Predation Events Research Articles

Predation of Rock Partridge Alectoris graeca saxatilis nests incubated by males and females in the French Alps

ABSTRACT Capsule The predation of incubated nests was investigated in an Alpine population of Rock Partridges, showing a double-nesting behaviour by females that can lay two clutches in succession, one incubated by the mated male and the second by the female. Aims To compare the nest predation rate and hatching success between incubating males and females in relation to the potential effects of year, nest age, and environmental characteristics (presence of nest cameras, visibility of the clutch, and vegetation cover around the nest). Methods The fate of 100 nests incubated by radio-tracked birds was monitored daily over 1738 days using cameras, and with temperature loggers placed in the nest cup. Nest predation rates and daily predation rates were calculated and modelled. Results Egg predation was the main cause of nest loss (87%) followed by predation of the incubating parent during recess periods off the nest (10%). Only mammals were identified as nest predators, and predation events were less frequent during the day than at night. We found no difference in predation rates between nests incubated by males or females. Daily and 25-day predation rates were calculated as 0.02 (95% CI: 0.01–0.03) and 0.39 (95% CI: 0.29–0.49), respectively. Median hatching success was 0.91 (n = 53 nests) and did not differ between sexes. Conclusions The similar level of nest predation between incubating males and females suggested a duplication of the reproductive output of a pair by double-nesting. Consequences of this breeding system were an increase in productivity at the population level. There was no difference in hatching success in nests incubated by either sex and there were no observations of surviving males deserting their nests, suggesting that care during incubation was similar in males and females. Variation in the rate of double-nesting may contribute more than nest predation to the annual variation in reproductive output.

Call for Your Life: Acoustic Structure and Age‐Sex Differences in Distress Calls of Red‐Necked Nightjars

ABSTRACTPredatory interactions result in strong selection pressures acting on multiple aspects of animal behaviour. Anti‐predator strategies are therefore common in most animals, typically signalling at various stages of a predation event. Many species of caprimulgids perform conspicuous anti‐predator displays, including stereotyped behaviours and vocal signals. Here, we described distress calls of red‐necked nightjars (Caprimulgus ruficollis), produced when birds are trapped and unable to escape during a predatory interaction. Distress calls are harsh, low‐frequency guttural vocalisations with irregular amplitude modulations. The age and sex of birds partially explained the acoustic variation observed, whereas size‐related morphological features were poor predictors of the acoustic structure. Age‐sex differences in distress calls may respond to physiological constraints associated with sexual dimorphism and/or developmental variation. Alternatively, directional selection associated with differential predation risk on each age‐sex class may have resulted in the observed differences in distress calls. The extremely deep voice and the harsh quality of distress calls fit the structure of aggressive signals and may resemble those produced by a larger animal. We propose that these calls serve as a last resort strategy to reduce post‐encounter risk of predation, either as a startling effect to facilitate escape or to attract other predators that could intimidate the captor.

Predation of eggs and incubating females in willow ptarmigan Lagopus l. lagopus

Nest predation is a major cause of reproductive loss in many ground-nesting birds. During 15 consecutive years the predation of nests and females throughout the incubation season were recorded in a willow ptarmigan Lagopus l. lagopus population in central Norway. The temporal predation patterns, factors affecting the predation probability and age-specific nesting patterns in this species were studied. There was a large annual variation in predation rate of both nests (0-50%) and incubating females (0-29%) in this area during the study period. The mean annual predation rate of nests (15%) was on average three times higher than the predation of incubating willow ptarmigan females (5%). Predation rate was not constant throughout the incubation season, and the nest predation rate increased with increasing number of available nests. The predation events started after the mean initiation day of incubation, and coincided with the highest number of available nests. None of the parameters we tested in a logistic regression analysis (physical condition, nest cover, experience and date for initiation of egg-laying) could predict the predation probability of nests and incubating females. However, “good” nest cover tended to have some predictive value on the predation probability. Yearling incubating females had significantly lower physical body condition than adults, and also there were differences in choice of nest site in relation to cover between the two age groups. Initiation of egg-laying in adult females tended to be distributed more evenly over the season, whereas yearling females had a more aggregated egg-laying pattern, compared to adults.

