Browsing by Author "López-Calleja, MV"

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    Dynamic energy and time budgets in hummingbirds
    (2003) López-Calleja, MV; Bozinovic, F
    Temperature and diet quality are two of the most important factors affecting the dynamic regulation of animal energy budgets. Because hummingbirds are very sensitive to energy stress, we used Green-backed Firecrowns (Sephanoides sephaniodes) to test the dynamics of their energy budget under different energetic challenges in chronic conditions (20 days). Experimental groups were: HQ-TNZ (high quality diet and thermoneutrality), HQ-LT (high quality diet and low temperature), LQ-TNZ (low quality diet and thermoneutrality), and LQ-LT (low quality diet and low temperature). Analysis of behavioral, morphological, and physiological variables revealed that thermal and dietary factors affect time and energy budgets independently. Hummingbirds increased energy intake during the first day of acclimation at LT, but after second day, the LQ-LT group did not maintain their energy intake and began to loose body mass. Moreover, diet quality affected digestive organs. The intestine, gizzard, liver and kidneys all increased in size when food quality was lowest, probably to obtain more food per feeding event and to more efficiently process the ingested food. Exposure to low ambient temperatures affected the most metabolically productive organs such as the heart, lungs, and muscular mass. Lower temperature increased basal and daily energy expenditure, and changed the time budget. Sephanoides sephaniodes spent more time perching when their energy balance was close to be negative. We suggest that energy budget regulation in hummingbirds does not reside exclusively in the energy output nor in the energy-input but in both pathways. (C) 2002 Elsevier Science Inc. All rights reserved.
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    Feeding behavior and assimilation efficiency of the Rufous-tailed Plantcutter
    (1999) López-Calleja, MV; Bozinovic, F
    We examined the feeding behavior and nutritional ecology of one of the smallest species of avian herbivores (ca. 44 g), the Rufous-tailed Plant-cutter Phytotoma rara (Phytotomidae). This species inhabits forests and scrublands, as well as crop fields and orchards in central Chile. Field and laboratory data revealed that P. rara is a herbivorous bird with marked preferences for leaves in comparison to fruits and insects. When P. rara eats a highly diluted plant material (such as lettuce), a shorter digesta retention time and a lower apparent digestibility was observed in comparison to a high-quality diet. Wet-mass daily intake of plant material was 5.4 times body mass, two times higher compared with the high-quality diet. The larger proportion of water and refractory materials in lettuce diet may explain the variation in ingestion rates. Feeding bouts were longer with lettuce diet, because birds spent more time handling and chewing previous ingesta. Chewing may increase overall digestibility through physical breakdown of cell walls, making available the highly digestible cell contents. These strategies may allow P. rara to maintain body mass balance when feeding on highly diluted plant material.
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    Interplay between the energetics of foraging and thermoregulatory costs in the green-backed firecrown hummingbird Sephanoides sephaniodes
    (2002) Fernández, MJ; López-Calleja, MV; Bozinovic, F
    In response to the interplay between variation in food quality and energetic demands, the foraging behaviour of captive green-backed firecrown hummingbirds Sephanoides sephaniodes was studied. Hummingbirds were exposed to two temperatures (25 degreesC vs 15 degreesC, two food qualities (0.5 vs 0.75 m sucrose solutions), and two costs of feeding (birds were provided with feeders with and without a perch). Food selection and consumption were measured, as well as time budgets and metabolic rate while feeding. We predicted that when given a choice, birds would minimize the cost of feeding by selecting feeders with a perch and with a high sugar concentration. However, rather than increasing energy consumption when energy availability was low and thermoregulatory demands were high, hummingbirds remained perched. They reduced feeding and spent most of their time perching. Our results identify a novel behavioural and physiological strategy in hummingbirds. These birds seem to shift their foraging behaviour depending on thermo regulatory and feeding costs. When these costs are high, rather than matching them with increased energy consumption, hummingbirds reduce energy costs by reducing activity. They seemed to adopt the following strategy: when food quality was high and thermoregulatory demands were low, they adopted a high-expense lifestyle. In contrast, when thermoregulatory costs were high, they adopted an energy conserving strategy even when food quality was high. We hypothesize that limitations imposed by physiological processes may explain why animals do not forage during all available time and why under some circumstances they choose foraging behaviours with lower rates of net energy gain.
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    Standard and comparative energetics of a small avian herbivore (Phytotoma rara)
    (2001) Rezende, EL; López-Calleja, MV; Bozinovic, F
    We studied the standard and comparative energetics of the Rufous-tailed Plancutter (Phytotoma rara), one of the smallest avian herbivores. The Rufous-tailed Plancutter had basal metabolic rate (BMR) values that so far are the highest mass-independent values observed in avian herbivores. Probably the BMR values attained by P.rara reflect its geographic distribution in temperate environments. Using a comparative analysis,we observed that herbivorous birds from temperate geographic areas tend to have higher BMR than tropical ones.
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    The integration of energy and nitrogen balance in the hummingbird Sephanoides sephaniodes
    (2003) López-Calleja, MV; Fernández, MJ; Bozinovic, F
    Floral nectars are rich in energy but contain only traces of amino acids, and it has been hypothesized that arthropods may be an important source of energy and amino acids for hummingbirds. We studied the nitrogen requirements of hummingbirds as well as how they use small arthropods to satisfy their nitrogen and energy requirements and how organ mass varies with nitrogen intake. Non-reproductive green-backed firecrowns Sephanoides sephaniodes were maintained for 10 days on diets containing 0%, 0.96%, 1.82%, 4.11% and 11.1% nitrogen (dry-matter basis). A second group of individuals were fed with varying amounts of nitrogen-free nectar supplemented with fruit flies. Finally, non-reproductive hummingbirds were captured as a control group for analysis of organ mass and size as well as fat content. The maintenance nitrogen requirement of green-backed firecrowns determined by regression was 1.42 mg N day(-1), yet they required nearly 10 mg N day(-1) to maintain body mass. When arthropods were available, we observed that hummingbirds required approximately 150 fruit flies to maintain body mass, which corresponds to a 5% nitrogen diet. Interestingly, when nectar was restricted (to 4 ml day(-1)), or was absent, arthropods alone were not able to satisfy the body mass balance requirements of hummingbirds, suggesting that arthropods are not adequate as an energy source. In the group offered an 11.1% nitrogen diet, the size and surface of the small intestine, and liver and kidney mass increased in comparison with the control group (non-reproductive field hummingbirds) or the nitrogen-free group, suggesting a nitrogen overload. Our results are in agreement with other studies showing low nitrogen requirements by nectarivores. An important point to stress is that nitrogen digestibility declined in the 11.1% nitrogen diet, which strongly supports our nitrogen absorption saturation hypothesis.