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First Evidence for Reproduction of Nile Monitors (Varanus niloticus) in Palm Beach County
Jennifer Ketterlin Eckles, Frank Mazzotti, Dennis Giardina, Dallas Hazelton, and H. LeRoy Rodgers

Southeastern Naturalist, Volume 15, Special Issue 8 (2017): 114–119

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Southeastern Naturalist J. Ketterlin Eckles, F. Mazzotti, D. Giardina, D. Hazelton, and H.L. Rodgers 2017 114 Vol. 15, Special Issue 8 114 First Evidence for Reproduction of Nile Monitors (Varanus niloticus) in Palm Beach County Jennifer Ketterlin Eckles1,*, Frank Mazzotti2, Dennis Giardina3, Dallas Hazelton4, and H. LeRoy Rodgers5 Abstract - Varanus niloticus (Nile Monitor) is a large, carnivorous lizard native to sub- Saharan Africa. A breeding population of Nile Monitors was documented in southwestern Florida (Lee County) in 2004. In 2011, the Florida Fish and Wildlife Conservation Commission began surveying the C-51 canal on the southeastern Florida coast in Palm Beach County in response to multiple reports of monitor lizards. These surveys resulted in observations of 9 Nile Monitors, including a hatchling and copulating pair. Three additional hatchlings were later reported by private citizens. These observations provide evidence of a breeding population of these non-native lizards in southeastern Florida. Introduction More non-native lizard species are reproducing in Florida than native lizard species (Engeman et al. 2011). In fact, the 4 largest species of lizards currently breeding in Florida are from other countries (Engeman et al. 2011). Varanus niloticus (L.) (Nile Monitor) is one of these large lizards (growing up to 2.4 m) and is native to sub-Saharan Africa. They are excellent climbers and swimmers and are known nest predators of the largest reptile in Africa, Crocodylus niloticus (Laurenti) (Nile Crocodile; Cott 1960, Mohda 1965). Nile Monitors are also opportunistic feeders in their native range and inhabit a variety of habitats adjacent to water, including residential and agricultural areas (Bennett 1995). Nile Monitors have been reproducing in the city of Cape Coral, Lee County, FL, for more than 20 years (Enge et al. 2004). In addition to the self-sustaining population in Cape Coral, sightings by government employees and other individuals indicate breeding populations may also exist near the Homestead-Miami Speedway in Miami-Dade County, the C-51 Canal in Palm Beach County, and in Broward County (Fig. 1). No documentation for reproducing populations of Nile Monitors in these counties has been published. In this paper, we report the first observations of reproduction for Nile Monitors in Palm Beach County, FL. 1Florida Fish and Wildlife Conservation Commission, University of Florida Fort Lauderdale Research and Education Center, Davie, FL 33314. 2Wildlife Ecology and Conservation, University of Florida Fort Lauderdale Research and Education Center, Davie, FL 33314. 3Florida Fish and Wildlife Conservation Commission, Naples, FL 34114. 4Natural Areas Management, Miami-Dade County Parks, Recreation and Open Spaces, Miami, FL 33170. 5Land Resources Bureau, South Florida Water Management District, West Palm Beach, FL 33406. *Corresponding author - jkett@ufl.edu. Manuscript Editor: John Placyk Everglades Invasive Species 2017 Southeastern Naturalist 15(Special Issue 8):114–119 Southeastern Naturalist 115 J. Ketterlin Eckles, F. Mazzotti, D. Giardina, D. Hazelton, and H.L. Rodgers 2017 Vol. 15, Special Issue 8 Field-Site Description The C-51 canal is the primary canal in the C-51 basin, which is part of the large system of canals and control structures in south Florida created for flood control and Figure 1. Map of Nile Monitor observations in south Florida as of 31 December 2015 (inset map) and the field site at the C-51 canal in Palm Beach County, with locations of Nile Monitors referenced in this publication. Southeastern Naturalist J. Ketterlin Eckles, F. Mazzotti, D. Giardina, D. Hazelton, and H.L. Rodgers 2017 116 Vol. 15, Special Issue 8 water delivery purposes (Lodge 2010). The canal runs parallel to Southern Boulevard/ US Hwy 98 in Palm Beach County (Fig. 1). The eastern section of the canal