Plumage maturation, molt, and morphology of the critically endangered Hooded Grebe (Podiceps gallardoi)

Ignacio Roesler; Laura Fasola; Juan M. Klavins; Carolina Facchinetti; María Emilia Giusti; Florencia Ayala; Estefanía P. Micheltorena; Julio L. Lancelotti; Bettina Mahler; Juan Carlos Reboreda

doi:10.56178/eh.v40i1.1505

Articles Published 18 June 2025 https://doi.org/10.56178/eh.v40i1.1505

Plumage maturation, molt, and morphology of the critically endangered Hooded Grebe (Podiceps gallardoi)

conservation Hooded Grebe molt molting migration natural history Patagonia plumage Podiceps gallardoi

Ignacio Roesler Laboratorio de Ecología y Comportamiento Animal, Instituto de Ecología Genética y Evolución de Buenos Aires (CONICET), Facultad de Cs. Exactas y Naturales, Universidad de Buenos Aires, Int. Güiraldes s/n, CABA 1428, Argentina | Programa Patagonia, Departamento de Conservación, Aves Argentinas/AOP, Matheu 1246, CABA 1249, Argentina | EDGE Fellowhip Programme, Zoological Society of London, Reagents Park, London, UK

Laura Fasola Programa Patagonia, Departamento de Conservación, Aves Argentinas/AOP, Matheu 1246, CABA 1249, Argentina | CONICET–Dirección Regional Patagonia Norte (APN), Vicealmirante O’connor 1188, S.C. de Bariloche 8400, Argentina

Juan M. Klavins Programa Patagonia, Departamento de Conservación, Aves Argentinas/AOP, Matheu 1246, CABA 1249, Argentina

Carolina Facchinetti 1 Laboratorio de Ecología y Comportamiento Animal, Instituto de Ecología Genética y Evolución de Buenos Aires (CONICET), Facultad de Cs. Exactas y Naturales, Universidad de Buenos Aires, Int. Güiraldes s/n, CABA 1428, Argentina

María Emilia Giusti Laboratorio de Ecología y Comportamiento Animal, Instituto de Ecología Genética y Evolución de Buenos Aires (CONICET), Facultad de Cs. Exactas y Naturales, Universidad de Buenos Aires, Int. Güiraldes s/n, CABA 1428, Argentina | Programa Patagonia, Departamento de Conservación, Aves Argentinas/AOP, Matheu 1246, CABA 1249, Argentina

Florencia Ayala Programa Patagonia, Departamento de Conservación, Aves Argentinas/AOP, Matheu 1246, CABA 1249, Argentina

Estefanía P. Micheltorena Programa Patagonia, Departamento de Conservación, Aves Argentinas/AOP, Matheu 1246, CABA 1249, Argentina

Julio L. Lancelotti Programa Patagonia, Departamento de Conservación, Aves Argentinas/AOP, Matheu 1246, CABA 1249, Argentina | Lab.Ecofluvial, IPEEC-CENPAT (CONICET), Blv. Brown 2915, Puerto Madryn 9120, Argentina

Bettina Mahler Laboratorio de Ecología y Comportamiento Animal, Instituto de Ecología Genética y Evolución de Buenos Aires (CONICET), Facultad de Cs. Exactas y Naturales, Universidad de Buenos Aires, Int. Güiraldes s/n, CABA 1428, Argentina

Juan Carlos Reboreda Laboratorio de Ecología y Comportamiento Animal, Instituto de Ecología Genética y Evolución de Buenos Aires (CONICET), Facultad de Cs. Exactas y Naturales, Universidad de Buenos Aires, Int. Güiraldes s/n, CABA 1428, Argentina

Abstract

The understanding of morphological and behavioral aspects of bird species can guide appropriate management actions for their conservation. Grebes (Podicipedidae) are peculiar in their molting strategy, since body feathers are continuously replaced during the whole year. Available information about natural history of Neotropical grebes is scattered. The Hooded Grebe (Podiceps gallardoi) is a critically endangered species with a global population of less than 800 individuals that inhabits the remote highlands plateaus of Austral Patagonia. In this work we present information about sexual differences in molting behavior, plumage coloration and morphological characteristics of this species. During seven years we monitored the whole population of Hooded Grebe and collected data from field observations and from collected individuals that had been killed by American mink. Our results show sexual differences in morphology, and in timing of molting, but not in coloration in the UV and visible range. Hooded Grebe’s molting strategy differs from that of other grebes, including closely related species, as it lacks molting migration and does not develop a visibly different alternate winter plumage. Molting strategies and morphological differences between sexes may represent adaptations to variable conditions in extreme environments of southern Patagonia.

