Keywords

9.1 Introduction

The ability to study sexual behaviors in odontocetes is first and foremost limited by access to the animals. Opportunistic observations of conceptive and non-conceptive sexual behaviors of free-ranging animals have accrued over the years; the contextual information is often limited (e.g., preceding behaviors, relationship between individuals), and the behaviors documented are those that are often more visible and frequent than others. Thus, many of the observations tend to be anecdotal, with years between observations, and/or are reliant upon retrospective sources, such as postmortem records. While retrospective methods are useful for some topics, they do not capture behavior directly. With advances in technology (e.g., drones and other sample methods), additional insights will be gained but will continue to be limited to the species, and individual animals, that are visible and present at the time of data collection.

Observations from managed care facilities can corroborate details gleaned from free-ranging populations. Data obtained from animals in such facilities can be used to better understand cetacean behavior in more detail and inform studies in the natural habitat. Although there are limitations to managed care facilities (e.g., limited existing populations), there are opportunities for close observation, longitudinal studies, and knowledge of biological state based on veterinary and care staff records. This chapter summarizes the knowledge that has been acquired on sexual behavior from odontocetes in managed care facilities over the past 70 years and how these data complement and expand on studies conducted on free-ranging animals. Research on behavior in managed care facilities aligns well with behavior of free-ranging animals to the extent that specific behaviors are documented within that context. Thus, there is little evidence to suggest the behaviors discussed in this chapter are not comparable to behaviors in free-ranging animals.

9.2 Reproductive Behavior

This section highlights topics related to reproductive behavior. We begin with mechanisms that influence reproductive behavior such as hormones and seasonality, and then we expand to behavioral processes. We defined reproductive behavior as any action of reproduction that promotes fertility and a conceptive outcome. Following this section, we elaborate on nonreproductive sexual behavior.

9.2.1 Hormonal Influences on Reproductive Behavior

Despite the advances in technology and our understanding of odontocete reproductive biology, the world of hormonal influences on reproductive behavior is still in its infancy with few clearly defined links identified between hormone levels and behavior. Many odontocete species have well-defined breeding seasons (e.g., Connor et al. 1996; Shelden et al. 2020), which are also observed for species in managed care (e.g., finless porpoises, Neophocaena spp., Daoquan et al. 2006; bottlenose dolphins, Tursiops spp. McBride and Kritzler 1951; Samuels and Gifford 1997; Pacific white-sided dolphins, Lagenorhynchus obliquidens, Robeck et al. 2009; Commerson’s dolphins, Cephalorhynchus commersonii, killer whales, Orcinus orca, Robeck et al. 1993; false killer whales, Pseudorca crassidens, beluga whales [or white whales], Delphinapterus leucas, Robeck et al. 2005; harbor porpoises, Phocoena phocoena, Desportes et al. 2003) and correspond to spikes in specific hormones for females and for males (Robeck et al. 2005). For all odontocetes studied, whether collected through blood, blow, or fecal samples, testosterone is the primary hormone associated with sexual maturity and sperm production in males (e.g., Robeck et al. 2005; Robeck and Monfort 2006; Katsumata et al. 2017). Female odontocetes present a more complex suite of reproductive hormones than males. Hormonal analysis is further complicated by some species being spontaneous ovulators (e.g., bottlenose dolphins), while others appear to experience induced and/or spontaneous ovulation (e.g., beluga whales, Steinman et al. 2012). Spontaneous ovulators, in which ovulation can occur cyclically, appear to require an increase in estrogen and progesterone to stimulate the hypothalamus to release gonadotropin-releasing hormone (GnRH) (Steinman et al. 2012; Bergfelt et al. 2018). This hormonal increase then stimulates the pituitary to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH) to signal the ovary to release a mature follicle (reviewed by Bergfelt et al. 2018). In contrast, induced ovulators are believed to require physical stimulation through intromission and/or the presence of a biochemical component of semen to promote ovulation (reviewed by Bergfelt et al. 2018).

