Quick Dips

Keeping a Close Eye on Deer

Knowing what pasture species to use to maximise production from deer means getting down to the grass roots level to understand grazing habits, and that has involved some stealth for AgResearch Grasslands scientist Dr Warren Hunt, who has been using video and audio surveillance methods in his studies of deer grazing behaviour.

Valuable information has been provided for the model Hunt is developing on deer-grazing systems, which predicts how intake, and hence growth, of deer is determined from the variables of pasture height, mass and strength. The model will simulate interactions between grazing deer and pasture, and indicate how these may best be managed to improve deer productivity.

"Previous studies have already highlighted that deer favour some higher quality pasture species over others and therefore grow better, a chicory and red clover combination being one example. But knowing exactly how different seasons, climate and management affect pasture and deer well-being helps us to determine recommendations for optimum pasture management," he explains.

This will be of enormous benefit to scientists who can use the model to accurately predict how different pasture species will perform on-farm, reducing the amount of time-consuming trial work. But to do this, they need precise information on the basics -- like how deer chew pasture.

To understand pasture intake, studies to look closely at the grazing characteristics of deer are needed. None of the methods used in the past by scientists, such as automatic recording devices attached to animals, or human observation, were suitable for determining grazing characteristics of reasonable numbers of undisturbed red deer grazing pasture. The development of video-audio surveillance was the best option for watching deer grazing under normal farming conditions.

"We couldn't sit and observe in the paddock without disturbing the deer and affecting their grazing, thereby altering the results. But the deer didn't notice recording equipment in their paddock, so that made monitoring easy," he says.

"It was crucial for developing the grazing model that the deer eating information was precise, which is why we had to go to such lengths to monitor and measure their grazing behaviour."

This newly developed technique allowed Hunt and his team to watch the real fundamental grazing behaviour. This meant measuring bite rates and bite mass by watching grazing to count bites, measure herbage mass removed by the bites, and measure the time taken to make those bites -- something only videoing and audio recording could monitor successfully. The techniques can even differentiate between grazing on short or tall pasture.

It's not widely known that animals graze at night as well as during the day, so infrared filming of an entire paddock at night gave the scientists 24 hour monitoring of grazing.

"This has now given us sound scientific methods for understanding grazing behaviour. Combine this with the pasture quality variables that affect deer growth and information about climate, and we are starting to build accurate predictions of how well deer will grow on a particular pasture over time," says Hunt.