chapter 1

1. General introduction

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CHAPTER 1

LIFE-HISTORY CONSEQUENCES OF SOCIALITY IN THE YELLOW-EYED PENGUIN (MEGADYPTES ANTIPODES) IN RELATION TO SOCIAL FACILITATION, VOCAL RECOGNITION AND FIDELITY TOWARDS MATES AND NEST SITES: GENERAL INTRODUCTION

ALVIN N. SETIAWAN

Department of Zoology, University of Otago, Dunedin, New Zealand


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1.1. The relationship between sociality and life-history

Social behaviour is defined as the interaction between individuals of the same species (Brown 1975; Slobodchikoff and Shields 1988). The types and amount of social interaction are determined by the social organization of a species, which can be expressed in terms of the distances between individuals (McBride 1964). Proximity between conspecifics should facilitate interaction and transference of information while large distances and/or physical barriers (e.g. thick vegetation, mountain ranges, a body of water, etc.) will hinder interactions. Thus, among birds, social interactions are higher in colonial species, which nest in high densities or close proximity to one another (Coulson 2002; Nelson and Baird 2002). This is particularly apparent in seabirds, of which 96-98% breed colonially (Lack 1968; Coulson 2002).

However, distance between individuals affects not only social behaviour, but also exerts a strong influence in the evolution of various life history traits. For example, the amount of social stimuli in a colony, which is usually correlated to the size and density of the colony, is said to affect breeding behaviour, breeding schedules and physiology (Darling 1938). Increased social stimuli has been shown to affect the timing of breeding and sexual behaviour in gulls (Burger 1979; Jones 1986; Danchin 1988) and penguins (Waas 1988; Waas et al. 2000), while influences of social stimuli on physiology can be seen in changes in the plasma levels of reproductive hormone (Farner and Wingfield 1980; O'Connell et al. 1981a; O'Connell et al. 1981b; Wingfield 1986; Dufty Jr. and Wingfield 1990; Wingfield et al. 1990; Vleck and Brown 1999). Furthermore, maternally-derived testosterone in yolk is known to influence chick growth, making it possible that socially-stimulated increases in


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testosterone levels of gravid females may influence chick or embryonic growth rates (Schwabl 1993, 1996a, 1996b, 1997; Schwabl et al. 1997; Birkhead et al. 2000; Lipar and Ketterson 2000; Eising et al. 2001; Groothuis and Schwabl 2002; Whittingham and Schwabl 2002; Pilz et al. 2003). The evolution of vocal communication may also be influenced by the degree of coloniality. The increased risk of misidentifying mates or kin as a result of high nest densities is typically associated with increased individual vocal distinctiveness, which enables individual recognition (Jouventin 1982; Bretagnolle 1996; Jouventin and Aubin 2002).

1.2. The social behaviour of yellow-eyed penguins

Like other seabirds, most penguins are colonial breeders with many species nesting cheek-by-jowl with each other (Williams 1995; Davis and Renner 2003). However, unlike other penguins, yellow-eyed penguins (Megadyptes antipodes) are said to be solitary breeders (Darby and Seddon 1990). Nests are sparsely distributed with densities ranging from 1 to 5 nests per hectare depending on the type and density of vegetation (Darby and Seddon 1990). They nest under dense vegetative cover (e.g. flax bush Phormium tenax, hebe Hebe elliptica, ngaio Myoporum laetum), which is mostly obscured from the open (Seddon and Davis 1989; Darby and Seddon 1990) and creates physical barriers between each nest. Normally, therefore, nests are visually, but not aurally, isolated from each other. During the pre-egg laying period, an area of up to 20 m may be defended (Marchant and Higgins 1990) but territorial disputes are said to be rare (Seddon and Darby 1990). Therefore, apart from intra-pair interactions, visual cues from other birds, even during the pre-egg period, are mostly received when birds land together, or remain on the beach. Vocalisations are usually


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given from the nest or near it, and mainly restricted to periods of arrival on the shore at dusk or before returning to the sea at dawn. All of these make them the least colonial of all penguins.

Therefore, the social environment of yellow-eyed penguins is very different from that of other more colonial penguins. The separation between nests greatly limits the amount of perceived visual stimuli. Furthermore, the limited period in which they vocalize suggests that the amount of vocal stimuli available is also less than for other penguins. Jouventin (1982), in a review of social signals of penguins considered yellow-eyed penguins to have little social interaction and to be ‘quiet’. The overall amount of social stimuli within a yellow-eyed penguin breeding area is also likely to be much lower than that of a colonial species with the same number of nests, as the distances between nests also limit the potential for social facilitation (the increase in the performance of a given behaviour as a result of perceiving a related or similar behaviour in conspecifics).

1.3. Aim of the thesis

The aim of this thesis is to investigate the life-history consequences associated with the low intensity of colonial breeding in yellow-eyed penguins. I do this by first reviewing the available literature to examine the possible cause(s) for the low degree of coloniality in yellow-eyed penguins and the implications of this for the species (Chapter 2). As hormones control reproductive behaviour (Farner and Wingfield 1980) and social behaviour (McBride 1964; Wingfield 1990), I measure and describe the changes in the reproductive hormone levels of yellow-eyed penguins during the


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breeding season (Chapter 3). The influence of social stimuli on reproductive schedule and behaviour through social facilitation has been well documented in the past (Darling 1938; Danchin 1988; Waas 1995; Murphy and Schauer 1996). I investigate the susceptibility of yellow-eyed penguins to social facilitation by supplementing the amount of vocal stimuli using playbacks of natural calls and measuring its effects on hormone levels, reproductive schedule and chick growth (Chapter 4). As the lack of coloniality in yellow-eyed penguins is largely due to their nest site selection behaviour, in Chapter 5, I present a study that examines the rates of mate and site fidelity, any relationship between them and the degree to which they are related to reproductive success in yellow-eyed penguins. Finally, in Chapters 6 and 7, I examine the possible consequences of large inter-nest distances on the use of vocalisations for recognition between adults and between adults and chicks, and the development of chick vocalisations.