Recording potential predators of herpetofauna in southern Mexico using camera traps and realistic models

ABSTRACT Knowledge of biotic predator–prey interactions is essential for understanding the role of species in the food web; however, information on these interactions is scarce for most species. Our aim in this study was to gather information on the potential predators of two species of herpetofauna abundant in the rainforest they inhabit, the frog Craugastor loki and the snake Ninia sebae. For this, realistic models of the two species were placed, and monitored using camera traps, in 13 sites located in a forest fragment belonging to a private protected natural area in southern Veracruz in three seasons (dry, rainy and windy) in 2019. In addition, the temporality and seasonality of the events and some behaviours of the potential predators are described. The recorded events were classified into four categories: presence, interest, contact and aggression. For C. loki, 159 events of appearances of potential predators were identified (32 with interaction: 18 events of interest, 2 contact and 12 aggressions). The aggressions were carried out by the mammals Didelphis marsupialis and Peromyscus sp. In the case of N. sebae, 201 appearances of potential predators were identified (75 with interaction: 36 events of interest, 7 contact and 32 aggressions). The aggressions were carried out by 10 species (seven birds and three mammals). Bird predation events towards models of both species occurred during daytime while the attacks by mammals occurred at night. Agonistic behaviours included pecking, biting and urine marking, previously unknown. Events of each category were recorded every season. Our results indicate that C. loki and N. sebae may have more predators than were previously known, and suggest that these species can be an important food resource for different species of birds and mammals in the environments where they live.

Identifying insect predators using camera traps reveal unexpected predator communities in oilseed rape fields

Cameras are common tools for ecologists studying species abundance, richness, and interactions. They are mainly used to study large animals but are increasingly used to study invertebrates. Camera traps could be a powerful tool to identify and quantify the natural enemies, such as predators, of specific agricultural pests. This knowledge can then be applied to adapt farming practices to favour the predators identified and improve conservation biocontrol.Here, cameras were used to identify predators of two insect pests of oilseed rape (Brassica napus): the pollen beetle (Brassicogethes aeneus) and the brassica pod midge (Dasineura brassicae). These insects are spring pests of oilseed rape and are both susceptible to predation by ground-dwelling arthropods during their development cycle. The objectives of this study were to 1) identify the predators of the pest species, and 2) investigate the hypothesis that the diel activity periods of the predators match the timing of pest larval presence on the ground. Field observations were conducted in two locations over two consecutive years in the UK.In contrast to previous reports, our data collected using cameras showed that larval stages of predatory beetles are responsible for most of the predation events and that adult stages were not frequently observed feeding on the prey. Our data also showed that the traditional method, using pitfall traps, failed to detect the presence of large numbers of beetle larvae. Interestingly, the pests dropped to the ground and were therefore most susceptible to predation at the time when predators were most active.These results give new insight on the predators of the two most important spring pests of oilseed rape in Europe. This knowledge can be used by practitioners to develop framing practices targeted on enhancing the abundance of the larval stages of these beneficial arthropods to better control the pests in a more sustainable way.

Oceanic whitetip shark cookies: Evidence of multiple predation events by an opportunistic mesopelagic predator on a large epipelagic shark

Oceanic whitetip shark cookies: Evidence of multiple predation events by an opportunistic mesopelagic predator on a large epipelagic shark

Predation of the social wasp Polybia occidentalis (Hymenoptera:Vespidae) by the water scorpion Ranatra obscura (Hemiptera:Nepidae)

The genus Ranatra (Nepomorpha) is a formidable predator with significant importance in trophic webs, playing a crucial role in regulating aquatic and semi-aquatic communities through population control. However, studies on the diet of Ranatra species remain scarce, particularly in poorly understood Amazonian regions such as Marajó Island. This lack of data hampers our understanding of species behavior and the development of targeted conservation actions needed to maintain the ecological balance of complex networks, especially in areas under anthropogenic threat. Our study was conducted in the municipality of Salvaterra, within the Marajó Island archipelago, where we observed predation of the predatory species Polybia occidentalis (Olivier, 1791) by Ranatra obscura Montandon, 1907. We captured the insects using a sieve in the water column of a stream, which had been previously divided into three 50-m sections. Subsequently, we monitored Ranatra's behavior during the predation event, revealing its predatory aggressiveness and hunting ability—traits often underestimated due to its piercing-sucking mouthparts. This new record enhances our understanding of the diet and natural history of Nepomorpha and Ranatra, and highlights the importance of allochthonous material for predator species, revealing their role in terrestrial and semi-aquatic ecological networks.

