Pampas foxes as prey of yellow anacondas

Abstract

Carnivore predation by other predators is rarely observed in nature. Here we describe two predation events and report a third one of adult pampas foxes being eaten by yellow anacondas in Corrientes, north east Argentina.

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Chatellenaz et al. Anaconda predation on pampas fox
The following is the established format for referencing this article:
Chatellenaz, M.L., Müller, G.C. and Vallejos, G.A. 2018. Pampas foxes as prey of yellow anacondas. Canid Biology & Conservation 21(1):1-3. URL:
http://www.canids.org/CBC/21/anaconda_predation_on_pampas_fox.pdf.
Canid Biology & Conservation | http://www.canids.org/cbc/ 1
Field report
Pampas foxes as prey of yellow anacondas
Mario L. Chatellenaz1*, Gisela C. Müller2,3 and Gilberto A. Vallejos2
1 Laboratorio de Ornitología y Mastozoología. Facultad de Ciencias Exactas y Naturales y Agrimensura,
Universidad Nacional del Nordeste. Av. Libertad 5470 (CP 3400), Corrientes, Argentina.
Email: mlchatellenaz@gmail.com
2 Parque Nacional Mburucuyá. Administración de Parques Nacionales. Belgrano 997 (CP 3427), Mburucuyá, Corrientes, Argentina.
3 Parque Nacional Baritú. Administración de Parques Nacionales. Ruta Nacional 19 Los Toldos, Salta, Argentina.
Email: gmuller@apn.gov.ar
* Correspondence author
Keywords: Eunectes notaeus; Lycalopex gymnocercus; predation.
Abstract
Carnivore predation by other predators is rarely observed in nature. Here we describe two predation events and report a third
one of adult pampas foxes being eaten by yellow anacondas in Corrientes, north east Argentina.
Introduction
The pampas fox Lycalopex gymnocercus is a medium-sized fox (4.6kg)
whose geographical distribution comprises the south of South America from
eastern Bolivia, western and central Paraguay, and southern Brazil, to Uru-
guay and northern and central Argentina (Lucherini and Luengos Vidal
2008). It lives in a variety of habitats including open forests, grasslands,
marshes, coastal dunes and even agricultural and rangelands (Redford and
Eisenberg 1992, Lucherini and Luengos Vidal 2008). The main threat to
the pampas fox is from hunting, both for predator control (foxes are blamed
for lamb losses in sheep breeding farms) and for the pelt trade (Lucherini
and Luengos Vidal 2008, Macdonald and Sillero-Zubiri 2010). Little is
known about natural causes of death, or the fox’s potential predators. Fox
remains have been found in puma Puma concolor excrements in National
Park Lihue Calel (Argentina) and some cases of foxes killed by feral dogs
have been cited (Pessino et al. 2001, Lucherini and Luengos Vidal 2008).
In this note we describe predation events of adult pampas foxes by yellow
anacondas Eunectes notaeus in the Iberá Provincial Reserve and the Mbu-
rucuyá National Park (Corrientes province, Argentina).
Results
The first predation event took place on 8 October 2013 at 19:45h, during a
nocturnal mammal survey in Estancia Yaguareté Corá (27º56’S, 57º00’W)
in the Iberá Provincial Reserve. In the marsh vegetation at the water’s edge,
a yellow anaconda was observed, wrapped around a fox. The observation
was conducted by torch light. This fox was identified as a pampas fox by
the colour of its back legs and tail. The fox appeared to be already dead at
the time of the observation, and the snake was beginning to swallow it. Sev-
eral caimans Caiman yacare were seen a short distance away but none of
them approached the snake. The observation lasted 15 minutes but unfor-
tunately no photographic or video record of the event could be obtained.
Some days later we received information about a similar event, which hap-
pened in Estancia San Ignacio (27º49’S, 56º50’W), located at approximately
40km of the former Estancia (M. Blanco, pers. comm.).
The second event took place on 31 March 2017 in the Mburucuyá National
Park at approximately 8:00h, in a short-grass area at one side of the entrance
road to the Santa María Park Ranger Department (28º02’S, 58º05’W). A
yellow anaconda was observed, mid-way through the constriction process
of a pampas fox which appeared to be dead (Figure 1). Two adult foxes
were circling the snake and harassing it by biting its tail while they vocal-
ized. The snake reacted with sudden movements but without releasing its
prey (Figure 2). The foxes ran away once the snake started to swallow the
fox, beginning with its head (Figure 3). This process lasted an hour, after
which the snake moved slowly towards a small nearby marsh. When its
body was fully extended its total length reached 3.5m (Figure 4). [There is
a video of this event https://youtu.be/LDnvO4dE0LU].
Discussion
There are no previous records of pampas fox predation by boas, although
Almirón et al. (2011) suggest that foxes are potential prey of the Argentinian
boa constrictor Boa constrictor occidentalis.
Copyright © 2018 by the IUCN/SSC Canid Specialist Group. ISSN 1478-2677

