The comprehensive study of organisms is often hindered by the difficulty of consistently capturing, detecting, and tracking all life stages and age classes. This challenge is particularly pronounced for aquatic amphibians such as Siren intermedia (lesser siren), which can aestivate underground in dry burrows during extended droughts. In addition, obtaining year-round data on the habitat use, occupancy, and movement ecology of S. intermedia is notably difficult due to their cryptic nature, mobility, aestivation behaviors, trap-shy habits, and the impracticality of outfitting hatchlings and small juveniles with telemetry devices like subcutaneous Passive Integrated Transponder (PIT) tags. Moreover, there is the lack of a non-physical method to distinguish retained tags from those that have been dropped. In this study, we developed a novel indicator to assess the field retention status of PIT tags inserted into the tail tissue of S. intermedia. This was achieved by analyzing individual spatial redetection patterns of 8- and 12-mm PIT tags inserted into juveniles and adults, respectively, over 2 years in a remnant Cypress–Tupelo swamp wetland complex in southern Illinois, using systematic dipnetting, trapping, and PIT scanning telemetry surveys. Tags were considered dropped if the average distance between subsequent scanned PIT detections after the first redetection was ≤ 5 m and if the distance between the second detection and final redetection location was also ≤ 5 m. We then examined PIT tag retention in relation to initial body size and marking parameters. Ultimately, 29% of the 8-mm PIT tags initially injected into juveniles with tail lengths (Tail) 46–84 mm were redetected at least once. Using our spatial–temporal PIT telemetry indicator, we found that 45% of the redetected PIT tags had been dropped by juveniles. In contrast, all three of the 12-mm tagged adults were redetected at least once, with movement patterns indicative of tag retention. Our findings suggest that 8-mm PIT tags are likely to be expelled from juvenile S. intermedia with a mean ± standard deviation (SD) Tail of 50.2 ± 2.8 mm. This study underscores the importance of determining appropriate size requirements and cutoffs for effective telemetry device application across different age classes of a species.

BackgroundSeabirds like penguins and petrels, living in Antarctic and sub-Antarctic regions, often feed hundreds or even thousands of kilometers away from the islands where they breed. They therefore adapted to endure prolonged fasting during egg incubation, enabling their partner to undertake foraging trips that can last up to two weeks. Aside from accumulating and consuming fat reserves, it is unclear whether seabirds have developed further adaptations to extended fasting periods. This lack of knowledge is in part due to their remote nesting location and their extreme sensitivity to manipulation. To overcome this lack of knowledge, we developed a non-invasive device to record the heart rate (HR) of burrow-nesting blue petrels (Halobaena caerulea) during egg incubation. For that, we encapsulated a small-size logger in a dummy egg to record electrocardiograms (ECGs) through the featherless incubation patch of the birds.ResultsThe blue petrels’ HR (208 ± 15 beats per min [bpm]; n = 6) that we recorded during egg incubation was slower than the HR predicted by two different allometric functions regressing HR against body mass (242 and 250 bpm). Blue petrels’ HR also presented cyclical variation correlated to respiration, resembling the physiological Respiratory Sinus Arrhythmia (RSA) described in humans and other species, and that is mainly modulated by the vagal nerve. Moreover, the basal HR of incubating blue petrels increased about every minute during egg movements that presumably reflect egg turning, important for embryo survival and development. During these events, blue petrels’ HR increased up to a maximum of 296 ± 27 bpm for 18 ± 2 s (n = 6). We estimated that those egg movements increased energy expenditure (EE) by 8.4 ± 1.3%, which is approximately 10 times less than the energy increase induced by the disturbance linked with the removal of the dummy egg at the end of the experiment. Interestingly, we noticed that the beginning of HR increase preceded egg movements by 4.3 ± 0.9 s (n = 6), as if birds needed to gradually increase their metabolism to achieve the following action. As well, blue petrels needed 9.1 ± 1.3 s (n = 6) to recover basal levels of HR after the end of egg movements.ConclusionWe recorded for the first time ECGs, HR and RSA in blue petrels in a completely non-invasive way. This allowed us to observe (1) slow basal HR during egg incubation, which could save energy for prolonged fasting and (2) temporal HR increase, possibly necessary to reposition the egg for proper embryonic development.

