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Do chinstrap penguins use olfactory cues for partner recognition?

Published online by Cambridge University Press:  25 February 2025

Luisa Amo Open the ORCID record for Luisa Amo [Opens in a new window] ,
Miguel Ángel Rodríguez-Gironés Open the ORCID record for Miguel Ángel Rodríguez-Gironés [Opens in a new window]  and
Andrés Barbosa Open the ORCID record for Andrés Barbosa [Opens in a new window]
Luisa Amo*
Affiliation:
Area of Biodiversity and Conservation, Universidad Rey Juan Carlos, Móstoles, Spain Departamento de Ecología Evolutiva, Museo Nacional de Ciencias Naturales (CSIC), Madrid, Spain Departamento de Ecología Funcional y Evolutiva, Estación Experimental de Zonas Áridas (CSIC), La Cañada de San Urbano, Almería, Spain Instituto de Cambio Global, Universidad Rey Juan Carlos, Móstoles, Madrid, Spain
Miguel Ángel Rodríguez-Gironés
Affiliation:
Departamento de Ecología Funcional y Evolutiva, Estación Experimental de Zonas Áridas (CSIC), La Cañada de San Urbano, Almería, Spain
Andrés Barbosa
Affiliation:
Departamento de Ecología Evolutiva, Museo Nacional de Ciencias Naturales (CSIC), Madrid, Spain
*
Corresponding author: Luisa Amo; Email: luisa.amo@mncn.csic.es
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Abstract

Although there is increasing evidence that birds have individual chemical profiles that can be used in different social contexts, partner scent recognition has only been explored in procellariiform seabirds, a group of birds known for their highly developed olfactory system. However, olfaction is not restricted to Procellariiformes, and birds with smaller olfactory bulbs can also use chemical cues in different social contexts. More evidence from different bird groups is needed to disentangle whether olfaction plays a general role in partner recognition. We performed a choice experiment to examine whether chinstrap penguins Pygoscelis antarcticus can discriminate the scent of their partner from the scent of other conspecifics. Our results do not suggest a preference of penguins for the scent of their partners. Our results highlight the need to carry out additional studies to determine the mechanisms underlying partner recognition in penguins.

Keywords

Antarctic penguinavian olfactionpartner scent recognitionPygoscelis antarcticus
Type
Biological Sciences
Information
Antarctic Science , First View , pp. 1 - 6
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This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of Antarctic Science Ltd

Introduction

The size of the olfactory bulb, relative to brain size, has been proposed as an indicator of the ability of birds to detect and use chemical cues. The first studies on the olfactory capability of birds were performed with species with bigger olfactory bulb sizes, such as Procellariiformes (Bang & Cobb Reference Bang and Cobb1968). However, subsequent evidence suggests that birds with smaller bulbs, such as Passeriformes, can also detect odours in different contexts and with several functions (Avilés & Amo Reference Avilés and Amo2018). Today, a growing body of evidence shows that many bird species use chemical cues in their interactions with other species and their abiotic environment (for reviews, see Hagelin Reference Hagelin and Jamieson2007a, Hagelin & Jones Reference Hagelin and Jones2007, Caro & Balthazart Reference Caro and Balthazart2010, Abankwah et al. Reference Abankwah, Deeming and Pike2020). Examples of the use of chemical cues by birds include, among others, the assessment of predation risk (Amo et al. Reference Amo, Galván, Tomás and Sanz2008, Reference Amo, Visser and van Oers2011, Roth et al. Reference Roth, Cox and Lima2008), the detection of the aromatic plants that some bird species introduce into their nests (Petit et al. Reference Petit, Hossaert-McKey, Perret, Blondel and Lambrechts2002, Mennerat et al. Reference Mennerat, Bonadonna, Perret and Lambrechts2005, Gwinner & Berger Reference Gwinner and Berger2008) and orientation and navigation (Wallraff Reference Wallraff2004, Mahr et al. Reference Mahr, Nowack, Knauer and Hoi2022). Olfaction also seems to play an important role in foraging, from the acceptance of novel foods (Marples & Roper Reference Marples and Roper1996, Kelly & Marples Reference Kelly and Marples2004) to food/prey location (e.g. Nevitt Reference Nevitt2011, Amo et al. Reference Amo, Rodríguez-Gironés and Barbosa2013a,Reference Amo, Jansen, van Dam, Dicke and Visserb, Mrazova et al. Reference Mrazova, Sam and Amo2019, Hernández et al. Reference Hernández, Villada and Barja2023). The results of a comparative study suggest that the olfactory capability of birds varies across bird species in relation to diet type and ecological conditions, suggesting that foraging mode has played an important role in the evolution of olfaction in birds (Avilés & Amo Reference Avilés and Amo2018). Furthermore, the olfactory capability of birds seems also to be related to their social complexity, with colonial species having relatively larger olfactory bulbs (i.e. greater olfactory abilities) than territorial breeders (Avilés & Amo Reference Avilés and Amo2018).

