Ornithol Sci 7: 123–134 (2008) ORIGINAL ARTICLE Food-niche differentiation in sympatric species of kingfishers, the Common Kingfisher Alcedo atthis and the Greater Pied Kingfisher Ceryle lugubris Satoe KASAHARA# and Kazuhiro KATOH Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1051 Hata-machi, Hanamigawa-ku, Chiba 262–0018, Japan Abstract The Common Kingfisher Alcedo atthis and the Greater Pied Kingfisher ORNITHOLOGICAL Ceryle lugubris breed sympatrically along the Chikuma River in central Japan. These SCIENCE kingfisher species differ in body size, with the latter being much larger than the for- © The Ornithological Society mer. To understand the potential mechanisms that might play a role in food-niche dif- of Japan 2008 ferentiation between these two species, we studied their foraging ecology in the breeding seasons of 2005 and 2006. Specifically, we compared the foraging habitat, foraging behavior, and food delivered to nestlings between the two kingfishers. We video-recorded the food delivered to nestlings during the day, and our results indi- cated that these species differed in their foraging ecology in several respects: (1) Common Kingfishers caught prey at sites where the water flow was calm, while Greater Pied Kingfishers hunted at sites where the water flowed rapidly; (2) Greater Pied Kingfishers dove from a higher position and caught fish in deeper water than Common Kingfishers; and (3) Common Kingfishers preferred smaller fish than Greater Pied Kingfishers. Overall, Common Kingfishers used a wider variety of for- aging sites and food types than Greater Pied Kingfishers in the study area. As inter- specific territorially and aggressive interactions between the two species were rarely observed, the food-niche differentiation between the two species was not likely the outcome of competitive exclusion. We conclude that the realized food-niches of the two kingfisher species reflect their respective body sizes. Key words Alcedo atthis, Ceryle lugubris, Diet, Foraging ecology, Kingfisher Species with similar resource requirements are 2004; Martínes 2004). Food resource partitioning often allopatric, occupying separate geographical based on prey type or prey size and segregation of the areas that abut or overlap over part of the range foraging area are important mechanisms that reduce (Newton 1998). In the area adjoining or overlapping the possibility of competition and/or allow related their distribution, niche differentiation or resource bird species to coexist in the same area (Lack 1971; partitioning is necessary to avoid competition and to Cody 1985; Newton 1998; Garcia & Arroyo 2005). allow their stable coexistence (Newton 1998). Re- Many studies have focused on congeneric species lated sympatric species often show segregation of the (e.g. Moskát & Fuisz 2002; Dale & Manceau 2003; habitat, such as nesting or feeding sites (Lack 1971; Garcia & Arroyo 2005). According to the concept of Cody 1985; Newton 1998). The mechanisms allow- the guild, i.e., a group of species that exploit a class ing coexistence of related species have long intrigued of environmental resources in a similar way (Root ecologists and have been studied in a wide range of 1967), food-niche differentiation could play an im- bird species, including songbirds (Moskát & Fuisz portant role in the coexistence of heterogeneric 2002; Dale & Manceau 2003), raptors (Garcia & Ar- species with similar niche requirements (e.g. Libois royo 2005), and waterfowl (Libois & Laudelout & Laudelout 2004; Martínes 2004). To understand the mechanisms underlying such co- (Received 12 July 2008; Accepted 5 October 2008) existence, it is important to study how sympatric # Corresponding author, E-mail: [email protected] species share food resources and foraging habitats 123 S. KASAHARA and K. KATOH during the breeding season, which is associated with habitats (Nishimura 1979; Jimbo et al. 1986a, b). The a demand for greater amounts and larger food items overlapping distribution of the two kingfisher species (e.g. Libois & Laudelout 2004) for the brood than could make them potential resource competitors. consumed by the parents. As larger birds need more With the exception of Nishimura (1979), who com- and/or larger prey to obtain energy to support the in- pared nest site preferences between the two king- creased body size (Reyer et al. 1988; Marti et al. fisher species in an area of southwest Kyoto Prefec- 1993), many studies have shown that food size could ture, central Japan, no other studies have compared be one aspect of differentiation among congeneric or food or foraging sites or examined interspecific terri- heterogeneric species that differ in body size (e.g. Li- torial interactions between these two species within a bois & Laudelout 2004; Garcia & Arroyo 2005). As single area. The present study was performed to iden- food size, food type, and foraging site selection are tify differences in foraging sites and prey, and to un- mutually interrelated (Kelly 1996; Libois & Laude- derstand the potential mechanisms