No abstract

The regional Barrovian facies metamorphic rocks of the High Himalayan Slab in Zanskar are bounded along the base by the southwest vergent Main Central Thrust (MCT) with its characteristic zone of inverted isograds, and along the top of the slab by the northeast dipping Zanskar Shear Zone (ZSZ), part of the South Tibetan Detachment (STD) System of normal faults. Summarized here are the results of systematic mapping combined with detailed P-T-t data from the Zanskar Himalaya, and models for the thermal and mechanical evolution of the middle and deep crustal rocks of the Himalaya are discussed. Temperatures and pressures increase dramatically up-structural section across the MCT Zone from biotite through garnet, staurolite and kyanite grade to sillimanite + muscovite, and decrease along the top of the stab beneath the ZSZ normal faults. In Zanskar, peak P-T conditions of the M1 kyanite-grade rocks are 550–680°C and 9.5–10.5kbar, and M2 sillimanite-grade gneisses were formed at 650–770°C and 4.5–7 kbar. The core of the High Himalayan Zone is a 30 km wide zone of sillimanite + K-feldspar-grade gneisses, migmatites and anatectic leucogranites with a right way-up isograd sequence above and an inverted sequence below. Thermal models of thrusting a hot slab over a cold slab and frictional heating along the MCT are not supported by the structural and thermobarometric data. Mechanical models of post-metamorphic structural disruption by folding and thrusting of a pre-existing, right way-up metamorphic sequence are compatible with structural and P-T data. Ductile shearing along the MCT Zone has structurally condensed the isograds, and final motion along the ZSZ postdated leucogranite crystallization (21.5-19.5 Ma; U-Pb monazite ages) and emplacement in the footwall. Crustal shortening and thickening, resulting in prograde metamorphism, lasted from the time of India-Asia collision at 54-50Ma until at least 30-25 Ma. Crustal melting is constrained at 20.8-19.5 Ma along the core of the stab. Late stage out-of-sequence thrusting within the High Himalayan Slab effectively maintained the crustal thickening process enabling P-T conditions to remain high for 10-5 Ma. Rapid exhumation between 21-18.5 Ma was accompanied by removal of 18–25 km of overburden by erosion at exhumation rates of 6–10 mm yr −1 . This early Miocene period of high exhumation rates, rapid erosion and exhumation of rocks buried at τ25 km depth is interpreted to indicate the uplift of high mountains and erosion of deep valleys, probably with high precipitation during that time.

Gaze behavior offers valuable insights into attention and cognition. However, technological limitations have prevented the examination of animals' gaze behavior in natural, information-rich contexts; for example, during navigation through complex environments. Therefore, we developed a lightweight custom-made logger equipped with an inertial measurement unit (IMU) and GPS to simultaneously track the head movements and flight trajectories of free-flying homing pigeons. Pigeons have a limited range of eye movement, and their eye moves in coordination with their head in a saccadic manner (similar to primate eye saccades). This allows head movement to act as a proxy for visual scanning behavior. Our IMU sensor recorded the 3D movement of the birds' heads in high resolution, allowing us to reliably detect distinct saccade signals. The birds moved their head far more than necessary for maneuvering flight, suggesting that they actively scanned the environment. This movement was predominantly horizontal (yaw) and sideways (roll), allowing them to scan the environment with their lateral visual field. They decreased their head movement when they flew solo over prominent landmarks (major roads and a railway line) and also when they flew in pairs (especially when flying side by side, with the partner maintained in their lateral visual field). Thus, a decrease in head movement indicates a change in birds' focus of attention. We conclude that pigeons use their head gaze in a task-related manner and that tracking flying birds' head movement is a promising method for examining their visual attention during natural tasks.

Flapping flight is the most energetically demanding form of sustained forwards locomotion that vertebrates perform. Flock dynamics therefore have significant implications for energy expenditure. Despite this, no studies have quantified the biomechanical consequences of flying in a cluster flock or pair relative to flying solo. Here, we compared the flight characteristics of homing pigeons ( Columba livia ) flying solo and in pairs released from a site 7 km from home, using high-precision 5 Hz global positioning system (GPS) and 200 Hz tri-axial accelerometer bio-loggers. As expected, paired individuals benefitted from improved homing route accuracy, which reduced flight distance by 7% and time by 9%. However, realising these navigational gains involved substantial changes in flight kinematics and energetics. Both individuals in a pair increased their wingbeat frequency by 18% by decreasing the duration of their upstroke. This sharp increase in wingbeat frequency caused just a 3% increase in airspeed but reduced the oscillatory displacement of the body by 22%, which we hypothesise relates to an increased requirement for visual stability and manoeuvrability when flying in a flock or pair. The combination of the increase in airspeed and a higher wingbeat frequency would result in a minimum 2.2% increase in the total aerodynamic power requirements if the wingbeats were fully optimised. Overall, the enhanced navigational performance will offset any additional energetic costs as long as the metabolic power requirements are not increased above 9%. Our results demonstrate that the increases in wingbeat frequency when flying together have previously been underestimated by an order of magnitude and force reinterpretation of their mechanistic origin. We show that, for pigeons flying in pairs, two heads are better than one but keeping a steady head necessitates energetically costly kinematics.

Japanese encephalitis virus (JEV) appears nearly annually in the Torres Strait in far northern Queensland, Australia, and is a threat to invade the Australian mainland. Surveillance has involved the use of sentinel pigs that develop detectable viremias and antibody titers to JEV. However, pigs are amplifying hosts for JEV, and thus pose a health risk to the public and to pig handlers who bleed the pigs. A remote mosquito trap system would not have these risks. We report on trials using a remote mosquito trap system for the surveillance of JEV in the Torres Strait. The Mosquito Magnet (MM) Pro, MM Liberty Plus, and a novel updraft trap, the NAQS Mozzie Trap, were run at Badu and Moa islands in the Torres Strait and at Bamaga in the northern Cape York Peninsula from 2002-2005. TaqMan real-time polymerase chain reaction (PCR) was used to detect JEV nucleic acid in weekly mosquito collections. Sentinel pigs located at Badu were also bled and the serum processed by reverse transcriptase (RT)-PCR for JEV antigen and enzyme-linked immunosorbent assay (ELISA) for anti-JEV antibodies. JEV was detected in mosquito collections each year but not in each trap. No JEV was detected in trapped mosquitoes before detection in sentinel pigs. The mosquito trap system cost ca. AU$10,000 per site, about AU$5,000 less than a pig-based system. However, trap failures caused by mosquito-clogged motors, electrical faults, and blocked gas lines reduced the efficacy of some mosquito traps. Nonetheless, a remote mosquito trap system, employing stand alone traps and PCR for viral antigen detection, can be a safe, economical way to detect arbovirus activity in remote areas.