Therefore, olfaction seems to play an important role in social behaviour, although our knowledge regarding the importance of chemical cues in these intraspecific interactions is still far from what we have with regards to other taxa (Hagelin Reference Hagelin and Jamieson2007a,Reference Hagelinb, Caro & Balthazart Reference Caro and Balthazart2010, Abankwah et al. Reference Abankwah, Deeming and Pike2020). Birds have been shown to use chemical cues to identify their own nests (e.g. De León et al. Reference De León, Mínguez and Belliure2003, Bonadonna et al. Reference Bonadonna, Villafane, Bajzak and Jouventin2004, Caspers & Krause Reference Caspers and Krause2011, Krause & Caspers Reference Krause and Caspers2012). It has also been shown that chemical signals play a role in the social behaviour of crested auklets (Hagelin Reference Hagelin2007b), and Hirao and collaborators (Reference Hirao, Aoyama and Sugita2009) found that mate preference of domestic cockerels involves olfactory responsiveness to the female’s uropygial secretions. Psittaciformes (Zhang et al. Reference Zhang, Wei, Zhang and Yang2010) and Passeriformes (Whittaker et al. Reference Whittaker, Richmond, Miller, Kiley, Burns, Atwell and Ketterson2011, Amo et al. Reference Amo, López-Rull, Pagán and Macías Garcia2012b) can discriminate the sex of conspecifics using chemical cues alone, and the source of scent that these birds are detecting is the uropygial gland secretion (Whittaker et al. Reference Whittaker, Richmond, Miller, Kiley, Burns, Atwell and Ketterson2011) that these birds spread on their feathers (Jacob & Zisweiler Reference Jacob, Zisweiler, Farner, King and Parkes1982). The activity of the uropygial gland as well as the composition of its secretion have been shown to vary not only between the sexes (e.g. Whittaker et al. Reference Whittaker, Richmond, Miller, Kiley, Burns, Atwell and Ketterson2011, Amo et al. Reference Amo, López-Rull, Pagán and Macías Garcia2012b, Gilles et al. Reference Gilles, Fokkema, Korsten, Caspers and Schmoll2024), but also among seasons (e.g. Reneerkens et al. Reference Reneerkens, Piersma and Sinninghe Damsté2002, Amo et al. Reference Amo, López-Rull, Pagán and Macías Garcia2012b, Grieves et al.,. Reference Grieves, Bernards and MacDougall-Shackleton2019a, Reference Grieves, Gilles, Cuthill, Székely, MacDougall-Shackleton and Caspers2022), age classes (Amo et al. Reference Amo, López-Rull, Pagán and Macías Garcia2012b), diets (e.g. Sandilands et al. Reference Sandilands, Savory and Powell2004a,Reference Sandilands, Powell, Keeling and Savoryb), hormone levels (e.g. Whelan et al. Reference Whelan, Levin, Owen and Garvin2010, Whittaker et al. Reference Whittaker, Rosvall, Slowinski, Soini, Novotny and Ketterson2018), levels of parasite infection (Pap et al. Reference Pap, Vágási, Osváth, Mureçan and Barta2010, Grieves et al. Reference Grieves, Kelly, Bernards and MacDougall-Shackleton2018), body condition and immune status (Moreno-Rueda Reference Moreno-Rueda2010, Reference Moreno-Rueda2015), polymorphism (Tuttle et al. Reference Tuttle, Sebastian, Posto, Soini, Novotny and Gonser2014), individuals (Mardon et al. Reference Mardon, Saunders, Anderson, Couchoux and Bonadonna2010, Whittaker et al. Reference Whittaker, Soini, Atwell, Hollars, Novotny and Ketterson2010, Leclaire et al. Reference Leclaire, Merkling, Raynaud, Giacinti, Bessière, Hatch and Danchin2011a) and even with genetic heterozygosity (Leclaire et al. Reference Leclaire, Merkling, Raynaud, Mulard, Bessière and Lhuillier2011b, Reference Leclaire, van Dongen, Voccia, Merkling, Ducamp and Hatch2014, Strandh et al. Reference Strandh, Westerdahl, Pontarp, Canbäck, Dubois and Miquel2012, Slade et al. Reference Slade, Watson, Kelly, Gloor, Bernards and MacDougall-Shackleton2016, Whittaker et al. Reference Whittaker, Slowinski, Greenberg, Alian, Winters and Ahmad2019). Birds are even known to discriminate the immunological characteristics of potential partners by using chemical cues (Leclaire et al. Reference Leclaire, Strandh, Mardon, Westerdahl and Bonadonna2017, Grieves et al. Reference Grieves, Gloor, Bernards and MacDougall-Shackleton2019b, but see Amo et al. Reference Amo, Amo de Paz, Kabbert and Machordom2022). Therefore, the chemical cues that birds emit may convey potentially useful information during social interactions (for reviews, see Campagna et al. Reference Campagna, Mardon, Celerier and Bonadonna2012, Alves Soares et al. Reference Alves Soares, Caspers and Loos2024), such as kin recognition (Coffin et al. Reference Coffin, Watters and Mateo2011, Bonadonna & Sanz-Aguilar Reference Bonadonna and Sanz-Aguilar2012, Krause et al. Reference Krause, Krüger, Kohlmeier and Caspers2012, Leclaire et al. Reference Leclaire, Strandh, Mardon, Westerdahl and Bonadonna2017), rival assessment (Amo et al. Reference Amo, Avilés, Parejo, Peña, Rodríguez and Tomás2012a, Amo & López Rull Reference Amo and López-Rull2024) and mate choice (Bonadonna & Sanz-Aguilar Reference Bonadonna and Sanz-Aguilar2012, Grieves et al. Reference Grieves, Gloor, Bernards and MacDougall-Shackleton2019b).