1.4. Thesis outline

Each chapter is presented as a scientific paper as it has been, or will be, submitted to a journal. These papers may be submitted under multiple authors, with myself as the primary author. As such, there may be repetition of some information in a number of chapters.

CHAPTER 2, Sociality in penguins with particular emphasis on the yellow-eyed penguin (Megadyptes antipodes): a review, examines the causes and possible consequences of the lack of coloniality in yellow-eyed penguins. In this chapter, I highlight the possible differences in the roles of social facilitation and vocal


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recognition, and retention of mates or nest sites, between yellow-eyed penguins and other penguins.

CHAPTER 3, Sex steroids and prolactin hormone levels in breeding yellow-eyed penguins (Megadyptes antipodes), examines the changes in the plasma levels of testosterone, estradiol, progesterone and prolactin in yellow-eyed penguins during the breeding season in relation to shifts in reproductive stages. I also examine the possible effects of age on hormone levels. This chapter will be submitted with the following authors: Alvin N. Setiawan,. Lloyd S. Davis, John T. Darby, P. Mark Lokman, Graham Young, Margaret A. Blackberry, Belinda L. Cannell and Graeme B. Martin.

CHAPTER 4, Effects of artificial social stimulation on hormone levels, reproductive schedule and chick growth in yellow-eyed penguins (Megadyptes antipodes), examines the various effects of increasing vocal stimuli in yellow-eyed penguins. The amount of vocal stimuli was enhanced through playback of pre-recorded calls, and the effects of this on hormone levels, reproductive schedule and chick growth were measured simultaneously. This simultaneous measurement is hoped to show for the first time in free-living birds, that the effects of increased social stimuli on reproductive schedule is mediated by hormonal mechanisms. This chapter will be submitted with the following authors: Alvin N. Setiawan,. Lloyd S. Davis, John T. Darby, P. Mark Lokman, Graham Young, Margaret A. Blackberry, Belinda L. Cannell and Graeme B. Martin.

CHAPTER 5, Mate and site fidelity in yellow-eyed penguins (Megadyptes antipodes), examines the rates of mate and site fidelity, and whether reproductive success is


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correlated with pair dissolution and/or site changes. In this paper, the spatial unit for breeding site is measured in terms of territory (an area of 20 m radius around the nest) instead of nest site. This is done because yellow-eyed penguins are known to defend an area of up to 20 m from the nest, and thus unlike other penguins, nest site changes do not necessarily equate to territory changes. This chapter will be submitted with the following authors: Alvin N. Setiawan, Melanie Massaro, John T. Darby and Lloyd S. Davis.

CHAPTER 6, The potential for vocal recognition in yellow-eyed penguins (Megadyptes antipodes), examines the use of vocal recognition between adults of this species. Here, I examined whether the amount of individual variation in adult vocalizations is sufficient to allow vocal recognition to occur, and whether incubating adults respond differentially to calls from familiar and unfamiliar conspecifics. This chapter will be submitted with the following authors: Alvin N. Setiawan, Lloyd S. Davis and John T. Darby.

CHAPTER 7, Parent-chick vocal recognition in yellow-eyed penguins (Megadyptes antipodes), examines the use of vocalizations in parent-offspring recognition. The amount of individual variation in vocalizations is measured in chicks of different ages to determine whether vocal recognition of chicks by parents can potentially occur, and if so, the age at which sufficient individual variation in calls develops. I also examine whether chicks respond differentially to calls of parents and strangers. This chapter will be submitted with the following authors: Alvin N. Setiawan, Lloyd S. Davis and John T. Darby.

1. General introduction CHAPTER 8, General discussion, summarizes the findings and conclusions from the different chapters.

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2. Sociality in penguins review

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CHAPTER 2

SOCIALITY IN PENGUINS, WITH PARTICULAR EMPHASIS ON THE YELLOW-EYED PENGUIN (MEGADYPTES ANTIPODES): A REVIEW

ALVIN N. SETIAWAN



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2.1. Introduction

Social interactions are most evident in species that breed colonially. Among vertebrates, this behaviour is most commonly observed among birds (Rolland et al. 1998), of which 13% are colonial breeders (Lack 1968). However, among seabirds, 96-98% are colonial breeders (Lack 1968; Coulson 2002). Colonial breeding is defined as a form of communal living in which conspecific nests are densely distributed within territories which fulfill no role other than as breeding sites (Perrins and Birkhead 1983). Nests within breeding colonies may range from a few loosely aggregated nests of royal albatross Diomedea epomophora at Otago Peninsula (Warham 1990), to 225000 pairs of Magellanic penguins Spheniscus magellanicus at Punta Tombo, Argentina (Boersma et al. 1990).

