400 North-Western Journal of Zoology 12(2) / 2016
Viorel Dumitru GAVRIL2,5,6, Mato Grosso, Brazil. Răzvan POPESCU-MIRCENI5 and Alexandru STRUGARIU7 We made the observations on May 30, 2014, in the Base Avançada de Pesquisas do Pantanal (S16º 29’ 53.5”; W56º 1. Faculty of Biology, University of Bucharest, Splaiul 25’ 00.3”) of the Universidade Federal do Mato Grosso Independenței Blvd., No. 91-95, Bucharest, 050095, Romania. (UFMT), close to Poconé municipality, Mato Grosso, Bra- 2. Moldavica Herpetological Group, zil. The Pantanal has three distinct seasons, flooded Carol I Blvd. no 20A, Iaşi, 700505, Romania. (January to April), run-off (May to August) and dry (Sep- 3. Faculty of Natural and Agricultural Sciences, Ovidius University, Mamaia Str., No. 124, Constanța, 900470, Romania. tember to December) season (Pinho & Marini 2012, Prado 4. “Emil Racoviță” Institute of Speleology of Romanian Academy, et al. 1994). The climate is classified as tropical wet and 13 Septembrie Road, No. 13, Bucharest, 050711, Romania. dry (Aw, according to Kottek et al. 2006), with average 5. Oceanographic Research and Marine Environment Protection temperatures of 25.8°C and annual precipitation ranging Society OCEANIC-CLUB, Decebal Street, No. 41, Constanța, from 1,000 to 1,500 mm (Cordeiro & Hofmann 2003, Kot- 900674, Romania. tek et al. 2006). The flooding in the region occurs between 6. Romanian Academy Institute of Biology, Independenței Blvd. No 296, sector 6, 06031, Bucharest, Romania. January and March and the drainage between April and 7. Faculty of Biology, Research Department “Alexandru Ioan Cuza” June (Hamilton et al. 2002, Prado et al. 1994). University, Carol I Blvd., No. 20 A, Iaşi, 700505, Romania. We identified the feeding perches due to the pres- *Corresponding author, E-mail: [email protected] ence of empty shells of snails and crabs. Because prey re- mains accumulate around the feeding perch and some items were already decomposing, we assume that our re- cords represent the prey items consumed days to weeks prior to our accounting. We identified the food item re- Crab as food resource for the Snail mains around each feeding perch and measured their size Kite, Rostrhamus sociabilis sociabilis (diameter for snails and width and length for crabs) using (Aves, Accipitridae), in the Pantanal a caliper with precision of 0.1 mm. We report median and range due to non-normality of data. Calculations and wetland, Brazil graphics were done in program R (R Development Core Team 2012) and with ‘ggplot2’ package (Wickham & The Snail Kite Rostrhamus sociabilis (Vieillot, 1817), Chang 2014), respectively. a widely distributed species in the Neotropical re- Four fence posts were used as feeding perches within 25 m along a farm fence in a flooded area between a pas- gion found in marshes, lakes and flooded pas- ture and a shrub field. We assume that only one Kite cre- tures, feeds almost exclusively on Pomacea snails ated the prey-shell piles because they were within a short (Beissinger 1983, Haverschmidt 1962, 1970, Ma- distance (25 m). We also did not find other prey-shell galhães 1990, Sick 2001). It has behavioral and ana- piles on the same and other fences within 300 m. In addi- tomical specializations (e.g. hunting strategies, tion, during the time we collected the items for measure- curved and terminally slender beak) to feed on ment we only saw a single Snail Kite individual close to these snails (Beissinger 1983, Murphy 1955). It de- the feeding perches. tects its prey visually from perches or flying over We identified between four and 19 feeding items the water (Beissinger 1983). Prey consumption oc- on each perch (Fig. 1), totaling 39 items. The items curs on perches that are used exclusively by a sin- were identified as shells of the red freshwater gle individual (Magalhães 1990) in R. s. sociabilis crab, Dilocarcinus pagei, (N = 32) and the channeled and on perches used by