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References

Adami MA (2016) Estructura Trófica de Una Laguna Clave Para La Reproducción Del Macá Tobiano (Podiceps Gallardoi). Degree dissertation University San Juan Bosco, Puerto Madryn
Beltrán J, Bertonatti C, Johnson A, Serret A, Sutton P (1992) Actualizaciones sobre la distribución, biología y estado de conservación del Macá Tobiano (Podiceps gallardoi). El Hornero 13:193–199. https://doi.org/10.56178/eh.v13i3
BirdLife International (2024) Species factsheet: Podiceps gallardoi. BirdLife International, Cambridge (URL: http://www.birdlife.org)
Cuthill IC, Partridge JC, Bennett ATD, Church SC, Hart NS, Hunt S (2000) Ultraviolet vision in birds. Advances in the Study of Behaviour 29:159–214. https://doi.org/10.1016/S0065-3454(08)60105-9
Eaton MD (2005) Human vision fails to distinguish widespread sexual dichromatism among sexually “monochromatic” birds. Proceedings of the National Academy of Sciences of the United States of America 102:10942–10946https://doi.org/10.1073/pnas.0501891102
Erize F (1983) Observaciones sobre el Macá Tobiano. El Hornero 12(5):256–268
Fasola L, Roesler I (2018) A familiar face with a novel behavior raises challenges for conservation: American mink in arid Patagonia and a critically endangered bird. Biological Conservation 218:217–222. https://doi.org/10.1016/j.biocon.2017.12.031
Fjeldså J (1983) Ecological character displacement and character release in grebes Podicipedidae. Ibis 125:463–481. https://doi.org/10.1111/j.1474-919X.1983.tb03142.x
Fjeldså J (1986) Feeding ecology and possible life history tactics of the Hooded Grebe Podiceps gallardoi. Ardea 74:40–58
Fjeldså J (2004) Bird families of the world: the grebes. Oxford University Press, Oxford
Gilli A, Anselmetti FS, Ariztegui D, Bradbury JP, Kelts KR, Markgraf V, Mckenzie JA (2001) Tracking abrupt climate change in the Southern Hemisphere: a seismic stratigraphic study of Lago Cardiel, Argentina (49ºS). Terra Nova 13:443–448
Hartman CA, Ackerman JT, Herzog MP, Eagles-Smith CA (2017) Season, molt, and body size influence mercury concentrations in grebes. Environmental Pollution 229:29–39. https://doi.org/10.1016/j.envpol.2017.05.058
Howell SN (2010) Molt in North American Birds. Volume 1. Houghton Mifflin Harcourt, USA
Humple DL, Nevins HM, Henkel LA (2013) Revisiting winter wing molt in western grebes (Aechmophorus occidentalis) and Clark’s grebes (A. clarkii). Waterbirds 36:426–431. https://doi.org/10.1675/063.036.0413
Hunter LA (1988) Status of the endemic Atitlan Grebe of Guatemala: is it extinct? Condor 90:906–912. https://doi.org/10.2307/1368847
Imberti S, Casañas H, Roesler I (2020) Hooded Grebe (Podiceps gallardoi), version 1.0. In: Billerman SM, Keeney BK, Rodewald PG, Schulenberg TS, editors. Birds of the World. Cornell Lab of Ornithology, Ithaca. https://doi.org/10.2173/bow.hoogre1.01
Jehl JR (1997) Cyclical changes in body composition in the annual cycle and migration of the Eared Grebe Podiceps nigricollis. Journal of Avian Biology 28:132–142. https://doi.org/10.2307/3677306
Konter A (2001) Grebes of Our World. Lynx Edicions, Barcelona
Lancelotti JL, Bandieri LMB, Pascual MA (2015) Diet of the exotic Rainbow Trout in the critical habitat of the threatened Hooded Grebe. Knowledge and Management of Aquatic Ecosystems 416:1–11. https://10.1051/kmae/2015022
Lancelotti J, Marinone MC, Roesler I (2016) Rainbow Trout effects on zooplankton in the reproductive area of the critically endangered Hooded Grebe. Aquatic Conservation: Marine and Freshwater Ecosystems 27:128–136. https://doi.org/10.1002/aqc.2629
Lange CE (1981) A Season of observations on Podiceps gallardoi (Aves Podicipediformes). Ecology and Etology. Neotropica 27:39–56
Llimona F, del Hoyo J (1992) Family Podicipedidae (grebes). Pp. 174–197 in: del Hoyo J, Elliott A, Christie D (eds). Handbook of the Birds of the World. Volume 1: Ostrich to Ducks. Lynx Edicions, Barcelona
Mayr G (2004) Morphological evidence for sister group relationship between flamingos (Aves: Phoenicopteridae) and grebes (Podicipedidae). Zoological Journal of the Linnean Society 140:157–169. https://doi.org/10.1111/j.1096-3642.2003.00094.x
