Evaluation of the use of drones to monitor a diverse crocodylian assemblage in West Africa
Clément Aubert
A B C K , Gilles Le Moguédec D , Cindy Assio A , Rumsaïs Blatrix E , Michel N’dédé Ahizi C F , Georges Codjo Hedegbetan G , Nathalie Gnanki Kpera H , Vincent Lapeyre I , Damien Martin G , Pierrick Labbé B J and Matthew H. Shirley A C
+ Author Affiliations
- Author Affiliations
A Institute of Environment, Florida International University, Biscayne Bay Campus, AC1 210, 3000 N.E. 151st Street, North Miami, FL 33181, USA.
B Institut des Sciences de l’Evolution de Montpellier (UMR 5554, CNRS-UM-IRD-EPHE), Université de Montpellier, Montpellier, 34095 Cedex 5, France.
C Project Mecistops, 615 Waterside Way, Sarasota, FL 34242, USA.
D AMAP, Université Montpellier, INRAE, CIRAD, CNRS, IRD, Montpellier, France.
E CEFE, University of Montpellier, CNRS University Paul Valéry Montpellier 3, EPHE, IRD, 1919 route de Mende, 34293 Montpellier, France.
F Laboratoire d’Environnement et de Biologie Aquatique, Université de Nangui, Abrogoua, 02 BP 801 Abidjan 02.
G Centre Régional de Recherche et d’Education pour un Développement Intégré (CREDI-ONG), BP 471 Abomey-Calavi, République du Bénin.
H National Institute of Agricultural Research of Benin (INRAB), BP 1915 Abomey-Calavi, République du Bénin.
I Conservation Program, Zoological Society of London, Regent’s Park, London, England NW1 4RY.
J Institut Universitaire de France, 1 Rue Descartes, 75231 Cedex 05, Paris.
K Corresponding author. Emails: clement.aubert34@hotmail.fr; clement.aubert@umontpellier.fr
Wildlife Research 49(1) 11-23 https://doi.org/10.1071/WR20170
Submitted: 1 October 2020 Accepted: 2 March 2021 Published: 17 June 2021
Abstract
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.
Keywords: Crocodylus, Mecistops, suchus, elephant, UAV, Pendjari.
References
Aké Assi, L. (1984). Flore de la Côte-d’Ivoire. Étude descriptive et biogéographique avec quelques notes ethnobotaniques. Tome I. II. III. Doctoral dissertation, Ph.D., Ès-Sc. Nat., FAST Université Felix Houphouët-Boigny, Abidjan, Ivory Coast.Avenard, J. M. (1971). ‘Le Milieu naturel de la Côte d’Ivoire’. (IRD Editions.)
Bayliss, P., Webb, G., Whitehead, P., Dempsey, K., and Smith, A. (1986). Estimating the abundance of saltwater crocodiles, Crocodylus porosus Schneider, in tidal wetlands of the Northern Territory: a mark–recapture experiment to correct spotlight counts to absolute numbers, and the calibration of helicopter and spotlight counts. Wildlife Research 13, 309–320.
| Estimating the abundance of saltwater crocodiles, Crocodylus porosus Schneider, in tidal wetlands of the Northern Territory: a mark–recapture experiment to correct spotlight counts to absolute numbers, and the calibration of helicopter and spotlight counts.Crossref | GoogleScholarGoogle Scholar |
Bennitt, E., Bartlam-Brooks, H. L. A., Hubel, T. Y., and Wilson, A. M. (2019). Terrestrial mammalian wildlife responses to Unmanned Aerial Systems approaches. Scientific Reports 9, 2142.
| Terrestrial mammalian wildlife responses to Unmanned Aerial Systems approaches.Crossref | GoogleScholarGoogle Scholar | 30765800PubMed |
Bevan, E., Whiting, S., Tucker, T., Guinea, M., Raith, A., and Douglas, R. (2018). Measuring behavioral responses of sea turtles, saltwater crocodiles, and crested terns to drone disturbance to define ethical operating thresholds. PLoS One 13, e0194460.