Detection of chemical cues during the breeding period may be useful in sexually monomorphic species, long-term monogamous species and those that breed in colonies. In these cases, chemical cues may allow birds to discriminate between individuals. To our knowledge, the only studies in which a recognition of the scent of partners has been examined have been performed with procellariiform seabirds, finding that Antarctic prions Pachyptila desolata (Bonadonna & Nevitt Reference Bonadonna and Nevitt2004), Wilson’s storm petrels Oceanites oceanicus (Jouventin et al. Reference Jouventin, Mouret and Bonadonna2007) and blue petrels Halobaena caerulea (Mardon & Bonadonna Reference Mardon and Bonadonna2009) preferred the odour of their partner to the odour of another conspecific. Procellariiformes are known to have one of the most developed olfactory systems among birds (Bang & Cobb Reference Bang and Cobb1968), and it is also already known that they use olfaction for locating food (Nevitt Reference Nevitt2008, Reference Nevitt2011) and finding their burrows at night (e.g. Minguez Reference Minguez1997, Bonadonna et al. Reference Bonadonna, Hesters and Jouventin2003a,Reference Bonadonna, Cunningham, Jouventin, Hesters and Nevittb, Reference Bonadonna, Villafane, Bajzak and Jouventin2004, De León et al. Reference De León, Mínguez and Belliure2003). While there is no reason to expect that all bird species use the same type of information in social contexts, recent evidence suggests that olfaction plays a role in intraspecific interactions in other groups apart from Procellariiformes (Coffin et al. Reference Coffin, Watters and Mateo2011, Whittaker et al. Reference Whittaker, Richmond, Miller, Kiley, Burns, Atwell and Ketterson2011, Amo et al. Reference Amo, Avilés, Parejo, Peña, Rodríguez and Tomás2012a, Krause et al. Reference Krause, Krüger, Kohlmeier and Caspers2012, Grieves et al. Reference Grieves, Gloor, Bernards and MacDougall-Shackleton2019b), and therefore it is clearly necessary to increase the range of bird species in which chemical recognition of their partners is investigated.

