Publications
(Click on the title to see the abstract or on "pdf" to obtain a pdf version)
Journal of Experimental Biology, 211: 3478-3489 (2008)
Iriarte-Diaz J & Swartz SM
ABSTRACT: Maneuvering abilities have long been considered key factors that influence habitat selection and foraging strategies in bats. To date, however, very little experimental work has been carried out to understand the mechanisms that bats use to perform maneuvers. Here we examined the kinematics of slow-speed turning flight in the lesser short-nosed fruit bat, Cynopterus brachyotis, to understand the basic mechanics employed to perform maneuvers and to compare them with previous findings in bats and other flying organisms. Four individuals were trained to fly in an L-shaped flight enclosure that required them to make a 90-degree turn midway through each flight. Flights were recorded with three low light, high-speed videocameras, allowing the three-dimensional reconstruction of the body and wing kinematics. For any flying organisms, turning requires changes of the direction of travel and the reorientation of the body around the center of mass to maintain the alignment with the flight direction. In C. brachyotis, changes in body orientation (i.e., heading) took place during upstroke and preceded the changes in flight direction, which were restricted to the downstroke portion of the wingbeat cycle. Mean change in flight direction was significantly correlated to the mean heading angular velocity at the beginning of the downstroke and to the mean bank angle during downstroke, although only heading velocity was significant when both variables were considered. Body reorientation previous to changes in direction might be a mechanism to maintain the head and body aligned with the direction of travel and thus maximizing spatial accuracy in three-dimensionally complex environments.
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Journal of Theoretical Biology, 254: 604-615 (2008)
Riskin DK, Willis DJ, Iriarte-Diaz J, Hedrick TL, Kostandov M, Chian J, Laidlow DH, Breuer KS & Swartz SM
ABSTRACT: Body motions (kinematics) of animals can be dimensionally complex, especially when flexible parts of the body interact with a surrounding fluid. In these systems, tracking motion completely can be difficult, and result in a large number of correlated measurements, with unclear contributions of each parameter to performance. Workers typically get around this by deciding a priori which variables are important (wing camber, stroke amplitude, etc.), and focusing only on those variables, but this constrains the ability of a study to uncover variables of influence.
Here, we describe an application of proper orthogonal decomposition (POD) for assigning importances to kinematic variables, using dimensional complexity as a metric. We apply this method to bat flight kinematics, addressing three questions: (1) Does dimensional complexity of motion change with speed? (2) What body markers are optimal for capturing dimensional complexity? (3) What variables should a simplified reconstruction of bat flight include in order to maximally reconstruct actual dimensional complexity?
We measured the motions of 17 kinematic markers (20 joint angles) on a bat (Cynopterus brachyotis) flying in a wind tunnel at nine speeds. Dimensional complexity did not change with flight speed, despite changes in the kinematics themselves, suggesting that the relative efficacy of a given number of dimensions for reconstructing kinematics is conserved across speeds.
By looking at subsets of the full 17-marker set, we found that using more markers improved resolution of kinematic dimensional complexity, but that the benefit of adding markers diminished as the total number of markers increased. Dimensional complexity was highest when the hindlimb and several points along digits III and IV were tracked. Also, we uncovered three groups of joints that move together during flight by using POD to quantify correlations of motion. These groups describe 14/20 joint angles, and provide a framework for models of bat flight for experimental and modeling purposes.
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Journal of Experimental Biology, 209 (20): 4061-4066 (2006)
Iriarte-Diaz J, Bozinovic F and Vasquez RA
ABSTRACT: The transition from trot to gallop in quadruped mammals has been widely hypothesized to be a strategy to minimize the energetic costs of running. This view, however, has been challenged by some experimental evidence suggesting instead that this transition might be triggered by mechanical cues, and would occur when musculoskeletal stresses reach a certain critical value. All previous experiments to test those hypotheses have used relatively large species and their results, therefore, may not be applicable to small mammals. In this study we evaluated the effect of carrying loads on the locomotor energetics and gait transitions of the rodent Octodon degus running on a treadmill. Metabolic rate and cost of transport increased about 30% with a 20% increment in body mass. This increment was higher than expectations based on other mammals, where energy consumption increases in proportion to the added mass, but similar to the response of humans to loads. No abrupt change of energy consumption between gaits was observed and therefore no evidence was found to support the energetic hypothesis. The trot–gallop transition speed did not vary when subjects were experimentally loaded, suggesting that the forces applied to the musculoskeletal system do not trigger gait transition.