Nuechterlein GL, Johnson A (1981) The downy young of the Hooded Grebe. Living Bird 19:69–71
Ogilvie MA (2003) Grebes of the World. Bruce Coleman, Uxbridge
Osorio D, Ham AD (2002) Spectral reflectance and directional properties of structural coloration in bird plumage. Journal of Experimental Biology 205:2017–2027. https://doi.org/10.1242/jeb.205.14.2017
Osorio D, Vorobyev M, Jones CD (1999) Colour vision of domestic chicks. Journal of Experimental Biology 202:2951–2959. https://doi.org/10.1242/jeb.202.21.2951
Otto J (1985) Wing molt by nesting Pied-billed Grebe. The Wilson Bulletin 97:52–53
Payne RB (1972) Mechanisms and control of molt. Avian biology 2:103–155
Piersma T (1988) The annual moult cycle of the Great Crested Grebes. Ardea 76:82–95
Piersma T, Van Eerden MR (1988) Feather eating in Great Crested Grebes Podiceps cristatus: a unique solution to the problems of debris and gastric parasites in ash-eating birds. Ibis 131:477–486. https://doi.org/10.1111/j.1474-919X.1989.tb04784.x
Pyle P (2008) Identification Guide to North American Birds, part II. Slate Creek Press, Point Reyes Station
Pyle P, Leitner WA, Lozano-Angulo L, Avilez-Teran F, Swanson H, Limón EG, Chambers MK (2009) Temporal, Spatial, and Annual Variation in the Occurrence of Molt-Migrant Passerines in the Mexican Monsoon Region. Condor 111:583–590. https://doi.org/10.1525/cond.2009.090085
Pyle P, McPherson M (2017) Why So Many White Eared Grebes? Possible interactions among leucism, molt, and pollutants. Birding (October):58–65
R Core Team (2015). _R: A Language and Environment for Statistical Computing_. R Foundation for Statistical Computing, Vienna, Austria. https://www.R-project.org/
Roesler I (2016) Conservación del Macá Tobiano (Podiceps gallardoi): factores que afectan la viabilidad de sus poblaciones. PhD dissertation, University of Buenos Aires, Buenos Aires
Roesler I, Fasola L, Casañas H, Hernández PM, De Miguel A, Giusti ME, Reboreda JC (2016) Colony guardian programme improves recruitment in the critically endangered hooded grebe Podiceps gallardoi in Austral Patagonia, Argentina. Conservation Evidence 13:62–66
Roesler I, Imberti S, Casañas H, Mahler B, Reboreda JC (2012a) Hooded Grebe Podiceps gallardoi population decreased by eighty per cent in the last twenty-five years. Bird Conservation International 22:371–382. https://doi.org/10.1017/S0959270912000512
Roesler I, Imberti S, Casañas H, Volpe N (2012b) A new threat for the globally Endangered Hooded Grebe Podiceps gallardoi: the American mink Neovison vison. Bird Conservation International 22:383–388. https://doi.org/10.1017/S0959270912000019
Rumboll MAE (1974) Una nueva especie de Macá (Podicipitidae). Revista del Museo Argentino de Ciencias Naturales 4:33–35
Sáez-Gómez P, Camacho C, Álvarez A, Varo N, Ramo C, Green AJ (2017) Sexual dimorphism and sex determination in Black-necked Grebes Podiceps nigricollis: on the need to account for geographical variation in morphology and sex ratio. Bird Study 64:502–512. https://doi.org/10.1080/00063657.2017.1410096
Storer RW (1967) Observations on Rolland’s Grebe. El Hornero 10:339–350. https://doi.org/10.56178/eh.v10i4.1297
Storer RW (1982) The Hooded Grebe on Laguna De Los Escarchados: ecology and behavior. Living Bird 19:51–67
Storer RW, Jehl JRJ (1985) Moult patterns and moult migration in the Black-necked Grebe Podiceps nigricollis. Ornis Scandinavica 16:253–260. https://doi.org/10.2307/3676688
Stout BE, Cooke F (2003) Timing and location of wing molt in Horned, Red-necked and Western Grebes in North America. Waterbirds 26:88–93. https://doi.org/10.1675/1524-4695(2003)026[0088:TALOWM]2.0.CO;2
Straneck R, Johnson A (1984) Vocalizaciones en relación al comportamiento del Macá Tobiano (Podiceps gallardoi). Revista del Museo Argentino de Ciencias Naturales 19:177–188
Sutherland WJ (1998) The importance of behavioral studies in conservation biology. Animal Behaviour 56:801–809. https://doi.org/10.1006/anbe.1998.0896
Winkler DW, Billerman SM, Lovette IJ (2020) Grebes (Podicipedidae), version 1.0. En: Billerman SM, Keeney BK, Rodewald PG, Schulenberg TS (eds). Birds of the World. Cornell Lab of Ornithology, Ithaca. (URL: https://doi.org/10.2173/bow.podici1.01)

