## 4 Discussion  
This study evaluated the suitability of GNSS collars with Iridium satellite communication and paired VIT to detect calving time and location in the extensive beef production systems of northern Australia where no cellular network is available. To the best of our knowledge, this is the first study to use this technology to detect calving events in cattle and to compare two brands of commercially available birth alert systems. The study also provided new information about the movement patterns of animals around calving time in a large-scale cattle breeding operation. This information could help to improve animal production and welfare in extensive beef cattle industries. In this study, important features for detecting birth alerts included: the time and location of a birth or VIT expulsion within the shortest possible timeframe. The thresholds for triggering a birth alert were 50 and 60 min (Brand 1 and 2) of no activity; therefore, it was expected that a birth alert notification would be available as soon as possible after this time lapse using satellite communication. A key feature of birth alerts would be their ability to capture all true birth events, so that no missed or false alerts were received. Remote areas with difficult terrain, dense vegetation, and lack of infrastructure (e.g., electricity, office, internet) reduced accessibility, and therefore the ability to locate and observe cattle to understand losses. Using birth alert systems could provide vital information during the calving period to gain knowledge about calf mortality. However, only 27.6% of births were accurately identified, 41.4% were false alerts and 31.0% of births were missed on average for both brands. Therefore, these systems were unsuitable and inaccurate to reliably detect calving or find newborn calves in this environment. These poor results agree with previous findings using similar technology in elk, deer, and bighorn sheep [4; 14; 15; 30; 31]. Possible reasons for low accuracy of birth alert devices could include the following: (1) devices were not designed for long term deployment, (2) delays with connection and data transmission using satellite technology, (3) inappropriate thresholds for triggering alerts under these environmental conditions, (4) limitations of accessibility to the calving sites, and (5) other environmental conditions that may have affected cattle behavior around calving, such as the presence of wild dogs [32]. The length of time the VIT was inserted and that subsequently remained implanted was dependent on stage of pregnancy at the time of VIT insertion, which could not be predicted prior to clustering of  
Figure 7: Satellite image showing the tracks and fixes of three cows from Trial 1, one week each side of calving. White outline shows the boundary of the paddock. The eight true birth alerts are shown with their respective collars, as well as supplement and water points within the 33 km\({}^{2}\) paddock. the animals. Previous research demonstrated that the retention of VIT declined with time [10; 12; 13] and was evident in this study with a 70% early expulsion rate in Trial 2, where most VIT were expelled after approximately 3 months. Intrauterine devices are commonly used in cattle to deliver hormones to bring cattle into estrus using slow release devices [20]. These devices have similar design to the VIT used in this study and are generally implanted for 7 to 12 days [33]. The developers of the CIDR device stated that their product may not be suitable for intravaginal insertion for periods longer than four weeks [34], much less than the time frames used in this study. In a study with Japanese Black cows [16], VIT were only implanted seven days prior to calving, making the chance of early expulsion much lower than the present study. The availability of WIFI and having cattle in a housing environment also made communication with the sensor more reliable and timely compared to the present study.