Predation of Natalus macrourus (Chiroptera: Natalidae) by Trachops cirrhosus (Chiroptera: Phyllostomidae) in a ferriferous Brazilian Amazon cave

Abstract Trachops cirrhosus bats are especially notable for feeding on various types of preys throughout its range, including other bat species. Here we report predation events of T. cirrhosus on Natalus macrourus, a new bat species among a wide range of prey.

Anthropogenic and environmental risk factors of salmonid predation in a tidal freshwater delta

Abstract Water diversions that support agricultural and municipal use result in fish mortality through entrainment and impingement. Additionally, this infrastructure may attract both predators and prey fishes, thereby increasing predation rates and prey mortality near these anthropogenic contact points. The Sacramento–San Joaquin Delta (the Delta) in California's Central Valley is a tidal freshwater ecosystem that exports large volumes of water for municipal and agricultural use while at the same time providing valuable migratory and rearing habitat for imperilled fishes. Emigrating juvenile salmonids experience high mortality in the Delta, with predation by non‐native fishes contributing substantially. Therefore, this study had three main objectives. First, we determined if small water diversions aggregated piscivorous fishes like other similar structures in freshwater ecosystems. Second, we determined how small diversions may influence juvenile salmon predation risk in conjunction with other known predation risk factors (e.g. predator abundance, temperature and depth). Third, we assessed the predator assemblage, abundance and distribution to determine the likely predator composition in objectives one and two. Throughout the spring of 2021, we used ARIS (adaptive resolution imaging sonar; Sound Metrics) sonars to compare piscivore abundance at 30 water diversions in the north Delta to shorelines adjacent to diversions that did not contain these structures. We used predation event recorders (PERs) to assess the predation risk juvenile salmonids were exposed to, with linear distance (m) from diversions, and other predation risk factors in the north Delta. Finally, we used a boat electrofishing survey to determine the piscivore assemblage and compare spatial trends in black bass (Micropterus spp.) CPUE and relative abundance throughout these waterways. Piscivore abundance was greater near small water diversions than at adjacent shorelines and the predation risk of juvenile salmonids increased with diversion proximity. Additionally, predation risk increased with increasing piscivore abundance and decreasing water depth. The north Delta predator assemblage was dominated by black basses (Micropterus spp.), which likely drove the negative relationship of predation risk with water depth, given habitat requirements of these species. Furthermore, increasing smallmouth (Micropterus dolomieu) and spotted bass (Micropterus punctulatus) abundance in our northern study sites may have weakened temperature effects on predation, given metabolic requirements of these species. Our work demonstrated that small water diversions are likely to increase mortality of endangered salmonids, and that the north Delta predator assemblage was different than recorded by previous work in this system, changing predation risk factors. Although more work is needed to determine the population level impacts of diversions, the ubiquitous distribution of these structures warrants management solutions to reduce mortality from this source. These results indicate that in addition to entrainment and impingement, water diversions may increase mortality of small‐bodied fishes by attracting predators and elevating predation risk. Given the continual human demand for freshwater, predator–prey interactions should be considered along with entrainment and impingement when assessing intake infrastructure mitigation, especially when diversions co‐occur along migratory routes and essential habitat of imperilled fishes.

Use of livestock by jaguar (Panthera onca) in an agrolandscape of northeastern Mexico

ABSTRACT Jaguars are endangered in Mexico, with negative interactions with livestock producers being one of the main threats to their populations. We collared three jaguars with search Global Positioning System (GPS) clusters to document prey species eaten by them in the Sierra del Abra-Tanchipa Biosphere Reserve (RBSAT) and surrounding agrolandscape, in northeastern Mexico, to determine the relative use of natural prey and livestock. We detected, through examination of the carcasses (scavenging and predation events), 35 individual prey at feeding sites, primarily collared peccary (40% of sites), cattle (23%), and white-tailed deer (20%). Cattle comprised 64% and wild ungulates provided 34% of the estimated biomass in jaguar diets (biomass was calculated based on the estimated mass consumed and the assumption of an edible portion), with cattle consumed only during the dry season. Seasonal use apparently reflected increased encounters between jaguars and livestock during the dry season, probably due to the presence of limited permanent water sources concentrating livestock (and natural prey) along with jaguars taking advantage of the increased vulnerability of livestock during the dry season (either through predation or scavenging).