| Measuring behavioral responses of sea turtles, saltwater crocodiles, and crested terns to drone disturbance to define ethical operating thresholds.Crossref | GoogleScholarGoogle Scholar | 29561901PubMed |
Bonnin, N., Van Andel, A., Kerby, J., Piel, A., Pintea, L., and Wich, S. (2018). Assessment of chimpanzee nest detectability in drone-acquired images. Drones (Basel) 2, 17.
| Assessment of chimpanzee nest detectability in drone-acquired images.Crossref | GoogleScholarGoogle Scholar |
Boucher, M., Tellez, M., and Anderson, J. T. (2017). A tail of two crocs: coding tail-spot patterns for individual identification of American (Crocodylus acutus) and Morelet’s (Crocodylus moreletii) crocodiles. Mesoamerican Herpetology 4, 14.
Bouwman, H., and Cronje, E. (2016). An 11-digit identification system for individual Nile crocodiles using natural markings. Koedoe 58, a1351.
| An 11-digit identification system for individual Nile crocodiles using natural markings.Crossref | GoogleScholarGoogle Scholar |
Brashares, J. S., Arcese, P., Sam, M. K., Coppolillo, P. B., Sinclair, A. R. E., and Balmford, A. (2004). Bushmeat hunting, wildlife declines, and fish supply in West Africa. Science 306, 1180–1183.
| Bushmeat hunting, wildlife declines, and fish supply in West Africa.Crossref | GoogleScholarGoogle Scholar | 15539602PubMed |
Brisson-Curadeau, É., Bird, D., Burke, C., Fifield, D. A., Pace, P., Sherley, R. B., and Elliott, K. H. (2017). Seabird species vary in behavioural response to drone census. Scientific Reports 7, 17884.
| Seabird species vary in behavioural response to drone census.Crossref | GoogleScholarGoogle Scholar | 29263372PubMed |
Brito, J. C., Martínez-Freiría, F., Sierra, P., Sillero, N., and Tarroso, P. (2011). Crocodiles in the Sahara Desert: an update of distribution, habitats and population status for conservation planning in Mauritania. PLoS One 6, e14734.
| Crocodiles in the Sahara Desert: an update of distribution, habitats and population status for conservation planning in Mauritania.Crossref | GoogleScholarGoogle Scholar | 21364897PubMed |
Chirio, L. (2009). Inventaire des reptiles de la région de la Réserve de Biosphère Transfrontalière du W (Niger/Bénin/Burkina Faso: Afrique de l’Ouest). Bulletin de la Société Herpétologique de France 132, 13–41.
Choquenot, D., and Webb, G. J. W. (1987). A photographic technique for estimating the size of crocodiles seen in spotlight surveys and for quantifying observer bias. Wildlife Management: Crocodiles and Alligators 217–224.
CILSS (2016). Landscapes of West Africa – A Window on a Changing World. (U.S. Geological Survey: Garretson, SD, USA.)
Coetzee, B. W. T., Ferreira, S. M., and Maciejewski, K. (2018). Challenges and opportunities for monitoring wild Nile crocodiles with scute mark–recapture photography. Koedoe 60, 1–5.
| Challenges and opportunities for monitoring wild Nile crocodiles with scute mark–recapture photography.Crossref | GoogleScholarGoogle Scholar |
Covey, R., and McGraw, W. S. (2014). Monkeys in a West African bushmeat market: implications for cercopithecid conservation in eastern Liberia. Tropical Conservation Science 7, 115–125.
| Monkeys in a West African bushmeat market: implications for cercopithecid conservation in eastern Liberia.Crossref | GoogleScholarGoogle Scholar |
Cunningham, S. W., Shirley, M. H., and Hekkala, E. R. (2016). Fine scale patterns of genetic partitioning in the rediscovered African crocodile, Crocodylus suchus (Saint-Hilaire 1807). PeerJ 4, e1901.
