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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
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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.
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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.
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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.
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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
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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.
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