Context West African crocodylian populations are declining and in need of conservation action. Surveys and other monitoring methods are critical components of crocodile conservation programs; however, surveys are often hindered by logistical, financial and detectability constraints. Increasingly used in wildlife monitoring programs, drones can enhance monitoring and conservation efficacy. Aims This study aimed to determine a standard drone crocodylian survey protocol and evaluate the drones as a tool to survey the diverse crocodylian assemblage of West Africa. Methods We surveyed crocodile populations in Benin, Côte d’Ivoire, and Niger in 2017 and 2018, by using the DJI Phantom 4 Pro drone and via traditional diurnal and nocturnal spotlight surveys. We used a series of test flights to first evaluate the impact of drones on crocodylian behaviour and determine standard flight parameters that optimise detectability. We then, consecutively, implemented the three survey methods at 23 sites to compare the efficacy of drones against traditional crocodylian survey methods. Key results Crocodylus suchus can be closely approached (>10 m altitude) and consumer-grade drones do not elicit flight responses in West African large mammals and birds at altitudes of >40–60 m. Altitude and other flight parameters did not affect detectability, because high-resolution photos allowed accurate counting. Observer experience, field conditions (e.g. wind, sun reflection), and site characteristics (e.g. vegetation, homogeneity) all significantly affected detectability. Drone-based crocodylian surveys should be implemented from 40 m altitude in the first third of the day. Comparing survey methods, drones performed better than did traditional diurnal surveys but worse than standard nocturnal spotlight counts. The latter not only detected more individuals, but also a greater size-class diversity. However, drone surveys provide advantages over traditional methods, including precise size estimation, less disturbance, and the ability to cover greater and more remote areas. Drone survey photos allow for repeatable and quantifiable habitat assessments, detection of encroachment and other illegal activities, and leave a permanent record. Conclusions Overall, drones offer a valuable and cost-effective alternative for surveying crocodylian populations with compelling secondary benefits, although they may not be suitable in all cases and for all species. Implications We propose a standardised and optimised protocol for drone-based crocodylian surveys that could be used for sustainable conservation programs of crocodylians in West Africa and globally.

Mecistops leptorhynchus (Bennett, 1935) is among the least studied crocodylians worldwide, and little information exists on its movement patterns and habitat use.Using VHF radio tracking, we determined home range, core use areas and spatiotemporal interactions for 30 individual M. leptorhynchus (14 females and 16 males), as well as providing a preliminary assessment of their habitat preferences and emergence dynamics in the Echira and Ngové Rivers, Loango National Park (Gabon). During two periods in 2010 (March to June-106 days, and October to November-49 days) we recorded 447 relocations of all tagged individuals (mean of 15 relocations/crocodile). Individual home range varied from 3.03 to 164.83 ha (median = 17.91 ha) and core use area from 0.25 to 25.37 ha (median = 1.50 ha). Males exhibited the largest home ranges whereas females recorded the largest core areas. Subadults covered the largest areas at both spatial scale. These difference were not statistically significant.Interestingly, M. leptorhynchus showed more space sharing than other crocodylian species, though with significant temporal avoidance-likely an adaptive behaviour used to reduce risks of conflict in high density environments. Our emergence assessment, though potentially confounded by transmitter placement, indicated limited basking behaviour in this species with unknown effect on its detection probability. All individuals, irrespective of size and sex, principally used main water courses. Ultimately our findings provide the first data on M. leptorhynchus home range and social organisation, which may help direct targeted management strategies for this species. K E Y W O R D S emergence, habitat use, home range, protected area, spatial ecology, VHF telemetry Résumé Mecistops leptorhynchus (Bennett, 1935) est l'un des crocodyliens les moins étudiés au monde, dont très peu d'informations relatives à la structure des mouvements et l'utilisation de l'habitat existent. Nous avons utilisé un suivi radio VHF, pour déterminer le domaine vital et la zone d'utilisation centrale, la dynamique des interactions spatiotemporelles de 30 individus de Mecistops leptorhynchus (14 femelles et 16 mâles), et

West African crocodylians are among the most threatened and least studied crocodylian species globally. Assessing population status and establishing a basis for population monitoring is the highest priority action for this region. Monitoring of crocodiles is influenced by many factors that affect detectability, including environmental variables and individual‐ or population‐level wariness. We investigated how these factors affect detectability and counts of the critically endangered Mecistops cataphractus and the newly recognized Crocodylus suchus. We implemented 195 repetitive surveys at 38 sites across Côte d’Ivoire between 2014 and 2019. We used an occupancy‐based approach and a count‐based GLMM analysis to determine the effect of environmental and anthropogenic variables on detection and modeled crocodile wariness over repetitive surveys. Despite their rarity and level of threat, detection probability of both species was relatively high (0.75 for M. cataphractus and 0.81 for C. suchus), but a minimum of two surveys were required to infer absence of either species with 90% confidence. We found that detection of M. cataphractus was significantly negatively influenced by fishing net encounter rate, while high temperature for the previous 48 h of the day of the survey increased C. suchus detection. Precipitation and aquatic vegetation had significant negative and positive influence, respectively, on M. cataphractus counts and showed the opposite effect for C. suchus counts. We also found that fishing encounter rate had a significant negative effect on C. suchus counts. Interestingly, survey repetition did not generally affect wariness for either species, though there was some indication that at least M. cataphractus was more wary by the fourth replicate. These results are informative for designing future survey and monitoring protocols for these threatened crocodylians in West Africa and for other endangered crocodylians globally.