Main research topics

I am currently part of a team of researchers and technicians at the Royal Veterinary College (UK) that investigates the locomotion, hunting and habitat utilisation among large African carnivores and their prey (LOCATE). During my time at the RVC, I have also worked on human locomotion and bird flight.

I have previously worked at Darmstadt University of Technology (Germany) and Brown University (USA) with the focus on bird and bat flight.

Tracking collars and equipment development

Innovative tracking collars equipped with high-accuracy GPS and motion sensors are used to capture every detail of the animal’s movements in our studies. The collars were developed in house. They are capable of switching dynamically between different operational states, depending on the animal’s activity level. Therefore, combining the need for high sample rate data during high-speed locomotion events with the necessity to preserve battery life. We are constantly working on the improvement of the collar technology. We have recently incorporated sensors to record additional factors such as ambient temperature, solar gain, light levels and humidity and facilitated the use of dead reckoning in order to increase data resolution. Simultaneously, we develop new ways of analyzing collar data for gait analysis.

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Flight

Birds

The characteristic ‘V’ formation flight of birds has fascinated scientists for centuries. One of the main theories that has persisted to explain this distinctive V-formation is that birds are attempting to conserve energy by taking advantage of the upwash vortex fields created by the wings of the other birds within the flock. A fixed wing aerodynamic theory has traditionally been applied to understand V-formation flocking in birds, very much unlike that of the actual scenario of a flapping bird and wing. Previously, little consideration, either theoretically or empirically, has been possible concerning the effects of flapping on V-formation aerodynamics. Recent technological advances have now made it possible to explore factors of V-formation flapping flight for extended periods of time, in free-flying birds. Using high-frequency sampling GPS and accelerometer units, we collected data from two migratory flights of the critically endangered Waldrapp Ibis. This opportunity was made possible by human-led migrations taking place as part of a reintroduction scheme, whereby imprinted young ibis are taught to follow a microlight. These data allowed insight into aspects of V-formation flocking previously not possible, in particular the temporal and spatial wing-beat phasing of flock members during flapping V-formation flight.

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Ibises flying in formation (photo credit: Mark Unsöld)

Bats

Bats, as the only mammals capable of flight, occupy a vast variety of habitats and are with over 1200 different species the second largest group of mammals. They are ideal study subjects for one interested in the correlation between morphological differences and ecologically based flight requirements. Bat wings are much more flexible than those of birds and insects. Consequently, shape and camber of the wings are highly susceptible to applied aerodynamic and inertial forces, any change in shape in turn affects the force generation and so far it is widely unknown to what extent bats are able to actively control their wings.  I investigated the wake structure and wing kinematics of several different bat species by training them to fly in a wind tunnel over a range of speeds. The goal was to investigate variation in force generation and wing motion among individuals and species, and to tie these differences to the species’ morphological and ecological history.

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Terrestrial locomotion

Point mass models, gait transition and gait ontogeny in humans

Reductionist point mass models are useful in understanding the underlying mechanical principles of walking and running. However, investigating deviations from the point mass model can be equally insightful. I have explored the implications of small deviations from pure point mass models, the purpose of feet and the change in force generation and power in toddlers and small children with increasing age.

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Cheetah locomotion (ongoing)

Some of the cheetahs at the Ann van Dyk Cheetah Centre are used to people and have been trained to chase a lure to simulate their natural hunting behaviour. This enabled us to investigate turning performance and tail movement, take high-speed video and test collars.