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Ignacio Roesler, Laura Fasola, Juan M. Klavins, Carolina Facchinetti, María Emilia Giusti, Florencia Ayala, Estefanía P. Micheltorena, Julio L. Lancelotti, Bettina Mahler, Juan Carlos Reboreda (2025). Plumage maturation, molt, and morphology of the critically endangered Hooded Grebe (Podiceps gallardoi). El Hornero, Vol. 40 No. 1 (2025), 51-59. https://doi.org/10.56178/eh.v40i1.1505

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[1] Adami MA (2016) Estructura Trófica de Una Laguna Clave Para La Reproducción Del Macá Tobiano (Podiceps Gallardoi). Degree dissertation University San Juan Bosco, Puerto Madryn

[2] Beltrán J, Bertonatti C, Johnson A, Serret A, Sutton P (1992) Actualizaciones sobre la distribución, biología y estado de conservación del Macá Tobiano (Podiceps gallardoi). El Hornero 13:193–199. https://doi.org/10.56178/eh.v13i3

[3] BirdLife International (2024) Species factsheet: Podiceps gallardoi. BirdLife International, Cambridge (URL: http://www.birdlife.org)

[4] Cuthill IC, Partridge JC, Bennett ATD, Church SC, Hart NS, Hunt S (2000) Ultraviolet vision in birds. Advances in the Study of Behaviour 29:159–214. https://doi.org/10.1016/S0065-3454(08)60105-9

[5] Eaton MD (2005) Human vision fails to distinguish widespread sexual dichromatism among sexually “monochromatic” birds. Proceedings of the National Academy of Sciences of the United States of America 102:10942–10946https://doi.org/10.1073/pnas.0501891102

[6] Erize F (1983) Observaciones sobre el Macá Tobiano. El Hornero 12(5):256–268

[7] Fasola L, Roesler I (2018) A familiar face with a novel behavior raises challenges for conservation: American mink in arid Patagonia and a critically endangered bird. Biological Conservation 218:217–222. https://doi.org/10.1016/j.biocon.2017.12.031

[8] Fjeldså J (1983) Ecological character displacement and character release in grebes Podicipedidae. Ibis 125:463–481. https://doi.org/10.1111/j.1474-919X.1983.tb03142.x