Rapid prey manipulation and bite location preferences in three species of wandering spiders

Predator-prey interactions are the interspecific relationships of greatest interest in ecology. Spiders are among the most diverse and ubiquitous terrestrial predators on the planet. Their large dietary breadth is often linked with the development of specific predatory behaviors and morphological adaptations. However, studies on the predatory behavior of spiders have mostly focused on specialist species, leaving behind the ethological variability occurring in generalist species that allow them to respond to the different prey types. For three species of generalist wandering spiders, we searched images of predation events on the Internet to determine the most common prey. Subsequently, the focal predator species were then used in behavioral experiments. Using high-speed videos, handling patterns for different prey types (spider and cricket) were analyzed. Our results show a notable difference in handling patterns between prey types. We found that the spider prey was often rotated around the axis allowing the predator to bite in the ventral region of the prey and thus avoid a counterattack. Contrary, crickets were arbitrarily rotated. Our work may be an indication that these three species of generalist spiders have a preference for manipulating prey differently with a preference to rotate spiders, allowing them to exploit prey with various defensive mechanisms.

Proximity of shrub nests to ground nests increases the chance of ground nest predation

In nature, ground-nesting birds rarely nest under an active shrub nest of another species. In the case of the proximity of the two nest types, we assumed that if a nest predator finds one nest, it will most likely rob the other nest as well. To test this, we exposed artificial nests with one quail and one plasticine egg on shrubs and underneath on the ground, in oleaster shrub rows and forest edges. We found a higher predation on ground nests than on shrub nests in both habitats. More importantly, predation events in shrub nests resulted in a higher predation of more concealed ground nests too. Our results suggest that proximity of two nest types can be detrimental to predation pressure, especially in forest edges.

Activity of predators in seabird colonies decreases during the darkest compared to the brightest phase of the diel cycle below, but not above, the Arctic Circle

ABSTRACT Predator activity can structure communities temporally and influence the spatial distribution of prey. Yet, despite the influence this may have on prey species’ activity or geographic persistence, our understanding of whether diel predator activity changes geographically remains limited. Here, we conduct a case study to test whether predator activity during the darkest phase of the diel cycle increases with the duration of daylight (i.e. photoperiod) at high latitudes during summer, aligning with the photoperiod constraint hypothesis. Using both observations and experiments at one seabird colony above and one below the northern polar (Arctic) circle, we compared predator activity between the brightest and darkest phases of the diel cycle. Avian predator counts were greater and nest predation events were more common during the brightest phase of the diel cycle below the Arctic Circle (i.e. where the sun goes below the horizon) but similar across phases during polar summer (i.e. above the Arctic Circle when the sun does not set). Our results highlight the potential influence of light on activity of predator communities and suggest a possible latitudinal limit to the advantage gained by dark-active strategies for avoidance of visually hunting predators.

Bimodal response strategy in Daphnia to ambush predation risk.

Predation's consequences can manifest through either consumptive or nonconsumptive effects, but the prey response may also vary depending on the predator hunting strategy. Considerable attention has been paid to coursing predators, whereas less information is available regarding responses to ambush predators. To remedy this paucity, we utilized a three-dimensional tracking platform to record groups of Daphnia magna under predation risk from the ambush invertebrate predator red-eyed damselfly, Erythromma najas. This design allowed us to test individual antipredator responses in multiple metrics of swimming behaviors. We demonstrate that predation risk was greatest for those that swam at 85% of the available depth and averaged 8.1 mm/s. Examining the swimming behavior of each individual separately showed that predation risk did not affect any of the prey response metrics. Interestingly, however, Daphnia did conform to one of two strategies while under predation risk: either swim fast high up in the water column or swim slowly close to the bottom. Hence, this dichotomous behavior is driven by strategies combining speed and depth in different constellations. In a broader context, our findings highlight the importance of considering both the spatial and temporal dimensions of predation events in order to correctly detect antipredator responses.

