The dynamics and energetics of hunting in the cheetah

A cheetah can sprint at 65 mph, making it the fastest land animal by far - elite racing greyhounds and racehorses (and zoo cheetahs chasing a lure) only manage 40 mph. Cheetahs are also highly manoeuvrable, allowing them to catch even the most agile of prey. But what is it about the cheetah that enables it to do this? At the moment we simply don't know. The highly cited 'cheetah top speed' comes from just three measured runs by one individual cheetah in 1965. To find out, we need to measure the performance of cheetah during hunting in the wild - the only time that peak speed and manoeuvring are achieved. However, whilst cheetahs are believed to hunt almost daily, hunting is hard to observe directly.

We plan to fit wild cheetah with collars equipped with unique technology that we have developed especially for this type of work. Each collar contains a special high accuracy GPS to pinpoint location and speed along with acceleration sensors, miniature gyroscopes, a compass and a tiny low power computer. The sensors can detect the cheetah's exact footfall pattern - how many strides and when each foot is on the ground. The collars monitor where the cheetah is and what it is doing - resting, walking, and most importantly, hunting and only collects detailed information when the cheetah is moving quickly (logging data up to 300 times per second). From the data, we can reconstruct the exact movement of the cheetah during a hunt. At other times, regular position updates and behaviour are recorded and the integrated solar panels recharge the batteries. The collar data is stored for later download via an integral radio-link.

We aim to film cheetah hunts from the ground and air using a high resolution high speed video camera on a mount that automatically points at a GPS derived location. The collars tell the mount where to point the camera via a radio link and the camera tracks the cheetah's movement (we actually aim the camera just ahead of the cheetah to see the prey as well). Because the cameras and collars are exactly synchronised in time, we can examine the collar data and video footage of the hunt step by step, including the terrain, obstacles and interaction with the prey. We will use a combination of statistical analysis techniques and computer modelling to examine limits and aids to performance like grip, muscle power requirements, turn initiation and tail movement.
The key to explaining the cheetah's speed and agility may lie in its muscles. Therefore we will study how quickly and powerfully cheetah muscle fibres can contract (by studying miniscule samples taken using a fine biopsy needle) to find out whether its properties differ from those of other cats or other elite performance animals such as humans, racehorses or greyhounds.

This project will be the first to record such detailed data on wild cheetahs 24 hours a day. As well as enabling us to find out how cheetahs achieve their speed and manoeuvrability, these data will also enable us to explore - in unprecedented detail - cheetah behaviour, home range use and territory size, which is necessary to develop management strategies for the cheetah's long-term survival. The muscle studies may contribute new information for scientists working to develop new treatments for muscle problems in humans and animals. Our results and data collection techniques will provide new tools for scientists working not only on biomechanics, behaviour and ecology, but also those wanting to understand the spread of disease in wild populations. We expect our work also to be of interest to engineers, as understanding the cheetah's design may contribute to the design of lighter weight, faster legged robots and the military too, as the technology and analytical methods could be used for tracking soldiers on the battlefield. Finally, we hope our work will engage the public, showcasing how maths, engineering, and biology can help us unravel nature's secrets and inspire scientists of the future.