runs along a busy road to the north and is bordered by a county park, businesses, and residences to the south. Further west, the canal is bordered by residential areas to the north and south and Stormwater Treatment Area (STA) 1E and the Arthur R. Marshall Loxahatchee National Wildlife Refuge to the south. Numerous smaller canals and ditches drain into the C-51 canal from the north and south. Methods In response to numerous observations of Nile Monitors in southeastern Florida, staff with the Florida Fish and Wildlife Conservation Commission (FWC) conducted a status assessment in 2011 in coordination with other partners of the Everglades Cooperative Invasive Species Management Area (ECISMA). During May and June of that year, a total of 4 surveys were conducted by boat in the C-51 canal from the intersection of the canal with I-95 to canal barrier at SR 7/US Hwy 441, a stretch measuring ~15 km. Observations of Nile Monitors were recorded. Results Three of the surveys along the C-51 canal in Palm Beach County by boat in May–June 2011 yielded 7 observations of monitors. No monitors were captured and thus no lengths were recorded, but 6 of the monitors were estimated to be longer than 1 m, and 1 monitor was estimated to be ~30 cm in total length (TL), consistent with the size of a hatchling (Gore et al. 2003). During the fourth survey on 10 June 2011, two adult Nile Monitors that appeared to be copulating were observed on the north side of the C-51 canal bank, east of the Florida Turnpike (Fig. 2). On 12 Figure 2. Copulating behavior of Nile Monitors along C-51 canal in Palm Beach County, FL. Photograph © Florida Fish and Wildlife Conservation Commission. Southeastern Naturalist 117 J. Ketterlin Eckles, F. Mazzotti, D. Giardina, D. Hazelton, and H.L. Rodgers 2017 Vol. 15, Special Issue 8 January 2012 and on 4 February 2012, two separate private citizens living adjacent to the C-51 canal found single hatchling Nile Monitors in their pools (Figs. 3, 4) and reported the sightings to FWC. The hatchling monitor removed in January had a snout–vent-length (SVL) of ~130 mm and a TL of ~371 mm, as reported by the pet Figure 3. Hatchling Nile Monitor collected 12 January 2012 in Palm Beach County, FL. Photograph © Wild Cargo Pets, Inc. Figure 4. Hatchling Nile Monitor collected 4 February 2012 in Palm Beach County, FL. Photograph © Florida Fish and Wildlife Conservation Commission. Southeastern Naturalist J. Ketterlin Eckles, F. Mazzotti, D. Giardina, D. Hazelton, and H.L. Rodgers 2017 118 Vol. 15, Special Issue 8 shop where the animal was deposited. The second hatchling monitor removed was turned over to FWC and was kept live for outreach purposes. It measured 121 mm SVL and 297 mm TL. On 13 November 2014, FWC received a verified, secondhand report of a hatchling monitor recovered at another residence along the C-51 canal. This occurrence is the easternmost sighting of a hatchling monitor. Discussion This paper describes the first confirmed reproducing population of Nile Monitors in southeastern Florida. Nile Monitors are known to be associated with freshwater and marine habitats (Gore et al. 2003), both abundant in southeastern Florida (Lodge 2010). Similar to the Cape Coral (Enge et al. 2004) sightings, monitors belonging to the Palm Beach County population have been observed along canals, especially in residential areas. This trend could be the result of increased opportunities for detection along canals and, more recently, regular surveys in the area but is also consistent with habitat use by the species in their native range. In Africa, Nile Monitors also thrive near human settlements and are usually associated with swamps, marshes, and rivers (Bennett 1995). Nile Monitors spend most of their daily activity time in the water (de Buffrénil and Hémery 2002), basking on logs, banks of rivers, and edges of wetlands (Edroma and Ssali 1983, Muhigwa 1998). Besides observations of direct predation by Nile Monitors on individual animals (Campbell 2005; Enge et al. 2004; F. Mazzotti, 2016 unpubl. data) adverse impacts of Nile Monitors on a species or ecosystem as a whole have yet to be detected in Florida. However, observations of direct predation from the Cape Coral and Palm Beach