The level of coloniality in turn, exerts a strong influence on a species’ life-history traits. The amount of social stimuli in a colony, usually correlated to the size and density of the colony, is said to affect breeding behaviour, breeding schedules and physiology (Darling 1938). In gulls (Burger 1979; Jones 1986; Danchin 1988) and penguins (Waas 1988; Waas et al. 2000), increase in social stimuli has been shown to increase sexual behaviour, and hasten and synchronize egg-laying schedules. The influence of social stimuli on physiology is evident from its effects on hormone levels (Farner and Wingfield 1980; O'Connell et al. 1981a; O'Connell et al. 1981b; Wingfield 1986; Dufty Jr. and Wingfield 1990; Wingfield et al. 1990; Vleck and Brown 1999). The highly social environments of large colonies resulted in greater testis size of cliff swallows (Petrochelidon pyrrhonata) than those breeding in small colonies (Brown and Brown 2003). Furthermore, social stimulation may increase


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testosterone levels of gravid females, resulting in higher testosterone deposition in the developing egg and faster chick growth (Schwabl 1993, 1996a, 1996b, 1997; Schwabl et al. 1997; Birkhead et al. 2000; Lipar and Ketterson 2000; Eising et al. 2001; Groothuis and Schwabl 2002; Whittingham and Schwabl 2002; Pilz et al. 2003). Colonies may provide greater opportunities and access for mate-prospecting, resulting in lower mate retention among more highly colonial species (Dubois et al. 1998). Coloniality may also affect the evolution of vocal communication in a species. Nest density and the corresponding amount of noise from conspecifics has been shown to increase the difficulty in locating mates or kin (Jouventin 1982; Jouventin and Aubin 2002), and is closely associated with the degree of individual vocal distinctiveness within a species, which can be used for individual recognition (Jouventin 1982; Bretagnolle 1996; Jouventin and Aubin 2002).

Penguins (Family Spheniscidae), like most seabirds, are mostly colonial breeders. Although nest construction differs between species (e.g., surface nest built of pebbles or vegetation, burrow nests, or no nest at all), they all form concentrations of nests within which birds often live cheek-by-jowl with each other (Williams 1995; Davis and Renner 2003) except for one species, the yellow-eyed penguin (Megadyptes antipodes).

Yellow-eyed penguins are endemic to New Zealand, with a breeding distribution confined to the south-east of the South Island and the Subantarctic islands (Auckland, Campbell Islands) (Marchant and Higgins 1990). Unlike other penguins and seabirds in general, yellow-eyed penguins are said to be solitary breeders (Darby and Seddon 1990). It is believed that they traditionally nested in the cool coastal podocarp or


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hardwood forests in their breeding range. Before egg-laying, they defend a large area around their nest (up to 20 m from their nest) (Marchant and Higgins 1990), although aggressive encounters are rare (Seddon and Darby 1990). Depending on the amount and type of vegetation, nests densities range from 1 to 5 nests per hectare (Darby and Seddon 1990) with averages of 12, 16 and 32 m of inter-nest distances in scrub, flax and forest habitats, respectively (Seddon 1988). Nests are enclosed under dense vegetative cover (e.g. flax bush Phormium tenax, hebe Hebe elliptica, ngaio Myoporum laetum) (Seddon and Davis 1989; Darby and Seddon 1990), creating physical barriers from each other. Nests are therefore normally visually, but not aurally, isolated from each other.

They vocalise mainly upon arrival on the shore at dusk or before returning to the sea at dawn from the nest or near it. Therefore, apart from intra-pair interactions, visual cues from other birds, even during the pre-egg period, are mostly received when birds land together or remain on the beach, making them the least colonial of all penguins.

As such, the social environment of yellow-eyed penguins is very different compared to those of highly colonial penguins (see Table 2.1). The physical separation greatly limits the potential amount of perceived visual stimuli from conspecifics, and the amount of physical or agonistic behaviour. Furthermore, the amount of social stimuli within a yellow-eyed penguin breeding area is likely to be lower than that of a colonial species with the same number of nests, as the distances between nests also limit the potential for social facilitation.


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The central questions therefore are, (i) why are the yellow-eyed penguins the least colonial penguin species, and (ii) what are the consequences of their solitary nesting behaviour on other aspects of their life-history relative to other penguin species? The aim of this paper is to use the available literature to explore the consequences of coloniality on the reproductive behaviour, reproductive physiology, mate or site retention and vocal communication system among penguins and, by comparison, the implications of a lack of coloniality in yellow-eyed penguins.


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Table 2.1: Nest densities and distances between nests in different species of penguins. In most cases distances or densities denote averages of different populations rather than absolute minima or maxima.

Species

King penguin

Nest density

Distance between

(nest/m2)

nests (m)

1.3 – 2.2

1

Source

Williams 1995

(Aptenodytes patagonicus) Emperor penguin (A.

8.7 (in huddles)

Williams 1995

forsteri) Gentoo penguin

0.25

2–3

Williams 1995

2

0.36

Warham 1974

1.25

0.66

Williams 1995

(E. pachyrhynchus) Snares penguin (E. robustus) Erect crested


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penguin (E. sclateri) Macaroni penguin

0.74 – 1.27

0.3 – 0.9

Williams 1995

0.041 - 0.025

2-3 m apart) under the shelter of dense vegetation or boulders and caves (Williams 1995; Heather and Robertson 1996), most likely to protect the downy chicks from rain and hypothermia (Davis and Renner 2003).

