LAUSR

The ability to track animal movements has been integral for answering the most basic and complex of ecological questions. Tracking devices have evolved over time, starting with very high frequency (VHF) units that require field personnel to physically locate and track animals, to transmitters that require communication with cellular towers and cellular phones, to platform terminal transmitters, which provide locations to researchers via a remote, satellite-enabled internet download. As a result of technological advances including reduced overall mass of the device, prolonged battery life, and improved aerodynamic design, tracking devices are now deployed on smaller animals. However, despite these technological improvements, the ratio of transmitter mass to body mass remains an issue when selecting a tracking device with sufficient battery life for small raptors. In the United States, to minimize the potential for negative impacts to tracked birds, researchers typically do not exceed 3% of the body mass of the bird with tracking equipment and the associated harness. Tracking devices for large raptors that are below maximum mass thresholds and have sufficient battery life have long been available for use when research objectives include documenting spatial movements. However, for meeting similar objectives in the study of small raptors, there are few tracking devices that meet these same mass ratio and battery requirements. Low-mass tracking options do exist but they are typically VHF, and battery life is limited to a few weeks. Small VHF transmitters are satisfactory for answering questions over a brief time period, such as seasonal survival (Roth et al. 2005) or to facilitate observations on behavior (Roth and Lima 2007). For researchers wishing to track small migrant raptors throughout their annual cycle, options are still limited. As part of a research project focused on American Kestrels (Falco sparverius; hereafter ‘‘kestrel’’) in northwestern Wyoming (Craighead Beringia South 2018), we wanted to identify nonbreeding-season locations for kestrels nesting in Teton County, Wyoming (43851.216 N, 110837.884W). Breeding Bird Survey data show a significant decline of breeding kestrels in Wyoming from 1966 to 2015 (period trend1⁄4 –1.01, 95% CI1⁄4 –1.87; –0.10) and in the Northern Rockies Bird Conservation Region (period trend 1⁄4 –1.88, 95% CI 1⁄4 –2.53, –1.21), which includes Teton County (Sauer et al. 2017). Our objectives were to identify the distance kestrels travelled on migration, to identify where kestrels spent the nonbreeding season, and to estimate kestrel winter home-range sizes. Kestrels nesting in Teton County are migratory, but prior to our study, nonbreeding-season locations were unknown. We trapped kestrels during the 2015 and 2017 nesting seasons using bal-chatri traps (Berger and Mueller 1959), mist nets with a decoy owl (Steenhof et al. 1994), and by hand in nest boxes. Male kestrels typically weigh between 80 and 143 g, whereas females typically weigh between 86 and 165 g (Smallwood and Bird 2002); therefore, we needed a device and harness material that weighed between 2.4 and 5.0 g, and that could be programmed to collect locations a few months after deployment. We used PinPoint 10 Global Positioning System (GPS) data loggers (hereafter referred to as ‘‘tags’’; Lotek Wireless Inc., Newmarket, Ontario, Canada), which weighed 1.7 6 0.2 g after they were prepared for use on kestrels. We used 2.5mm Teflon ribbon for the harness material and attached the transmitters using a backpack-style attachment technique (Buehler et al. 1995) with a leather breast patch and brass ferrules to secure the GPS tag in place. The mass of the harness, breast patch, and brass ferrules was 1.5 g before trimming to fit each captured bird, for a total mass with the tag of 3.0–3.4 g. We measured the mass of all kestrels prior to tag deployment to ensure they met the mass requirements to carry the tags. The PinPoint GPS tags stored locations on the tracking device. Therefore, retrapping tagged individuals was necessary to retrieve the movement data. To relocate tagged individuals, we searched territories where kestrels were captured, and we searched surrounding territories during the 2016–2018 breeding seasons. After we downloaded the data, we used 1 Email address: [email protected]