Head triangulation as anti-predatory mechanism in snakes

Abstract

triangulation as anti-predatory mechanism in snakes. Biota Neotrop. 12(3): http://www.biotaneotropica.org.br/v12n3/en/ abstract?short-communication+bn01912032012Abstract: Anti-predator mechanisms in snakes are diverse and complex, including mimetic behavior. Some snakes triangulate their head, probably mimicking other more dangerous snakes. However, there is a lack of studies that demonstrate the effectiveness of this behavior with natural predators. The aim of this study was to verify, using artificial snakes, if snakes with triangular heads are less susceptible to attack by predators, and if predatory attack is targeted to the head of serpents. Artificial snakes were systematically arranged on a road border. The rate of attacked models was 48.71%. Number of attacks on models with rounded head was significantly higher than in models with triangular head. There was a significant difference between the places of attack on the snakes in relation to different head shapes. Therefore, snakes that have head triangulation may be a less frequent target of attacks by predators than those without such behavior. Keywords: artificial models, defensive behavior, mimicry, predation rate, reptiles. Resumo: Mecanismos anti-predação em serpentes são diversos e complexos, incluindo comportamentos miméticos. Algumas serpentes triangulam a cabeça, possivelmente mimetizando outras serpentes mais perigosas. No entanto, são escassos os estudos demonstrando a eficiência deste comportamento frente a predadores naturais. O objetivo deste estudo foi verificar, utilizando serpentes artificiais, se os indivíduos com cabeça triangular são menos suscetíveis ao ataque de predadores e, se o ataque predatório é direcionado à cabeça das serpentes. Serpentes artificiais foram dispostas sistematicamente na margem de uma estrada. A taxa de modelos atacados foi 48,71%. O número de ataques em modelos de cabeça arredondada foi significativamente maior do que nos modelos com cabeça triangular. Houve diferença significativa entre as partes atacadas nas serpentes quando comparados aos diferentes formatos de cabeça. Portanto, as serpentes que possuem triangulação da cabeça podem ser um alvo menos frequente de ataques por predadores do que as que não possuem esse tipo de comportamento. Palavras-chave: modelos artificiais, comportamento defensivo, mimetismo, taxa de predação, répteis. Biota Neotrop., vol. 12, no. 3 spatial homogeneity of the surrounding vegetation. The models were exposed for 17 hours, overnight, and collected the next morning. In field, each model was analyzed for attack presence, number of attacks, part of the model that suffered the attack (head or other parts of the body) and type of attack. Data analysis was performed in the program Past (Hammer et al. 2001) using Chi-square test (α = 0.05) to compare proportion of attacks on triangular and round head snakes models and proportion of attacks in the head and body between the two kinds of snake models. ResultsFrom the 80 snake models, one of each treatment was excluded from analysis bec...

New records and notes on defensive behavior of Thamnodynastes rutilus (Prado 1942)

“…Still, the pattern of cryptic coloration and the defensive behavior repertoire (head triangulation, false strike, S-shape posture and elevation of the anterior portion of the body) similar to that described for the genus Bothrops (Sazima, 1988;Araújo and Martins, 2006) suggests that T. rutilus mimics sympatric species of this genus. Other similar cases among colubrid species mimicking viperids or elapids based on the similarity of the color patterns and behavior have been reported (Gans and Latifi, 1973;Sánchez-Herrera et al, 1981;Yanoski and Chani, 1988;Marques and Puorto, 1991), and experiments using models mimicking dangerous species showed that in most cases, such characteristics prevent predators from striking (Dell'Aglio et al, 2012).…”

A different kind of ecological modelling: the use of clay model organisms to explore predator–prey interactions in vertebrates

“…Models have been constructed of various materials. ‘Plasticine’ is often named as the modelling material, but this often seems to be used as a synonym of ‘modelling clay’ rather than as a brand name, for example, ‘plasticine’ (Caran D'Ache, Modela Noir) (Valkonen et al ., ), ‘plasticine’ (Rainbow modelling clay) (Webb & Whiting, ), ‘modelling plasticine’ (no brand) (Diego‐Rasilla, ; Dell'Aglio et al ., ). Others named are Sculpey III modelling clay (Brodie, ; Bittner, ; Husak et al ., ) and Plastalina (Bateman, Fleming & Rolek, ).…”

“…Where potential predators attack the models, they leave quantifiable evidence as beak, claw or teeth marks (e.g. Webb & Whiting, ; Dell'Aglio et al ., ; Santos et al ., ; Fresnillo, Belliure & Cuervo, ), or if the models are removed entirely, they can leave predator tracks nearby.…”

“…Dell'Aglio et al . () in Brazil and Valkonen et al . () in Spain found that clay model snakes were attacked more often if they had the rounded head shape typical of non‐venomous colubrids than if they had the triangular head shapes of venomous viperids, but Guimaraes & Sawaya () found no support for the viper mimicry hypothesis in Brazil.…”

The snake hiss: potential acoustic mimicry in a viper-colubrid complex

“…N. maura resembles vipers in size, shape, colour, and pattern, and displays the entire anti-predatory behavioural panel seen in vipers. When threatened, N. maura will flatten its head in a triangular shape, strike repeatedly at the intruder (usually with its mouth closed), and produce a loud hiss (Werner & Frankenberg, 1982;Greene, 1988;Dell'Aglio et al, 2012). The viper mimicry observed in the viperine snake is fine-tuned to the point that inexperienced human observers will almost systematically mistake it for a genuine viper (F. Aubret, pers.…”