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Home range and movements of radio-tracked estuarine crocodiles (Crocodylus porosus) within a non-tidal waterhole

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Wildlife Research
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We radio-tracked five male and eight female estuarine crocodiles (Crocodylus porosus) in a non-tidal waterhole in Lakefield National Park in northern Queensland during the late dry/mid-wet season (2003–04) and the following dry season (2004). Individual crocodiles occupied larger home ranges (River Channel Areas (RCA) during the late dry/mid-wet season (10.64 ± 2.86 ha) than in the dry season (3.20 ± 1.02 ha), and males occupied larger home ranges (23.89 ± 2.36 ha) than females (5.94 ± 1.34 ha) during the late dry/mid-wet season. There were no obvious differences in home range between sexes during the dry season. During the late dry/mid-wet season, adult males often travelled long distances along the waterhole while females moved less. During the dry season, movement patterns were quite variable, with no clear difference between sexes. All crocodiles were most active from late afternoon (1500–1800 hours) until midnight. Individual home ranges (RCA) overlapped considerably during the late dry/mid-wet season. The extent of home-range overlap between three adult males and the number of times they either passed each other or were located near each other was particularly striking. Previous research has come to conflicting conclusions about the extent of territoriality in wild estuarine crocodiles, although it has been widely believed that males are highly territorial. The findings imply that large adult male estuarine crocodiles are not highly territorial in non-tidal freshwater systems that are geographically confined.
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... The kernel density estimates (KDE) summarize the area used by individuals with relatively small biases (Balaguera-Reina et al., 2016;Brien et al., 2008;Campbell et al., 2013;Combrink, 2014;Fujisaki et al., 2014). GLM was used to investigate the ecological variables associated with the sites used by gharials (Aarts et al., 2008). ...
... Balaguera-Reina et al. (2016) reported that female C. acutus moved further than males. For C. porosus and C. niloticus, the opposite trend seems to occur with males moving more than females (Brien et al., 2008;Hutton, 1989;Kay, 2004). Yet high individual variation is apparent, which could reflect traits such as shyness-boldness, exploration avoidance, sociability and aggressiveness (Eam et al., 2017;Réale et al., 2007). ...
... Seasonal differences found in this study are also reported for crocodilians elsewhere, with seasonal temperatures implicated (Brien et al., 2008;Campbell et al., 2013;Combrink, 2014). As is obvious in crocodilians including gharials, they spend more time basking in winter (Whitaker & Basu, 1982). ...
Article
1. Gharials (Gavialis gangeticus) are endemic to the Indian subcontinent and meet IUCN Red List criteria for critically endangered. 2. The Mahanadi River, located in the southernmost part of the gharial range, currently has a few individuals survived although historically had many more. 3. Between 2019 and 2021, the movement, habitat use and survival rate of 13 captive-bred (juvenile = 6, subadult = 5, adult = 2) reintroduced gharials were monitored using very high frequency (VHF) radio transmitters tracked manually from the river banks. Kernel density estimates and generalized linear model (GLM) were used to investigate the home range and habitat use of individuals. 4. Tagged gharials travelled throughout the river system, with the highest movement during summer and the least in winter. Females moved further and established larger linear home ranges than males. Kernel home ranges were established in and around the Satkosia Gorge wildlife sanctuary, which has favourable ecological conditions for gharials, namely, deep water, sandbars, abundant fish and low human disturbance. 5. Gharial mortality was detected during the study, and post-mortem examination indicated anthropogenic causes. The use of explosives for fishing, entanglement in fishing nets and a lack of ecological awareness within local communities were identified as key factors that need to be addressed if gharials are to survive the Mahanadi River.
... Prior to placement, we cleaned the skin surface with ethanol. We then attached each unit to the neck of each individual using surgical grade polymer around the transmitter, over the cervical scutes and below the osteoderms ( Fig. 2; Brien et al., 2008;Calverley and Downs, 2015;Balaguera-Reina et al., 2016). ...
... We used a portable receiver radio (model R-600-A, Commu- nications Specialists Inc., Orange, California) with an H antenna or a five-element Yagi antenna (Kay, 2004;Brien et al., 2008;Pough et al., 2016;Landeo-Yauri et al., 2017) to track the tagged crocodiles from a fixed point (i.e., at the top of a 15-m-high tower). We also located individual tagged crocodiles during visual encounter surveys while aboard a boat that was operated within presumed occupied habitat at the release site. ...