multiple individuals in R. applesnail, Pomacea canaliculata, (N = 7). However, s. plumbeus (Sykes 1987). Prey remains (e.g. empty crabs were the majority (77%) of items we re- shells) are dropped and accumulate around the corded. Crab shells were more abundant than feeding perch (Sick 2001). snail shells in all feeding perches (Fig. 2). Despite its specializations, alternative prey Diameter of channeled applesnail shells aver- items may be consumed if snails are scarce (Mader aged 52.0 mm ranging from 35.0 to 78.8 mm (N = 1981, Sykes & Kale 1974). For example, crabs may 7). Red freshwater crab shell length averaged 34.0 be consumed during the rainy season when it is mm ranging from 18.9 to 38.8 mm and width av- hard to find snails (Beissinger 1990, Mader 1981). eraged 41.7 mm ranging from 23.7 to 49.1 mm (N However, few studies reported the proportion of = 23, Fig. 3). Nine crab shells were already decom- preyed crabs and none reported measurements of posing and were not measured. All crabs had only eaten crabs. Herein, we report the largest propor- their viscera consumed. All legs and chelae were tion of crabs found in a feeding perch of a Snail intact. Kite and the first measurements of crabs eaten by The Snail Kite is specialized to find, capture, this species in the Pantanal of Poconé, state of and consume Pomacea snails (Beissinger 1983, Correspondence –Notes 401
Haverschmidt 1962, 1970, Magalhães 1990). In two localities of the Brazilian Pantanal, both crabs and Marisa snails were rare among Snail Kite prey items during wet and dry seasons (Magalhães 1990, Posso et al. 2012). Crabs averaged only 10% of items in Venezuela, reaching 25% by the second half of the rainy season (Beissinger 1990) and up to 68% of all prey items during the rainy season, be- tween April and October (Mader 1981). The Snail
Kite may also eat small vertebrates, such as turtles and mammals (Sykes & Kale 1974). In Florida, be- Figure 1. Empty shells of red freshwater crabs (Dilocar- tween 8% and 71% of preyed items were small cinus pagei) and Pomacea snails under one of the four chelonians, especially during the dry season feeding perches of a Snail Kite in the Pantanal of Po- coné, Mato Grosso, Brazil (Photo by Neander M. (Beissinger 1990). Pomacea snails are easily cap- Heming). tured during the dry season, when their density is higher in small water bodies (Magalhães 1990). However, in Florida Pomacea snails became either scarce or unavailable during the peak of dry sea- son. During this period one Snail Kite fed mostly on the banded mystery snail (Viviparus georgianus), which inhabits the bottom of lakes and streams, and were exposed by the low water level (Beissinger 1990). Golden apple snails (P. dolioides) consumed by the Snail Kite (R. s. sociabilis) in Guiana averaged 42.1 mm (N = 117), 48.2 mm (N = 310), and 51.2 Figure 2. Number of empty shells of red freshwater mm (N = 354, Bourne 1993). Golden apple snails crabs (Dilocarcinus pagei) and Pomacea snails found tended to be slightly smaller in two of three sam- under the four feeding perches of a Snail Kite in the Pantanal of Poconé, Mato Grosso, Brazil. pled sites than channeled applesnails consumed in our study site. Florida applesnails (P. paludosa) eaten by the Snail Kite (R. s. plumbeus) averaged 35.9 mm (N = 144) and ranged from 17 to 89 mm in Cuba (Fortes & Denis 2014). In Florida native florida applesnails averaged 31 ± 8 mm (Darby et al. 2007) and 45.8 ± 5.1 mm and ranged from 27.4 to 82.4 mm (Sykes 1987). Therefore, Florida apple- snails consumed by R. s. plumbeus were usually smaller than channeled applesnails consumed by R. s. sociabilis. Non-native island applesnails (P. maculata, previously called P. insularum) averaged Figure 3. Size frequency (bars) and median (dotted 81 ± 6 mm, but were handled with difficulties lines) of empty shells of red freshwater crabs (Dilo- (Darby et al. 2007). The size of snails consumed