BackgroundTo reduce heat loss underwater, marine mammals cover their bodies with insulation. Cetaceans in particular rely solely on blubber for insulation which has low conductivity. Blubber establishes a great thermal gradient between the warmer body core and cooler body surface, reducing heat transfer to the environment. A temperature gradient within the blubber determines the conductive heat transfer from the body trunk, where conduction and convection are the primary heat transfer mechanisms in cetaceans. Therefore, measuring the temperature at the innermost part of the blubber, i.e., the temperature at the muscle–blubber interface (Tmbi), can enhance our understanding of thermoregulatory mechanisms in cetaceans. In thermoregulation, activity-induced heat produced by increased muscle metabolism is another factor that plays an important role, however, the effects of activity on Tmbi have not been investigated in cetaceans. To assess this relationship in free-swimming cetaceans, we measured Tmbi and activity levels in a captive Risso’s dolphin (Grampus griseus) using an implantable biologging device.ResultsTmbi and activity data were analyzed for 11 days. The average Tmbi was 35.1 ± 0.6 ºC and the temperature gradient between Tmbi and the water temperature was 13.0 ± 0.7 ºC. Tmbi was higher during the daytime and lower in the early morning. The variation in Tmbi was best explained by both the activity levels and time of day. Tmbi did not simply increase with activity levels; it appeared to remain relatively constant at most activity levels. However, Tmbi appeared to decrease when the animal was inactive and increase when it was intensely active.ConclusionOur results provide important insights into how a dolphin regulates its body temperature underwater. Thermal insulation by blubber and heat production by activity were suggested to play important roles in thermoregulation. Whole-body heat dissipation might be used to regulate temperature increases when heat production is excessive due to intense activity. During inactive periods, decreasing temperature gradient may help reduce heat loss from the body.

BackgroundThe advent of telemetry has revolutionized wildlife research in recent decades. For telemetry to be effective, transmitting devices must remain attached to study animals throughout a period of interest and without impacting pertinent behaviors. Surgical implantation remains the most common method used to attach transmitters to snakes, but concerns about the effects of transmitter implantation on snake health and behavior have motivated many researchers to opt for external transmitter attachments. Despite the increasing use and diversification of external transmitter attachment techniques in snake research, to date there have been no comprehensive reviews examining the methods, efficacies, and adverse impacts reported in the literature. We therefore conducted a systematic review of past research involving external attachment of transmitters on wild snakes. We extracted data from relevant studies to determine whether and how snake traits and transmitter attachment details correlated with efficacy and likelihood of adverse effects.ResultsThe 54 cases that met inclusion criteria covered 33 species and 3 families. External attachment was biased toward smaller-bodied snakes (median = 186 g), although larger snakes had longer retention durations. Adverse impacts were reported in 37% of studies (n = 20), and included altered behavior and movement, skin wounds at the attachment site, and death. Smaller snakes were more likely to exhibit adverse impacts from attached transmitters. Except for caudal attachments in rattlesnakes, attachment method did not have a significant effect on attachment duration. However, attachment method did influence the probability of causing adverse effects, with glue being the most likely to cause negative impacts.ConclusionsExternally attaching transmitters to snakes is an increasingly popular alternative to surgical implantation. To provide guidance to researchers considering this approach, we conclude our systematic review with recommendations for attaching external transmitters to snakes. Actions such as minimizing transmitter weight and protrusion, using shorter and stiffer antennas, and using flexible adhesives may help to avoid commonly reported problems. We encourage more consistency in reporting methodological details and results pertaining to efficacy and animal welfare.

Small- to medium-sized shorebirds (< 200 g) can be particularly difficult to track with electronic devices due to their small size and long-distance migrations which place restrictions on device weight and size. A lack of comparative information on suitable tracking devices makes selecting the most appropriate technology time consuming and complex and can result in duplication of effort for each research project. The purpose of this paper is to address this issue by presenting a review of the scientific literature and commercially available devices to help inform device selection as well as options for attachment. The ideal device for tracking small to medium migratory shorebirds would be light weight (< 5% of a bird bodyweight), flat in profile, durable, have high battery longevity, remote data download, easy to attach from a bird welfare perspective, high spatiotemporal resolution and would be low in cost (so that a large enough sample size can be obtained). This ideal device does not yet exist due to the limitations on the weight of the power supply necessary to obtain frequent, high resolution location fixes over long time periods. As a result, the current choice of device depends on the purpose of the study. Platform Transmitter Terminal (PTT) doppler devices are suitable for tracking long distance movement due to their smaller size and lighter weight (around 2 g), but produce lower resolution location data and are expensive. For tracking smaller-scale movements (i.e., tens of kilometres), Global Positioning System (GPS) devices are more suitable, because they produce higher-resolution location data and are often more cost effective but tend to be heavier. Other device options for obtaining movement data include radio telemetry and light-level geolocators, which are generally lighter and cheaper than GPS or Doppler devices but require more effort to retrieve data and often produce lower resolution location data. Attachment methods and materials vary, but the most suitable is usually leg loop harnesses made with soft materials that are likely to degrade (e.g., elastic). Device type and harness design need to be carefully chosen to minimize potential impacts on the animal.