| Fine scale patterns of genetic partitioning in the rediscovered African crocodile, Crocodylus suchus (Saint-Hilaire 1807).Crossref | GoogleScholarGoogle Scholar | 27114867PubMed |
Dallmeier, F., Alonso, A., Campbell, P., Lee, M. E., Buij, R., and Pauwels, O. S. G. (2006). Ecological indicators for the industrial corridor in the Gamba Complex of Protected Areas: a zone of high biodiversity value and oil exploration in southwest Gabon. Bulletin of the Biological Society of Washington 12, 243–252.
Djaha, K., Yves, A. Y. C., Edouard, K. K., Edouard, N. G. K., and Kouadio, A. (2008). Preliminary floristic inventory and diversity in Azagny National Park (Côte d’Ivoire). European Journal of Scientific Research 23, 537–547.
Droulers, M. (2004). ‘L’Amazonie: vers un développement durable.’ (Armand Colin.)
Dulava, S., Bean, W. T., and Richmond, O. M. W. (2015). Environmental reviews and case studies: applications of unmanned aircraft systems (UAS) for waterbird surveys. Environmental Practice 17, 201–210.
| Environmental reviews and case studies: applications of unmanned aircraft systems (UAS) for waterbird surveys.Crossref | GoogleScholarGoogle Scholar |
Eaton, M. J. (2010). Dwarf crocodile Osteolaemus tetraspis. In ‘Crocodiles. Status Survey and Conservation Action Plan’. 3rd edn. (Eds S. C. Manolis and C. Stevenson.) pp. 127–132. (Crocodile Specialist Group: Darwin, NT, Australia.)
Elsey, R. M., and Trosclair, P. L. (2016). The use of an unmanned aerial vehicle to locate alligator nests. Southeastern Naturalist (Steuben, ME) 15, 76–82.
| The use of an unmanned aerial vehicle to locate alligator nests.Crossref | GoogleScholarGoogle Scholar |
Evans, L. J., Jones, T. H., Pang, K., Saimin, S., and Goossens, B. (2016). Spatial ecology of estuarine crocodile (Crocodylus porosus) nesting in a fragmented landscape. Sensors 16, 1527.
| Spatial ecology of estuarine crocodile (Crocodylus porosus) nesting in a fragmented landscape.Crossref | GoogleScholarGoogle Scholar |
Ezat, M. A., Fritsch, C. J., and Downs, C. T. (2018). Use of an unmanned aerial vehicle (drone) to survey Nile crocodile populations: a case study at Lake Nyamithi, Ndumo game reserve, South Africa. Biological Conservation 223, 76–81.
| Use of an unmanned aerial vehicle (drone) to survey Nile crocodile populations: a case study at Lake Nyamithi, Ndumo game reserve, South Africa.Crossref | GoogleScholarGoogle Scholar |
Ferreira, S. M., and Pienaar, D. (2011). Degradation of the crocodile population in the Olifants River Gorge of Kruger National Park, South Africa. Aquatic Conservation 21, 155–164.
| Degradation of the crocodile population in the Olifants River Gorge of Kruger National Park, South Africa.Crossref | GoogleScholarGoogle Scholar |
Floreano, D., and Wood, R. J. (2015). Science, technology and the future of small autonomous drones. Nature 521, 460–466.
| Science, technology and the future of small autonomous drones.Crossref | GoogleScholarGoogle Scholar | 26017445PubMed |
Fukuda, Y., Saalfeld, K., Lindner, G., and Nichols, T. (2013). Estimation of total length from head length of saltwater crocodiles (Crocodylus porosus) in the Northern Territory, Australia. Journal of Herpetology 47, 34–40.