There is a long-standing assertion that solitary nesting in yellow-eyed penguins is driven not only by the need to find sufficient cover but also because they actively seek nests that are visually isolated from each other (Darby 1985; Darby pers. comm.). This assertion mainly comes from the fact that over the years very few nests have


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been found in visual contact with another, and that one or both nests in this situation invariably fail (Darby pers. comm.). Although this may explain the nest dispersion and lack of coloniality in yellow-eyed penguins, no plausible reason for this supposed behaviour has been put forward. In an attempt to test this hypothesis, Seddon (1988) found no difference in terms of visual isolation from neighbouring nests between an actual nest and a random site (selected using a random table for direction [8 compass points] and distance from the actual nest site) (Seddon 1988). This suggests that visual isolation between nests is simply a consequence of the habitat in which the species breeds. Nevertheless, only a direct experiment that involves artificially creating visual contact between nests and comparing the reproductive success, behaviour and stress levels (e.g., through corticosterone measurement, non-invasive heart rate measurement) of birds with and without visual access with other nests would settle the validity of this hypothesis.

The need for yellow-eyed penguins to find a suitable habitat has had broad consequences for their biology and life histories. The large distances between nests reduces the probability for cuckoldry and aggression (Darby and Seddon 1990; Seddon and Darby 1990; Davis and Renner 2003), while nesting under heavy vegetation would conceal and protect them from predation (aerial predation from skuas [Catharacta lonnbergi] in the Subantarctic and traditionally, weka [Galliralus australis] on the mainland, which are a native land predators of Fiordland crested penguins [St. Clair 1992]). Further consequences of their solitary lifestyle are discussed in the following sections.


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2.3. Social facilitation in penguins

Darling (1938) observed that females of herring gulls (Larus argentatus) in larger colonies tended to lay their eggs earlier and more synchronously than those in smaller colonies. He suggested that social stimuli within a colony could influence reproductive physiology and behaviour, which ultimately hastened and synchronized egg laying among females. As the amount of social stimuli is likely to be correlated with colony size or density, egg laying in larger colonies should be earlier and more synchronous. This effect has subsequently been demonstrated in other seabird species (Burger 1979; Gochfeld 1980; Jones 1986; Mougin et al. 2001; Coulson 2002).

Reproductive behaviour is largely controlled by the actions of reproductive hormones such as testosterone, estradiol, progesterone and prolactin (Balthazart 1983; Silverin 1986; Buntin 1996; Vleck 2002). Therefore, any effects of social stimuli on reproductive behaviour would likely be mediated by changes in hormone levels (Darling 1938; Bluhm et al. 1984; Cheng et al. 1988; Cohen-Parsons and Roy 1989), and vice versa (Goodson 1998a, 1998b; Leboucher et al. 2000; Peters et al. 2002). For example, social stimuli during the courtship period and territorial intrusion elevated testosterone levels, consistent with its role in modulating courtship and aggression associated with breeding (O'Connell et al. 1981a; Wingfield 1986; Dufty Jr. and Wingfield 1990; Wingfield 1990; Wingfield et al. 1990; Wingfield 1991; Wikelski et al. 1999; Hirschenhauser et al. 2003).

Being mostly colonial, these effects are also evident among penguins. Breeding was more synchronous among African penguins (Spheniscus demersus) within a colony


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than between colonies (Seddon et al. 1991). Social facilitation is also said to occur in copulating Adelie penguins Pygoscelis adeliae (Davis pers. comm.). The evidence for social facilitation in penguins has been most elegantly demonstrated in a series of playback experiments done by Waas (1988, 1995, 2000). During playback of penguin calls, little and Royal penguins increased copulation and display rates (Waas 1988; Waas et al. 2000). Royal penguins that heard playback of calls from their own colony also laid earlier and more synchronously than control birds (Waas 1995). However, although Waas only increased auditory stimuli, visual stimuli were also likely to play a part in producing the observed effects. Birds that displayed in response to artificial calls would have increased the amount of visual stimuli in the colony to cause further social facilitation.

Yellow-eyed penguins would seem to be susceptible to social facilitation also. Richdale (1951) reported that lone males responded to trumpet calls of other males with the same type of call. He suggested that subsequent males may have responded due to “the power of suggestion” of the initial trumpet call. I have similarly observed that lone males respond to playbacks of trumpet calls during the incubation and guard periods (Setiawan personal observation).

The question is then, to what extent do conspecific social stimuli influence reproductive behaviour in yellow-eyed penguins? The amount of social stimuli available to an animal may influence its susceptibility to social facilitation, although the reverse could also be true (Waas 1995). Compared to other penguins, yellow-eyed penguins have much reduced opportunities to receive visual stimuli. Indeed, social facilitation in yellow-eyed penguins may largely be mediated through vocal stimuli.


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Lone males responding to the trumpet calls of other males often do so without them being able to see each other (Richdale 1951; Setiawan personal observation). Yet, yellow-eyed penguins seem much less vocal compared to other penguins, with calling mainly restricted to periods of arrival (dusk) and departure (dawn) to sea. In a review on the vocalizations of penguins, yellow-eyed penguins were considered as having little social interaction and being ‘quiet’ (Jouventin 1982). Furthermore large internest distances lessen the intensity of auditory stimuli. Given the relative low occurrence of social stimuli, social facilitation may not play a major role in modulating reproductive hormones and behaviour of yellow-eyed penguins. A playback experiment similar to that used by Waas (1995) while simultaneously measuring hormone levels and reproductive schedules would go a long way towards addressing this issue.

2.4. Vocal recognition

The ability to recognise individuals is vital for the expression of appropriate behaviours towards conspecifics. Inappropriate behaviour such as misdirected parental care, aggression towards kin or partners, or indifference towards usurpers may result in lower reproductive success, unnecessary injury, or death. Experiments have shown that penguins rely heavily on vocal cues for individual recognition although, in addition, they may also use visual cues or nest location (Jouventin 1982; Clapperton and Jenkins 1987; Proffitt and McLean 1991; Speirs and Davis 1991; Nakagawa et al. 2001; Aubin and Jouventin 2002).