The production of sperm and the releasing of eggs require increases in reproductively relevant hormones over time. Research has begun to explore the development of sexual maturity in male odontocetes with evidence suggesting that as males approach sexual maturity, testosterone begins to spike in concert with breeding season timing even in the years prior to the concentration necessary to produce sperm (e.g., beluga whales, Richard et al. 2017b; killer whales, Robeck and Monfort 2006; Katsumata et al. 2021; Yangtze finless porpoises, N. asiaeorientalis, Wu et al. 2010). Sexual maturity for females appears to be dependent upon relevant ratios of specific hormones, including progesterone and estradiol (e.g., Indo-Pacific bottlenose dolphins, T. aduncus, Zhang et al. 2021). However, the interplay between hormone levels and onset of sexual maturity for females is more complex. More work is needed on male and female reproductive biology, in spite of research efforts conducted to develop artificial insemination procedures in females (Robeck et al. 1993; O’Brien et al. 2008, 2019; Katsumata 2010).

There may be evidence of suppressed ovulation in the case of matriarchal societies, such as killer whales (Croft et al. 2017; O’Brien et al. 2019), which suppression has been proposed as a mechanism by which reproductive fitness can be maximized. Research with free-ranging killer whales suggested that older females have less success rearing offspring, which may lead to a menopausal state (Croft et al. 2017; Dalton 2022). Research on killer whales in managed care facilities suggested that not all females cycle during the same breeding period and that cycling may be suppressed in younger females who are not the matriarch (O’Brien et al. 2019). As one of the few mammalian species to exhibit reproductive senescence, killer whales in managed care facilities provide a unique opportunity to track the development of reproductive senescence over time.

Currently, the mechanisms by which males detect a cycling female are unknown. There is recent evidence that bottlenose dolphins can discriminate familiar from unfamiliar conspecifics using urine samples (Bruck et al. 2022) and rostrum-to-genital behaviors have been observed in many different odontocete species (Table 9.1; Dudzinski 1998; Mann and Smuts 1999; Kuczaj and Yeater 2007; Horback et al. 2012). Anecdotal observations suggest that there are some behavioral correlates associated with increases in fertility for females and interest by males, many of which involve genital stimulation (both self- and conspecific-initiated), behavioral displays by males and perhaps females, increased vocalizations, and increased pair swimming between females and males (Table 9.1). However, only two studies have attempted to systematically correlate changes in reproductive hormone levels to behavior with minimal success or insight (two Hawaiian spinner dolphins, Stenella longirostris, Wells 1984; a killer whale, Horback et al. 2012; see summary in courtship display section). Despite all efforts made thus far on understanding the reproductive biology of odontocetes, there are many more opportunities for further research.

Table 9.1 Abbreviated anecdotal observations of sexual behaviors of odontocetes in managed care. For the complete description of observations from each source per observed behavior, please see Supplemental Table 9.1
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9.2.2 Seasonality

Seasonality of odontocete reproductive biology has been examined in detail through ultrasound and hormone analysis and corroborated with behavioral observations and the seasonality of when calves are born (beluga whales, O’Brien et al. 2008; Glabicky et al. 2010; Steinman et al. 2012; Richard et al. 2021). The detailed observations of behavior and biological samples from managed care facilities are the same as those documented from free-ranging populations through research and traditional knowledge (Shelden et al. 2020; Hill et al. 2021). Both in free-ranging animals and in managed care facilities, reproductive sex is rarely documented in the literature; however, voluntary husbandry behaviors with animals in managed care facilities have yielded biological samples that can be collected year-round from animals, in concert with known health and behavior records. This set of conditions and information allows additional conclusions to be drawn regarding when sexual behavior is non-conceptive (e.g., sociosexual) in nature and when sexual behavior can lead to conception. For example, in male beluga whales, testosterone concentrations peak in February to April (Richard et al. 2017a), and in female beluga whales, estrous cycles occur from March to June (Steinman et al. 2012). As described briefly above, female beluga whales may experience spontaneous and induced ovulation (Steinman et al. 2012), although the exact mechanism responsible for inducing ovulation requires further investigation. Even when housed in mixed-sex groups, male beluga whales typically only display pelvic thrusts (Glabicky et al. 2010) and genital presentations toward adult females during their estrous cycle, as confirmed by hormone measurements (Richard et al. 2021; Inyakina et al. 2022).