[9] Fjeldså J (1986) Feeding ecology and possible life history tactics of the Hooded Grebe Podiceps gallardoi. Ardea 74:40–58

[10] Fjeldså J (2004) Bird families of the world: the grebes. Oxford University Press, Oxford

[11] Gilli A, Anselmetti FS, Ariztegui D, Bradbury JP, Kelts KR, Markgraf V, Mckenzie JA (2001) Tracking abrupt climate change in the Southern Hemisphere: a seismic stratigraphic study of Lago Cardiel, Argentina (49ºS). Terra Nova 13:443–448

[12] Hartman CA, Ackerman JT, Herzog MP, Eagles-Smith CA (2017) Season, molt, and body size influence mercury concentrations in grebes. Environmental Pollution 229:29–39. https://doi.org/10.1016/j.envpol.2017.05.058

[13] Howell SN (2010) Molt in North American Birds. Volume 1. Houghton Mifflin Harcourt, USA

[14] Humple DL, Nevins HM, Henkel LA (2013) Revisiting winter wing molt in western grebes (Aechmophorus occidentalis) and Clark’s grebes (A. clarkii). Waterbirds 36:426–431. https://doi.org/10.1675/063.036.0413

[15] Hunter LA (1988) Status of the endemic Atitlan Grebe of Guatemala: is it extinct? Condor 90:906–912. https://doi.org/10.2307/1368847

[16] Imberti S, Casañas H, Roesler I (2020) Hooded Grebe (Podiceps gallardoi), version 1.0. In: Billerman SM, Keeney BK, Rodewald PG, Schulenberg TS, editors. Birds of the World. Cornell Lab of Ornithology, Ithaca. https://doi.org/10.2173/bow.hoogre1.01

[17] Jehl JR (1997) Cyclical changes in body composition in the annual cycle and migration of the Eared Grebe Podiceps nigricollis. Journal of Avian Biology 28:132–142. https://doi.org/10.2307/3677306

[18] Konter A (2001) Grebes of Our World. Lynx Edicions, Barcelona

[19] Lancelotti JL, Bandieri LMB, Pascual MA (2015) Diet of the exotic Rainbow Trout in the critical habitat of the threatened Hooded Grebe. Knowledge and Management of Aquatic Ecosystems 416:1–11. https://10.1051/kmae/2015022

[20] Lancelotti J, Marinone MC, Roesler I (2016) Rainbow Trout effects on zooplankton in the reproductive area of the critically endangered Hooded Grebe. Aquatic Conservation: Marine and Freshwater Ecosystems 27:128–136. https://doi.org/10.1002/aqc.2629

[21] Lange CE (1981) A Season of observations on Podiceps gallardoi (Aves Podicipediformes). Ecology and Etology. Neotropica 27:39–56

[22] Llimona F, del Hoyo J (1992) Family Podicipedidae (grebes). Pp. 174–197 in: del Hoyo J, Elliott A, Christie D (eds). Handbook of the Birds of the World. Volume 1: Ostrich to Ducks. Lynx Edicions, Barcelona

[23] Mayr G (2004) Morphological evidence for sister group relationship between flamingos (Aves: Phoenicopteridae) and grebes (Podicipedidae). Zoological Journal of the Linnean Society 140:157–169. https://doi.org/10.1111/j.1096-3642.2003.00094.x

[24] Nuechterlein GL, Johnson A (1981) The downy young of the Hooded Grebe. Living Bird 19:69–71

[25] Ogilvie MA (2003) Grebes of the World. Bruce Coleman, Uxbridge

[26] Osorio D, Ham AD (2002) Spectral reflectance and directional properties of structural coloration in bird plumage. Journal of Experimental Biology 205:2017–2027. https://doi.org/10.1242/jeb.205.14.2017

[27] Osorio D, Vorobyev M, Jones CD (1999) Colour vision of domestic chicks. Journal of Experimental Biology 202:2951–2959. https://doi.org/10.1242/jeb.202.21.2951

[28] Otto J (1985) Wing molt by nesting Pied-billed Grebe. The Wilson Bulletin 97:52–53

[29] Payne RB (1972) Mechanisms and control of molt. Avian biology 2:103–155

[30] Piersma T (1988) The annual moult cycle of the Great Crested Grebes. Ardea 76:82–95