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Bioinspiration & Biomimetics, 1: S10-S18 (2006)
Tian X, Iriarte-Diaz J, Middleton K, Galvao R, Israeli E, Roemer A, Sullivan A, Song A, Swartz SM and Breuer K
ABSTRACT: Experimental measurements and analysis of the flight of bats are presented, including kinematic analysis of high-speed stereo videography of straight and turning flight, and measurements of the wake velocity field behind the bat. The kinematic data reveal that, at relatively slow flight speeds, wing motion is quite complex, including a sharp retraction of the wing during the upstroke and a broad sweep of the partially extended wing during the downstroke. The data also indicate that the flight speed and elevation are not constant, but oscillate in synchrony with both the horizontal and vertical movements of the wing. PIV measurements in the transverse (Trefftz) plane of the wake indicate a complex ‘wake vortex’ structure dominated by a strong wing tip vortex shed from the wing tip during the downstroke and either the wing tip or a more proximal joint during the upstroke. Data synthesis of several discrete realizations suggests a ‘cartoon’ of the wake structure during the entire wing beat cycle. Considerable work remains to be done to confirm and amplify these results.
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Acta Chiropterologica, 7 (1): 65-72 (2005)
Canals M, Atala C, Grossi B and Iriarte-Diaz J
ABSTRACT: We estimated the heart and lung size of several species of small bats (Tadarida brasiliensis, Mormopterus kalinowski, Myotis chiloensis, Histiotus macrotus, H. montanus, Lasiurus borealis and L. cinereus) and compared these values to those of bats of larger size and other mammals. Our results confirmed that bats have the largest relative heart and lung size of all mammals. This is associated with the high energetic costs of flight. As expected, the mass-specific lung and heart sizes of small bats were larger than those of large bats. However, although relative heart mass decreased according to body mass, Mb-0.21, lung volume was nearly isometric with body mass (exponent = 0.90). This exponent was close to unity, and between exponents reported previously (0.77 and 1.06). This suggests that small bats compensate the energetic cost of flight mainly by changes in cardiovascular morphology. The relative heart mass of both, H. macrotus and H. montanus was particularly large, representing 1.71 and 2.18% of total body mass, respectively. These values correspond to 121.3 and 162.7%, respectively, of the expected values from allometric relationships. In these big-eared bats, the large hearts could be attributed to the energetic costs induced by the ears' drag.
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Revista Chilena de Historia Natural, 78 (2): 215-227 (2005)
Canals M, Grossi B, Iriarte-Diaz J and Veloso C
ABSTRACT: In this study we compared the wing morphology of eight species of bats inhabiting Chile, including two previously studied species. We correlated our results with ecological information. Aspect ratio, wing span, wing area, wing loading and the second moment of area of the midshaft of the humerus were estimated for the molossid Mormopterus kalinowskii, the phyllostomidae Desmodus rotundus and the vespertilionids Histiotus montanus, Histiotus macrotus, Lasiurus borealis, and Lasiurus cinereus. The free-tailed bats T. brasiliensis and M.kalinowskii and D. rotundus, without uropatagyum, showed low wing areas, but whilst the molossids showed large aspect ratios, that of D. rotundus was only moderate. Desmodus rotundus showed the lowest wing span (relative to the expected value) and the largest wing loading. The second moment of area of the midshaft of the humerus of M. chiloensis was lower than the predicted values from allometric equations, suggesting poor resistance to bending and torsional forces. All other vespertilionids showed high second moment of area of the humerus. This may be explained by the energetically expensive form of locomotion, especially in species with high parasite power as a consequence of their long ears. The high Ih of D. rotundus can be explained by its low aspect ratio and its high body mass. A principal component analysis showed two orthogonal axes. The first correlated positively with wing loading and negatively with the mass, corrected wingspan. The second component was correlated with the aerodynamic efficiency parameter, aspect. Four functional groups, one per quadrant. were described: (1) Desmodus rotundus, with high wing loading but low corrected wing span, was in the increased agility zone, with moderate power consumption during flight; (2) the molossids were located within the high speed flight and low total power zone, showing high aerodynamic efficiency; (3) most of vespertilionids were in the zone of low speed but increased maneuverability, with relatively low aspect ratios and wing loading; (4) Lasiurus cinereus was in the zone of fast speed flight and the low aspect ratio predicts an increased agility. The functional groups (2) and (3) exploit similar habitats but with different life styles. The molossids foraging in open areas at fast flight speed and the vespertilionids foraging in more wooded areas with maneuverable and slow flight. Desmodus rotundus clearly constitute a single group that may be related to commuting flights from communal roost and their particular mode of locomotion.