BackgroundAcoustic telemetry is an important tool to study the movement of aquatic animals. However, studies have focussed on particular groups of easily tagged species. The development of effective tagging methods for ecologically important benthic species, such as sea stars, remains a challenge due to autotomy and their remarkable capacity to expel any foreign material. We tested three methods to surgically attach acoustic transmitters to the common sea star Asterias rubens; two methods attached the tag to the aboral side of the central body and the third attached the transmitter to the aboral side of an arm. Laboratory experiments evaluated each method in terms of survivability, tag retention, associated injuries, and changes in feeding behaviour and physical condition.ResultsLaboratory results were highly variable; however, all tagging methods caused significant injury to the epidermis and deeper tissue around the attachment site over periods greater than 4 weeks. Attaching a tag by horizontally piercing the central body (method HPC) had minimal effects in the short-term (2–3 weeks) and this method was used for a pilot tagging study in the field, where 10 sea stars were tagged and placed within an existing acoustic telemetry array. Although, the interpretation of field data was challenging due to the characteristic slow movement of sea stars, movements of a similar magnitude to previous studies were identified during the 2–4 weeks after sea stars were tagged and released. However, this apparent period of tagging success was followed by a reduction in movement that, when viewed in conjunction with laboratory results, potentially indicated a deterioration in the sea stars’ physical condition.ConclusionsWhile acoustic telemetry continues to provide novel insights into the ecology of a wide variety of marine species, species-specific effects of tagging should be evaluated before starting field studies. If the autonomous study of benthic movement is to expand beyond hard-bodied macroinvertebrates current methodological and analytical challenges must be addressed.

BackgroundBycatch mortality in longline fisheries is a major contributor to global declines in shark populations. The duration of time that an animal is hooked and the impacts of hooking on behavior affect the likelihood of mortality. However, limited information exists on the behavior of sharks to longline capture because of difficulties observing hooking events. Using a fortuitous recovery of an archival satellite tag, we describe the movement of an oceanic whitetip shark (Carcharhinus longimanus) and examine the behavior prior to its mortality in response to hooking on a longline.ResultsA 1.5 m (fork length) C.longimanus was tagged and released in good condition by a fisheries observer following initial capture on a US longline fishing vessel. After release, the shark resumed normal vertical behavior within 5 h. Over 198 days, the shark undertook wide-ranging movements throughout the Pacific between Samoa, Niue, and Tonga. The shark was hooked by a second longline vessel while conducting routine yo-yo diving between 0 and 120 m depth. For the first hour after being hooked the shark exhibited high swimming activity with rapid vertical movements between 20 and 40 m indicative of an initial struggle against the line. After this, the shark struggled at the surface for approximately 5 h, until it succumbed to exhaustion and died on the line.ConclusionFight time has a strong influence on the mortality rates of sharks captured in commercial longline fishing operations. Data obtained from this shark offers further understanding of capture behavior and time to mortality on a longline for C.longimanus which may assist managers as they work on options to reduce mortality rates for this threatened species.

The body temperature of animals can be measured by thermistors, thermocouples, or radiotelemetry devices that are implanted surgically under the skin, although the suitability of subcutaneous temperature as an indicator of core temperature can be limited because of abnormal temperature readings, probably affected by ambient temperature and animal inactivity. This study compared the use of bio-loggers designed to monitor subcutaneous temperature (Tsub), with their use embedded in intravaginal sponges to measure vaginal temperature (Tvag). Three ewes were implanted with a subcutaneous temperature bio-logger that was configured to record Tsub every 30 min for a month. Ewes were given an intravaginal sponge for 12 days two days later. Inside the sponges were installed programmed bio-loggers that measured Tvag every 5 min. The ambient temperature (Tamb) and relative humidity were monitored using mini data-loggers. Mean Tsub was lower (P < 0.001) during the day (38.02 ± 0.02 °C) than at night (38.10 ± 0.02 °C), with maximum Tsub (38.57 °C) at 20:00 h and minimum temperature (37.36 °C) at 08:00 h; however, mean Tvag was higher (P < 0.001) during the day (38.71 ± 0.01 °C) than at night (38.62 ± 0.01 °C), with maximum Tsub (39.02 °C) at 20:55 h and minimum temperature (38.33 °C) occurred at 08:25 h. Mean Tsub (38.08 ± 0.02 °C) was lower (P < 0.0001) than was Tvag (38.65 ± 0.10 °C) in the daytime and at night (P < 0.001). Both temperatures had a 24-h rhythm (P < 0.0001), but differed (P < 0.001) in the mean midline estimating statistic of rhythm (MESOR) (Tvag: 38.67 ± 0.02 °C, Tsub: 38.09 ± 0.02 °C), amplitude (Tvag: 0.21° ± 0.01C; Tsub: 0.25 ± 0.01 °C), and acrophase (Tvag: 18:27 ± 0.38 h, Tsub: 20:48 ± 0.44 h). The coefficient of correlation between the two temperatures, measured simultaneously for 12 d was 0.644 (P < 0.01), and between Tamb and the two physiological temperatures, measured at the same time throughout the 12 d experiment, was 0.319 (P < 0.01) for Tsub and 0.287 (P < 0.01) for Tvag. The linear regression analysis of the 24 h circadian rhythm in Tsub and Tvag indicated a high coefficient of determination with Tvag (0.9255) and a lower coefficient of determination with Tsub (0.4292). In conclusion, the integration of a mini body temperature logger into a vaginal sponge, or their subcutaneous insertion, provided a continuous and accurate record of body temperature. Furthermore, the strong correlation between mean 24 h circadian Tvag and Tamb, demonstrated the usefulness of Tvag in biometeorological studies in sheep. As an alternative to employing these devices subcutaneously, they can also can be utilized as a biomarker of core body temperature inserted in vaginal sponges.

