Amphibia-Reptilia 30 (2009): 533-544 Food habits of Brazilian boid snakes: overview and new data, with special reference to Corallus hortulanus Lígia Pizzatto1,2,4, Otavio A.V. Marques2, Kátia Facure3 Abstract. This study examines the diet of eight boid snakes: Boa c. constrictor, Boa c. amarali, Corallus caninus, C. hortulanus, Epicrates cenchria, E. crassus, E. assisi and Eunectes murinus mainly by analyzing the gut contents of preserved museum specimens, and includes a literature review to present an overview of the diet of Brazilian boids. Mammals constitute the primary prey consumed by the majority of the species. Birds are also frequently consumed by C. hortulanus and Boa contrictor, and are the most important prey for B. c. amarali. Ectotherms (mostly lizards) were only consumed by immature snakes. Such prey is rarely consumed by B. c. amarali and not recorded for Epicrates and Eunectes species in our dissections. C. caninus is likely a mammal specialist and Epicrates prey on birds more opportunistically. The niche overlap index varied from 0.27-0.52 for species occurring in the same bioma and geographic range but it is possible this overlap is lower as most sympatric species explore different macrohabitat. C. hortulanus exhibited a significant relationship between prey size and predator head size; this relationship did not differ among mature and immature snakes. In comparison to immature individuals heavier adult snakes fed on heavier prey items however, the ratio between prey/predator mass decreased with increase in predator mass (or size). Most boids exploit diurnal and nocturnal preys, probably using both sit-and-wait and active tactics. They feed on the ground but boas and C. hortulanus and possibly E. cenchria also exploit arboreal prey. Keywords: Boidae, diet, dietary niche, foraging strategies, prey items, prey size. Introduction Burghardt, 1978; Greene, 1983a). While some species are specialists (e.g., the colubrid Tan- Food habits have attracted the attention of many tilla melanocephala feeds only on centipedes; herpetologists over the years. The diet and food Marques and Puorto, 1998), the diet can vary habits of snakes usually reflect singular adap- broadly in many others and ontogenetic varia- tations in the snake morphology and anatomy tion is a common trait among snakes (Mushin- (Mushinsky, 1987; Greene 1997). Most of sky, 1987; Greene, 1997; Glaudas et al., 2008). these adaptations are evident in the skull, Foraging strategies of Squamata are generally jaws and teeth (Savitzky, 1981, 1983; God- recorded as being active search or sit-and-wait ley, McDiarmid and Rojas, 1984; Mushinsky, (ambush) (Schoener, 1971). The first is char- 1987), but also include vertebrae (Gans, 1952, acteristic of slender and fast-moving colubrids 1961) and behavior (Franz, 1977; Geene and and elapids while the ambush behavior usu- ally occurs in most heavy-bodied viperids, boids 1 - Pós-Graduação em Ecologia, Depto de Zoologia, Uni- and pythonids (Greene, 1997). However, some versidade Estadual de Campinas, CP 6109, 13083-130, snakes can use both strategies and can also vary Campinas, SP, Brazil which strategy they adopt based on body size Corresponding author; e-mail: [email protected] due to ontogenetic switch in prey types (Greene, 2 - Laboratório Especial de Ecologia e Evolução, Instituto 1997). Butantan, Av. Dr. Vital Brasil 1500, 05503-900, São Understanding the relationships between Paulo, SP, Brazil e-mail: [email protected] prey size and predator size is the first step in 3 - Rua Marcolino Ribeiro, 181, Jardim Karaíba, 38411- evaluating the application of optimal foraging 382, Uberlândia, MG, Brazil theories to snakes (Mushinsky, 1987). Usually e-mail: [email protected] larger snakes tend to exploit larger prey items 4 - Present address: School of Biological Sciences, Heydon-Laurence Building A08, The University of (see Mushinsky, 1987; Arnold, 1993; Greene, Sydney, NSW, 2006, Australia 1997), but there are some large snakes that ac- © Koninklijke Brill NV, Leiden, 2009. Also available online - www.brill.nl/amre 534 L. Pizzatto, O.A.V. Marques, K. Facure tively search for very small prey (Shine et al., The relationship between prey mass and predator mass 2004). was analyzed using linear regression. To verify if both variables increased at the same rate (i.e., if small snakes In this study we review the food habits of eat proportionally the same size prey as large snakes), we Brazilian boines and present new data on prey compared if the slope of regression differed from one, using items, relationships between prey size and snake t-test where t = (1 − observed slope)/standard error of size among adult males, females and young the slope (Stearns, 1992). The same analysis was performed using prey length and snake HL, and snake HL vs. snake individuals, inferring about hunting tactics and SVL. Sexual divergence in prey size was investigated using behavior. We compare our findings and trends ANCOVA, with prey SVL as the dependent variable, sex with published data for other boines, and the as the factor and snake SVL as the covariate (Zar, 1999). The same analysis