FORTI, LR e NOBREGA, PFA. Prey-capture efficiency between juveniles and adults, feeding habitat and abundance of Wattled Jacana foragers in northern Pantanal, Mato Grosso state, Brazil. Braz. J. Biol. [online]. 2012, vol.72, n.2, pp. 275-279. ISSN 1519-6984. http://dx.doi.org/10.1590/S1519-69842012000200007.
When experience is not a synonymous of efficiency: the case of the juveniles Wattled Jacanas from the Brazilian Pantanal
Two colleagues from Federal University of Mato Grosso, Brazil, developed a research on predation behavior and prey capture efficiency in juveniles and adults of the aquatic bird Wattled Jacana. The study showed that juveniles are so efficient to catch prey than adults. This fact corroborates the hypothesis that active foraging (posture adopted by Jacanas for catch prey) is an instinctive behavior and it demands no learning. This is opposite to hunt by "sit and wait" behavior, which usually demands training to use and is commonly executed by hawks. In that sense, it is important to emphasize that this work was based on the "optimal foraging theory". Animals generally choose for alternative strategies to obtain food, maximizing the energy gain and balancing the time spent searching and handling prey with the amount of energy obtained by the food resource.
The results of the research were published in the scientific periodic Brazilian Journal of Biology, in the volume 72.2. The article was based in a field experiment carried during a graduation discipline. The birds were observed directly using binoculars during one week in different ponds of the Poconé wetland, in the state of Mato Grosso, Brazil.
The jacanas have body adaptations to seek small preys amidst the aquatic plants of the margins of ponds of the Brazilian Pantanal. These birds join in small groups usually formed by polyandric harems. After reproduction juveniles stay about two months in their original group, where they acquire survival techniques. During that period it is possible to distinguish juveniles and adults based on the plumage coloration.
Another interesting result find by the authors, there was no significant difference in the abundance of foraging individuals relative to the observation periods (the beginning of the morning, the middle of the day and the end of the afternoon). This is contrary to the behavior expected by ornithologists that birds are usually more active during the beginning of the morning. The jacanas were active all day long, even under the high temperatures of the Pantanal during the middle of the day.
Wattled Jacanas feed on several prey types, including small fishes, toads and insects. However, studies about the diet of juveniles are needed to verify if they share with adults the ability to select a meal of high energy quality, besides their comparable efficiency in capturing prey.
The study of animal behavior under natural conditions is important not only to recover threatened species, but also to discover their role in the maintenance of the ecological processes. Thereby, such discoveries allow us to understand the biodiversity components lifestyle, which are fundamental to a correct management of ecosystems.
The research was supported by the "Núcleo de Estudos Ecológicos do Pantanal / UFMT / Ministério de Ciências". The authors are thankful to the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for financial support.
Lucas Rodriguez Forti