Chatellenaz et al. Anaconda predation on pampas fox
Canid Biology & Conservation | http://www.canids.org/cbc/ 2
Figure 1. A 3.5m long yellow anaconda in the constriction process of a
pampas fox while observed by two other foxes in the Mburucuyá Na-
tional Park, Corrientes, Argentina.
Figure 2. While harassed by one of the pampas foxes, the anaconda be-
gins to position itself in order to swallow the captured fox, starting with
its head.
Figure 3. The anaconda has already swallowed half the fox. Notice the
jaws and body distension of the snake to swallow the prey. Figure 4. The anaconda leaves the capture site after swallowing the fox
completely. The swelling in the central part of the snake’s body is due to
the fox it has eaten.
The yellow anaconda, known as curiyú in north east Argentina, is the largest
boa in size of the region, exceeding 4m long and weighing approximately
30kg (Cei 1993, Waller et al. 2007). Its habits are mainly aquatic and it is
found in large rivers and their flood plains, lagoons, swamps and marshes.
This snake is one of the main predators in these environments, capturing a
wide variety of prey: fish, large snakes e.g. Hydrodynastes gigas, young
caimans Caiman latirostris and C. yacare, aquatic birds, and small- and me-
dium-size mammals including crab-eating raccoons Procyon cancrivorus,
crab-eating foxes Cerdocyon thous and young capybaras Hydrochoerus hy-
drochaeris up to 6kg (Strüssmann 1997, Waller et al. 2007, Miranda et al.
2017). As with other boas, the yellow anaconda hunts its prey by means of
the “sit-and-wait” ambush technique. It kills the larger prey during con-
striction by significantly affecting the cardiovascular system of the prey,
squeezing until circulatory arrest occurs (Boback et al. 2015).
However, it also eats eggs and even carrion, which means that it carries out
an active search for food, or that it is an occasional predator (Strüssmann
and Sazima 1991). The predation event in the Mburucuyá National Park
happened in a short-grass area where the boa was visible and it is unlikely
that it was unnoticed in an attempt to ambush the fox. However, as the
initial strike was not observed, it cannot be confirmed whether it was an
ambush or an opportunistic capture. Predation is rarely observed in nature;
these records and documentation are important because they contribute to
the knowledge of the ecology of the species involved.
Acknowledgements
We thank the National Parks Administration (APN). We are grateful to the
Corrientes Province Parks and Reserves Administration for authorizing our
work in the Iberá Provincial Reserve, and thank park ranger Marcelo Blanco
for the information provided. We also thank Dr. Sillero-Zubiri and an anon-
ymous reviewer for improvements to the manuscript. The records of the
Iberá Provincial Reserve were obtained during fieldwork financed by the
project Mastofauna de los Esteros del Iberá: diversidad, distribución, ca-
racterísticas ecológicas y perfil parasitológico (C.12IF07), of the program
Iberá+10 (SGCyT-UNNE).
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Biographical sketch
Mario Chatellenaz is a zoologist in the Universidad Nacional del Nordeste
(Corrientes, Argentina). He is currently studying the effects of forestations
of exotic species and other crops on birds and mammals in north-east Ar-
gentina.
Gisela Müller and Gilberto Vallejos are park rangers working in the Ad-
ministration de Parques Nacionales of Argentina. They carry out fieldwork
on subjects regarding control and surveillance, environmental monitoring
and research assistance in protected areas of the national system.