in carcinus pagei) and Pomacea snails found under the our study site were within the known range of, four feeding perches of a Snail Kite in the Pantanal but were usually larger than, snails consumed by of Poconé, Mato Grosso, Brazil. the Snail Kite in other sites. We did not find information about size of is possible that the Snail Kite also avoid small crabs consumed by the Snail Kite in the literature. crabs as it does with snails due to energetic cost- The size of adult red freshwater crabs may range benefit (Beissinger 1983, Bourne 1993, Magalhães from 24.2 to 58.3 mm (Davanso et al. 2013). In ad- 1990). The Snail Kite consumed only the crab vis- dition, the frequency of crab size class may vary cera, while legs and claws were always intact; in during the year (Davanso et al. 2013). Medium the same way that fresh water crabs (Dilocarcinus sized crabs (40 to 44 mm) were considerably more dentatus) were consumed in Venezuela (Beissinger frequent than smaller or larger crabs (Fig.3) and it 1990). 402 North-Western Journal of Zoology 12(2) / 2016
We highlight that little is known in the Pan- Murphy, R.C. (1955): Feeding habits of the Everglade Kite (Rostrhamus sociabilis). The Auk 2: 204–205. tanal about temporal changes in the Snail Kite diet Pinho, J.B., Marini, M.Â. (2012): Using birds to set conservation composition. This is the largest proportion of priorities for Pantanal wetland forests, Brazil. Bird Conservation preyed crabs recorded and suggests that the diet International 22: 155–169. Posso, S.R., Cintra, F.B., Frias, J. (2012): Temporal influence on of this specialist is more plastic than previously foraging strategies, territoriality and nomadic tendencies of thought. However, it is not clear yet if we re- Snail Kite, Rosthramus sociabilis (Viellot, 1817) in an urban corded an isolated event or if the Snail Kite sea- Neotropical wetland. Brazilian Journal of Biology 72: 235–241. Prado, A.L., Heckman, C.W., Martins, F.R. (1994): The seasonal sonally eats alternative food items. More impor- succession of biotic communities in wetlands of the Tropical tantly, if its diet varies seasonally due to the Pan- Wet-and-dry Climatic Zone: II. The aquatic macrophyte tanal hydrological cycle, changes on this cycle re- vegetation in the Pantanal of Mato Grosso, Brazil. Internationale Revue Der Gesamten Hydrobiologie Und Hydrographie 79: sulting from climatic changes or the construction 569–589. of dams may affect prey availability. We hope this R Development Core Team (2012): R: a language and environment contribution stimulates more studies about sea- for statistical computing version 3.1.1. R Foundation for Statistical Computing, Vienna. sonal changes in the composition of the Snail Sick, H. (2001): Ornitologia Brasileira (2nd ed.). Editora Nova Kite’s diet related to prey availability. Fronteira, Rio de Janeiro. Sykes, P.W., Jr. (1987): The Feeding Habits of the Snail Kite in Acknowledgments. We thank to L.G. de Castro and A. Florida, USA. Colonial Waterbirds 10: 84–92. Sykes, P.W., Kale, H.W. (1974): Everglade Kites feed on nonsnail Morais for helping with data collection, M.Â. Marini, J.B. prey. The Auk 91: 818–820. Pinho, and R.A. Brandão for their valuable suggestions, Wickham, H., Chang, W. (2014): ggplot2: An implementation of the comments, and for improving the English on previous Grammar of Graphics in R (Version 1.0.0).
Cordeiro, J.L.P., Hofmann, G.S. (2003): O clima da RPPN Sesc 1. Departamento de Zoologia, IB, Universidade de Brasília, Brasília, Pantanal (Technical Report). Porto Alegre, Brazil: UFRGS, IB, DF, 70.910-900, Brazil. Centro de Ecologia. 2. Instituto de Biologia, Universidade de Brasília, Brasília, Brazil. Darby, P.C., Mellow, D.J., Watford, M.L. (2007): Food handling *Corresponding author, N.M. Heming, E-mail: [email protected] difficulties for snail kites capturing non-native apple snails.
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