Gademer, A., Mainfroy, F., Beaudoin, L., Avanthey, L., Germain, V., Chéron, C., Monat, S., and Rudant, J. P. (2009). Faucon noir UAV project development of a set of tools for managing, visualizing and mosaicing centimetric UAV images. In ‘2009 IEEE International Geoscience and Remote Sensing Symposium’, Cape Town, South Africa. pp. III-228–III-231.
Harvey, K. R., and Hill, G. J. E. (2003). Mapping the nesting habitats of saltwater crocodiles (Crocodylus porosus) in Melacca Swamp and the Adelaide River wetlands, Northern Territory: an approach using remote sensing and GIS. Wildlife Research 30, 365–375.
| Mapping the nesting habitats of saltwater crocodiles (Crocodylus porosus) in Melacca Swamp and the Adelaide River wetlands, Northern Territory: an approach using remote sensing and GIS.Crossref | GoogleScholarGoogle Scholar |
Hodgson, J. C., Mott, R., Baylis, S. M., Pham, T. T., Wotherspoon, S., Kilpatrick, A. D., Segaran, R. R., Reid, I., Terauds, A., and Koh, L. P. (2018). Drones count wildlife more accurately and precisely than humans. Methods in Ecology and Evolution 9, 1160–1167.
| Drones count wildlife more accurately and precisely than humans.Crossref | GoogleScholarGoogle Scholar |
Inman, V. L., Kingsford, R. T., Chase, M. J., and Leggett, K. E. A. (2019). Drone-based effective counting and ageing of hippopotamus (Hippopotamus amphibius) in the Okavango Delta in Botswana. PLoS One 14, e0219652.
| Drone-based effective counting and ageing of hippopotamus (Hippopotamus amphibius) in the Okavango Delta in Botswana.Crossref | GoogleScholarGoogle Scholar | 31805046PubMed |
Inoussa, M. M., Padonou, E. A., Lykke, A. M., Glèlè Kakaï, R., Bakasso, Y., Mahamane, A., and Saadou, M. (2017). Contrasting population structures of two keystone woodland species of W National Park, Niger. South African Journal of Botany 112, 95–101.
| Contrasting population structures of two keystone woodland species of W National Park, Niger.Crossref | GoogleScholarGoogle Scholar |
Ipavec, A., Maillard, D., Chardonnet, P., Danés, C., Wally, M., Lompo, M., and Dulieu, D. (2007). Elephant movement in W regional park, western Africa. Pachyderm 43, 36–42.
Kelaher, B. P., Colefax, A. P., Tagliafico, A., Bishop, M. J., Giles, A., and Butcher, P. A. (2020). Assessing variation in assemblages of large marine fauna off ocean beaches using drones. Marine and Freshwater Research 71, 68.
| Assessing variation in assemblages of large marine fauna off ocean beaches using drones.Crossref | GoogleScholarGoogle Scholar |
King, L. E., Lala, F., Nzumu, H., Mwambingu, E., and Douglas‐Hamilton, I. (2017). Beehive fences as a multidimensional conflict-mitigation tool for farmers coexisting with elephants. Conservation Biology 31, 743–752.
| Beehive fences as a multidimensional conflict-mitigation tool for farmers coexisting with elephants.Crossref | GoogleScholarGoogle Scholar | 28221699PubMed |
Kiszka, J. J., Mourier, J., Gastrich, K., and Heithaus, M. R. (2016). Using unmanned aerial vehicles (UAVs) to investigate shark and ray densities in a shallow coral lagoon. Marine Ecology Progress Series 560, 237–242.
| Using unmanned aerial vehicles (UAVs) to investigate shark and ray densities in a shallow coral lagoon.Crossref | GoogleScholarGoogle Scholar |
Kofron, C. P. (1992). Status and habitats of the three African crocodiles in Liberia. Journal of Tropical Ecology 8, 265–273.
| Status and habitats of the three African crocodiles in Liberia.Crossref | GoogleScholarGoogle Scholar |
Koh, L. P., and Wich, S. A. (2012). Dawn of drone ecology: low-cost autonomous aerial vehicles for conservation. Tropical Conservation Science 5, 121–132.