[31] Piersma T, Van Eerden MR (1988) Feather eating in Great Crested Grebes Podiceps cristatus: a unique solution to the problems of debris and gastric parasites in ash-eating birds. Ibis 131:477–486. https://doi.org/10.1111/j.1474-919X.1989.tb04784.x

[32] Pyle P (2008) Identification Guide to North American Birds, part II. Slate Creek Press, Point Reyes Station

[33] Pyle P, Leitner WA, Lozano-Angulo L, Avilez-Teran F, Swanson H, Limón EG, Chambers MK (2009) Temporal, Spatial, and Annual Variation in the Occurrence of Molt-Migrant Passerines in the Mexican Monsoon Region. Condor 111:583–590. https://doi.org/10.1525/cond.2009.090085

[34] Pyle P, McPherson M (2017) Why So Many White Eared Grebes? Possible interactions among leucism, molt, and pollutants. Birding (October):58–65

[35] R Core Team (2015). _R: A Language and Environment for Statistical Computing_. R Foundation for Statistical Computing, Vienna, Austria. https://www.R-project.org/

[36] Roesler I (2016) Conservación del Macá Tobiano (Podiceps gallardoi): factores que afectan la viabilidad de sus poblaciones. PhD dissertation, University of Buenos Aires, Buenos Aires

[37] Roesler I, Fasola L, Casañas H, Hernández PM, De Miguel A, Giusti ME, Reboreda JC (2016) Colony guardian programme improves recruitment in the critically endangered hooded grebe Podiceps gallardoi in Austral Patagonia, Argentina. Conservation Evidence 13:62–66

[38] Roesler I, Imberti S, Casañas H, Mahler B, Reboreda JC (2012a) Hooded Grebe Podiceps gallardoi population decreased by eighty per cent in the last twenty-five years. Bird Conservation International 22:371–382. https://doi.org/10.1017/S0959270912000512

[39] Roesler I, Imberti S, Casañas H, Volpe N (2012b) A new threat for the globally Endangered Hooded Grebe Podiceps gallardoi: the American mink Neovison vison. Bird Conservation International 22:383–388. https://doi.org/10.1017/S0959270912000019

[40] Rumboll MAE (1974) Una nueva especie de Macá (Podicipitidae). Revista del Museo Argentino de Ciencias Naturales 4:33–35

[41] Sáez-Gómez P, Camacho C, Álvarez A, Varo N, Ramo C, Green AJ (2017) Sexual dimorphism and sex determination in Black-necked Grebes Podiceps nigricollis: on the need to account for geographical variation in morphology and sex ratio. Bird Study 64:502–512. https://doi.org/10.1080/00063657.2017.1410096

[42] Storer RW (1967) Observations on Rolland’s Grebe. El Hornero 10:339–350. https://doi.org/10.56178/eh.v10i4.1297

[43] Storer RW (1982) The Hooded Grebe on Laguna De Los Escarchados: ecology and behavior. Living Bird 19:51–67

[44] Storer RW, Jehl JRJ (1985) Moult patterns and moult migration in the Black-necked Grebe Podiceps nigricollis. Ornis Scandinavica 16:253–260. https://doi.org/10.2307/3676688

[45] Stout BE, Cooke F (2003) Timing and location of wing molt in Horned, Red-necked and Western Grebes in North America. Waterbirds 26:88–93. https://doi.org/10.1675/1524-4695(2003)026[0088:TALOWM]2.0.CO;2

[46] Straneck R, Johnson A (1984) Vocalizaciones en relación al comportamiento del Macá Tobiano (Podiceps gallardoi). Revista del Museo Argentino de Ciencias Naturales 19:177–188

[47] Sutherland WJ (1998) The importance of behavioral studies in conservation biology. Animal Behaviour 56:801–809. https://doi.org/10.1006/anbe.1998.0896

[48] Winkler DW, Billerman SM, Lovette IJ (2020) Grebes (Podicipedidae), version 1.0. En: Billerman SM, Keeney BK, Rodewald PG, Schulenberg TS (eds). Birds of the World. Cornell Lab of Ornithology, Ithaca. (URL: https://doi.org/10.2173/bow.podici1.01)