Energetics of hummingbird foraging at low ambient temperature

1999 ◽  
Vol 77 (2) ◽  
pp. 314-320 ◽  
Author(s):  
C L Gass ◽  
M T Romich ◽  
R K Suarez
Keyword(s):  
Energy Balance ◽  
Ambient Temperature ◽  
Energy Intake ◽  
Energy Gain ◽  
Energetic Cost ◽  
Net Energy ◽  
Metabolic Rates ◽  
Energetic Costs ◽  
Net Energy Gain ◽  
Low Ambient Temperature

Because of their small size and the high energetic costs of hovering and forward flight, hummingbirds achieve the highest mass-specific metabolic rates known among vertebrates. Rufous hummingbirds (Selasphorus rufus) stop to refuel on floral nectar in subalpine meadows as they migrate south from British Columbia to Mexico. In such habitats they face the challenge of achieving daily net energy gain despite the high energetic costs of flight and thermoregulation at near-freezing morning temperatures. Hummingbirds provided with 15 or 20% sucrose while subjected to these conditions for 4 h in the laboratory did not remain in energy balance and lost mass. However, they achieved energy balance or net energy gain on 30% sucrose. Because these sucrose concentrations are within the range observed in the nectar of hummingbird-visited flowers, the results suggest that the energetic cost of thermoregulation may influence the coevolution of hummingbirds and flowers. Hummingbirds maintaining energy balance at low ambient temperature via high foraging frequencies and high rates of energy intake can sustain average metabolic rates of about 250 W/kg over a 4-h period. These are the highest metabolic rates known among vertebrates at which rates of dietary energy intake equal rates of energy expenditure.

scholarly journals Incompletely Informed Shorebirds That Face a Digestive Constraint Maximize Net Energy Gain When Exploiting Patches

2003 ◽  
Vol 161 (5) ◽  
pp. 777-793 ◽  
Author(s):  
Jan A. van Gils ◽  
Ingrid W. Schenk ◽  
Oscar Bos ◽  
Theunis Piersma
Keyword(s):  
Energy Gain ◽  
Net Energy ◽  
Net Energy Gain ◽  
Digestive Constraint

Responses of rufous hummingbirds to midday fasts

1985 ◽  
Vol 63 (10) ◽  
pp. 2249-2253 ◽  
Author(s):  
Zena J. Tooze ◽  
Clifton Lee Gass
Keyword(s):  
Body Weight ◽  
Energy Balance ◽  
Food Intake ◽  
Energy Intake ◽  
Laboratory Tests ◽  
Net Energy ◽  
Energy Reserves ◽  
Metabolic Costs ◽  
Net Energy Intake ◽  
Highly Correlated

This study investigates how rufous hummingbirds regain energy balance after experimentally imposed midday fasts reduce their energy reserves. Net energy balance calculated from food intake, activity budgets, and allometric equations for the costs of flying and perching was highly correlated with change in body weight in laboratory tests of 3 h or more. Individuals accumulated energy and body weight at the same rate after fasts as before, resulting in energy deficits at the end of the day compared with control conditions. Energy balance relative to control values was regained by the following morning, primarily by reducing metabolic costs in the dark through torpor. Net energy intake increased the following day, but this increase was relatively unimportant to reestablishing equilibrium.

Environmental cues of estrus in the North American red squirrel (Tamiasciurus hudsonicus Bangs)

1993 ◽  
Vol 71 (7) ◽  
pp. 1326-1333 ◽  
Author(s):  
C. Dustin Becker
Keyword(s):  
Annual Cycle ◽  
Energy Gain ◽  
Day Length ◽  
Tamiasciurus Hudsonicus ◽  
Positive Energy ◽  
Net Energy ◽  
Circannual Rhythm ◽  
Red Squirrels ◽  
Short Day ◽  
Net Energy Gain

During three breeding seasons, variation in the timing of estrus was monitored in wild red squirrels (Tamiasciurus hudsonicus) in a jack pine forest in central Alberta. The proximate environmental factors that affect the timing of the onset of the breeding season in female squirrels, and variation in dates of estrus, were studied in parallel laboratory and field manipulations. Wild squirrels given ad libitum sunflower seed experienced a positive energy balance (weight gains) earlier in the season than did females on a normal diet. Seed addition advanced dates of estrus by an average of 3 weeks. Three potential cuing mechanisms for the seasonal onset of estrus were proposed and tested: onset of estrus is cued by (i) a simple response to net energy gain, (ii) an interaction between an endogenous circannual rhythm and net energy gain, or (iii) an interaction between annual changes in photoperiod and net energy gain in the absence of a circannual rhythm. Our results refute the first and third mechanisms, and support the idea that red squirrels have a circannual reproductive cycle entrained by photoperiod. Net energy gain interacts with this annual cycle to fine tune the time of ovulation. In laboratory experiments, female squirrels exposed to increasing day length experienced estrus within the normal season. Squirrels kept in constant short-day conditions (< 12 h), had delayed estrus cycles. Short-day conditions did not prevent the annual cycle of reproduction, indicating that an endogenous rhythm exists and is entrained by increasing day length. Comparisons with hibernating squirrels are discussed.

Microalgae biofuels: can we achieve net energy gain and water savings?

Biofuels ◽  
2012 ◽  
Vol 3 (1) ◽  
pp. 5-8 ◽  
Author(s):  
Raymond KW Tham ◽  
Wei Zhang
Keyword(s):  
Energy Gain ◽  
Net Energy ◽  
Water Savings ◽  
Net Energy Gain

Energetics of free-ranging large herbivores: when should costs affect foraging behaviour?

2000 ◽  
Vol 78 (9) ◽  
pp. 1604-1615 ◽  
Author(s):  
Helen M Armstrong ◽  
Antony Robertson
Keyword(s):  
Energy Balance ◽  
Foraging Behaviour ◽  
Ovis Aries ◽  
Energetic Cost ◽  
Domestic Sheep ◽  
Net Energy ◽  
Large Herbivores ◽  
Wind Speeds ◽  
Free Ranging ◽  
The Impact

Published relationships were used to build a mathematical model that predicts the daily net energy balance of free-ranging domestic sheep (Ovis aries L.) grazing in the U.K. hills. Net energy balance was predicted for a plausible range of environmental conditions. The behaviour of the model suggested the following predictions. Locomotion will be a relatively unimportant energetic cost. Ambient temperature and rainfall alone will rarely affect energy expenditure, whereas wind will greatly increase energetic costs in winter. These are further increased, but to a relatively small extent, by any concurrent rainfall. Predictions of foraging behaviour based on maximisation of energy intake alone are likely to significantly overestimate dry matter intake from climatically exposed vegetation in winter. Where shelter is available, such models will also overestimate total intake in winter by not taking account of sheltering behaviour. This effect will be most pronounced when forage is of low digestibility or availability, wind speeds are high, or the level of coat insulation is low. Foraging models based instead on maximisation of net energy balance are likely to greatly improve predictions of the impact of large herbivores on vegetation and the mechanisms driving their population dynamics.

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