Techlink :: Tech Practice :: Electronics

Techlink would like to thank Megan Rodden and Dave Ward for their contributions to this case study.

The days of sending people out to scan trees trying to estimate numbers of birds or search the forest floor counting deer poo may not be over but they've certainly been superseded. Radio Tracking Devices are increasingly being used to monitor numbers of animals, where they travel and how long they survive. Sirtrack, formed in 1986 and based in Havelock North, makes radio transmitters and receivers, which it supplies to markets in New Zealand and around the world.

A radio transmitter unit is placed on an animal (insect, bird or reptile). This unit transmits information back to the researcher about where the animal is, if the group is together and whether they are still alive.

Satellite technology has been used over the last fourteen years for tracking animals. However it is only in the last three years that Sirtrack has been building its own satellite transmitters. They are now interfacing transmitters with Global Positioning System (GPS). This means that the units can now transmit via satellite or store the information. The receivers are accurate to more or less 6 to 10 metres.

Sirtrack is a subsidiary of Landcare Research which was formed in 1992 when the government decided to abolish departments such as the Department of Scientific and Industrial Research and create Crown Research Institutes. The CRI are government owned companies with a focus on servicing the technology and innovation needs of important sectors of the economy.

When Sirtrack starting work in this area their first job was making transmitters for possums, and the small mammal market remains quite a significant one. The company moved on from possums to foxes and bigger creatures such as kangaroos and camels.

The transmitters are constructed and assembled in the company's headquarters in Havelock North. 80% of the packaging (what protects the transmitter) is done here. Some of this work is done by sub-contractors and some by people working from home.

COP Brief development

The transmitters need to be very sensitive to pass on all the information possible about the animal's condition eg whether it is still breathing. Obviously designing a unit which covers a large range is more useful to many researchers whose animal subjects may travel vast distances. One aspect which has had a lot of attention is making the units waterproof, as earlier versions were not always able to keep out water. In making units which can't be too big or may need to run for a long time there is also a requirement for a lower power output and Sirtrack puts its attention to this also. Some units are made with a stealth mode, where the unit is only transmitting at certain set time periods. Some researchers may need to track large numbers of their subjects so the receivers are made with a wide range of frequencies. They can monitor up to 200 channels and the users can reconfigure the receivers in the field if necessary.

Designing a transmitter

Often Sirtrack is designing a transmitter for a customer on the other side of the world. Once the customers have provided their specifications the staff consult books to find out in depth the habits of the animal and the terrain and weather of its territory.

Staff also need to think about how long the transmitters need to run plus the size and weight of the animal. Sirtrack has made transmitters for over 500 species. These have included transmitters for tiny animals such as 10g bats, giant weta and frogs. The smallest transmitter is .9 g and runs for thirty days. The largest equipment was designed for elephants and required a 3.5m collar.

The designer tries to keep to 20% of the weight of the animal. They use different types of collar materials. For example synthetic collars are used for kangaroos as these animals damage leather collars with their sharp claws.

When designing a collar they need to work out how to attach it depending on whether it's for a bird, a snake or a mammal. Some collars need to be especially designed so that eventually they will fall off the animal and be retrieved later.

Colour is important too as it can help a researcher identify which animal they are watching when there is a crowd. In one instance the colour of the collar made a fatal difference to the project. The white collars had been designed for Judas goats , enabling them to wear a transmitter to allow hunters to follow the herd. Unfortunately these particular goats were white as well and ended up being shot by the hunters, who could not distinguish the collars at a distance.

COP Outcome development and evaluation

Obviously it is difficult to trial the transmitters in the field when dealing with international customers. When the transmitter is being designed for a particularly difficult animal or environment the designer may make up a test model to send to the customer on a sale or return basis, depending on how it worked out. The trial model may be sent free of charge if there is the possibility of a big order.

Problems to be Overcome

As well as the challenge of designing appropriate transmitters there have sometimes been problems to overcome as well. Sometimes the design is wrong for the situation or the designer can underestimate what damage a particular animal can do to the product. There can be batch failures where the whole lot of the receivers have failed to completely do the job.

Tracking Lynx in Colorado, United States of America, proved a problem in 2000 when receivers started failing after 3 months instead of the expected 12. Sirtrack had won a contract to supply 50 satellite transmitters for a new lynx release programme. The transmitters would only be transmitting 12 hours a week. It turned out that in this environment the transmitters, which used lithium batteries, weren't running enough to prevent a preservation layer from forming, which resulted in no current coming through to power the units. Sirtrack replaced all the recovered transmitters and the Colorado researchers have since bought another 50 VHF and satellite receivers.

Challenges from the environment

Each contract brings its own challenges in designing the transmitter. In low temperatures the capacity of the batteries is reduced so people working in an arctic environment understand they will only have 50% radio capacity. In the tropics of Northern Queensland the collars can't be made of leather as the hot, wet environment causes them to rot.

The Department of Conservation (DOC) is a major New Zealand customer. They use transmitters on endangered species plus other wildlife. (Some groups of native birds may wear a transmitter whereas in the small population of kakapo, each bird wears a transmitter).

Transmitters are also used on pests such as possums, ferrets, stoats and weasels. These introduced animals have proven very destructive to our native species as they compete for food, destroy habitat and eat various birds and insects. The transmitters are used to determine the home range size of a particular species in an area, how frequently DOC needs to set traps or how densely it needs to lay poison. With transmitters they can tell how many animals have died and work out what percentage of the area population this would be.

A significant part of Sirtrack's work is repacking batteries in transmitters. Some animals are difficult to recapture to check or replace the battery but most are recovered. The equipment is pretty robust so generally breakage is not a problem. The transmitter is able to sense if the animal dies. Recovery of the unit will then give information on where and when the animal died.