that may play a lout 2004; Sullivan et al. 2006), it is important to role in food-niche differentiation between these two identify these factors in the same research to evaluate species. We compared foraging habitats, foraging be- food-niche overlap or partitioning between species. havior, and food sources for nestlings between the However, few studies have included detailed compar- species in a sympatric breeding area. isons between species with regard to habitat selection and foraging behavior with data on diet (e.g. Chap- MATERIALS AND METHODS man & Rosenberg 1991). The Common Kingfisher (Alcedo atthis) and the 1) Study Area Greater Pied Kingfisher (Ceryle lugubris) are resi- We carried out field surveys between late March dents of Honshu, the main island of Japan. Both and late July in both 2005 and 2006, coinciding with species regularly nest on riverbanks and are primarily the breeding season of both Common and Greater piscivorous. Although the two kingfisher species be- Pied Kingfishers (Satoe Kasahara unpublished data). long to different families, they have a similar bill The study site was located along the middle course of form and foraging ecology in that they perch on the Chikuma River, Nagano Prefecture, central Japan. branches or rocks and hover in the sky before diving The upstream and downstream ends of the study site into the water. The average body size and weight were Sakaki (36°25ЈN, 138°11ЈE, 405 m elevation) range of the Common Kingfisher are 16 cm and and Nagano (36°32ЈN, 138°6ЈE, 360 m elevation), re- 34–44 g, respectively, while those of the Greater Pied spectively. The length of the river channel was about Kingfisher are 41–43 cm and 230–280 g, respectively 25 km (Fig. 1). (Fry et al. 1992). The Greater Pied Kingfisher is now In this area, the major land use along the river is considered a threatened species in 32 of the 47 pre- agricultural, and the river partly flows through urban- fectures in Japan because its population size and dis- ized areas. As the riverbed, riverbanks, and river tribution have decreased markedly due to large-scale channels have been artificially altered only slightly, habitat loss (e.g. Red Data Books of Nagasaki Prefec- the natural features and topography are still largely ture 2001; Aichi Prefecture 2002; Kyoto Prefecture intact in and along the river. The flow rate in the 2002; and Nagano Prefecture 2004). Common King- study area fluctuated widely. Although the flow rate fishers hold near-threatened status in 12 prefectures during irregular floods that occur once every one or in Japan (e.g. Red Data Books of Osaka Prefecture two decades is up to 30-fold greater than the normal 2000 and Tottori Prefecture 2001) for similar reasons. flow rate (Okino 2006), no such flooding occurred However, Common Kingfisher populations have re- during the study period. Sandbars are formed within covered and their distribution has recently expanded and along the main channel. The sandbars have no or into anthropogenic habitats, such as ponds in urban only sparse vegetation cover, consisting of willow parks (Norinomiya et al. 1991; Yano 1994). (Salix spp.) or reed (Phragmites spp. and Miscanthus The habitats of the two kingfishers in Japan are sacchariflorus) communities. Major vegetation types often separated: Greater Pied Kingfishers live along within the riparian area, other than sandbars, are rivers at higher altitudes, while Common Kingfishers Phragmites japonica grasslands and Salix shrubs in usually inhabit areas at middle or lower altitudes the lower areas (i.e., closer to the river) and Robinia (Nakamura & Nakamura 1995). On the other hand, pseudoacacia woods in higher areas. Some of the they coexist in some regions and have similar nesting higher land has been converted to agricultural fields 124 Food-niches of two sympatric kingfishers Fig. 1. Study area. Branching lines represent the watercourse of the Chikuma River, and the shaded area shows the water area. Solid rectangles and the broken line show the study areas for Common Kingfishers and Greater Pied Kingfishers, respectively. or playgrounds. Small channels and ponds form 2) Field Observations within reed grasslands in the lower riparian area. We searched for nests of the two kingfisher species Most ponds are not connected to the main channel in three study areas at the beginning of the study pe- except during floods. riod each year. The locations of all nests were We established two study sites for the Common recorded on a map drawn based on aerial photos at a Kingfisher surveys. The first, located in Sakaki, scale of 1 : 12,500. We observed each nest every 7 to measured 400ϫ3500 m, while the second was an area 10 days with 10ϫ binoculars and a 20–60ϫ telescope of 500ϫ1000 m in Nagano (Fig. 1). For the surveys to determine if the pair was rearing nestlings. The of Greater Pied Kingfishers, we used the two Com- day on which a parent began to carry food to the nest mon Kingfisher survey study sites as well as the en- was regarded as the beginning of the brooding period.