Published November 17, 2021. Updated January 28, 2024. Open access.

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Collared Whorltail-Iguana (Stenocercus humeralis)

Reptiles of Ecuador | Sauria | Tropiduridae | Stenocercus humeralis

English common names: Collared Whorltail-Iguana, Patterned Whorltail-Iguana.

Spanish common name: Guagsa verde collareja.

Recognition: ♂♂ 30.5 cmMaximum distance from the snout to the tip of the tail. Snout–vent length=11.2 cm. ♀♀ 27.2 cmMaximum distance from the snout to the tip of the tail. Snout–vent length=10.8 cm..13 The Collared Whorltail-Iguana (Stenocercus humeralis) differs from most other green diurnal and arboreal lizards in its area of distribution (particularly species in the family Iguanidae and Polychrotidae) by having keeled dorsal scales with pointed ends, instead of granular scales, on the tail.4 In some areas, S. humeralis occurs alongside S. ornatus, from which it differs by having granular, instead of keeled, scales on the dorsum.2 Stenocercus humeralis resembles S. simonsii, but this species occurs further north and is easily distinguishable by its strongly spiny tail (not spiny in S. humeralis).2 Males of S. humeralis differ from females by being larger in body size and by having a broader head (Fig. 1).2

Figure showing variation among individuals of Stenocercus humeralis

Figure 1: Individuals of Stenocercus humeralis from Madrigal del Podocarpus, Loja province, Ecuador. j=juvenile.

Natural history: Stenocercus humeralis is a diurnal lizard that inhabits humid to seasonally dry montane shrublands, cloud forests, and human-modified environments near the forest.1,5 The species is found in undisturbed vegetation as well as in pastures, clearings,6 gardens, city parks, planted forests, and human infrastructures.3 Collared Whorltail-Iguanas are arboreal and most active during sunny hours.3,5 They bask and forage on stones, rock walls, fences, rooftops, dirt walls, shrubs, eucalyptus tree trunks, Agave plants, and tree branches up to 4.5 m above the ground.16 When not active, individuals can be found hidden under rocks or in crevices of dirt walls.3 Collared Whorltail-Iguanas are insectivorous, but the specific prey items consumed are not known.7 In the presence of a disturbance, individuals usually retreat into their hiding places or run up along trees.3 If captured, they may shed the tail or bite. A couple of S. humeralis were found mating on a rock. The male held the female by biting her behind the head; when disturbed, the male dragged the female into a crevice.5 Gravid females contain four eggs, although the real clutch size is not known.2

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Conservation: Endangered Considered to be facing a high risk of extinction in the near future.. Stenocercus humeralis is proposed to be listed in this category, instead of Least Concern,8 because it meets the following IUCN Redlist9 criteria: the species’ extent of occurrence is estimated to be less than 5,000 km2 (Fig. 2), its habitat is severely fragmented, and there is continuing decline in the extent and quality of the ecosystems where it occurs. Based on maps of Ecuador’s vegetation cover published in 2012,10 it is estimated that, in total, there is no more than ~530 km2 of suitable habitat remaining for S. humeralis. Although found in protected areas (Podocarpus National Park and Utuana Biological Reserves), only 5% of the species’ total potential distribution is inside these areas, and these populations are in a fragmented landscape mosaic rather than in connected suitable habitats.

Distribution: Stenocercus humeralis is native to an area of approximately 1,132 km2 area in the Pacific slopes of the Andes in southern Ecuador (provinces Loja and Zamora Chinchipe; Fig. 2) and northern Peru (department Piura).

Distribution of Stenocercus humeralis in Ecuador

Figure 2: Distribution of Stenocercus humeralis in Ecuador. The star corresponds to the type locality: Loja, Loja province. See Appendix 1 for a complete list of the presence localities included in the map.

Etymology: The generic name Stenocercus, which comes from the Greek words stenos (=narrow) and kerkos (=tail), refers to the laterally-compressed tail in some members of this genus, which contrasts with the dorsally flattened tail of other Tropiduridae.11 The specific epithet humeralis comes from the Latin words humerus (=shoulder) and the suffix -alis (=pertaining to),12 and probably refers to the black patch on the shoulder.

See it in the wild: Collared Whorltail-Iguanas are becoming increasingly uncommon. They are arboreal in an area where the majority of the trees have been cut down and most surviving populations are not in protected areas. Two localities where the species can be seen with relative ease are Madrigal del Podocarpus and Utuana Biological Reserve. The lizards may be spotted by slowly walking along dirt roads and rock fences during hot sunny hours.

Author: Amanda QuezadaaAffiliation: Tropical Herping (TH), Quito, Ecuador.,bAffiliation: Laboratorio de Herpetología, Universidad del Azuay, Cuenca, Ecuador.

Editor: Alejandro ArteagacAffiliation: Khamai Foundation, Quito, Ecuador.