was performed using predator and prey close related erycinaes and pythonids. masses. In all these cases variables were log-transformed to meet assumptions of parametric test. Dietary niche overlap was calculated for pairs of sym- patric species using the MacArthur-Levins index modified Material and methods by Pianka and by expressing the prey item overlap in terms of percentage (see Krebs, 1998 for both procedures). We Gut contents of Boa c. constrictor (38 adult females, 76 did not include E. murinus in the niche overlap analysis be- males and 308 immature), 201 B. c. amarali (47 females, cause our results on stomach contents clearly do not reflect 70 males and 84 immature), Corallus caninus (25 fe- the range of prey items explored by this species. males, 11 males and 51 immature), C. hortulanus (109 fe- Published data are presented for giving a more complete males, 132 males and 234 immature), Epicrates cenchria overview on the diet of the species occurring in Brazil and (35 female, 48 males and 155 immature), E. assisi (18 fe- to evince trends within major groups. males, 25 males and 86 immature), E. crassus (28 females, 35 males and 64 immature) and Eunectes murinus (4 fe- males, 35 males and 375 immature) were analyzed. These specimens, originally collected in many different areas in Results Brazil, are housed in the collections of Instituto Butantan (IB), Museu de História Natural da Universidade Estad- General trends from original data ual de Campinas (ZUEC), Museu Paraense Emilio Goeldi (MPEG), Museu de Zoologia da Universidade de São Paulo All species examined fed exclusively on ver- (MZUSP), Universidade de Brasília (CHUNB) and Comis- são Executiva do Plano da Lavoura Cacaueira (CEPLAC). tebrates including mammals, birds, lizards and Additionally, we obtained faeces from live specimens col- frogs. Variation within the composition of ver- lected by other researchers in the areas where several of tebrate prey that comprised the diet of differ- the museum specimens originated. We considered the three ent species was evident. Overall, the dominant Epicrates as different species, according to Passos and Fer- nandez (2008), instead of E. cenchria subspecies, as orig- prey item consumed were mammals followed inally known. Because the two Boa constrictor subspecies by birds (table 1, fig. 1). The diet of the majority occur in different biomas in Brazil (B. c. constrictor in the of species contained only these two prey types. rainforests of the Amazon and Atlantic Forest in north and northeast while B. c. amarali occurs in the cerrado [savan- nah] of central and southwest Brazil) we opted for not pool- Boa constrictor ing the subspecies together, so information for each one can be easily accessed in future works. Our data show that Boa c. constrictor and Boa For each snake we measured snout-vent length (SVL, c. amarali fed on lizards, birds and mammals mm) using a flexible measuring tape, head length (from the (table 1) but diet composition differed between quadratum to the snout: HL, mm) with vernier calipers and body mass with Pesola® scales (g) after drainage of the mature and immature specimens (fig. 1a, b). Ec- excess preservative liquid. Snakes were recorded as imma- tothermic preys were consumed only by imma- ture or mature. Females were considered mature if they had ture individuals, though still only made up a oviductal embryo or ovarian follicles larger than 10 mm and males were mature if they had turgid testes and deferent duct small proportion of the diet, and birds were the convoluted (see Pizzatto and Marques, 2007). Prey species most common item for immature B. c. amarali were identified to the lowest taxonomic level by compari- (fig. 1a, b). Our limited data suggests that im- son of whole specimens, fur, skull, paws, teeth, feathers and mature snakes do not reject large prey (fig. 2a- beak to reference individuals in scientific collections (cf. Lobert et al., 2001); intact prey were weighed and measure d), but there are also reports of young B. con- in length (SVL or snout-anus). strictor feeding on small prey (16% of preda- Food habits of boids 535 Table 1. Prey items identified from gut in Brazilian boid snakes. PREY Boa c. Boa c. Corallus Corallus Epicrates Epicrates Epicrates Eunectes amarali constrictor caninus hortulanus assisi cenchria crassus murinus Amphibia unidentified Hylidae 1 Reptilia Ameiva ameiva 14 1 Tropidurus sp. 1 unidentified 2 Gymnophtalmidae unidentified lizard 1 unidentified 1 (scales) Aves Cacicus haemorrhous 1 Gallus gallus 1 Thraupis sayaca 2 Zonotrichia capensis 1 unidentified Psittacidae 3 unidentified Passeriformes 2 1 1 1 1 unidentified 7 2 24 2 Mammalia Rodentia Caviidae Cavia sp. 1 Cricetidae unidentified 1 Sigmodontinae Echimyidae Clyomys laticeps 1 unidentified 1 1 3 Cricetidae 1 2 1 3 13 Akodon cursor 1 Necromys lasirus 1 Nectomys squamipes 1 Oligoryzomys nigripes 1 Rhipidomys mastacalis 3 Thaptomys nigrita 1 unidentified rodent 3 1 6 3 1 Muridae Rattus rattus 3 Marsupialia Didelphis marsupialis 11 Didelphis albiventris 1 1∗ Gracilinanus microtarsus 1 Marmosa murina 3 Micoureus demerarae 11 Monodelphis sp.