Individual vocal recognition requires individual variation in calls, i.e., the amount of variation between individuals must be greater than variation within individuals (Falls


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1982). Amount of variation is commonly expressed in terms of coefficient of variation (CV) of the parameter being measured. Individual variation is useful for recognition when the ratio of CV between individuals (CVb) over CV within individuals (CVi) is greater than 1, with values greater than 2 considered as high (Jouventin 1982; Robisson et al. 1993; Charrier et al. 2001).

Several factors are known to influence the structure of vocalizations. Individual recognition is particularly important when the potential for confusion is great, such as in species that live in dense aggregations like penguins (Falls, 1982). As such, there is a correlation between the amount of individual variation and the potential for confusion (e.g., amount of ambient noise, nesting density) (Lengagne et al. 1997; Gaston and Jones 1998). Ecological constraints may also dictate call features that carry individual coding. Some habitat types or situations may degrade certain features of calls (amplitude, frequency, or temporal parameters) making them unsuitable to carry information about individuals. For example, two unrelated burrowing species, the little penguin and short-tailed shearwater (Puffinus tenuirostris) use similar features (rhythmic succession of two sounds) to carry territorial information owing to the fact that these features are not easily degraded in their environment (Jouventin and Aubin 2000).

Similarly, differences in vocalizations among penguin species reflect the differences in the colony features. Emperor and King penguins are large bodied penguins that breed in high densities (Williams 1995). The vocal recognition system in these species must overcome the problem of loud and continuous background noise from conspecifics and the screening effect of bodies (Aubin and Jouventin 1998, 2002).


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Emperor (Aptenodytes forsteri) and King penguins (Aptenodytes patagonicus) accomplish this by emitting calls simultaneously containing two slightly different fundamental frequencies (the two-voice system) by simultaneously activating both parts of the syrinx (the sound producing structure in birds (Gaunt and Nowicki 1998)) (Aubin et al. 2000; Aubin and Jouventin 2002). The “beat” (Bradbury and Vehrencamp 1998b) generated by the interaction of the two frequencies is very resistant to degradation and, most importantly, contains information about caller identity (Robisson et al. 1993; Aubin et al. 2000; Aubin and Jouventin 2002). In addition to the challenge of sound degradation, unlike other penguins, Aptenodytes penguins do not have fixed nest-sites, thereby denying them the use of landmark cues that would aid reunion with mate or chick (Aubin and Jouventin 2002). This situation represents one extreme in terms of the potential for confusion of identity among penguins. As such, the amount of individual distinctiveness in the calls of Aptenodytes adults and chicks are the highest among penguins (Jouventin 1982; Lengagne et al. 1997). Lengagne et al. (1997) showed a direct relationship between the difficulty of partner identification and amount of individual call variation in different species of penguins.

Among penguins, vocalizations are the main cue used for chick recognition (Proffitt and McLean 1991; Aubin and Jouventin 2002; Jouventin and Aubin 2002), and interspecies differences relating to differences in colony features are also evident in the vocalizations of chicks. Parent-chick vocal recognition tends to develop when chicks are about enter a stage in their development when there is potential for confusion e.g. where there are high nest densities and chicks are becoming mobile (Falls 1982). Not having fixed nest sites and living in dense colonies, the chicks of Emperor penguins


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develop distinct individual calls much earlier (at hatching) than chicks of Adelie (22 d; when chicks are mobile and can leave the nest) (Falls 1982; Jouventin 1982) and Fiordland penguins (14 d) (Studholme 1994).

In the yellow-eyed penguin, nest locations should serve as very reliable visual cues for locating mates and chicks. The possibility of birds returning to the wrong nest site and partner should be very much lower than for other penguins due to large inter-nest distances. Therefore, the use of visual landmarks may lessen the importance of vocalizations as a recognition mechanism in this species. If this is the case, variation in individual vocalisations may be lower than for other penguins and/or responses towards calls of conspecifics would be similar (i.e. show no discrimination) regardless of caller identity.

On the other hand, there is no obvious reason why there should be selection pressure to lose individual vocal recognition ability, even in the presence of another individual identification mechanism. Yellow-eyed penguins most likely evolved from colonial nesting ancestors, which may have used vocalizations as a recognition cue. Vocalizations may be used to some extent by parent yellow-eyed penguins to recognise their chicks. During the post-guard stage, both parents leave to forage, and chicks may move a considerable distance from the nest (Richdale 1957), increasing the risk of confusion. Furthermore, chicks from nests that are relatively close together are sometimes found to form small crèches (3-6 chick aggregations) (Richdale 1957) and, in these situations, parents provision only their own chicks while ignoring the solicitations of neighbours’ chicks (Richdale 1957; Setiawan pers. obs.). It is possible that any vocal distinctiveness in yellow-eyed penguin chicks only develop at around


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50 d old, much older than for other penguins, as the chicks near the post-guard stage. Before this period, the potential for confusing chicks is relatively low as chicks normally remain near the nest and always within a short distance from at least one parent (Richdale 1957), so that nest location alone may be sufficient for chick recognition.

To carry information about the individual, yellow-eyed penguin calls need to contain features that will not be easily degraded by the surrounding environment. Other penguins seem to rely on temporal parameters of vocalizations to convey information on identity. However, sounds emitted from inside thick vegetation would travel through multiple paths through the foliage to be perceived by a receiver as a single compound signal containing reverberations (small echoes) that may result in serious temporal distortions (Bradbury and Vehrencamp 1998a). This distortion may make temporal variables unsuitable for carrying individual coding in yellow-eyed penguins. In these situations, frequency parameters may be more suitable for carrying information on identity, especially when nest location facilitates identification (Jouventin 1982).