... Some, however, are reported to have return to their original area after failed hunting or dispersal attempts (Brien et al., 2008). ...
... The total distance traveled for relocated crocodiles was 6991. 35 Tables 2 and 3). The only female crocodile (Elaine), which was wild, did not differ in distance traveled from the other wild crocodile, Kramer (F 1,4 = 32.89, ...
... Therefore, we urge future research on crocodilian conservation and management to treat these complex problems as coupled human and natural systems [3]. Despite growth in global crocodilian research focusing on connections between the ecological e.g., [13,35,36], social e.g., [37][38][39][40], and economic e.g., [41][42][43][44] factors influencing and influenced by, crocodilians, there are still knowledge gaps surrounding these linkages, including their magnitude and extent, underlying causes, and ultimate effects from local to global scales. Integration of (1) patterns and processes that link humans and natural systems, (2) reciprocal interactions and feedbacks between humans and the environment, and (3) understanding scalar-interactions between human and natural components (e.g., largescale phenomena that emerge from the interactions of multiple agents at the local scale, influencing local systems [45]) is required to address the increased complexity and help prevent the negative consequences that may occur due to fundamentally new and rapid changes [3,46,47] on successful crocodilian conservation. ...
Article
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Simple Summary We aimed to evaluate the efficacy of nuisance crocodile relocations using passive spatial quantification in Guanacaste, Costs Rica. Nuisance relocated crocodiles and wild crocodiles were fit with Iridium satellite trackers and movements of all individuals were monitored over months. Nuisance relocated crocodiles either returned to the area of nuisance, or potentially attempted to return, in short time frames. These results highlight the need for alternative management strategies. Abstract Anthropogenic alterations of the environment have increased, highlighting the need for human–wildlife coexistence and conflict mitigation. Spatial ecology, and the use of passive satellite movement technology in particular, has been used to identify patterns in human–wildlife conflict as a function of shared resources that present potential for dangerous situations. Here, we aim to remotely identify patterns indicative of human–crocodile conflict in Guanacaste, Costa Rica by exploring site fidelity and diverse modes of movement (i.e., land and water) across space between nuisance (relocated) and non-nuisance (wild) crocodiles. Advanced satellite remote sensing technology provided near-constant movement data on individuals at the regional scale. Telonics Iridium SeaTrkr-4370-4 transmitters were used with modified crocodilian fitting. Results indicate that relocated crocodiles exhibited large-scale movements relative to wild crocodiles. Nuisance relocated crocodiles either returned to the area of nuisance or potentially attempted to in short time frames. The results presented here highlight the need for alternative management strategies that facilitate relocation efficacy.
... We carefully reviewed all papers, reports and communications and, for each, we recorded the following information: (1) journal name; (2) type of publication; (3) year of publication; (4) country where telemetry tracking was applied; (5) species studied; (6) body attachment position of transmitters; (7) use of anesthetics during transmitter attachment; (8) tracking technology (VHF, GPS/ Satellite and Acoustic); (9) number of specimens tracked; (10) study duration; (11) sex, weight, and total length of studied specimens (when publication presented snoutvent length, we made an estimation of total length); (12) Transmitter weight and lifespan. Due to the limitation of information in CSG's documents, data related to items 6 to 11 were obtained only from manuscripts published in peer-reviewed journals. ...
... Valuable information on individual and population-level responses have been evaluated in a few crocodylian species by telemetry tracking approaches, and it should be encouraged in those of high conservation concern, considering threats such as illegal hunting [8], invasive species [64], water pollution [55], bycatch on fishing nets [74,119], and habitat fragmentation [7]. Movement patterns of crocodylians can vary between wet and dry periods, reproductive and non-reproductive seasons, or even between sexes, as male and female conspecifics can occupy and move across their environment in diverse ways [4,12,60,72]. For example, male saltwater crocodiles can exhibit a greater site fidelity then females [3], while in other species, such the Orinoco crocodile, males can move far distances then females and occupy larger home ranges [80]. ...
