Evaluation of physiological stress in free-ranging bears: current knowledge and future directions

Closing the air gap: the use of drones for studying wildlife ecophysiology

Techniques for non-invasive sampling of ecophysiological data in wild animals have been developed in response to challenges associated with studying captive animals or using invasive methods. Of these, drones, also known as Unoccupied Aerial Vehicles (UAVs), and their associated sensors, have emerged as a promising tool in the ecophysiology toolkit. In this review, we synthesise research in a scoping review on the use of drones for studying wildlife ecophysiology using the PRISMA-SCr checklist and identify where efforts have been focused and where knowledge gaps remain. We use these results to explore current best practices and challenges and provide recommendations for future use. In 136 studies published since 2010, drones aided studies on wild animal body condition and morphometrics, kinematics and biomechanics, bioenergetics, and wildlife health (e.g. microbiomes, endocrinology, and disease) in both aquatic and terrestrial environments. Focal taxa are biased towards marine mammals, particularly cetaceans. While conducted globally, research is primarily led by institutions based in North America, Oceania, and Europe. The use of drones to obtain body condition and morphometric data through standard colour sensors and single camera photogrammetry predominates. Techniques such as video tracking and thermal imaging have also allowed insights into other aspects of wildlife ecophysiology, particularly when combined with external sampling techniques such as biologgers. While most studies have used commercially available multirotor platforms and standard colour sensors, the modification of drones to collect samples, and integration with external sampling techniques, have allowed multidisciplinary studies to integrate a suite of remote sensing methods more fully. We outline how technological advances for drones will play a key role in the delivery of both novel and improved wildlife ecophysiological data. We recommend that researchers prepare for the influx of drone-assisted advancements in wildlife ecophysiology through multidisciplinary and cross-institutional collaborations. We describe best practices to diversify across species and environments and use current data sources and technologies for more comprehensive results.

Blood cortisol and faecal cortisol metabolite concentrations following an ACTH challenge in unanaesthetized brown bears (Ursus arctos)

Faecal cortisol metabolites (FCMs) are increasingly used to index physiological stress in wildlife. Cortisol and other stress hormones act to mobilize glucose, providing energy for the organism to respond to environmental perturbations. Cortisol, the predominant glucocorticoid (GC) in most mammals, is metabolized by the liver and excreted as FCMs. For FCMs to serve as a meaningful physiological index of stress in brown bears (Ursus arctos), we sought to quantify the relationship between blood cortisol and FCM concentrations. Consequently, we conducted an adrenocorticotropic hormone (ACTH) challenge on nine unanaesthetized captive brown bears at the Washington State University Bear Research, Education, and Conservation Center. We collected 10 ml of blood at 0, 3, 6, 24, 48 and 72 h post-injection to measure changes in blood cortisol concentrations. Faecal samples were collected between 7:00 am and 8:00 pm from 24 h prior to injection through 72 h post ACTH challenge. We found that FCM concentration was positively correlated with blood cortisol concentrations and that peak blood cortisol concentrations occurred between 3 and 6 h following an ACTH challenge, whereas FCMs peaked between 10 and 27 h after injection.

Physiological differences between wild and captive animals: a century-old dilemma

Laboratory-based research dominates the fields of comparative physiology and biomechanics. The power of lab work has long been recognized by experimental biologists. For example, in 1932, Georgy Gause published an influential paper in Journal of Experimental Biology describing a series of clever lab experiments that provided the first empirical test of competitive exclusion theory, laying the foundation for a field that remains active today. At the time, Gause wrestled with the dilemma of conducting experiments in the lab or the field, ultimately deciding that progress could be best achieved by taking advantage of the high level of control offered by lab experiments. However, physiological experiments often yield different, and even contradictory, results when conducted in lab versus field settings. This is especially concerning in the Anthropocene, as standard laboratory techniques are increasingly relied upon to predict how wild animals will respond to environmental disturbances to inform decisions in conservation and management. In this Commentary, we discuss several hypothesized mechanisms that could explain disparities between experimental biology in the lab and in the field. We propose strategies for understanding why these differences occur and how we can use these results to improve our understanding of the physiology of wild animals. Nearly a century beyond Gause's work, we still know remarkably little about what makes captive animals different from wild ones. Discovering these mechanisms should be an important goal for experimental biologists in the future.