In conclusion, nest location may serve as a reliable cue for individual recognition in yellow-eyed penguins, perhaps more so than for other penguins. Nevertheless, vocal recognition is also likely to be used to some extent in yellow-eyed penguins. Analyses on the amount of individual variation in yellow-eyed penguin vocalizations and their responses towards calls of different types of conspecifics (mate, neighbour, stranger, chick, parent) are needed to address these issues.


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2.5. Mate and nest site retention

For long-lived monogamous seabirds, retention of mates and nest sites are known to pose substantial benefits. Mating with the same individual avoids the need and costs associated with pair formation, confers better coordination of breeding activities due to familiarity and age or experience, and tends to be associated with higher reproductive success (Williams and Rodwell 1992; Bried and Jouventin 2002). Retaining the same nest site confers benefits through familiarity with the surrounding territory, is associated with better knowledge of neighbours (lower aggression) and potential mates (reviewed in Bried 2002), and allows the use of the nest to act as a reliable meeting point with the previous year’s mate (Davis and Speirs 1990; Bried and Jouventin 2002). On the other hand, fidelity to a nest site or mate could prove costly if they are of low quality or the costs of defense are high (e.g., aggressive competition for nest sites) (Bried and Jouventin 2002).

Mate and nest fidelity are often correlated as birds often use the previous year’s nest site as a reunion point at the beginning of the breeding season (Davis and Speirs 1990; Bried and Jouventin 2002). With the exception of the Aptenodytes, mate retention in penguins is high, around 60-90% (Williams 1996; Bried and Jouventin 2002). Variability in rates of mate retention may be associated with several factors e.g., previous year’s breeding success, latitude of breeding location, amount of time mates spend together (association) during the breeding season, etc. (Williams 1996; Bried and Jouventin 2002).


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From a social standpoint, high levels of association with conspecifics in highly colonial species opens the door for extra-pair copulations (Moller 1987; Moller and Birkhead 1993; Dubois et al. 1998), intense mate competition (Bried and Jouventin 2002) and/or site competition or aggression (Stokes and Boersma 2000; Davis 2001). Disruptions to breeding due to competition are most likely to occur in highly colonial species. Furthermore, even in the absence of extra-pair copulations, proximity between nests may allow for assessment of neighbour’s breeding success (a measure of quality), and may lead to mate prospecting (Bried and Jouventin 2002). All of these seem to show that coloniality may promote mate and/or nest site changes between years, especially for birds experiencing low breeding performance.

Being the two least colonial surface nesting penguins, mate fidelity in the yellow-eyed and Fiordland penguins might be expected to be relatively high. Pair dissolution rates of Fiordland and yellow-eyed penguins are 13% (Richdale 1957) and 9% (St. Clair et al. 1999) respectively. Among all surface nesting penguins, only Macaroni penguins, at 9%, have divorce rates as low (Dubois et al. 1998). An analysis conducted by Willliams (1996) showed that nearly 50% of the amount of interspecies variation in pair fidelity among penguins can be attributed to the amount of time partners spend together (degree of association). Incubation and guard shifts in yellow-eyed penguins are on average only 2 days (Darby and Seddon 1990) which implies a greater frequency of pair reinforcement compared to penguins with extended incubation shifts. Therefore, low pair dissolution rates in yellow-eyed penguins may largely be due to the high degree of association in this species and year-round residency.


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On the other hand, nest fidelity in yellow-eyed penguins was actually found to be less than 30% (Darby and Seddon 1990), which is the lowest for all penguins that use a nest site (Williams 1996). However, yellow-eyed penguins are known to defend a territory of up to 20 m around the nest (Darby and Seddon 1990). For most penguins, change in nest location equals territory change, which need not be the case in yelloweyed penguins. Indeed, territory retention in yellow-eyed penguins was found to be 52.3% (Setiawan et al. unpubl. data). However, this figure is still the lowest rate of site retention among penguins that use a nest site (Williams 1996).

The resident nature of yellow-eyed penguins may be one reason why mate retention rates can be high despite the low site fidelity in the species. For migratory species such as Adelie penguins, site fidelity is vital for the successful reunion with the previous year’s mate (Davis and Speirs 1990). However, year-round residency allows yellow-eyed penguins to maintain continual contact with their partners even during the non-breeding period, enabling them to locate each other in the event of a territory change, thus increasing the likelihood of re-mating. Although residency may alleviate the cost of site change on mate retention in yellow-eyed penguin, it is unlikely to be the only reason for the observed low site fidelity. Other resident penguins (Gentoo, little, African penguins) have high site fidelity values (60-100%), which are comparable to migratory species (Williams 1996). A detailed study on the causes and relationship between mate and site fidelity in yellow-eyed penguins is needed.


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2.6. Sociality in yellow-eyed penguins

The solitary nesting behaviour of yellow-eyed penguins may have been the consequence of the simple need to find a suitably sheltered nesting site. However, this seemingly innocuous need has resulted not only in changes to nest distribution patterns, but also quite possibly elements as diverse as their vocal communication system to their physiology.