Photographer: Alejandro ArteagacAffiliation: Khamai Foundation, Quito, Ecuador. and Jose VieiraaAffiliation: Tropical Herping (TH), Quito, Ecuador.,dAffiliation: ExSitu, Quito, Ecuador.

How to cite? Quezada A (2024) Collared Whorltail-Iguana (Stenocercus humeralis). In: Arteaga A, Bustamante L, Vieira J (Eds) Reptiles of Ecuador: Life in the middle of the world. Available from: DOI: 10.47051/JRLI6125

Literature cited:

  1. Torres-Carvajal O (2000) Ecuadorian lizards of the genus Stenocercus (Squamata: Tropiduridae). Scientific Papers Natural History Museum, The University of Kansas 15: 1–38. DOI: 10.5962/bhl.title.16286
  2. Torres-Carvajal O (2007) A taxonomic revision of South American Stenocercus (Squamata: iguania) lizards. Herpetological Monographs 21: 76–178. DOI: 10.1655/06-001.1
  3. Field notes, Reptiles of Ecuador book project.
  4. Peters JA, Donoso-Barros R (1970) Catalogue of the Neotropical Squamata: part II, lizards and amphisbaenians. Bulletin of the United States National Museum, Washington, D.C., 293 pp.
  5. Venegas PJ, Echevarría LY, Alvarez SC, Vásquez D (2010) Reptilia, Squamata, Iguanidae, Stenocercus humeralis Gunther, 1859: first country record, Peru. Check List 6: 250–252. DOI: 10.15560/6.2.250
  6. Fritts TH (1974) A multivariate and evolutionary analysis of the Andean iguanid lizards of the genus Stenocercus. Memoirs of the San Diego Society of Natural History 7: 1–89.
  7. Almendáriz A, Brito J (2011) Anfibios y reptiles. In: Albuja L (Ed) Biodiversidad de los valles secos interandinos del Ecuador. Escuela Politécnica Nacional, Quito, 41–48.
  8. Venegas P, Sánchez J, Yánez-Muñoz M (2017) Stenocercus humeralis. The IUCN Red List of threatened species. Available from: DOI: 10.2305/IUCN.UK.2017-2.RLTS.T50950660A50950669.en
  9. IUCN (2001) IUCN Red List categories and criteria: Version 3.1. IUCN Species Survival Commission, Gland and Cambridge, 30 pp.
  10. MAE (2012) Línea base de deforestación del Ecuador continental. Ministerio del Ambiente del Ecuador, Quito, 30 pp.
  11. Duméril AMC, Bibron G (1837) Erpétologie générale ou Histoire Naturelle complète des Reptiles. Librairie Encyclopédique de Roret, Paris, 571 pp. DOI: 10.5962/bhl.title.45973
  12. Brown RW (1956) Composition of scientific words. Smithsonian Books, Washington D.C., 882 pp.

Appendix 1: Locality data used to create the distribution map of Stenocercus humeralis in Ecuador (Fig. 2). Go to the section on symbols and abbreviations for a list of acronyms used. Asterisk (*) indicates type locality.

EcuadorLojaBase militar GuachaurcoElicio Tapia, pers. comm.
EcuadorLojaBosque Protector El BosquePhoto by Michael Moens
EcuadorLojaEl Empalme, Valle de CasangaUSNM 201261; VertNet
EcuadorLojakm 25 on Loja–Cuenca roadCAS 94111; VertNet
EcuadorLojaLoja*Fritts 1974
EcuadorLojaLoja, 1 km W ofMCZ R-126136; VertNet
EcuadorLojaLoja, 12.2 km S ofTorres-Carvajal 2007
EcuadorLojaLoja, 2 km E ofTorres-Carvajal 2007
EcuadorLojaLoja, 4 km S ofMCZ R-89795; VertNet
EcuadorLojaLoja, 5 km N ofTorres-Carvajal 2007
EcuadorLojaLoja, ChontacruziNaturalist; photo examined
EcuadorLojaLoja, El SagrarioiNaturalist; photo examined
EcuadorLojaLoja, Universidad Nacional de LojaiNaturalist; photo examined
EcuadorLojaMadrigal del PodocarpusThis work; Fig. 1
EcuadorLojaMalacatos, general regionTorres-Carvajal 2007
EcuadorLojaOrianga, environs ofMZUA.RE.0095; examined
EcuadorLojaUtuana Biological ReserveReptiles of Ecuador book database
EcuadorLojaVía al Cerro ToledoTorres-Carvajal et al. 2019
EcuadorZamora ChinchipeEstación Biológica San FranciscoMZUA.RE.0154; examined
EcuadorZamora ChinchipeLoja, 27 km W ofTorres-Carvajal 2007
PeruPiuraCerro ChacasTorres-Carvajal et al. 2019
PeruPiuraCerro YantumaVanegas et al. 2010