| Dawn of drone ecology: low-cost autonomous aerial vehicles for conservation.Crossref | GoogleScholarGoogle Scholar |
Linchant, J., Lhoest, S., Quevauvillers, S., Lejeune, P., Vermeulen, C., Semeki Ngabinzeke, J., Luse Belanganayi, B., Delvingt, W., and Bouché, P. (2018). UAS imagery reveals new survey opportunities for counting hippos. PLoS One 13, e0206413.
| UAS imagery reveals new survey opportunities for counting hippos.Crossref | GoogleScholarGoogle Scholar | 30427890PubMed |
Lisein, J., Bonnet, S., Lejeune, P., and Pierrot-Deseilligny, M. (2014). Modélisation de la canopée forestière par photogrammétrie depuis des images acquises par drone. Revue Française de Photogrammétrie et de Télédétection 206, .
Luiselli, L., Akani, G. C., Ebere, N., Angelici, F. M., Amori, G., and Politano, E. (2012). Macro-habitat preferences by the African manatee and crocodiles: ecological and conservation implications. Web Ecology 12, 39–48.
| Macro-habitat preferences by the African manatee and crocodiles: ecological and conservation implications.Crossref | GoogleScholarGoogle Scholar |
Martin, J., Edwards, H. H., Burgess, M. A., Percival, H. F., Fagan, D. E., Gardner, B. E., Ortega-Ortiz, J. G., Ifju, P. G., Evers, B. S., and Rambo, T. J. (2012). Estimating Distribution of Hidden Objects with Drones: from Tennis Balls to Manatees. PLoS One 7, e38882.
| Estimating Distribution of Hidden Objects with Drones: from Tennis Balls to Manatees.Crossref | GoogleScholarGoogle Scholar | 23300519PubMed |
Mazzotti, F. J., Best, G. R., Brandt, L. A., Cherkiss, M. S., Jeffery, B. M., and Rice, K. G. (2009). Alligators and crocodiles as indicators for restoration of Everglades ecosystems. Ecological Indicators 9, S137–S149.
| Alligators and crocodiles as indicators for restoration of Everglades ecosystems.Crossref | GoogleScholarGoogle Scholar |
McCullagh, P. (2018). ‘Generalized Linear Models.’ (Routledge.)
McEvoy, J. F., Hall, G. P., and McDonald, P. G. (2016). Evaluation of unmanned aerial vehicle shape, flight path and camera type for waterfowl surveys: disturbance effects and species recognition. PeerJ 4, e1831.
| Evaluation of unmanned aerial vehicle shape, flight path and camera type for waterfowl surveys: disturbance effects and species recognition.Crossref | GoogleScholarGoogle Scholar | 27020132PubMed |
Mukwazvure, A., and Magadza, T. B. (2014). A survey on anti-poaching strategies. International Journal of Science and Research 3, 1064–1066.
Mulero-Pázmány, M., Jenni-Eiermann, S., Strebel, N., Sattler, T., Negro, J. J., and Tablado, Z. (2017). Unmanned aircraft systems as a new source of disturbance for wildlife: a systematic review. PLoS One 12, e0178448.
| Unmanned aircraft systems as a new source of disturbance for wildlife: a systematic review.Crossref | GoogleScholarGoogle Scholar | 28636611PubMed |
Myers, N., Mittermeier, R. A., Mittermeier, C. G., da Fonseca, G. A. B., and Kent, J. (2000). Biodiversity hotspots for conservation priorities. Nature 403, 853–858.
| Biodiversity hotspots for conservation priorities.Crossref | GoogleScholarGoogle Scholar | 10706275PubMed |
Ngama, S., Korte, L., Bindelle, J., Vermeulen, C., and Poulsen, J. R. (2016). How bees deter elephants: beehive trials with forest elephants (Loxodonta africana cyclotis) in Gabon. PLoS One 11, e0155690.