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Mammalian biology, 68 (6): 365-371 (2003)
Saavedra B, Quiroz D and Iriarte J
ABSTRACT: We describe archaeozoological and extant small mammals from Isla Mocha, an island located in south-central Chile. Species composition was compared among past and present assemblages. Also composition, as well as individual and population parameters were compared among island habitats. Specimens from archaeological sites included Oligoryzomys longicaudatus, Abrothrix sp., and Octodon pacificus, whereas Abrothrix longipilis, A. olivaceus, Oligoryzomys longicaudatus, and Geoxus valdivianus were captured. Higher richness was observed in intermediate-disturbed habitat. Body size and tail length, as well as body mass did not vary among island habitats for A. longipilis or A. olivaceus. Higher abundance was associated to less perturbed habitat.
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Journal of Experimental Biology, 205 (18): 2897-2908 (2002)
Iriarte-Diaz J
ABSTRACT: It has been observed that the relationship between locomotor performance and body mass in terrestrial mammals does not follow a single linear trend when the entire range of body mass is considered. Large taxa tend to show different scaling exponents compared to those of small taxa, suggesting that there would be a differential scaling between small and large mammals. This pattern, noted previously for several morphological traits in mammals, has been explained to occur as a result of mechanical constraints over bones due to the differential effect of gravity on small and large-sized forms. The relationship between maximum relative running speed (body length s-1) and body mass was analysed in 142 species of terrestrial mammals, in order to evaluate whether the relative locomotor performance shows a differential scaling depending on the range of mass analysed, and whether the scaling pattern is consistent with the idea of mechanical constraints on locomotor performance. The scaling of relative locomotor performance proved to be non-linear when the entire range of body masses was considered and showed a differential scaling between small and large mammals. Among the small species, a negative, although nearly independent, relationship with body mass was noted. In contrast, maximum relative running speed in large mammals showed a strong negative relationship with body mass. This reduction in locomotor performance was correlated with a decrease in the ability to withstand the forces applied on bones and may be understood as a necessary stress reduction mechanism for assuring the structural integrity of the limb skeleton in large species.
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Acta Theriologica, 47 (2): 193-200 (2002)
Iriarte-Diaz J, Novoa FF and Canals M
ABSTRACT: The wing morphology of bats is very diverse, and may correlate with energetic behavioural, and ecological demands. If these demands conflict, wing shape may reflect compromise solutions. In this study, we compared the wing morphology of two bats Tadarida brasiliensis (Geoffroy, 1824) and Myotis chiloensis (Waterhouse, 1828), that differ in body size, habitat, and foraging behaviour. We analyzed features of biomechanical and energetic relevance, and sought evidence of compromise solutions to energetic, ecological, and behavioural demands. We found that wing span of both species conformed to expectations based on allometric relationships, but that although the wing area of M. chiloensis did not differ from predictions, the wing area of T. brasiliensis was lower. M. chiloensis possessed an unusually low second moment of area of the humerus. Wing form of M. chiloensis is consistent with highly maneuverable flight needed to live between shrubs and wooded habitats and its low aspect ratio and low wing loading indicate a high energetic cost and a low flight speed, respectively. The low humeral second moment of area may be related to a reduction of wing mass and may result in decreased inertial power. In contrast, T. brasiliensis showed high aspect ratio and wing loading, characteristic of high speed, energetically economic flight.
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Journal of Mammalogy, 83 (1): 145-152 (2002)
Bacigalupe LD, Iriarte-Diaz J and Bozinovic F
ABSTRACT: We studied morphological and functional variations in jaws of coastal and mountain populations of subterranean Spalacopus cyanus inhabiting soils with contrasting hardness. We found almost no morphological differentiation between populations in the variables we measured. However, there were clear differences in incisor resistance between them. Apparently, soil hardness did not represent a selective pressure on cururos' digging apparatus. An Andean origin of this genus could explain our results.
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Revista Chilena de Historia Natural, 74 (3): 699-704 (2001)
Canals M, Iriarte-Diaz J, Olivares R and Novoa FF
ABSTRACT: Wing morphology is related by one hand to biomechanical properties and energetics of flying, and on the other hand to ecological and behavioral aspects of flying, such as flight pattern, foraging behavior, habitat selection and size of prey. In this work we compare the wing morphology of Tadarida brasiliensis (Molossidae) and Myotis chiloensis (Vespertilionidae), as representatives of two flight patterns, and looking for trade-offs between wing morphology, ecology and behavior. Our results showed that T. brasiliensis is larger and with higher wing span than M. chiloensis, although the wing area does not differ between these bats. The latter species showed a smaller variability in body mass and cortical area of humerus, probably related with mechanic and energetic constraints. Without size effect, there were differences in the external diameter and medullar diameter of humerus, but with a similar cortical area. The humerus of T. brasiliensis is a bone of similar length, wider and with smaller cortical thickness than in M. chiloensis, which is related to a higher resistance to bending and torsional forces. The wing shape found in each bat is in agree with the life mode: slow, short and manoeuvrable flight in wooded zones of M. chiloensis and fast and long distance flight in open areas of T. brasiliensis.
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