Browsing by Author "Vásquez, RA"

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    Breeding biology of the Thorn-tailed Rayadito (Furnariidae) in south-temperate rainforests of Chile
    (2005) Moreno, J; Merino, S; Vásquez, RA; Armesto, JJ
    We conducted a study of the breeding biology of the Thorn-tailed Rayadito (Aphrastura spinicauda) in secondary forests on the continental island of Chiloe (42degreesS), southern Chile. Rayaditos are small insectivorous furnariids inhabiting the south-temperate forests of Chile and Argentina. We followed the reproduction of rayadito pairs breeding in nest-boxes. Rayaditos build their nests mainly of rhizomes and stems of epiphytic vines, grasses, and hairs during periods of at least a week, and show a marked population asynchrony in laying dates of more than two months (October-December). Rayaditos lay clutches of 3-6 eggs with a mode of 4 and laying occurs on alternate days. Eggs are 50% larger and hatchlings are 30% larger than expected from allometric equations. Most broods hatch synchronously. Nestling growth curves adjust well to logistic functions and at 2 weeks nestlings attain masses similar to asymptotic values. Nestling growth, which occurs over 3 weeks, is 27% slower than expected from allometry. Fledglings attain adult size with respect to tarsus length, but have less developed plumage and higher body mass than adults. Rayaditos exhibit clutch and brood reduction, suggesting possible food limitation. The protracted breeding periods may preclude second breeding attempts for most pairs in Chiloe. There is evidence for declines in parental quality with season. The low seasonal fecundity, large eggs, and prolonged dependence periods of a truly south-temperate species like the Thorn-tailed Rayadito reflect a 'slow' life history similar to that of tropical passerines.
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    Cost of living in free-ranging degus (Octodon degus)
    (2004) Bozinovic, F; Bacigalupe, LD; Vásquez, RA; Visser, GH; Veloso, C; Kenagy, GJ
    Animals process and allocate energy at different seasons at variable rates, depending on their breeding season and changes in environmental conditions and resulting physiological demands. Overall total energy expenditure, in turn, should either increase in some seasons due to special added demands (e.g. reproduction) or it could simply remain at about the same level, in which case the animals must show compensatory rebalancing of other expenditures that can be reduced. To test for the alternative hypotheses of seasonal variability or compensation, we measured total daily energy expenditure (DEE) in free-living degus (Octodon degus) at four seasons and followed this with determinations of basal metabolic rate (BMR) in the laboratory in the same individuals. DEE varied seasonally but was only significantly different (lower) in summer (non-breeding season), with a DEE:BMR ratio of only 1.6, whereas autumn, winter and spring DEE values were statistically indistinguishable from one another and showed DEE:BMR ratios ranging from 1.9 to 2.2. Our values of DEE in the field fall within the broad range of allometric expectation for herbivorous mammals in general, but the ratios of DEE:BMR are lower than expected. This, together with the lack of strong major shifts in total levels of DEE, suggests that degus are showing compensatory shifts among various categories of energy expenditure that allow them to manage their overall energy balance by minimizing total expenditure. (C) 2003 Elsevier Inc. All rights reserved.
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    Patch use in a diurnal rodent
    (1999) Bozinovic, E; Vásquez, RA
    1. The role of physiological complexity in animal foraging ecology was investigated through experiments to determine how animals manage time and energy during patch use under thermoregulatory costs. The Degu Octodon degus (Molina 1782), a diurnal rodent inhabiting the semiarid environments of central Chile, was studied.
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    Time and energy use under thermoregulatory constraints in a diurnal rodent
    (2000) Bozinovic, F; Lagos, JA; Vásquez, RA; Kenagy, GJ
    (1) This study was designed to understand how thermoregulatory constraints affect the timing of foraging bouts and amount of food obtained from a feeding station that was subject to an intense heat load. (2) The degu, Octodon degus, is a diurnal re-dent inhabiting hot arid environments in Chile. Two-hour trials were run in a laboratory experimental arena to determine time allocation between a food station located under a heavy radiant heat source (2500 W/m(2)) and the rest of the arena, including a cool burrow. A video camera recorded the animal's movements during the trial, and tapes were analyzed afterwards for seven degus with a heated food site and seven degus with a normal, unheated food station. (3) Degus with a food patch exposed to heat spent less time foraging and harvested less food than animals with no heat load. Over a two hour period time use of the food patch was significantly less when heated than when not heated (0.65 +/- 0.59 vs 4.90 +/- 1.73 min, respectively). Thus the degus subjected to heat above their food source minimized time exposure to a physiologically stressful condition by decreasing their visits to the heated food source, thereby reducing food (= energy) intake. (4) Oxygen consumption (VO2), evaporative water loss (EWL) and body temperature (T-b) at air temperatures (T-air) of 33-34, 36-37, and 39-40 degrees C were also determined. The metabolic response to rising T-air amounted to a doubling of VO2 and a five-fold increase of EWL at T-air 39-40 degrees C, compared with 25 degrees C; and T-b rose above 42 degrees C. (5) Using data from these metabolic measurements together with a theoretical heating model, heating curves were obtained that suggested that degus can exploit patches of food for only about 3 min at 60 degrees C and 8 min at 50 degrees C. These simulations are in agreement with our observations that degus reduced their time spent feeding when there was a thermal constraint on foraging. (C) 2000 Elsevier Science Ltd. All rights reserved.