The comparative biology of ethanol consumption: An introduction to the symposium

In classical Greek, the word “symposium” signifies a drinking party held for the purposes of intellectual discussion. This symposium introduces a new evolutionary perspective on an ancient question: why are many animals, including humans, attracted to ethanol? Recent research has shown that behavioral responses to ethanol and molecular pathways of inebriation are shared among many taxa (Wolf and Heberlein, 2003), and that the preferences of modern humans for alcohol consumption may derive from the diets of our fruit-eating ancestors (i.e., alcoholism as evolutionary hangover; Dudley, 2000, 2002). Placement of ethanol consumption within historical and comparative contexts may thus yield insight into contemporary patterns of human consumption and excessive use

The physiology and biomechanics of avian flight at high altitude

Many birds fly at high altitude, either during long-distance flights or by virtue of residence in high-elevation habitats. Among the many environmental features that vary systematically with altitude, five have significant consequences for avian flight performance: ambient wind speeds, air temperature, humidity, oxygen availability, and air density. During migratory flights, birds select flight altitudes that minimize energy expenditure via selection of advantageous tail- and cross-winds. Oxygen partial pressure decreases substantially to as little as 26% of sea-level values for the highest altitudes at which birds migrate, whereas many taxa reside above 3000 meters in hypoxic air. Birds exhibit numerous adaptations in pulmonary, cardiovascular, and muscular systems to alleviate such hypoxia. The systematic decrease in air density with altitude can lead to a benefit for forward flight through reduced drag but imposes an increased aerodynamic demand for hovering by degrading lift production and simultaneously elevating the induced power requirements of flight. This effect has been well-studied in the hovering flight of hummingbirds, which occur throughout high-elevation habitats in the western hemisphere. Phylogenetically controlled studies have shown that hummingbirds compensate morphologically for such hypodense air through relative increases in wing size, and kinematically via increased stroke amplitude during the wingbeat. Such compensatory mechanisms result in fairly constant power requirements for hovering at different elevations, but decrease the margin of excess power available for other flight behaviors

Kinematics of hovering hummingbird flight along simulated and natural elevational gradients

Hovering flight is one of the most energetically demanding forms of animal locomotion. Despite the cost, hummingbirds regularly hover at high elevations, where flight is doubly challenging because of reduced air density and oxygen availability. We performed three laboratory experiments to examine how air density and oxygen partial pressure influence wingbeat kinematics. In the first study, we experimentally lowered air density but maintained constant oxygen partial pressure. Under these hypodense but normoxic conditions, hummingbirds increased stroke amplitude substantially and increased wingbeat frequency slightly. In the second experiment, we maintained constant air density but decreased oxygen partial pressure. Under these normodense but hypoxic conditions, hummingbirds did not alter stroke amplitude but instead reduced wingbeat frequency until they could no longer generate enough vertical force to offset body weight. In a final combined experiment, we decreased air density but increased oxygen availability, and found that the wingbeat kinematics were unaffected by supplemental oxygen. We also studied hovering and maximally loaded flight performance for 43 hummingbird species distributed along a natural elevational gradient in Peru. During free hovering flight, hummingbirds showed increased stroke amplitude interspecifically at higher elevations, mirroring the intra-individual responses in our first laboratory experiment. During loaded flight, hummingbirds increased both wingbeat frequency and wing stroke amplitude by 19% relative to free-flight values at any given elevation. We conclude that modulation of wing stroke amplitude is a major compensatory mechanism for flight in hypodense or hypobaric environments. By contrast, increases in wingbeat frequency impose substantial metabolic demands, are only elicited transiently and anaerobically, and cannot be used to generate additional sustained lift at high elevations

Accelerational Implications of Hummingbird Display Dives

Integrative Biolog

How Well Does the U.S. Government Do Cost-Benefit Analysis?

To make prudent recommendations for improving the use of cost-benefit analysis in policy settings, some measures of how well it is actually done are essential. This paper develops new insights on the potential usefulness of government cost-benefit analysis by examining how it is actually performed in the U.S. We assess the quality of a particularly rich sample of cost-benefit analyses of federal regulations. The data set we use for assessing the quality of regulatory analysis is the largest assembled to date for this purpose. Theseventy-four analyses we examine span the Reagan administration, the first Bush and the Clinton administration. The paper is the first to assess systematically how government cost-benefit analysis has changed over time. There are three key findings. First, a significant percentage of the analyses in all three administrations do not provide some very basic economic information, such as information on net benefits and policy alternatives. For example, over 70% of the analyses in the sample failed to provide any quantitative information on net benefits. Second, there is no clear trend in the quality of cost-benefit analysis across administrations. Third, there is a great deal of variation in the quality of individual cost-benefit analyses.