Article
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Crocodylians are top predators that play key ecological roles in aquatic ecosystems. As in other groups of large predators, crocodylian populations are often impacted by habitat loss, habitat degradation or direct exploitation for commercial purposes or subsistence. Hence, understanding their spatiotemporal ecology can provide valuable information for conservation planning. We reviewed the published scientific literature on telemetry-tracking in crocodylians, combining the terms “telemetry”, “track” or “tag” and variations; “VHF”, “UHF”, “satellite”, “GPS”, “radio”, “acoustic” or “transmitters”; and “caiman”, “alligator”, “crocodile”, “gharial” or “Crocodylia”. Publications retrieved by our search were carefully reviewed for information on study length, geographic location, sample size, taxonomy, and telemetry technology used. We identified 72 research articles in indexed journals and 110 reports available from the IUCN’s Crocodile Specialist Group, published between 1970 and 2022. Publications included 23 of the 27-living described crocodylian species. We identified strong geographic and taxonomic biases, with most articles proceeding from the USA (21.2%) and Australia (14%), with Alligator mississipiensis and Crocodylus porosus as the main target species in studies conducted in these countries, respectively. Despite representing 22% of IUCN’s reports, Gavialis gangeticus was referred in a single indexed research article. VHF telemetry was the prevalent tracking method, followed by GPS and acoustic transmitters. Studies using VHF devices had generally shorter in length when compared to alternative technologies. Transmitter weight represented less than 2% of the body mass of the carrying individual in all studies. Although attachment site of transmitters was notified in all research papers, few described anaesthetic or clinical procedures during attachment (33%). Our review highlights the need to encourage publication of crocodylian telemetry studies in non-English speaking countries in Asia, Africa, and Latin America, where many endemic species are threatened. We also highlight the need of detailed information on methods and results to facilitate the choice and implementation of appropriate protocols in future telemetry-tracking studies.
... De manera que hasta el 2004 se publicó el primer estudio de telemetría VHF en Australia para la especie (Kay, 2004). No obstante, para las siguientes dos décadas se reportan más estudios de ecología espacial para la especie (Read et al., 2007;Brien et al., 2008;Brien et al., 2010;Thomas et al., 2010;Campbell et al., 2010;Campbell et al., 2013;Campbell et al., 2015;Hanson et al., 2014;Dwyer et al., 2015;Evans et al., 2017;Fukuda et al., 2019), siendo el pionero en utilizar telemetría satelital y acústica para estudiar los desplazamientos de largas y cortas distancias, respectivamente (Read et al., 2007). ...
... Por otro lado, se ha evidenciado que el sexo de los cocodrilos es una variable que influencia el rango de hogar y los desplazamientos en C. acutus (Balaguera-Reina et al., 2016), C. intermedius (Moreno-Arias y Ardila-Robayo 2020), C. porosus (Kay 2004, Brien et al., 2008 y M. leptorhynchus (Kouman et al., 2021), observándose mayores áreas de uso en los machos. Del mismo modo, para las tres primeras especies se ha podido registrar que las temporadas climáticas inciden sobre el área de actividad y desplazamientos (Muñoz y Thorbjarnarson, 2000;Kay, 2004;Balaguera-Reina et al., 2016; Moreno-Arias y Ardila-Robayo 2020). ...
Thesis
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Colombia is one of the most diverse countries regarding crocodylians in the world. However, the spatial ecology of Crocodylus acutus (American crocodile) and Caiman crocodilus (Spectacled caiman) in the wild is largely unknown. To date, no studies have been carried out in the country to understand the spatial dynamics of these species and their relationship with the environment through radiotelemetry. We evaluated the spatial ecology of C. acutus and C. crocodilus in the eastern sector of Tayrona National Natural Park (Arrecifes and Cañaveral) using VHF transmitters during February through July 2021. We collected 275 records from six monitored individuals with age ranges of juvenile and adult for C. acutus and subadults for C. crocodilus. Specifically, two males and one female were monitored for each species with an error rate of 12.69% and frequency of records per day of 1.02±0.56 and 0.61±0.37 respectively. The home range was determined with Minimum Convex Polygon (MCP), Local Convex hull (LoCoH), and the kernel density estimation (KDE) with isopleths at 100%, 95%, and 50%, finding in this method a maximum range for C. acutus of 0.189 km2 and 0.042 km2 for C. crocodilus, with LoCoH being the most accurate method. Only two individuals showed significant spatial autocorrelation (I-Moran z-score:2.65, p-value:0.08e-01 and z-score:2.23, p-value:0.26e-01) corresponding to a clustered distribution with confidence greater than 97%. However, all individuals had mean distances traveled (DMR) <1km in a period of five months (Feb-Jul), with an extended dry season in the field from 2021. It was checked that C. acutus presented significantly greater movements than C. crocodilus (p-value = 3.82e-06, p-value = 1.53e-05, respectively). On the other hand, with the onset of rains in July, the weekly DMR of C. acutus increased, a positive effect was found with the average precipitation (PP) (z-value: 2.04, p-value: 0.04, 95% confidence) , through generalized linear regressions based on binomial negative distributions. In contrast, the weekly DMRs of C. crocodilus were affected by more environmental co-variables: solar radiation, PP, mean and minimum temperature (z-value: 2.12, p- value: 0.33e-01; z-value: -2.01, p-value: 0.45e-01; z value: -2.42, p-value:0.16e-01, respectively). The most robust model obtained for C. crocodilus has an explanatory power of 87.76%, compared to 31.41% for C. acutus. Therefore, it is necessary to increase the number of individuals and monitoring time, as well as to explore more abiotic and biotic variables that may be influencing the DMR of the study species. Finally, these spatial data provide valuable information for management plans and future research inside and outside the protected area for the conservation and management of crocodylians and associated ecosystems.
