Abstract
The choice of foraging strategies implies an attempt at gaining energy by predators. Supposedly, the difference in employing the "sit and wait" or "active foraging" behavior lays in hunter skills, experience and the kind of prey consumed. With the hypothesis that "active foraging" demands no learning, in this study we compared the prey capture efficiency among Wattled Jacana juveniles and adults, and also present descriptive information about feeding habitat and the abundance variation of foragers throughout the day in the northern Pantanal. Prey capture efficiency did not differ significantly among juveniles and adults, corroborating our initial hypothesis that "active foraging" is an instinctive behavior and demands no experience to be effective. However, future work is necessary to compare the energetic quality of consumed items by juveniles and adults, searching for differences explained by adults' experience. Foraging individuals were found at an average distance of 14 m ranging from 2 to 42 m) from the margin of the sampled swamps, however 64% of the foragers were found closer to the margins. The average depth of foraging sites was 17 cm, ranging from 5 to 40 cm, although no preference for specific classes of depth was found (p > 0,05). Despite the accepted general pattern of birds being more active in the early morning, the largest number of individuals foraging was observed between 11:00 and 12:00 AM, but no significant difference was found in the abundance of foraging individuals among different periods of the day. Factors, which were not analyzed, such as food availability and presence of competitors and predators need to be studied to reveal the main factors of the spatial and temporal distribution of the Wattled Jacana.
Highlights
Prey-capture behavior demands high energy costs, as well as the ability to carry out successful captures (Valle, 2006)
The area is located in the northern Pantanal (16° 22’ 0.4” S and 56° 17’ 56.6” W), between the rivers Bento Gomes and Cuiabá, which are subject to seasonal flooding, attracting numerous waterfowl including Jacana jacana
The similarity found in the prey-capture efficiency between juveniles and adults is probably due to the foraging tactics used by the individuals (Nunes and Piratelli, 2005)
Summary
Prey-capture behavior demands high energy costs, as well as the ability to carry out successful captures (Valle, 2006). Foraging activity should be maintained until the energy gain, from the intake of food items, is larger than the energy spent on acquiring them (MacArthur and Pianka, 1966) Some bird species, such as Phalacrocorax brasilianus (Gmelin, 1789) (Morrison et al, 1978), Leucophaeus atricilla (Linnaeus, 1758) (Burger and Gochfeld, 1983) and Sturnus vulgaris (Linnaeus, 1758) (Stevens, 1985) may show ontogenetic changes in diet composition. This characteristic has been considered an evolutionary adaptation to avoid intra-specific competition (Werner and Gilliam, 1984). It is possible that this factor is coupled with the inability juveniles have in recognizing and capturing prey, attacking easier prey of less energetic value (Morrison et al, 1978)
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