| How bees deter elephants: beehive trials with forest elephants (Loxodonta africana cyclotis) in Gabon.Crossref | GoogleScholarGoogle Scholar | 27196059PubMed |
Nichols, J. D., Hines, J. E., Sauer, J. R., Fallon, F. W., Fallon, J. E., and Heglund, P. J. (2000). A double-observer approach for estimating detection probability and abundance from point counts. The Auk 117, 393–408.
| A double-observer approach for estimating detection probability and abundance from point counts.Crossref | GoogleScholarGoogle Scholar |
Ogden, L. E. (2013). Drone ecology. BioScience 63, 776.
| Drone ecology.Crossref | GoogleScholarGoogle Scholar |
Pomeroy, P., O’Connor, L., and Davies, P. (2015). Assessing use of and reaction to unmanned aerial systems in gray and harbor seals during breeding and molt in the UK. Journal of Unmanned Vehicle Systems 3, 102–113.
| Assessing use of and reaction to unmanned aerial systems in gray and harbor seals during breeding and molt in the UK.Crossref | GoogleScholarGoogle Scholar |
Pooley, A. C. (1982). National Report: Côte-d’Ivoire. In ‘Proceedings of the 5th Working Meeting of the IUCN/SSC Crocodile Specialist Group’, 12–16 August 1980, Florida State Museum, Gainesville, Florida, USA.
R Core Team (2018). ‘R: A language and environment for statistical computing.’ (R Foundation for Statistical Computing: Vienna, Austria.) Available at https://www.R-project.org/.
Ramsar (2018). ‘Fiche descriptive Ramsar, Site n° 790, Parc National d’Azagny, Côte d’Ivoire.’ (Service d’information sur les Sites Ramsar.) Available at https://rsis.ramsar.org/RISapp/files/RISrep/CI790RIS_1809_fr.pdf.
Rouxel, C. (2010). Conservation de la biodiversité et développement durable des territoires. Transition agraire et paysagère en zone tampon de la Réserve de biosphère du Parc régional du W, Afrique de l’ouest. Économie Rurale. Agricultures, Alimentations, Territoires 320, 39–52.
Rush, G. P., Clarke, L. E., Stone, M., and Wood, M. J. (2018). Can drones count gulls? Minimal disturbance and semiautomated image processing with an unmanned aerial vehicle for colony-nesting seabirds. Ecology and Evolution 8, 12 322–12 334.
| Can drones count gulls? Minimal disturbance and semiautomated image processing with an unmanned aerial vehicle for colony-nesting seabirds.Crossref | GoogleScholarGoogle Scholar |
Scarpa, L. J., and Piña, C. I. (2019). The use of drones for conservation: a methodological tool to survey caimans nests density. Biological Conservation 238, 108 235.
| The use of drones for conservation: a methodological tool to survey caimans nests density.Crossref | GoogleScholarGoogle Scholar |
Seydou, Y. Z., Charles, S. Y., Sabas, B. Y. S., Issouf, B., and Apollinaire, K. K. (2017). Diversite Floristique Et Structure Des Fragments Forestiers Du Sud-Ouest Du Parc National De La Comoe Apres Les Conflits Des Annees 2000 En Côte d’Ivoire. European Scientific Journal 13, 421–439.
Shirley, M. H. (2010). Slender-snouted Crocodile Crocodylus cataphractus. In ‘Crocodiles. Status Survey and Conservation Action Plan’, 3rd edn. (Eds S. C. Manolis and C. Stevenson.) pp. 54–58. (Crocodile Specialist Group: Darwin, NT, Australia.)
Shirley, M. H. (2014). Mecistops cataphractus. In ‘The IUCN Red List of Threatened Species 2014, e.T5660A3044332’. Available at https://dx.doi.org/10.2305/IUCN.UK.2014-1.RLTS.T5660A3044332.en.