Ovulation in female bottlenose dolphins in managed care facilities may occur throughout the year and have a less pronounced window of reproduction, although most conceptions and births occur from spring to fall with a peak in summer months (Zhang et al. 2021). Still, these individual bottlenose dolphins may have narrower windows for reproduction than the norm, which may be related to the population from which they genetically originated (Urian et al. 1996). These patterns are consistent with free-ranging populations (e.g., Connor et al. 1996), even for populations in the southern hemisphere, which also have an austral spring to summer peak.

Killer whales also have a seasonal increase in estrous activity during spring months, but hormonal cycling has been documented throughout the year (Robeck et al. 1993). For Pacific white-sided dolphins found only in the northern hemisphere, ovulation and conception occurs from August to October, and indicators of male fertility (e.g., peak testosterone, sperm production) occur in a similar timeframe from July to October (Robeck et al. 2009).

The above studies on the seasonality of reproductive sex are complemented by knowledge of odontocete non-conceptive sex. In some species, such as beluga whales, non-conceptive sexual behavior is present year-round (Hill et al. 2015; Ham et al. 2022) but varies seasonally in prevalence (Glabicky et al. 2010; Lilley et al. 2020). Seasonal fluctuations were also more apparent during the years when individuals approach sexual maturity (Ham et al. 2021). Behavioral variation corresponds with seasonal variation in hormone levels (Robeck et al. 2005; Richard et al. 2017a; Atkinson et al. 2022; Inyakina et al. 2022). For Yangtze finless porpoises, sociosexual behavior was most frequently initiated by sexually immature males, who engaged in same-sex interactions throughout the year (Wu et al. 2010; Serres et al. 2021). Year-round sociosexual behavior has also been documented for bottlenose dolphins (McBride and Hebb 1948; Brown and Norris 1956), harbor porpoises (Desportes et al. 2003), river dolphins (Inia spp. and Lipotes vexillifer) (Renjun et al. 1994; Entiauspe-Neto et al. 2022), and killer whales (Sánchez-Hernández et al. 2019). However, the extent to which this non-conceptive sexual behavior varies seasonally has not been examined explicitly for many odontocete species. The year-round, non-conceptive sexual behavior of odontocetes in managed care facilities matches what is known about free-ranging populations (e.g., Connor et al. 1996; Urian et al. 1996; Lomac-Mac Nair et al. 2016; O’Corry-Crowe et al. 2020; Shelden et al. 2020). Non-conceptive sex is discussed further in Sect. 9.3 of this chapter and Ham et al. (2023, this book).

9.2.3 Courtship Behaviors and Displays

Courtship displays are expressed by a number of odontocetes and range from sound emissions (e.g., whistles, clicks) to body postures (e.g., lateral presentations, s-postures, immobile hangs) to high energy swims (e.g., “shark” swims) and aerials (e.g., leaps, twists, spins) (e.g., Tavolga and Essapian 1957; Puente and Dewsbury 1976; Schaeff 2007; Muraco and Kuczaj 2015). In some species, object presentations may also occur (e.g., Amazon river dolphins, Martin et al. 2008; some bottlenose dolphins, Weaver and Kuczaj 2016; beluga whales, Lilley et al. 2022a, b; killer whales, Table 9.1). As a courtship progresses between a female and a male, the interaction can develop to include paired and synchronous swims, rubbing, and other close-proximity actions, such as pelvic thrusting and genital stimulation (Table 9.1).

Most odontocetes, including species in managed care facilities (e.g., bottlenose dolphins, Commerson’s dolphin, porpoises, Neophocaena spp., beluga whales, false killer whales), appear to have a polygynandrous mating system where females and males mate with multiple partners within a breeding season (e.g., Joseph et al. 1987). Many species show strong seasonality in their reproductive behavior, corresponding hormones, and anatomical changes to testes and ovaries (Robeck et al. 1993; Richard et al. 2017a, b; Funasaka et al. 2018; O’Brien et al. 2019; Katsumata et al. 2021; see Hormonal Influence section). Correspondingly, courtship behaviors increase in frequency with the onset of the breeding season (e.g., Glabicky et al. 2010). Many courtship behaviors displayed by males during the breeding season also occur during non-breeding seasons but typically with same-sex partners, especially in bottlenose dolphins, porpoises, and beluga whales (Ham et al. 2023, this book).