... A previous telemetry study involving broad-snouted caimans found that male movements outpaced those of females, as males may seek unpatrolled areas by other males [49]. Similar movement patterns have been documented in other crocodylian species [9,17,31,59]. The increase in male movement during the wet seasons corroborate with the positive association observed between movement and reservoir water levels. ...
Article
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Background Animal habitat use can be influenced by a suite of factors including intraspecific interactions and resource availability. The broad-snouted caiman (Caiman latirostris) is the largest crocodylian species distributed in freshwater environments of the Brazilian Atlantic Forest, where it inhabits many types of human-impacted and preserved habitats. Despite their ability to occupy ecologically different water bodies, little is known about their movement patterns and their habitat use. We investigated the variation in movements and space use of adult caimans relative to sex, body condition, and environmental conditions in northeastern Brazil. Methods We conducted long-term capture surveys from 2013 to 2022 and used GPS telemetry from 2021–2022 (n = 12 individuals) to assess movement patterns and home ranges of caimans and their habitat use based on Brownian Bridge Movement Modeling (BBMM) and Generalized Linear Mixed Modeling (GLMM). Results Females ranged farther from reservoir’s forested margins, exploring a greater diversity of habitats during the wet/non-reproductive season. During the dry/reproductive season, females remained close to nesting sites within forest fragments. The body condition of caimans did not change significantly over the wet and dry season, indicating that resources are available year-round. Caimans moved more at night than during daytime, likely due to nocturnal foraging and possibly avoiding periods of increased human activity. Female movement rates were positively associated with rainfall, in a pattern likely linked to nest attendance in the dry season. Male movement was positively correlated with reservoir volume in the wet season, possibly due to increased availability of habitats in comparison to dry periods and to decreased overlap with territories controlled by other males. Home ranges estimated as 95% utilization distributions were relatively small in both sexes, averaging 0.64 km² (range: 0.001–1.4 km²), as were their core areas estimated as 50% utilization distributions, which averaged 0.12 km² (range: 0.0003–0.12 km²). Small core areas may indicate that caimans remain most of their time in a specific habitat, suggesting abundant resource availability or territoriality. Conclusions Our work reveals the complexity of social interactions and how caimans select their habitats in a highly altered environment.
... Transmitters weighed less than 2% of individuals body mass, to avoid interference in their natural behaviours (Mascarenhas-Junior et al., 2023). The attachment procedure followed the protocol proposed by Brien et al. (2008). We programmed the transmitters to collect and transmit geographic co-ordinates by a flexible antenna at every six-hour interval, and both caimans were subsequently released at the same location where they were originally captured, 24 hours after attachment procedures. ...
Article
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Crocodylians exhibit parental care, guarding their eggs during incubation to ensure offspring survival. We present the first description of nest attendance of a wild broad-snouted caiman using GPS-telemetry. During the reproductive season of 2022, we tracked a 1.8-meter female in the Tapacurá reservoir, a water source bordered by Atlantic Forest remnants and human settlements in north-eastern Brazil. Telemetry data revealed that 75.8% of the female’s position records were near the nest, suggesting parental care and nest protection. However, the female periodically returned to water. We observed no differences in proximity to the nest between day and night-time, which could be possibly related to different egg predators in the area foraging at different times of the day. Furthermore, the period when the nest was unattended could be associated with either feeding activities or avoidance of human presence. This research brings light on an important part of the reproductive behaviour of broadsnouted caimans in their natural environment, highlighting the importance of GPS-telemetry as a tool for monitoring reproductive behaviour of crocodylians, while contributing to understanding their biology under human-influenced settings.
