Take-off mechanics in hummingbirds (Trochilidae)

Initiating flight is challenging, and considerable effort has focused on understanding the energetics and aerodynamics of take-off for both machines and animals. For animal flight, the available evidence suggests that birds maximize their initial flight velocity using leg thrust rather than wing flapping. The smallest birds, hummingbirds (Order Apodiformes), are unique in their ability to perform sustained hovering but have proportionally small hindlimbs that could hinder generation of high leg thrust. Understanding the take-off flight of hummingbirds can provide novel insight into the take-off mechanics that will be required for micro-air vehicles. During take-off by hummingbirds, we measured hindlimb forces on a perch mounted with strain gauges and filmed wingbeat kinematics with high-speed video. Whereas other birds obtain 80–90% of their initial flight velocity using leg thrust, the leg contribution in hummingbirds was 59% during autonomous take-off. Unlike other species, hummingbirds beat their wings several times as they thrust using their hindlimbs. In a phylogenetic context, our results show that reduced body and hindlimb size in hummingbirds limits their peak acceleration during leg thrust and, ultimately, their take-off velocity. Previously, the influence of motivational state on take-off flight performance has not been investigated for any one organism. We studied the full range of motivational states by testing performance as the birds took off: (1) to initiate flight autonomously, (2) to escape a startling stimulus or (3) to aggressively chase a conspecific away from a feeder. Motivation affected performance. Escape and aggressive take-off featured decreased hindlimb contribution (46% and 47%, respectively) and increased flight velocity. When escaping, hummingbirds foreshortened their body movement prior to onset of leg thrust and began beating their wings earlier and at higher frequency. Thus, hummingbirds are capable of modulating their leg and wingbeat kinetics to increase take-off velocity

Habitat Partitioning and Associated Morphological Differences Among Three Species of Catostomidae (Teleostei: Actinopterygii) in the South Fork Roanoke River, Virginia

The upper Roanoke River has 11 species of Catostomidae including Thoburnia rhothoeca, Torrent Sucker; Moxostoma cervinum, Blacktip Jumprock; and Moxostoma ariommum, Bigeye Jumprock. Resource partitioning appears to be a key component of maintaining diverse fish assemblages with habitat and food partitioning cited as especially important in communities containing members of the same family. The diets of these species have been documented in previous work revealing only modest differences among them. Snorkeling observations and subsequent quantification of microhabitat were conducted to illuminate habitat partitioning among these morphologically and ecologically similar species. Thoburnia rhothoeca inhabited the shallowest, fastest water, over the smallest substrate, and Moxostoma ariommum inhabited the deepest, slowest water, over the largest substrate, with M. cervinum intermediate for all habitat variables. In an effort to correlate morphological adaptations to these different microhabitats, 22 body measurements were included in a Principal Components analysis revealing a bigger eye for M. ariommum and more fusiform bodies for T. rhothoeca and M. cervinum consistent with findings in other species inhabiting faster waters. Other correlations among morphology and microhabitat were less clear

Microhabitat Comparison of Percina roanoka (Roanoke Darter) and Percina nevisense (Chainback Darter) in the Roanoke River

Snorkel observations of Percina roanoka and P. nevisense in the Roanoke River during summer months were followed by measuring current velocity, water depth, and substrate diameter at points of occupation. A total of 89 observations of P. roanoka and 81 observations of P. nevisense were compared using two-sample T-tests. Percina roanoka inhabited faster, shallower water than P. nevisense with the former found in a mean flow of 0.318 m/s and depth of 31.53 cm and the latter in a mean flow of 0.17 m/s and depth of 55.6 cm. Mean diameter of substrate at points of occupation did not differ significantly between the two species with P. roanoka over substrate 10.14 cm diameter, and P. nevisense over substrate of 9.7 cm diameter. Differences in habitat among age classes were not detected for either species. These findings suggest habitat partitioning along current velocity and depth help maintain the diverse darter assemblage in the Roanoke River

Size Differences Among Root-knot Nematodes on Resistant and Susceptible Alyceclover Genotypes

The influence of plant resistance on the size of individual root-knot nematodes was determined in greenhouse experiments. Five genotypes of alyceclover were inoculated with second-stage juveniles of Meloidogyne incognita race 3 or M. arenaria race 1. Plants were harvested at selected intervals and stained for detection of the nematodes, which were dissected from the roots. Length, width, and sagittal-sectional area of each animal were measured using an image-analysis system, and areas of nematodes in all stages were compared at different times and across alyceclover lines. Nematodes feeding on roots of resistant lines were consistently smaller than those on susceptible plants, with significant differences in growth detected after the final molt. Similar results were observed with both nematode species

Head-Group Conformation in Phospholipids: A Phosphorus-31 Nuclear Magnetic Resonance Study of Oriented Monodomain Dipalmitoylphosphatidylcholine Bilayers

Angular-dependent $^{31}P$ NMR spectra of oriented biaxial monodomain DPPG $H_20$ multilayers are employed to study head-group conformation in this phospholipid. The results indicate that the 0-P-0 plane of the phosphate, where the 0’s are the nonesterified oxygens of the phosphodiester, is tilted at $47 \pm 5^{\circ}$ with respect to the bilayer normal. This $PO_4$ orientation could result in the choline moiety being extended parallel to the bilayer plane, and it will explain the breadth of the axially symmetric $^{31}P$ powder spectrum observed for DPPC in excess water. This work is the first direct observation of this conformation for lecithins and it illustrates the utility of high-resolution solid-state NMR in structural studies of disordered systems.Engineering and Applied Science

Flight Mechanics and Control of Escape Manoeuvres in Hummingbirds. I. Flight Kinematics

Hummingbirds are nature’s masters of aerobatic manoeuvres. Previous research shows that hummingbirds and insects converged evolutionarily upon similar aerodynamic mechanisms and kinematics in hovering. Herein, we use three-dimensional kinematic data to begin to test for similar convergence of kinematics used for escape flight and to explore the effects of body size upon manoeuvring. We studied four hummingbird species in North America including two large species (magnificent hummingbird, Eugenes fulgens, 7.8 g, and blue-throated hummingbird, Lampornis clemenciae, 8.0 g) and two smaller species (broad-billed hummingbird, Cynanthus latirostris, 3.4 g, and black-chinned hummingbirds Archilochus alexandri, 3.1 g). Starting from a steady hover, hummingbirds consistently manoeuvred away from perceived threats using a drastic escape response that featured body pitch and roll rotations coupled with a large linear acceleration. Hummingbirds changed their flapping frequency and wing trajectory in all three degrees of freedom on a stroke-by-stroke basis, likely causing rapid and significant alteration of the magnitude and direction of aerodynamic forces. Thus it appears that the flight control of hummingbirds does not obey the ‘helicopter model’ that is valid for similar escape manoeuvres in fruit flies. Except for broad-billed hummingbirds, the hummingbirds had faster reaction times than those reported for visual feedback control in insects. The two larger hummingbird species performed pitch rotations and global-yaw turns with considerably larger magnitude than the smaller species, but roll rates and cumulative roll angles were similar among the four species