Shirley, M. H., and Eaton, M. J. (2008). Africa regional reports: trip report: Niger 2007. Crocodile Specialist Group Newsletter 27, 21–23.
Shirley, M. H., and Eaton, M. J. (2012). ‘Procédures Standard de Suivi des Populations de Crocodiles.’ (Groupe Spécialiste de Crocodiles.)
Shirley, M. H., and Yaokokore-Beibro, H. (2008). National Report: Côte-d’Ivoire. In ‘Proceedings of the 1st Meeting of the IUCN/SSC Crocodile Specialist Group in West Africa, Conservation and Breeding of Crocodiles’, Parc W, Niger, 13–15 November 2007.
Shirley, M. H., Oduro, W., and Beibro, H. Y. (2009). Conservation status of crocodiles in Ghana and Côte-d’Ivoire, West Africa. Oryx 43, 136–145.
| Conservation status of crocodiles in Ghana and Côte-d’Ivoire, West Africa.Crossref | GoogleScholarGoogle Scholar |
Shirley, M. H., Dorazio, R. M., Abassery, E., Elhady, A. A., Mekki, M. S., and Asran, H. H. (2012). A sampling design and model for estimating abundance of Nile crocodiles while accounting for heterogeneity of detectability of multiple observers. The Journal of Wildlife Management 76, 966–975.
| A sampling design and model for estimating abundance of Nile crocodiles while accounting for heterogeneity of detectability of multiple observers.Crossref | GoogleScholarGoogle Scholar |
Shirley, M. H., Carr, A. N., Nestler, J. H., Vliet, K. A., and Brochu, C. A. (2018). Systematic revision of the living African Slender-snouted crocodiles (Mecistops Gray, 1844). Zootaxa 4504, 151.
| Systematic revision of the living African Slender-snouted crocodiles (Mecistops Gray, 1844).Crossref | GoogleScholarGoogle Scholar | 30486023PubMed |
Somaweera, R., Nifong, J., Rosenblatt, A., Brien, M. L., Combrink, X., Elsey, R. M., Grigg, G., Magnusson, W. E., Mazzotti, F. J., Pearcy, A., Platt, S. G., Shirley, M. H., Tellez, M., van der Ploeg, J., Webb, G., Whitaker, R., and Webber, B. L. (2020). The ecological importance of crocodylians: towards evidence-based justification for their conservation. Biological Reviews of the Cambridge Philosophical Society 95, 936–959.
| The ecological importance of crocodylians: towards evidence-based justification for their conservation.Crossref | GoogleScholarGoogle Scholar | 32154985PubMed |
Swanepoel, D. G. J. (1996). Identification of the Nile crocodile Crocodylus niloticus by the use of natural tail marks. Koedoe 39, 113–115.
| Identification of the Nile crocodile Crocodylus niloticus by the use of natural tail marks.Crossref | GoogleScholarGoogle Scholar |
Tellería, J. L., El Mamy Ghaillani, H., Fernández-Palacios, J. M., Bartolomé, J., and Montiano, E. (2008). Crocodiles Crocodylus niloticus as a focal species for conserving water resources in Mauritanian Sahara. Oryx 42, 292–295.
| Crocodiles Crocodylus niloticus as a focal species for conserving water resources in Mauritanian Sahara.Crossref | GoogleScholarGoogle Scholar |
Thapa, G. J., Thapa, K., Thapa, R., Jnawali, S. R., Wich, S. A., Poudyal, L. P., and Karki, S. (2018). Counting crocodiles from the sky: monitoring the critically endangered gharial (Gavialis gangeticus) population with an unmanned aerial vehicle (UAV). Journal of Unmanned Vehicle Systems 6, 71–82.
| Counting crocodiles from the sky: monitoring the critically endangered gharial (Gavialis gangeticus) population with an unmanned aerial vehicle (UAV).Crossref | GoogleScholarGoogle Scholar |
Thorbjarnarson, J. (1999). Crocodile tears and skins: international trade, economic constraints, and limits to the sustainable use of crocodilians. Conservation Biology 13, 465–470.
| Crocodile tears and skins: international trade, economic constraints, and limits to the sustainable use of crocodilians.Crossref | GoogleScholarGoogle Scholar |
UNESCO (2003). ‘Convention concernant la protection des patrimoines mondiaux culturels et naturels comité du patrimoine mondial: Vingt-septième session’, 30 June – 5 July 2003. (Siège de l’UNESCO , Salle XII: Paris, France.)