... Adult individuals occupy home ranges and will travel significant distances to return to these areas following humanmediated translocation indicating high site fidelity (9). However, individual tracking shows there is overlap in the areas that adult males will occupy and travel behaviour within home ranges varies across seasons and between males and females (10)(11)(12). In general, there are few published studies characterising the behaviour of saltwater crocodiles, either free-living or captive. ...
Article
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Saltwater crocodiles (Crocodylus porosus) are farmed in Australia primarily for their skins and meat. Commercially, they are raised in group pens as hatchlings and grower crocodiles and then moved to unitised (individual) pens for the final finishing stage when they are several years old. They will exhibit aggressive behaviour towards each other in captivity. Unitised pens can prevent animal injury and teeth marks on the skins but may result in other social restrictions. Research into behavioural housing preferences could assist the industry and inform the process of guideline development for optimal crocodile management and welfare. This study assessed the impacts of two housing systems, unitised or group pens, in 20 commercial finishing crocodiles through measuring behavioural profiles of individuals from video recordings, including housing preference when given a choice. Both pens included water and an above-water shelf, but the crocodiles in unitised pens could also access underneath the shelf. A threat perception test was applied to assess anxiety when housed individually or in groups. However, it was difficult to apply a standardised stimulus to all animals that reliably elicited a behavioural response. Further work would be needed to validate this test for commercial reptiles as the outcomes were not robust. The behavioural observation results showed clear differences in where the crocodiles spent their time across the day and in their activity levels between the pen types. However, interpretation of this variation was confounded by the physical and social differences between the pen types given the inconsistency in shelf access. Behaviours exhibited also differed given there were social opportunities in the group pens where individuals were observed engaged in both aggressive and non-aggressive contact interactions. In the free choice environment, crocodiles spent similar amounts of time in both unitised and group pens, suggesting there were features of both pen types that were attractive to the animals. However, skins were damaged from teeth marks highlighting the physical and economical risks of group housing. Further work could validate behavioural tests to quantify affective state impacts in different housing environments and whether social interactions do provide benefits for improving crocodile welfare.
... Similar to monotremes, crocodilians also show crepuscular and even diurnal activity alongside nocturnality [27,[54][55][56][57]. Therefore, it is plausible that similarities in the rhodopsin phenotype across these two groups represent a case of functional convergence linked to their early visual adaptation to quickly changing twilight niches. ...
Article
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The visual ecology of early mammals remains poorly resolved. Studies of ancestral photopigments suggest an ancient transition from nocturnal to more crepuscular conditions. By contrast, the phenotypic shifts following the split of monotremes and therians-which lost their SWS1 and SWS2 opsins, respectively-are less clear. To address this, we obtained new phenotypic data on the photopigments of extant and ancestral monotremes. We then generated functional data for another vertebrate group that shares the same photopigment repertoire as monotremes: the crocodilians. By characterizing resurrected ancient pigments, we show that the ancestral monotreme underwent a dramatic acceleration in its rhodopsin retinal release rate. Moreover, this change was likely mediated by three residue replacements, two of which also arose on the ancestral branch of crocodilians, which exhibit similarly accelerated retinal release. Despite this parallelism in retinal release, we detected minimal to moderate changes in the spectral tuning of cone visual pigments in these groups. Our results imply that ancestral forms of monotremes and crocodilians independently underwent niche expansion to encompass quickly changing light conditions. This scenario-which accords with reported crepuscular activity in extant monotremes-may help account for their loss of the ultraviolet-sensitive SWS1 pigment but retention of the blue-sensitive SWS2.
... Matureeimmature dyads not only had a greater association rate than matureemature or immatureeimmature dyads, but they also had the most stable associations through time (for up to 5 years). This is consistent with previous work which found that mature individuals display greater tolerance towards immature conspecifics as they are more able to outcompete them for food or basking resources and they do not represent potential competitors for mates (Brien et al., 2008;Kay, 2004;Teichroeb et al., 2014). In contrast, dyads that were the same maturity status displayed less temporally stable associations. ...