The roles of extra-pair social interactions and, therefore, social facilitation, may be reduced compared to other penguins as the type and amount of social stimuli available is mainly restricted to vocal stimuli during dusk and dawn, the periods of returning from and departure to sea. Yellow-eyed penguins may be able to rely on nest locations as individual recognition cues, as inter-nest distances should greatly reduce the probability of birds arriving at the wrong nest site and partner. Vocal cues probably still play a role in individual identification, such as in parent-offspring recognition during the post-guard period where parents have been shown to differentiate between foreign and filial chicks; a period when landmark cues are less reliable due to chicks moving some distance from the nest site and sometimes even forming crèches. Solitary nesting is also thought to reduce the incidence of extra-pair copulation and mate changes. Consistent with this hypothesis, the pair dissolution rates of yellow-eyed penguins are low compared to other surface-nesting penguins, with the exception of the Fiordland and Macaroni penguins. However, nest site fidelity rates of yellow-eyed penguins were the lowest among penguins. This may be related to, but not wholly explained, by the resident nature of the species.


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Clearly, more observation and experimentation is needed to adequately determine the causes and consequences of their solitary behaviour.

2.7. Acknowledgements

I am deeply grateful for the help of Lloyd S. Davis and John T. Darby for constructive comments on this manuscript. We are also thankful for the support of the Department of Zoology technical and administrative staff. Institutional financial support was provided by the University of Otago through an Otago Research Grant (LSD), the Antarctic and Southern Ocean Research Group and The Yellow-eyed Penguin Trust.

3. Yellow-eyed penguin endocrinology

CHAPTER 3 SEX STEROIDS AND PROLACTIN LEVELS IN BREEDING YELLOW-EYED PENGUINS (MEGADYPTES ANTIPODES)

ALVIN N. SETIAWAN


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3.1. Abstract

The reproductive behaviour of yellow-eyed penguins (Megadyptes antipodes) has been studied for many years. However, very little is known about the changes in hormone levels of yellow-eyed penguins during the breeding season. This study is aimed at providing a description of the reproductive hormone (testosterone, estradiol, progesterone) levels during the breeding season and for the first time, to measure prolactin levels in yellow-eyed penguins. Hormone changes in yellow-eyed penguins were similar to that of other monogamous long-lived seabirds with altricial chicks. Testosterone in males and females, and estradiol in females were elevated before egglaying, declined precipitously shortly after laying, and remained low thereafter. Female progesterone levels were low early in the season but increased steadily, reaching a peak at laying, and dropped during early incubation, remaining low throughout the rest of incubation. Prolactin levels in males and females were shown to steadily increase from early in the season, reaching a peak during late incubation, and remained elevated up to the guard period although the level dropped slightly during this time. In addition, we also found an age effect on progesterone levels of males and females during pre-egg phase. Progesterone levels were higher in older females, but were lower in older males.


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3.2. Introduction

Reproductive behaviour in birds is controlled by reproductive hormones (Farner and Wingfield 1980; Silverin 1986; Silver 1990). Changes in reproductive behaviour and life histories are likely to be reflected in changes in endocrine status (Wingfield 1990, 1991).

All penguins are typically monogamous during the breeding season and require biparental care for incubation and brooding, with distinct behavioural shifts between the different breeding phases (pre-eggorcourtship, incubation, guard, post-guard) (Williams 1995; Davis and Renner 2003). Birds with a similar breeding system (monogamous and biparental) exhibit elevated levels of the gonadal steroids, testosterone and estradiol, during the pre-egg phase associated with sexual and territorial behaviour, and these fall to low levels during incubation (Ball 1990). Associated with the switch to parental care behaviour, prolactin levels are elevated during incubation and sometimes remain so through to the guard period of chickrearing (Buntin 1996). This general pattern has been described for various penguin species e.g. Macaroni Eudyptes chrysolophus (Williams 1992; Williams and Sharp 1993), Fiordland crested E. pachyrhynchus (McQueen et al. 1998), Adelie Pygoscelis adeliae (McQueen et al. 1999; Vleck and Brown 1999), gentoo P. papua (Williams 1992; Williams and Sharp 1993), Humboldt Spheniscus humboldti (Otsuka et al. 2000), Magellanic S. magellanicus (Fowler et al. 1994), emperor Aptenosytes forsteri (Groscolas et al. 1986; Lormee et al. 1999) and king A. patagonicus (Mauget et al. 1994).


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The yellow-eyed penguin (Megadyptes antipodes) is an endemic species found on the south east coast of the South Island and Subantarctic islands of New Zealand (Marchant and Higgins 1990). Unlike the other penguins, they are said to be solitary breeders (Williams 1995). Nests are located far apart from each other and are visually isolated from each other. They normally lay 2 eggs (3-5 d laying interval) in midSeptember to early October, which hatch synchronously within 24 h of each other (Darby and Seddon 1990). The chicks are provisioned similarly, so that there is little size difference during development (Van Heezik 1990).

Despite all that is known about their reproductive behaviour, very little is known about the reproductive endocrinology of the yellow-eyed penguin. Only one cursory study (Cockrem and Seddon 1994) has looked at broad scale hormonal changes that occur in yellow-eyed penguins. The present study is aimed at providing a description of the reproductive hormone (testosterone, estradiol, progesterone) levels during the breeding season and for the first time, to measure prolactin levels in yellow-eyed penguins.

3.3. Methods

3.3.1. Study site and population

The main data collection for the study was conducted on a banded population of yellow-eyed penguins of known age, sex, life and breeding histories at Boulder Beach Otago Peninsula (45° 53.9’ S 170° 37,0’ E) during the August 2001 – January 2002 breeding season. Sex was determined from long-term behaviour observations


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(Richdale 1957), DNA analyses, and morphometric measurements (Setiawan et al. 2004). As part of a preliminary study, we also collected samples from a small number of birds during the laying period of the previous season (September 2000). Unless specifically stated, reported results refer to data collected in 2001.