County populations along with literature from their native range suggest this species could potentially threaten a wide variety of species native to Florida (Enge et al. 2004; Engeman et al. 2011; F. Mazzotti, 2016 unpubl. data). The proximity of the Palm Beach County population to the Greater Everglades is especially concerning due to the presence of many threatened and endangered species and the vast area of suitable habitat in that area. Nile Monitors could impact species such as Alligator mississippiensis (Daudin) (American Alligator) or Crocodylus acutus (Cuvier) (American Crocodile) via competition due to their similar habits and via predation, as they are known nest-predators of Nile Crocodiles in Africa. FWC began control efforts soon after the discovery of this breeding population in Palm Beach County because of the potential threats the species could pose to a variety of native wildlife. The species had already been listed as a conditional species in 2010 by FWC, meaning they can no longer be sold or acquired as a personal pet in Florida, limiting the likelihood of new introductions. Management actions, including trapping, monthly surveys, and removal of individuals along the C-51 canal and other adjoined canals continue to be conducted by FWC, the University of Florida, and South Florida Water Management District. The effects of these management actions, along with additional detection and control efforts using remote cameras and different bait types and live trap models are currently being evaluated. Because the population appears to be relatively localized, eradication may be Southeastern Naturalist 119 J. Ketterlin Eckles, F. Mazzotti, D. Giardina, D. Hazelton, and H.L. Rodgers 2017 Vol. 15, Special Issue 8 possible, and ongoing research aims to keep track of the status of this Nile Monitor population and the efficacy of control measures. Acknowledgments We are grateful for information provided by an anonymous source regarding regular sightings of this species along the C-51 canal. Verification of this population of Nile Monitors was conducted by the Florida Fish and Wildlife Conservation Commission (FWC) with assistance from members of the Everglades Cooperative Invasive Species Management Area. As the managing fish and wildlife agency in Florida, FWC did not require a permit or IACUC for the collection or possession of animals obtained during this project. Literature Cited Bennett, D. 1995. A Little Book of Monitor Lizards. Viper Press, Glossop, UK. 207 pp. Campbell, T.S. 2005. Eradication of introduced carnivorous lizards from the Southwest Florida. Final Report to the National Fish and Wildlife Foundation General Challenge Grant Program, University of Tampa, Tampa, FL. Pp. 1–30. Cott, H.B. 1960. Scientific results of an enquiry into the ecology and economic status of the Nile Crocodile in Uganda and northern Rhodesia. Transactions of the Zoological Society of London 29:212–356. de Buffrénil, V., and G. Hémery. 2002. Variation in longevity, growth, and morphology in exploited Nile Monitors (Varanus niloticus) from Sahelian Africa. Journal of Herpetology 36:419–426. Edroma, E.L., and W. Ssali. 1983. Observations on the Nile Monitor Lizard (Varanus niloticus, L.) in Queen Elizabeth National Park, Uganda. African Journal of Ecology 21:197–201. Enge, K.M., K.L Krysko, K.R. Hankins, T.S. Campbell, and F.W. King. 2004. Status of the Nile Monitor, Varanus niloticus, in southwestern Florida. Southeastern Naturalist 3:571–582. Engeman, R., E. Jacobson, M.L. Avery, and W.E. Meshaka Jr. 2011. The aggressive invasion of exotic reptiles in Florida with a focus on prominent species: A review. Current Zoology 57(5):599−612. Gore, J., K. Enge, and P. Moler. 2003. Nile Monitor (Varanus niloticus) Bioprofile. Florida Fish and Wildlife Conservation Commission, Tallahassee, FL. Lodge, T.E. 2010. The Everglades Handbook: Understanding the Ecosystem. 3rd Edition. CRC, Boca Raton, FL. 392 pp. Mohda, M.L. 1965. The ecology of the Nile Crocodile (Crocodylus niloticucs) on Central Island, Lake Rudolf. East African Wildlife Journal 5:74–95. Muhigwa, J.B. 1998. Diel activity and biotope choices of the Nile Monitor Lizard in western Kenya. African Journal of Ecology 36:271–275.