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cheetah turning video

Energetics and hunting strategies in African wild dogs

The African Wild dog (Lycaon pictus) is often identified as the ultimate endurance hunter. Their hunting style has been described as running down prey over long distances with a high level of collaboration between the pack members until the prey is exhausted. This suggests that they represent one end on a spectrum of hunting styles with the opposite end occupied by the cheetah an extremely fast and maneuverable hunter. We collared a pack of six adult African Wild dogs with high resolution GPS/IMU collars and discovered that in their currently most common woodland habitat, while travelling considerable distances at preferred speeds, they did not capture prey after long chases or hunt collaboratively. Wild dogs are rather opportunistic in their hunting strategy, travelling through their habitat as a group with individuals chasing after chance encounters. When approaching a herd of impalas (their main prey) wild dogs chase after different prey mostly individually or as pairs, showing no synchronized approach focusing on only one prey. Chases are rather short and very fast, but acceleration, centre of mass power and turning (centripetal) acceleration are all lower than equivalent values for cheetahs. Lack in maneuverability and speed, compared to cheetahs, are compensated by multiple dogs hunting, larger distances travelled, consequently more prey encounters and more hunting attempts. To what extent hunting strategies in Wild Dogs are flexible and can be adapted to habitat and prey size has yet to be determined.

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Collared African wild dogs (photo credit: Julia Myatt)

Athletic performance and energetics in zebra, tsessebe and wildebeest (ongoing)

Zebra (Equus quagga), wildebeest (Connochaetes taurinus) and tsessebe (Damaliscus lunatus) are large African herbivores in the Okavango Delta ecosystem. Zebra and wildebeest are known for the ability to cover long distances and in some ecosystems seasonally migrate, while tsessebe are often described as the fastest antelope species. We collared eight members of each species with high resolution GPS/IMU collars to gain insight into their daily energy expenditure and the extent of their ranging and running performance. Our study animals are almost exclusively permanent residents of the study area, with the exception of two zebra that participated in the seasonal migration between the Delta and Makgadikgadi Pans National Park, the second longest known migration route. Resident zebra travel distances of up to 35 km per day on multiple occasions. All zebra frequently achieve speeds above 6 m/s, often multiple times per day with no diurnal pattern in when runs occurred. Energy expenditure is calculated from daily distances travelled, speed and size derived cost of transport. High speed running events are examined in regards of speed, acceleration and maneuverability (turning radius and centripetal acceleration).

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Physiological adaptations in zebra in the Boteti river region (ongoing)

The ranging of mammals living in arid environments is limited by their requirement to drink. Whilst Plain’s zebra usually drink daily, specific populations in arid regions of Botswana drink once every 3-5 days. This adaptation enables them to maximize the time spent in distal grazing grounds where forage is of better quality. Here we use force plates to determining water intake to enable evaluation of the physiology of these specialised zebra. This allows water balance of these specialised zebra to be modelled and with the goal to improve understanding of the population’s resilience in the face of increasing climatic variability.

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Biomechanics of predator prey interaction in four African mammals– Is it an arms race? (ongoing)

Carnivores hunt herbivores and herbivores evade carnivores. One facet of this, exemplified in the medium sized mammals of the African savannahs is pursuit predation. There is a strong selection pressure for both predator and prey to evolve to be ever faster and more maneuverable since hunt outcome and success rate are critical to survival. We focus on comparing athleticism during hunting in a large and a small wild pursuit predator, the lion (Panthera leo) and cheetah (Acinonyx jubatus) and their most common prey animal zebra (Equus quagga) and impala (Aepyceros melampus). We investigate muscle physiology and  whole body performance such as speed acceleration and turning performance. The studies are undertaken on free ranging wild animals in Botswana. Muscle measurements are made on skinned muscle fibres collected via biopsy during collaring events and locomotion (including hunting events) via collars of our own design that combine high rate inertial measurement (accelerometer, gyroscope and magnetometer) and high rate GPS measurements. The data show pairwise differences in performance that cannot be fully attributed to the inter species differences in muscle physiology. These data will be discussed in the light of the different ecological pressures the animals are subject to.

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Do thunderstorms determine where animals go? (ongoing)

At the end of the dry season water is a rare commodity in the Makgadikgadi. The rainy season starts with heavy thunderstorms and the question arises if animals move towards those storms and the water that comes with them. To answer this question we install lightning detection systems to track the storms and use the GPS collars on 20 zebra and 20 wildebeest that were collared in the Makgadikgadi.

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