas, there is a lack of information on jioka 1998) waterbirds. habitat use (Tourenq et al. 2003), and many 238 WATERFOWL FEEDING ON RICE FIELDS 239 studies have been solely focused on foraging pling time (Legagneux et al. 2007). Stable herons (Fasola et al. 1996). isotope analyses are another technique that Mediterranean wetlands, such as the can provide non-destructive and time-inte- Ebro Delta and those at the Albufera and grative information about the diet and often Doñana National Parks, are some of the provenance of food sources (Hobson and main wintering areas for waterfowl within Clark 1992a, 1992b, 1993; Inger and Bear- the Western Palearctic region (Sánchez- hop 2008). Since consumers feed on isotopi- Guzmán et al. 2007; Rendón et al. 2008). In cally distinct food items, their tissues reflect some of these wetlands, Mallard (Anas platy- the different stable isotopic compositions rhynchos) and Eurasian Coot (Fulica atra) are of their diets. This depends on the period the dominant species, especially in winter when the birds consumed the diet as well as (Martínez-Vilalta 1996; Mañosa et al. 2001). the turnover rates of the tissues (Legagneux Both species have been reported to feed et al. 2007), so it can be used to make infer- mainly on the submerged aquatic vegetation ences about diet and the type of habitats in of marshes and lagoons (Rodríguez-Villafra- which they live (Inger and Bearhop 2008). ñe et al. 2007; Marco-Méndez et al. 2015). The main objective of this study was to However, over the past few centuries these elucidate the importance of rice fields as al- Mediterranean wetlands have been reduced ternative feeding habitats for the two main to 10-20% of their original area (Fasola and waterfowl species (Mallard and Eurasian Ruiz 1997), which enhances the relative im- Coot) of the Ebro Delta during the growing portance of rice fields as an alternative feed- season. For this purpose we: 1) investigated ing habitat for waterfowl species (Fasola and seasonal abundances of both species within a Ruiz 1996). rice field; 2) quantified the seasonal grazing In Mediterranean countries, the rice impact of waterfowl on rice plant biomass cropping cycle begins in April when flooded and seeds using exclusion cage experiments; fields are sown (Longoni 2010). Rice reaches 3) quantified seasonal consumption of rice its maximum height in August and is usually plants using tethering experiments; and 4) then harvested in September or October, studied dietary contributions through gut after fields have been drained. In the Ebro content and stable isotope analyses. Addi- Delta, fields remain flooded until January in tionally, we investigated the role of nutrient a new agro-environmental initiative of the content in food selectivity. We hypothesized European Union to increase wintering areas that waterfowl use rice fields as alternative for migratory waterbirds. In those rice fields, feeding habitats, especially during the grow- waterfowl forage for the available food re- ing season when there is an increasing avail- sources: invertebrates, land plants and wa- ability of vegetative structure and food re- ter weeds, or rice seeds (Elphick and Oring sources. 1998; Manley et al. 2004). Waterfowl diet or selectivity can be in- METHODS fluenced by several factors, such as food availability (Petrie and Rogers 1996), high Study Area nutrient contents (McGlathery 1995; Prado The Ebro Delta is located in the Province of Tarra- et al. 2010), high protein and energy con- gona, Catalonia, in northeastern Spain. The area holds tents (Hughes 1980; Sedinger and Raveling a total breeding waterbird population of nearly 60,000 1984; Murphy and King 1987) or easier di- pairs, including gulls and terns (48%), ducks and coots (25%), waders (14%) and herons (13%). The ornitho- gestibility (Charalambidou and Santamaría logical importance of the Ebro Delta is also well-known 2002), the last especially affecting selectiv- during autumn and winter, when the area is visited by ity for seeds. Among methods for quantify- some 250,000 birds, including ducks and coots (50%), ing dietary contributions, stomach content gulls and terns (29%), waders (18%) and herons (3%) analysis is the most accurate, although it (Martínez-Vilalta 1996; Mañosa et al. 2001). The Ebro Delta is included on the Ramsar Convention list of wet- gives dietary information relative to a short lands of international importance and is considered an time period and requires an extended sam- Important Bird Area by BirdLife International (Viada 240 WATERBIRDS 1998). The area supports well-developed rice farming in summer 2010 (from mid-June to mid-July) when activity on which waterfowl conservation depends to rice was in the vegetative phase (seedlings with four a large extent.