Geology topics

S. Balachandran

Publications and source records attributed to S. Balachandran.

4 recordsLinked to original sources

USGS2017

High altitude flights by ruddy shelduck Tadorna ferruginea during trans-Himalayan migrations

Birds that migrate across high altitude mountain ranges are faced with the challenge of maintaining vigorous exercise in environments with limited oxygen. Ruddy shelducks are known to use wintering grounds south of the Tibetan Plateau at sea level and breeding grounds north of Himalayan mountain range. Therefore, it is likely these shelducks are preforming high altitude migrations. In this study we analyse satellite telemetry data collected from 15 ruddy shelduck from two populations wintering south of the Tibetan Plateau from 2007 to 2011. During north and south migrations ruddy shelduck travelled 1481 km (range 548–2671 km) and 1238 km (range 548–2689 km) respectively. We find mean maximum altitudes of birds in flight reached 5590 m (range of means 4755–6800 m) and mean maximum climb rates of 0.45 m s –1 (range 0.23–0.74 m s –1 ). The ruddy shelduck is therefore an extreme high altitude migrant that has likely evolved a range of physiological adaptations in order to complete their migrations.

Journal of Avian Biology↗

USGS2015

A new method for discovering behavior patterns among animal movements

Advanced satellite tracking technologies enable biologists to track animal movements at fine spatial and temporal scales. The resultant data present opportunities and challenges for understanding animal behavioral mechanisms. In this paper, we develop a new method to elucidate animal movement patterns from tracking data. Here, we propose the notion of continuous behavior patterns as a concise representation of popular migration routes and underlying sequential behaviors during migration. Each stage in the pattern is characterized in terms of space (i.e., the places traversed during movements) and time (i.e. the time spent in those places); that is, the behavioral state corresponding to a stage is inferred according to the spatiotemporal and sequential context. Hence, the pattern may be interpreted predictably. We develop a candidate generation and refinement framework to derive all continuous behavior patterns from raw trajectories. In the framework, we first define the representative spots to denote the underlying potential behavioral states that are extracted from individual trajectories according to the similarity of relaxed continuous locations in certain distinct time intervals. We determine the common behaviors of multiple individuals according to the spatiotemporal proximity of representative spots and apply a projection-based extension approach to generate candidate sequential behavior sequences as candidate patterns. Finally, the candidate generation procedure is combined with a refinement procedure to derive continuous behavior patterns. We apply an ordered processing strategy to accelerate candidate refinement. The proposed patterns and discovery framework are evaluated through conceptual experiments on both real GPS-tracking and large synthetic datasets.

International Journal of Geographical Information ↗

USGS2013

The paradox of extreme high-altitude migration in bar-headed geese Anser indicus

Bar-headed geese are renowned for migratory flights at extremely high altitudes over the world's tallest mountains, the Himalayas, where partial pressure of oxygen is dramatically reduced while flight costs, in terms of rate of oxygen consumption, are greatly increased. Such a mismatch is paradoxical, and it is not clear why geese might fly higher than is absolutely necessary. In addition, direct empirical measurements of high-altitude flight are lacking. We test whether migrating bar-headed geese actually minimize flight altitude and make use of favourable winds to reduce flight costs. By tracking 91 geese, we show that these birds typically travel through the valleys of the Himalayas and not over the summits. We report maximum flight altitudes of 7290 m and 6540 m for southbound and northbound geese, respectively, but with 95 per cent of locations received from less than 5489 m. Geese travelled along a route that was 112 km longer than the great circle (shortest distance) route, with transit ground speeds suggesting that they rarely profited from tailwinds. Bar-headed geese from these eastern populations generally travel only as high as the terrain beneath them dictates and rarely in profitable winds. Nevertheless, their migration represents an enormous challenge in conditions where humans and other mammals are only able to operate at levels well below their sea-level maxima.

Proceedings of the Royal Society B↗

USGS2011

The trans-Himalayan flights of bar-headed geese (Anser indicus)

Birds that fly over mountain barriers must be capable of meeting the increased energetic cost of climbing in low-density air, even though less oxygen may be available to support their metabolism. This challenge is magnified by the reduction in maximum sustained climbing rates in large birds. Bar-headed geese ( Anser indicus ) make one of the highest and most iconic transmountain migrations in the world. We show that those populations of geese that winter at sea level in India are capable of passing over the Himalayas in 1 d, typically climbing between 4,000 and 6,000 m in 7–8 h. Surprisingly, these birds do not rely on the assistance of upslope tailwinds that usually occur during the day and can support minimum climb rates of 0.8–2.2 km·h −1 , even in the relative stillness of the night. They appear to strategically avoid higher speed winds during the afternoon, thus maximizing safety and control during flight. It would seem, therefore, that bar-headed geese are capable of sustained climbing flight over the passes of the Himalaya under their own aerobic power.

Himalayas↗