Vas, E., Lescroël, A., Duriez, O., Boguszewski, G., and Grémillet, D. (2015). Approaching birds with drones: first experiments and ethical guidelines. Biology Letters 11, 20140754.
| Approaching birds with drones: first experiments and ethical guidelines.Crossref | GoogleScholarGoogle Scholar | 25652220PubMed |
Ventura, D., Bruno, M., Jona Lasinio, G., Belluscio, A., and Ardizzone, G. (2016). A low-cost drone based application for identifying and mapping of coastal fish nursery grounds. Estuarine, Coastal and Shelf Science 171, 85–98.
| A low-cost drone based application for identifying and mapping of coastal fish nursery grounds.Crossref | GoogleScholarGoogle Scholar |
Vollrath, F., and Douglas-Hamilton, I. (2002). African bees to control African elephants. Naturwissenschaften 89, 508–511.
| African bees to control African elephants.Crossref | GoogleScholarGoogle Scholar | 12451453PubMed |
Waitkuwait, W. E. (1989). Present knowledge of the West African slender-snouted crocodile, Crocodylus cataphractus Cuvier 1824 and the West African dwarf crocodile Osteolaemus tetraspis Cope 1861. In ‘Crocodiles. Ecology, Management and Conservation’. (Ed. Crocodile Specialist Group of the Species Survival Commission.) Gland, pp. 260–275. (International Union for the Conservation of Nature.)
Weimerskirch, H., Prudor, A., and Schull, Q. (2018). Flights of drones over sub-Antarctic seabirds show species- and status-specific behavioural and physiological responses. Polar Biology 41, 259–266.
| Flights of drones over sub-Antarctic seabirds show species- and status-specific behavioural and physiological responses.Crossref | GoogleScholarGoogle Scholar |
Weissensteiner, M. H., Poelstra, J. W., and Wolf, J. B. W. (2015). Low-budget ready-to-fly unmanned aerial vehicles: an effective tool for evaluating the nesting status of canopy-breeding bird species. Journal of Avian Biology 46, 425–430.
| Low-budget ready-to-fly unmanned aerial vehicles: an effective tool for evaluating the nesting status of canopy-breeding bird species.Crossref | GoogleScholarGoogle Scholar |
Wich, S., Dellatore, D., Houghton, M., Ardi, R., and Koh, L. P. (2015). A preliminary assessment of using conservation drones for Sumatran orang-utan (Pongo abelii) distribution and density. Journal of Unmanned Vehicle Systems 4, 45–52.
| A preliminary assessment of using conservation drones for Sumatran orang-utan (Pongo abelii) distribution and density.Crossref | GoogleScholarGoogle Scholar |
Wilson, A. M., Boyle, K. S., Gilmore, J. L., Kiefer, C. J., and Walker, M. F. (2020). Species-specific responses of bird song output in the presence of drones. BioRxiv , 2020.07.19.211045.
| Species-specific responses of bird song output in the presence of drones.Crossref | GoogleScholarGoogle Scholar |
Zahawi, R. A., Dandois, J. P., Holl, K. D., Nadwodny, D., Reid, J. L., and Ellis, E. C. (2015). Using lightweight unmanned aerial vehicles to monitor tropical forest recovery. Biological Conservation 186, 287–295.
| Using lightweight unmanned aerial vehicles to monitor tropical forest recovery.Crossref | GoogleScholarGoogle Scholar |