Jaguar predation on domestic horses in the dry forest of northwestern Costa Rica

AbstractDepredation of domestic horses (Equus caballus) by jaguars (Panthera onca) is an example of human–wildlife conflict that has not received much attention. We monitored spatio‐temporal activity and distribution of horses in a 2.64‐km2 fenced area in the dry forest of northwestern Costa Rica in response to 16 jaguar killings of horses during January‐November 2017. We monitored 4 horses (2 males, 2 females) equipped with global positioning system transmitters from February‐September 2018 to identify daily and seasonal patterns of use of cover types and a water source by horses. We then compared these results to the previous locations where jaguars killed horses to identify the circumstances under which horses seemed more vulnerable to jaguar predation. Based on 1,693 locations, horses spent most time in grassland (92%) rather than forest and edge vegetation (8%) and used a core area of 0.74 km2 (kernel density estimation) to 0.86 km2 (minimum convex polygon). Of 16 horse predation events by jaguars, 9 events (56%) occurred in grasslands, 4 in forested areas (25%), and 3 in the forest edge (19%), indicating predation events occurred disproportionately from expected counts based on horse use of vegetation. The predation sites were characterized by a higher proportion of edge and a lower proportion of forest compared to a random points. We suggest that when horses explored areas near the edge of forested areas, the chances of being preyed on by jaguars increased.

American big cats on the spotlight

ABSTRACT Through content analysis, we reviewed 853 news articles from 2015–2020 to assess how jaguars and pumas are portrayed in Latin America. Science Communication (27%) and Sighting reports (18%) were the most common topics. About half of the news had a positive framing, 37% were neutral, and 12% showed a negative frame. Most of the positive news were related to jaguars (66%), and the negative to pumas (80%). Government agents were the main interest group featured in the news. Residents were often mentioned in the news about pumas, while scientists were related to news on jaguars. Our study provides a baseline to monitor perceptions toward jaguars and pumas across media outlets and offers insights on people-big cats interactions. Efforts could be directed to the improvement of communication between scientists and journalists to disseminate news based on scientific evidence and avoid the use of sensationalism when describing encounters and/or predation events.

Nest site vegetation structure influences nest predators and nesting success of understory birds in a dry evergreen forest in northeastern Thailand

Abstract Nest predation is typically the main cause of nest failure in forest understory birds; thus, identification of primary nest predators is key to understanding nest predation patterns. Furthermore, responses of predators are likely affected by vegetation structure, but predator responses to micro-scale habitat characteristics are largely unknown, especially in tropical forests. We used a long-term study with one of the largest datasets of its kind to investigate the extent to which micro-habitat structure (5-m radius surrounding a nest) can predict the likelihood of predation and by which predator. In a secondary evergreen forest in northeastern Thailand, 2013–2021, we found 1,016 active nests of 13 species and 24-hr video-monitored 500 of them. We recorded 336 predation events from 16 nest predator species. From this and previous studies at our site, we identified the top 4 predator species/species-groups accounting for ~83% of predation events: Macaca leonina (northern pig-tailed macaque, 36% of predation events), cat snakes (Boiga cyanea [green cat snake] and Boiga siamensis [grey cat snake]) (20%), Lycodon cf. davisonii (Blandford’s bridle snake, 18%), and accipiters (A. trivirgatus [Crested Goshawk] and A. badius [Shikra]) (9%). These 4 predator species differed in their responses to vegetation structure likely reflecting differences in foraging behaviors. Macaque and accipiters, both diurnal and visually-oriented, tended to depredate more visible/open nests, but macaques depredated nests surrounded by more trees and short woody stems (<3 m tall) compared to raptors. For snakes, both nocturnal, cat snakes depredated nests with higher numbers of both short woody stems and woody climbers, whereas bridle snakes depredated nests with more trees and fewer climbers. As noted previously, nest predator identity is critical to understanding habitat-predation patterns. Our data suggest that nest site vegetation characteristics influence the likelihood of a given species of predator locating a nest and that even small changes in vegetation structure could significantly alter predation patterns.

Evaluating mountain lion diet before and after a removal of feral horses in a semiarid environment