In this context, we performed an experiment aimed at examining the ability of chinstrap penguins Pygoscelis antarcticus to discriminate the scent of their partners from the smell of other conspecifics. Although interindividual variation in the calls of chinstrap penguins (Bustamante & Marquez Reference Bustamante and Marquez1996) could allow acoustic communication to play a role in partner recognition, as has been observed in other penguin species (Clark et al. Reference Clark, Boersma and Olmsted2006), acoustic cues need not be the only ones involved in partner discrimination. Furthermore, non-acoustic cues may provide relevant information about the emitter, beyond its identity. For example, Humboldt penguins Spheniscus humboldti can use olfaction for kin recognition (Coffin et al. Reference Coffin, Watters and Mateo2011). Therefore, we hypothesized that chinstrap penguins may be able to discriminate the scent of their partners from other conspecifics, even if partner recognition is not exclusively based on chemical cues. We offered wild chinstrap penguins the scents of two individuals, their partner and a conspecific, and noted their choice. We expected that chinstrap penguins would spend longer close to the scent of their partner than to that of a conspecific.

Materials and methods

Study area

We performed an experiment in natural conditions at a breeding rookery (20 000 breeding pairs; Lynch et al. Reference Lynch, White, Black and Naveen2012) of chinstrap penguins in the Vapour Col rookery on Deception Island, South Shetlands (63°00´S, 60°40´W) during the summer (January/February) of 2011. The experiment was performed from 11h00 to 17h00.

Experimental design

We performed the experiment when penguins were rearing ~20 day-old nestlings in order to minimize the disturbances on nestlings due to the capture of adults. During this late time of the guard phase, one of the parents would be in the nest taking care of nestlings while the other parent foraged at sea. Therefore, both parents spent only short periods of time together, when one parent returned from the sea and replaced the other in taking care of the nestlings. We observed penguins and located nests where both parents met. When one of the parents left the nest to go to the sea, we simultaneously captured with a long-handle net both the penguin that went to the sea (focal penguin) as well as the penguin that had arrived from the sea and would be taking care of the nestlings (partner). Another researcher observed the nestlings to monitor where they were and to prevent predation by skuas, as they remained alone during the capture of the adults. No chicks were lost during these captures. We placed the focal penguin in the habituation area of the experimental enclosure (see below). We obtained the scent of the partner by rubbing its body with absorbent paper for 1 min, focusing mainly on the feathers close to the uropygial gland to transfer its secretions from the feathers to the absorbent paper. After that, the penguin was released, and we ensured that it returned to the nestlings. All of the adults returned to take care of their nestlings. Simultaneously, we also captured a different penguin that was walking from the sea to the nest and obtained its scent using the same methodology. By selecting conspecific penguins that were walking from the sea to the colony we ensured that the papers containing conspecific scents were marked similarly to those containing the partner scent. After that, we took a blood sample from the conspecific penguin’s foot vein using a needle and a heparinized capillary tube. A drop of blood was preserved in alcohol for molecular sexing following Ellegren (Reference Ellegren1996). The penguin was then immediately released at the point of capture, and we observed that it resumed its walk towards the colony.

The experiment was performed in a T-shaped mesh enclosure built using 50 cm-high chicken wire (mesh size 1.3 cm) and located in front of and 50 m away from the closest breeding sub-colony and 300 m away from the coast (Fig. 1). Both experimental arms of the enclosure were equally distant from the colony and the sea to avoid any confounding effects due to the possible attraction of penguins to such places. We used a mesh enclosure as chinstrap penguins are not burrow nesters. Both the ‘vertical’ and ‘horizontal’ segments of the T-shaped mesh enclosure were 150 × 50 cm corridors (Fig. 1). Just outside these arms, in the outer side of the experimental area (Fig. 1), we placed the two absorbent papers marked with the scents of the partner and the conspecific. The locations of the treatments in the enclosure were balanced between sides between trials (in nine trials the partner scent was located to the right and in nine trials the partner scent was located to the left). After each trial, the enclosure was cleaned with ethanol.

We captured 54 adult penguins (18 focal penguins and their partners and 18 conspecifics). After a brief habituation period of 10 min at the base of the central arm (habituation area; Fig. 1), focal penguins were released into the choice area, from which they could enter the left and right arms (experimental areas; Fig. 1) of the T-maze. The penguins moved continuously between both arms of the enclosure. Therefore, all penguins moved close to the absorbent papers marked with the scents, and so they could detect these scents.

An observer situated 20 m from the enclosure recorded the times that penguins spent in each sector of the enclosure over a period of 10 min. Due to methodological restrictions, the observer was not blind to the treatments. After the trials, we took a blood sample (see above) from the experimental penguin, marked it with an indelible pen on one foot to avoid recapture and immediately released it in the exact place where it had been captured. Birds were kept in captivity for a maximum of 20 min. All of the birds showed normal behaviour after release (i.e. they continued on their way to the sea).