Ages of birds were obtained from a 20-year population database. Most birds were banded as chicks or juveniles for which age can be calculated accurately. Yelloweyed penguins are able to reproduce at 2 years of age. Nineteen percent of sampled birds were banded as adults and were taken as a minimum of 2 years of age at banding.

In both years, nests were visited daily throughout the pre-egg and laying periods, allowing us to calculate laying dates (± 1 day). Nests were also visited every 2 days near the hatching period to obtain hatching dates and incubation spans for most nests (± 1 day). At particular intervals during the incubation and guard periods, these visits would include blood sampling from the bird at the nest (see following section).

3.3.2. Blood sampling and storage

Birds were captured near nests (during pre-egg period) or on nests (during incubation and guard periods). Samples of 0.5-3.5 ml of blood were taken from the brachial vein on the flipper within 2-10 minutes of capture using heparinised syringes. Due to low numbers of birds breeding, repeated sampling of individuals within and between seasons was necessary, but most penguins were sampled only once within a 14 d period to minimise disturbance. Blood sampling was conducted from pre-egg (early


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August) through to the guard period when chicks have hatched but were still being brooded by an adult on the nest (middle of December) in 2001. In addition, in 2000 birds were sampled within 24 h of laying the first (A-egg) and second egg (B-egg), giving us detailed data on the hormonal changes that may occur during the laying interval. The sampling protocol is shown in Table 3.1. Blood was centrifuged at 6000 rpm for 3 minutes within 3 h of sampling. Plasma was then recovered and stored in liquid nitrogen in the field and subsequently stored in –20°C freezer until assay.

The regularity of our nest visits was likely to have habituated the penguins, reducing the possible effects of disturbance on hormone levels. The uniform and consistent treatment (frequency of nest visits and blood sampling) of individuals in this study would also ensure that any possible effects of disturbance on hormone levels would not affect the analyses.

3.3.3. Radioimmunoassays

Plasma samples were assayed for testosterone (T), estradiol (E2), progesterone (P4) and prolactin (Prl). Testosterone, estradiol and progesterone assays were conducted at the Zoology Department, University of Otago for all samples. Prolactin was assayed at the School of Animal Biology, University of Western Australia according to a previously described procedure (Blache et al. 2001). Not all assays were conducted on all samples due to restrictions in the size of some samples (i.e. the amount of plasma available). In particular, for estradiol we were able to assay only the 2001 samples. When sample volumes permitted, assays were conducted in duplicates. Serial


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dilutions of penguin plasma gave displacement of tracer parallel to the standard curves in all assays.

Pools of plasma from emu and chicken (neat and diluted 5-fold) were used as quality controls to calculate intra-assay coefficients of variation for the prolactin assay. Testosterone, estradiol and progesterone were added to pools of chicken and yelloweyed penguin plasma to calculate inter- and intra-assay coefficient of variation. A single prolactin assay was conducted on all samples, avoiding inter-assay variations. Antisera against all testosterone and for assays of progesterone (samples of 2001females only) were obtained from Esoterix (previously Endocrine Sciences), USA. Antisera against estradiol and progesterone (except that for females sampled in 2001) were obtained from Sirosera (Total Reproduction), Australia. Prolactin was measured using an assay for ring dove (Streptopelia risorea) according to the method of (Talbot et al. 1995).

Depending on the type of assay, sex and breeding stage, 10-150 µl of plasma was used. Samples were extracted in 4 ml of diethyl-ether for testosterone, estradiol and progesterone assays. Recoveries for testosterone, estradiol and progesterone were 94100%, 82-96% and 66-82%, respectively. Reported values were recovery-adjusted. The sensitivities of assays were 0.07, 0.03, 0.14 and 0.3 ng/ml for testosterone, estradiol, progesterone and prolactin, respectively. Inter-assay coefficients of variation were 15%, 14.% and 16% for testosterone, estradiol and progesterone assays. Intra-assay coefficients were 4-9% (average 7%), 8-11% (average 9%), 3-10% (average, 7%) and 5% for testosterone, estradiol, progesterone, and prolactin assays.


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3.3.4. Effects measured and statistical analyses

Data were analysed using univariate general linear model (GLM), linear regression or Student’s T-tests where appropriate. Within each model only one data point from each individual was selected randomly to avoid individual effects. When the assumptions of the parametric tests were violated, data were log transformed. If this did not remedy the problem, the non-parametric equivalents were used (Kruskal-Wallis, Spearman’s rank correlation and Mann-Whitney tests). All statistical tests were done using SPSS 11.0 (2001).


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Table 3.1: Sampling schedule of yellow-eyed penguins in this study.

Sample type

Sampling period

Year of sampling

PE1 (Pre-egg 1)

60–44 d before laying

2001

PE2 (Pre-egg 2)


2001

PE3 (Pre-egg 3)


2000, 2001

LA (Laying of A-egg)

0-3 d after laying of A-egg

2000, 2001

LB (Laying of B-egg)

Within 24 h of laying of

2000

B-egg I1 (Incubation 1)

11-28 d of incubation

2000, 2001

I2 (Incubation 2)

30-43 d of incubation

2001

G2 (Guard 1)

13-23 d after hatching

2001


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3.4. Results

Levels of testosterone and prolactin were found to change significantly in the males during the breeding period (Kruskal-Wallis T: H =16.692, P=0.010; Prl: H=24.510, P