AbstractNon‐native species can affect ecosystems by influencing native predator‐prey dynamics. Therefore, management interventions designed to remove non‐natives may inadvertently lead to increased predation on native species. Feral horses are widely distributed throughout the arid parts of western North America. A growing body of research indicates that horses can be an important prey species to mountain lions in ecosystems where they overlap. In December 2020, the Bureau of Land Management removed 455 horses from the Delamar Mountains, Nevada, USA. We leveraged this management intervention to implement a before–after–control–impact study to test hypotheses about predation on horses and native ungulates. We predicted (1) that horses would comprise an important part of the diet in this mixed‐prey community, (2) following removal, the proportion of horses in the diet would decrease and native ungulates would increase, and (3) mountain lion home ranges overlapping the treatment areas would increase in response to decreased prey availability. From 2018 to 2022, we investigated 1360 clusters from 29 GPS‐collared lions and identified 1056 prey items. To model the probability of a predation event (a kill), we fit a mixed‐effects logistic regression model for ungulate prey as a function of lion sex, treatment area (in/out), and treatment period (pre‐/post‐removal). We used a log‐linear regression model to evaluate changes in home range size. The most common prey were mule deer (55%), feral horses (32%), and coyotes (4%). Twenty‐two of 29 lions consumed horses, although the rate of horse consumption was highly variable across individuals. Horses of both sexes and all age classes were predated. In contrast to predictions, our models detected no effect of removals on diet composition (βinteraction = 0.30 ± 1.1), nor did the removal influence home range size (βinteraction = 0.02 ± 0.02). Despite a 46% reduction in horse abundance, we found no evidence for prey‐switching following the horse removal treatment. Removal magnitude, rapid horse immigration, and/or behavioral specialization of individual mountain lions may help explain these results. Our findings have important implications for mountain lion and feral horse management in arid environments characterized by high prey diversity, but low prey abundance.

Are Eurasian badgers responsible for lamb predation? An investigation using farmer interviews, post‐mortem examination and molecular tools

Abstract This study investigates farmers' reports of lamb predation by badgers on Scottish sheep farms. Differentiating between predation and scavenging, and identifying the species responsible, is essential for livestock managers to effectively mitigate risk. Questionnaire‐style interviews established farmer perceptions of lamb predation by badgers and incidents of suspected predation were investigated on farms in 2022 and 2023 using post‐mortem examination and molecular tools. Farmers submitted 29 carcasses for post‐mortem. Of these, evidence of predation was present on 14 lambs (48%) and predation could not be ruled out for six further lambs (21%). No evidence of predation, but wounds consistent with scavenging after death, were present on nine lambs (31%). Nine (64%) of the 14 predated lambs also showed evidence of scavenging after death. Swabs were taken from 39 dead or injured lambs for potential predator/scavenger DNA recovery, and from 20 live control lambs. Badger DNA was obtained from the partial remains of two (5%) lambs. Badger DNA was not present on any of the carcasses submitted for post‐mortem or from any living, wounded lambs. Fox DNA was obtained from 34 (87%) dead or injured lambs, including all lambs that exhibited evidence consistent with predation at post‐mortem. Dog DNA was present on 12 (31%) lambs. While the results of this study cannot fully rule out the occurrence of lamb predation by badgers, no direct evidence was found to suggest that it does occur. The overall contribution of wildlife predation to lamb losses is considered to be low, but the results strongly suggest that foxes are likely to be responsible for lamb predation where it does occur. For livestock managers, a review of predator management strategies should be a key response to prevent future predation incidents. Practical implications. This study highlights the value of using post‐mortem examination and molecular evidence to accurately confirm predation events and to identify predator species, informing appropriate management interventions.

Validation of a new acoustic telemetry transmitter for the study of predation events in small fishes.

Acoustic telemetry has emerged as an important tool for studying the movement and behavior of aquatic animals. Predation-sensing acoustic transmitters combine the functions of typical acoustic transmitters with the added ability to identify the predation of tagged animals. The objective of this paper was to assess the performance of a newly miniaturized acid-based predation-sensing acoustic transmitter (Innovasea V3D; 0.33 g in air). We conducted staged predation events in the laboratory where acoustically tagged rainbow trout (Oncorhynchus mykiss) were fed to largemouth bass (Micropterus nigricans) at 3.3-7.0, 9.0-10.8, 16.0-20.0, and 22.0-25.8°C. We also conducted false-positive tests where tagged rainbow trout were held at 10.0 and 16.8°C without the risk of predation. Predation events were successfully identified in 92% of the staged predation trials. Signal lag (i.e., the time required for a predation tag to indicate that predation occurred) ranged from 0.11 to 6.29 days and decreased strongly with increasing water temperature and increased with increasing body mass of the tagged prey. Tag retention in the gut of the predator was much more variable than signal lag and was influenced by water temperature and individual predators but not by prey mass. No false positives were detected after 60 days at either temperature (n = 27 individuals). Although the relationships between water temperature, signal lag, and retention time are likely species-specific, the data reported here provide useful information for the use of these transmitters to study predation in wild fishes, especially for temperate, freshwater fish.