Cheetahs are highly specialised pursuit predators, with a top speed of around 65 mph. In contrast, the racing greyhound and racehorse only achieve 40 mph. Comparison of zoo cheetahs and racing greyhounds at 30-40 mph show they are remarkably convergent in their anatomy and biomechanics. We propose to explore the high speed locomotion of the cheetah by recording the dynamics of hunting in wild cheetahs using collar-mounted high-accuracy GPS and inertial measurement units (GPS_IMU) developed in our lab. The collars comprise an ultra-low-power Texas Instruments MSP430 microcontroller, running highly power-optimised software written in-house. Sensors on the logger include a 5Hz raw data GPS receiver, a 3-axis MEMS accelerometer, 3 axis MEMS gyroscope, and a 3 axis magnetometer. The data are fused using a tuned Kalman filter to provide acceleration, velocity and position, angular velocity, orientation heading and track. We will use the data we collect to build and test models of limits to speed, acceleration and manoeuvring and examine mechanical aspects of cheetah anatomy and locomotion that may account for its extreme hunting strategy. An important aspect of this research is the dynamics and energetics of the cheetah's muscle. We propose to examine muscle contractile characteristics on skinned fibres from needle biopsies and intact fibres from cheetahs that are admitted as hospital cases. We will combine the apparent power and force limits to locomotion with measurements of muscle power, force and activation to explore limits to locomotor performance, particularly speed, acceleration, manoeuvring and turn initiation. Further, we will use our collar technology to pilot measurements of behaviour and fine-grained location data to inform the statistical design of future projects on how cheetah and other animals interact with each other and their environment. The work is of relevance to understanding extreme muscle physiology, limits to locomotor dynamics and ecology.

We have identified three key areas in which our project could have societal and economic impact. Our plans to achieve these are described in Pathways to Impact.
1. Inspiring future scientists
We see great potential to use this project to engage with young scientists, from school age to early career graduates. For example, we will be able to use the appeal of the cheetah and the very simple question our project seeks to address - "How do they [cheetahs] do that?" - to inspire young scientists to explore biomechanics as a subject and science as a career choice.
2. Public understanding of science
Our previous work measuring speed and gait of cheetahs at ZSL Whipsnade Zoo attracted considerable media interest (front page of BBC website and prime-time TV and radio). We expect the proposed project to similarly engage public interest given the British public's appetite for television programmes about large carnivores on the African continent (eg "Big Cat Diary", BBC). AW contributed to a recent (Sept 2011) episode of Channel 4's "Inside Nature's Giants" which was seen by 1.5-2 million viewers (leading the dissection of a racehorse and explaining how the animal is designed and built for speed). Windfall Films, who make the Inside Nature's Giants series, have expressed interest in filming this research for a mainstream TV channel. Such coverage would provide an opportunity to reveal to a wide public audience how basic scientific research is undertaken in the field, and at the same time increase public awareness of the unique attributes of the threatened cheetah.
Athletes and sports physiologists want to know how a human could run faster, and are likely to be very interested to know why cheetahs are so much faster than any other animal. What we learn from the cheetah may have direct relevance to human athletes' training and coaching regimes. We have active links with UK athletics through our EPSRC Sensing for Sport and Managed Exercise project and the PI is a regular speaker at the London Marathon Sports Medicine Conference, providing direct routes for engaging with sports scientists, athletes and coaches. Potential for impact on athletics will also appeal to the popular media and will give us an opportunity to compare this animal study to human physiology and performance in a way people can relate to.
3. Engineering of bio-inspired legged robots.
Understanding how cheetahs elicit their top speed and manoeuvring performance can be used to inform the design and control of legged robots. These have military and civilian applications (eg to survey and sample disaster areas or regions experiencing nuclear fallout). The challenge remains to develop legged robots and prosthetics that can move with speed, stability and economy over uneven terrain. Quantifying the body kinematics of cheetahs during peak performance may provide new insights for solving this challenge. Through our ongoing collaborations with technology companies Forsberg Services and Toumaz Technology in the UK, with whom we have BBSRC CASE studentships, and US company Boston Dynamics, world leading developer of legged robots (with whom we have a US Defence Agency research grant) the mechanical principles of cheetah locomotion will be directly translated to robotics applications (as in the "Big Dog" robot). Working with the RVC technology transfer team we will protect intellectual property with commercial potential; we have successfully sold our GPS-IMU loggers to the UK defence industry.

In addition, we have identified a further area of impact which could bring major benefits for cheetah conservation and survival. The results of our behaviour study will be reported to the IUCN Species Survival Commission so that this science can directly influence policy at government level, inform future work and contribute technical and specialist knowledge for the development of conservation guidelines and management practices for wild cheetah populations throughout Africa.