Figure 1. The enclosure where the experiment was carried out, with sizes indicated in metres. Grey boxes represent the absorbent papers soiled with the scent of a conspecific or a partner. The enclosure was located 50 m perpendicularly from the nearest sub-colony and 300 m from the coast. Dotted lines separating the choice and experimental areas do not represent physical barriers: penguins were free to move throughout the enclosure once the door of the habituation area was opened.

Data analysis

We compared the time that penguins spent close to their partner’s scent and the time they spent close to the conspecific’s scent by using two-tailed Wilcoxon matched pairs tests. The molecular analysis of sex determined that the focal birds consisted of 8 females and 10 males. Seven of the eight females were tested with their partner and the scent of a female conspecific, and only one was offered the choice between her partner scent and the scent of another male (see Table I). By contrast, the sample was more balanced in the case of males, with six males choosing between their partner’s scent and a conspecific male scent and four males choosing between their partner’s scent and the scent of another conspecific female (see Table I). Statistical analyses were performed with STATISTICA 8.0. We calculated the power of the statistical test with G*Power 3.1.9.7.

Table I. Numbers of male and female focal penguins that were offered the choice between the scent of their partners and the scent of a male or a female conspecific.

Results

Penguins did not spend more time close to their partner’s scent than close to the conspecific’s scent (Wilcoxon matched pairs test, Z = 1.16, P = 0.25, n = 18). This lack of preference for the scent of conspecifics was observed in males (Wilcoxon matched pairs test, Z = 0.65, P = 0.51, n = 10) as well as in females (Wilcoxon matched pairs test, Z = 0.70, P = 0.48, n = 8; Fig. 2).

With this sample size and fixing an alpha value of 0.1 (to minimize the probability of incurring a type II error), as well as a large effect size of 0.25 (to simulate the magnitude estimate of an effect of biological interest), the power of our test is 0.40. Furthermore, with a smaller effect size of 0.15, the power of our test is 0.25. Therefore, even with a large effect size, we may not be able to detect true choice differences.

Figure 2. Mean time (± SE) in seconds that focal male (white squares, n = 10) and female (black squares, n = 8) penguins spent in the side of the enclosure containing the scent of their partner or the scent of a conspecific.

Discussion

We found no preference of penguins for the scent of their partners. Chinstrap penguins are monogamous, and no extra-pair fertilizations have been observed in this species (Moreno et al. Reference Moreno, Boto, Fargallo and Potti2000). They do not renest if their nest is lost (Viñuela et al. Reference Viñuela, Amat and Ferrer1995). Furthermore, the experiment was performed at the end of the breeding season, so we might not expect penguins to be interested in the scent of a conspecific in a context of mate searching. However, interpreting scent preferences in a choice experiment can be difficult because, even though the study was performed during the reproductive period of the species and we may expect a preference for the scent of their partners, odour preferences may be related to other behaviours that also take place during the reproductive period, such as territorial defence. Chinstrap penguins defend their nests against intruders (Müller-Schwarze Reference Müller-Schwarze1984, Viñuela et al. Reference Viñuela, Amat and Ferrer1995), and therefore, despite the recognition of their partner, they may also spend time close to a conspecific scent to evaluate their rival instead of remaining close to their partner’s scent. These aggressive interactions have also been observed outside the territory and have been proposed to explain previous results in the case of sex discrimination in other bird species. For example, in both dark-eyed juncos Junco hyemalis (Whittaker et al. Reference Whittaker, Richmond, Miller, Kiley, Burns, Atwell and Ketterson2011) and spotless starlings Sturnus unicolor (Amo et al. Reference Amo, López-Rull, Pagán and Macías Garcia2012b) males were attracted to the scents of other males instead of female scents, probably because males may be more motivated to expel potential rivals than to search for a female. Our results do not show differences in the scent preferences of males and females, despite chinstrap penguin males being more aggressive than females, at least against human intruders (Viñuela et al. Reference Viñuela, Amat and Ferrer1995). Therefore, our results suggest that chinstrap penguins do not use olfaction to recognize their partners, in contrast with previous results in procellariform species such as Antarctic prions (Bonadonna & Nevitt Reference Bonadonna and Nevitt2004), Wilson’s storm petrels (Jouventin et al. Reference Jouventin, Mouret and Bonadonna2007) and blue petrels (Mardon & Bonadonna Reference Mardon and Bonadonna2009).