Article
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Animal social systems are inherently dynamic, with individuals moderating how they associate with conspecifics according to spatiotemporal shifts in population demography and resource availability. Understanding such variation is important not only to further our knowledge of a species' ecology but also to gain insights into the factors influencing the evolution of animal social systems. Using a 10-year acoustic telemetry data set containing the movements and co-occurrences of 166 tagged individuals, we investigated how time of year, individual sex and maturity status affect the social organization and connectivity of a wild population of estuarine crocodiles, Crocodylus porosus. We found that our tagged population of crocodiles displayed social structure, where individuals segregated spatially into distinct communities along 120 km of river and estuary. The social organization and structure of these com- munities were temporally dynamic, with association rates and the connectedness of individuals peaking during the dry season before disintegrating prior to the onset of the wet season. The formation of communities was found to coincide with an increase in the frequency of co-occurrence events between mature and matureeimmature dyads prior to the onset of the mating season. Together these findings indicate that estuarine crocodiles have a structured social system, where the proximity to the mating season and an individual's maturity status dictate how they associate with conspecifics.
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A new method of calculating centers and areas of animal activity is presented based on the harmonic mean of an areal distribution. The center of activity is located in the area of greatest activity; in fact, more than one "center" may exist. The activity area isopleth is related directly to the frequency of occurrence of an individual within its home range. The calculation of home range allows for the heterogeneity of any habitat and is illustrated with data collected near Corvallis, Oregon, on the brush rabbit (Sylvilagus bachmani.)
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Ten month old Crocodylus acutus stayed within 300 m of the nest and had home ranges averaging 330 m of shoreline; 80% of movements occurred within core areas averaging < 200 m. A 22 mo old animal dispersed about twice as far and included within its range at least twice as much shoreline as the younger animals. Some 35-45% of the animals were in exposed locations on the surface during the day, and < 65% at night. Movements between locations were rare from 0900-1700 h, increased markedly after dusk, peaked around 0300 h, and dropped to near zero 2 h after dawn. Nocturnal movements were significantly reduced during periods of bright moonlight, although the percentage of animals exposed at the surface did not noticeably change. -Author
Chapter
Steady technological advancements including subminiaturization of telemetry components, smaller and more accurate global positioning systems (GPSs), and increasingly available geographic information systems (GISs) continue to influence the way researchers collect and analyze wildlife radio-tracking data. These developments have increased the diversity of animals that can be studied and have boosted the number and accuracy of location estimates, within a framework of contemporary conservation issues. This chapter conducts a literature review using the Wildlife Worldwide (WW) database to assess the specific topics and number of studies using radiotelemetry in wildlife research. Databases within the WW search engine include Wildlife Review Abstracts (formerly Wildlife Review), Swiss Wildlife Information Service, Wildlife Database, BIODOC, and the Waterfowl and Wetlands database. The most critical assumption in any radiotelemetry study is that the transmitter has no appreciable effect on the study animal. One can assume that a marked animal behaves, functions, and survives in a manner similar to that of an unmarked animal. Despite this critical assumption, the impact of radio marking of animals has often been subjectively evaluated. Generally, researchers assume that large animals are not affected by radio marking, whereas smaller animals, particularly birds, are impacted more.
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To test the feasibility of using captive-reared Orinoco crocodiles to restock depleted wild populations we used radio-telemetry to monitor eight crocodiles (103.3-139.3 cm total length) released in the Capanaparo River in southwestern Venezuela. Crocodiles were located every 1-2 d from April 1991 to March 1992 to determine movement patterns, survivorship, and growth rates. The crocodiles moved considerably during the first month following release, and the maximum distance moved was 11.6 km upstream by one crocodile four months after release. However, following an initial period of movement, crocodiles became more sedentary and by the end of the study the maximum distance from the point of release was less than 8 km. Six of the eight crocodiles moved upstream while two moved up to 3.3 km downstream. Crocodiles remained principally along the main course of the river in areas with mixed shallow and deep water habitats and abundant sand beaches. As the river rose during the wet season, crocodiles remained in the same areas, but moved into shallow-water areas among flooded riparian vegetation. The mean growth rate of released crocodiles (0.079 cm TL/day) was similar to that of smaller wild-born juvenile crocodiles. One animal was accidentally killed by a local resident who was hunting spectacled caiman. Based on the results of this study, we feel that a carefully designed program of releases of captive-reared crocodiles can be an effective conservation tool to speed the recovery of depleted populations of Orinoco crocodiles. However, care must be taken to insure that the release program is designed as one component of an overall crocodile strategy and not an excuse to avoid the onerous issues of the protection of wild crocodile populations and their habitat.