Post provided by Christine Beardsworth
Tracking animal movements is important for informing conservation practices, but can present logistical hurdles, especially when trying to track smaller species with large GPS tags. Using existing technologies in new ways can help overcome these barriers and provide alternative approaches to the accurate tracking of a large number of relatively small species. In this blog post, Christine Beardsworth discusses the findings from the latter Methods in Ecology and Evolution Document “ATLAS Validation: a regional, high-performance tracking system”.
Tracking where animals go and when, is key to understanding how they affect and how they are affected by the environment. With this information, we can make predictions that aid conservation efforts and help scientists understand basic aspects of animal life.
Nowadays, there are many tracking systems available. Take GPS as an example. The same technology that helps people switch from A to B in a car can also be used to track where animals are going. However, lightweight GPS devices for small animals can be very expensive, which means that few animals can be monitored if a project is not well funded. Often, tracking devices also have to be taken from the animal to download the data, which can be problematic if a species is not easily caught. There is not yet a perfect system for all species, but technology is always advancing and great strides have been made in using radio transmitters to locate animals remotely.
Radio tracking is not new. Scientists have been manually tracking animals with hand antennas for decades and have estimated the location of animals through the triangle. Radio transmitters are cheap, easy, and long-lasting (even with transmissions every few seconds), however, finding each animal can be time consuming and can only give one or two locations per day, per individual.
Attempts have been made to automate this practice and ATLAS is one such system. ATLAS uses a number of receiving stations – each with its own antenna – to detect the arrival time of transmissions from ultra-high frequency radio transmitters. These transmitters (or labels, as they are often referred to) may weigh less than one gram, but the total weight of the label depends largely on the size of the battery used.
A new system on a regional scale: ATLAS
Since it was developed over the last decade by Ran Nathan (Hebrew University of Jerusalem) and Sivan Toledo (Tel Aviv University), along with colleagues at the Minerva Center for Motion Ecology, the use of ATLAS systems has expanded. There are currently 6 ATLAS systems operating worldwide and over 50 types have been labeled and tracked using a range of ATLAS receivers. In our paper, we use the largest of these systems – the Wadden Sea ATLAS system (or WATLAS, as we like to call it) – to categorize the accuracy and precision of ATLAS.
The Wadden Sea is an ideal location for this test as it is an interstitial area with little radio interference nearby. The mud flats – on which some of the receivers are built – offer a large uninterrupted area on the horizon, such as buildings or trees, that can block radio signals, so the “line of sight” between transmitters and receivers is largely limited. . from the curvature of the ground.
We tested the system using a combination of ‘stationary’ and ‘mobile’ tests, where the lead author, Christine, took with her an ATLAS tag and a GPS unit through the mud on predetermined roads to specific locations within the group. By comparing ATLAS and GPS locations, we could get an idea of the accuracy of the system. We found little difference (<10 m) between ATLAS and GPS location estimates, demonstrating that the system was quite reliable. We also used data that had been collected on labeled red nodes to determine how well the system worked for small coastal birds.
Shorezogj in the Wadden Sea
In addition to the technical aspects that make WATLAS an excellent model system, the Wadden Sea itself is a UNESCO World Heritage Site and a very important ecosystem that is home to millions of coastal birds. Many of these coastal birds overwinter here or on the scene during much longer global migrations. Our focus so far has been on tracking red knots, a migratory species of coastal bird that breeds in the Arctic. There are several subspecies of red node, including canutus subgroup, which stops briefly in the Wadden Sea, en route to West Africa for the winter, and islandica sub-species – which we study – that lies in the Wadden Sea during winter.
We focused our search around Griend Island and discovered that ATLAS was able to track red knots while they were in the mud. We also discovered that we tracked red nodes in flight, with trails across the western Wadden Sea where the nearest receiver stations were more than 15 km away. This means that the system can be very effective, even for small animals. This is good news for the co-author Evy Gobbens, which will use ATLAS during its doctorate to monitor the movement of five species of shorebirds, including the very small dunlin (~ 50 g). ATLAS will assist in its assessment of how these species may be affected by future sea level rise.
Biography of the main author
Christine Beardsworth is a postdoctoral researcher at NIOZ (Royal Netherlands Institute for Marine Research). She works with Allert Bijleveld to investigate the ecology of red node movement in the Wadden Sea and has a keen interest in individual-level factors influencing behavior.
You can read the full paper “ATLAS Validation: A Regional, High-Performance Tracking System”.