Of hummingbirds and helicopters: Hovering costs, competitive ability, and foraging strategies

Wing morphology and flight kinematics profoundly influence foraging costs and the overall behavioral ecology of hummingbirds. By analogy with helicopters, previous energetic studies have applied the momentum theory of aircraft propellers to estimate hovering costs from wing disc loading (WDL), a parameter incorporating wingspan (or length) and body mass. Variation in WDL has been used to elucidate differences either among hummingbird species in nectar-foraging strategies (e.g., territoriality, traplining) and dominance relations or among gender-age categories within species. We first demonstrate that WDL, as typically calculated, is an unreliable predictor of hovering (induced power) costs; predictive power is increased when calculations use wing length instead of wingspan and when actual wing stroke amplitudes are incorporated. We next evaluate the hypotheses that foraging strategy and competitive ability are functions of WDL, using our data in combination with those of published sources. Variation in hummingbird behavior cannot be easily classified using WDL and instead is correlated with a diversity of morphological and physiological traits. Evaluating selection pressures on hummingbird wings will require moving beyond wing and body mass measurements to include the assessment of the aerodynamic forces, power requirements, and power reserves of hovering, forward flight, and maneuvering. However, the WDLhelicopter dynamics model has been instrumental in calling attention to the importance of comparative wing morphology and related aerodynamics for understanding the behavioral ecology of hummingbirds

Resolution of a paradox: Hummingbird flight at high elevation does not come without a cost

Flight at high elevation is energetically demanding because of parallel reductions in air density and oxygen availability. The hovering flight of hummingbirds is one of the most energetically expensive forms of animal locomotion, but hummingbirds are nonetheless abundant at high elevations throughout the Americas. Two mechanisms enhance aerodynamic performance in high-elevation hummingbirds: increase in wing size and wing stroke amplitude during hovering. How do these changes in morphology, kinematics, and physical properties of air combine to influence the aerodynamic power requirements of flight across elevations? Here, we present data on the flight performance of 43 Andean hummingbird species as well as a 76-taxon multilocus molecular phylogeny that served as the historical framework for comparative analyses. Along a 4,000-m elevational transect, hummingbird body mass increased systematically, placing further aerodynamic demands on high-elevation taxa. However, we found that the minimum power requirements for hovering flight remain constant with respect to elevation because hummingbirds compensate sufficiently through increases in wing size and stroke amplitude. Thus, high-elevation hummingbirds are not limited in their capacity for hovering flight despite the challenges imposed by hypobaric environments. Other flight modes including vertical ascent and fast forward flight are more mechanically and energetically demanding, and we accordingly also tested for the maximum power available to hummingbirds by using a load-lifting assay. In contrast to hovering, excess power availability decreased substantially across elevations, thereby reducing the biomechanical potential for more complex flight such as competitive and escape maneuvers

Reviewing the Government's Numbers on Regulation

This paper has two objectives: first, to provide more information on the data used to construct a controversial economic analysis published by the Joint Center that makes use of over 100 government regulatory impact analyses; and second, to provide further sensitivity analysis of key variables in that study. A key finding of this paper is that the results of the earlier analysis of government regulatory impact analyses appear to be fairly robust within the data set that was constructed. We offer the following conclusions. First, aggregate net benefits for final regulations are positive under a wide variety of assumptions. Second, a substantial number of final regulations do not pass a benefit-cost test under a wide variety of assumptions. By rejecting at least some of these regulations, government could have increased aggregate net social benefits. Third, aggregate net benefits exhibit a wide range across regulations. And fourth, agencies should improve the quality of their regulatory impact analyses. Also of interest from the Joint Center: The Economic Analysis of Regulation: A Response to the Critics Robert W. Hahn

Ontogeny of aerial righting and wing flapping in juvenile birds

Mechanisms of aerial righting in juvenile Chukar Partridge (Alectoris chukar) were studied from hatching through 14 days post hatching (dph). Asymmetric movements of the wings were used from 1 to 8 dph to effect progressively more successful righting behaviour via body roll. Following 8 dph, wing motions transitioned to bilaterally symmetric flapping that yielded aerial righting via nose down pitch, along with substantial increases in vertical force production during descent. Ontogenetically, the use of such wing motions to effect aerial righting precedes both symmetric flapping and a previously documented behaviour in chukar (i.e., wing assisted incline running) hypothesized to be relevant to incipient flight evolution in birds. These findings highlight the importance of asymmetric wing activation and controlled aerial manoeuvres during bird development, and are potentially relevant to understanding the origins of avian flight