This lack of preference of chinstrap penguins for the scent of their partners cannot be explained by the lack of olfactory capability of the species because results from a previous study showed that chinstrap penguins are able to use olfaction to detect dimethyl sulphide (Amo et al. Reference Amo, Rodríguez-Gironés and Barbosa2013a), a molecule that signals high-productivity areas in the oceans (Nevitt Reference Nevitt2011). In addition, it has been recently shown that other penguin species can use olfaction not only in foraging (African penguins; Cunningham et al. Reference Cunningham, Strauss and Ryan2008, Wright et al. Reference Wright, Pichegru and Ryan2011), but also in social interactions such as kin recognition (Humboldt penguins; Coffin et al. Reference Coffin, Watters and Mateo2011). However, despite previous evidence showing that chinstrap penguins have a functional olfactory apparatus, our results suggest that they do not use olfaction to recognize their partners, or at least that they do not exhibit a preference for the scent of their partners. Therefore, other senses may be responsible for partner recognition in this species. All penguin species studied to date can discriminate between conspecific calls (Jouventin Reference Jouventin1982), including discrimination of their partners from other conspecifics (e.g. Clark et al. Reference Clark, Boersma and Olmsted2006). Therefore, in chinstrap penguins, acoustic communication (Bustamante & Marquez Reference Bustamante and Marquez1996) may be sufficient for partner recognition, and they might not need to use olfaction in partner recognition. In contrast, although procellariiform species also use vocalizations in social communication, predation pressures and the lack of visual cues due to their nocturnal habits may have also favoured the use of chemical cues in their social life (Nevitt Reference Nevitt2008, van Buskirk & Nevitt Reference van Buskirk and Nevitt2008).

The lack of partner scent preference might, in principle, be a methodological artefact if we had been unable to capture the penguin scents in the absorbent papers. The strong penguin smell detected by the human nose (L. Amo, pers. obs.) makes this explanation improbable. Furthermore, Coffin and collaborators (Reference Coffin, Watters and Mateo2011) used a similar methodology to show that Humbolt penguins can use scents to assess kinship. Therefore, we do not think that the lack of preference for a partner’s scent can be attributed to a methodological artefact related to the scent source or the protocol of scent collection. We performed the experiment when penguins were rearing ~20 day-old nestlings in order to minimize the disturbances on nestlings due to the capture of the adults. Therefore, we also cannot exclude the possibility that penguins might behave differently at the start of the season, when partners are meeting again.

To summarize, chinstrap penguins do not exhibit a preference for the scent of their partners over a conspecific’s scent, at least under the experimental conditions tested. However, a potential explanation of the lack of partner scent preference found in our study could be that our study had low statistical power. Thus, with a sample size of 18 penguins and fixing an alpha value of 0.1, we might have not detected even large differences in preference (i.e. effect size: 0.25; power: 0.40). This low statistical power calls into question whether our results are conclusive, and these results should be interpreted with caution. Therefore, our study highlights the need for carrying out further experiments to disentangle the possible role of olfaction in partner recognition and other social relationships in penguins.

Acknowledgements

We thank two anonymous reviewers for their useful comments. We are grateful to the Spanish Antarctic Base ‘Gabriel de Castilla’, the Spanish Polar Ship Las Palmas and the Marine Technology Unit (CSIC) personnel for their hospitality and logistical support. We thank Eva de Mas for laboratory assistance with molecular sexing. Permission to work in the study area and for handling penguins was granted by the Spanish Polar Committee.

Financial support

This study has been funded by the Acción Complementaria project (CTM2009-08154-E) of the Spanish Ministerio de Ciencia e Innovación. LA was supported by the Juan de la Cierva programme.

Author contributions

LA, MAR-G and AB conceived the study and performed the experiments, the data analysis and the interpretation of results. LA prepared the first version of the manuscript.

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Figure 0

Figure 1. The enclosure where the experiment was carried out, with sizes indicated in metres. Grey boxes represent the absorbent papers soiled with the scent of a conspecific or a partner. The enclosure was located 50 m perpendicularly from the nearest sub-colony and 300 m from the coast. Dotted lines separating the choice and experimental areas do not represent physical barriers: penguins were free to move throughout the enclosure once the door of the habituation area was opened.

Figure 1

Table I. Numbers of male and female focal penguins that were offered the choice between the scent of their partners and the scent of a male or a female conspecific.

Figure 2

Figure 2. Mean time (± SE) in seconds that focal male (white squares, n = 10) and female (black squares, n = 8) penguins spent in the side of the enclosure containing the scent of their partner or the scent of a conspecific.