BackgroundMany regions of the ocean are under-sampled in terms of their biology and physical structure. Increasingly sophisticated animal-borne electronic tags are capable of measuring and transmitting in situ environmental data such as ocean temperature–depth profiles. This has the potential to significantly augment the volume of data acquired from under-sampled regions of the ocean. These data would enhance interpretation of animal behavior and distribution and could be used to inform oceanographic and meteorological models. Building on results obtained from marine mammals and turtles, we present a case study of depth–temperature profiles obtained from a tagged tiger shark.ResultsDuring a 102-day deployment, 1350 geolocations were obtained from a shark from waters around Oahu, Hawaii. Of these, 520 were associated with depth–temperature profiles—some of which were from depths exceeding 500 m. Delay between profile creation and transmission to satellite or land-based receiver averaged 8.9 h (range: 35 s–43 h, median 6.32 h). The profiles were in close agreement with profiles extracted from nearby locations in an operational ROMS model. Land-based receivers played a significant role in augmenting data throughput obtained via satellites.ConclusionsShark-borne transmitters offer a viable option for collecting ocean profiles with reporting latencies that make them suitable for operational oceanography. They can significantly increase sampling frequency (especially subsurface) and sample geographic areas that are otherwise difficult to monitor with Lagrangian methods such as Argo floats. They sample locations and depths that are important to the animal and which in some cases may be biological hotspots. The resolution of the data is comparable with that derived from traditional platforms. By targeting appropriate species of shark, different areas of the ocean could be monitored at significantly higher rates than is currently the case.

BackgroundLocomotion is often a necessity for animal survival and can account for a large proportion of an individual’s energy budget. Therefore, determining the energy costs of locomotion is an important part of understanding the interaction between an animal and its environment. Measures of animal acceleration, specifically ‘dynamic body acceleration’ (DBA) has proved to be a useful proxy of the energy cost of locomotion. However, few studies have considered the effects of interacting factors such as the animal’s speed or changes to the terrain slope on the putative acceleration versus energy expenditure relationship and how this may affect the relationship between DBA and energy expenditure.MethodsHere we conducted a methodological study to evaluate the ability of the metric ‘vectorial dynamic body acceleration’, VeDBA, obtained from tri-axial accelerometer data loggers, to act as a proxy for energy expenditure in non-uniform environments. We used indirect calorimetry to measure the oxygen consumption (V̇O2) of domestic sheep (Ovis aries) that were exposed to different ambient temperatures when immobile (resting) and that walked at various speeds (0.8 to 2.9 km h−1) and slope angles (− 6° to 6°) on a treadmill while simultaneously measuring tri-axial acceleration recorded at 40 Hz by body-mounted tags.ResultsThe lower critical temperature of sheep was identified as 18 °C, and V̇O2 when they were immobile was 3.67 mL O2 kg−1 min−1. There were positive relationships between V̇O2, VeDBA, and speed of walking. However, VeDBA correlated less well with V̇O2 when the terrain slope either inclined or declined.ConclusionsWe advocate caution when using DBA metrics for establishing energy use in animals moving over uneven terrain and suggest that each study species or location must be examined on a case-by-case basis. Reliance upon the relationship described between acceleration and energy expenditure on horizontal-surface treadmills can lead to potential under- or over-estimates of energy expenditure when animals walk on uneven or inclined ground.