Courtship behaviors and displays during breeding seasons are more commonly documented for males compared to females of most odontocete species in managed care facilities. While females likely present chemical cues to indicate that an estrous cycle is occurring and at times solicit attention from conspecifics, including genital rubbing, genital presentations, and immobility (Muraco and Kuczaj 2015; Table 9.1), more research is needed to better understand the more subtle cues from females as it is possible that females initiate sexual interactions more frequently than is known due to the less obvious nature of their cues. In bottlenose dolphins, anecdotal reports indicate that males will follow, swim with, vocalize at, and perform many different aerial and fast swim behaviors around a female that appears to be of interest to the male (Table 9.1). Male killer whales, bottlenose dolphins, and beluga whales in managed care facilities swim with a female of interest and refuse to leave her when requested by humans for different activities (Table 9.1). Male beluga whales also engage in directed gazes at a female of interest and match her swim patterns while also increasing variability in vocalizations (H. Manitzas Hill personal observation), presenting static s-postures, and mouthing the female when pair swimming with her (Hill et al. 2015; Lilley et al. 2020). At times, bubbles are released as different types of trails/streams, presumably both in concert with and independent of vocalizations that are emitted. Similar types of behaviors have also been observed with smaller delphinids such as Pacific white-sided dolphins, common dolphins (Delphinus delphis), and porpoises (Brown 1962; Nakahara and Takemura 1997).

While little is known of sexual selection strategies of odontocetes, Orbach et al. (2019) extended Schaeff’s (2007) review of the literature. Both authors emphasized that female and male choice occurs in all odontocetes. Aside from narwhals (Monodon monoceros) and several others (Würsig et al. 2023, this book), most odontocetes do not have obvious ornaments or sexually selected armaments that could be used to discriminate between candidates – rake marks, however, may be used to evaluate how successful others are in conspecific fighting, which may be used in mate selection (MacLeod 1998; Orbach 2019) – and male odontocetes generally do not engage in head-to-head reproductive competition as is the case in some terrestrial species, such as deer or giraffe (except for narwhals, beaked and larger whales; see Orbach 2019). However, females may select among possible males based on the speed, displays, or other courtship activities presented by the males (Schaeff 2007; Orbach 2019). Furthermore, male courtship displays in addition to certain physical attributes (e.g., postanal ventral hump in Hawaiian spinner dolphins, caudal peduncle in bottlenose dolphins, melon position in beluga whales, dorsal fin in killer whales) and indirect behaviors (e.g., male Atlantic spotted dolphins “babysitting” young calves while the adult females forage) may facilitate female choice (Schaeff 2007; Orbach 2019, H. Hill, personal observations, K. Dudzinski, personal observations). This conclusion remains conjecture as no systematic experimental study has been conducted.

Ultimately, odontocete females have much control in mating as males are less easily able to restrain or coerce them (with the exception of male bottlenose dolphin alliances cooperating to coerce an ovulating female, Scott et al. 2005), unlike many terrestrial species. Aquatic mammals live in a three-dimensional world that allows females to maneuver their genitalia away from males most of the time, even in species selected for sexual dimorphism with larger body size for males (e.g., beluga whales, killer whales, bottlenose dolphins, Pacific white-sided dolphins, false killer whales, harbor porpoises). In some instances, females actively participate in copulation either by soliciting the attention of males or actively joining a male that is displaying toward her but at some distance away (Hill et al. 2022; Lilley et al. 2022a, b; Table 9.1). More work is needed to uncover the mechanisms involved in female mating strategies.

Little is known about male mate choice in odontocetes. Longitudinal work on the role of male alliances and female access in Indo-Pacific bottlenose dolphins in Monkey Mia has suggested that male alliances facilitate male reproductive success, but the characteristics by which the males select females remains poorly understood (Connor et al. 2022).

Since many odontocete species appear to be spontaneous ovulators (e.g., killer whales, bottlenose dolphins; Sawyer-Steffan et al. 1983, Pacific white-sided dolphins; Robeck et al. 2009, false killer whales, reviewed by Bergfelt et al. 2018) and some species appear to be induced ovulators (e.g., beluga whales, Steinman et al. 2012), males could increase their opportunities to breed if they were considered “attractive” to females.

9.2.4 Copulation

Copulation in odontocetes is defined as the intromission or insertion of a male’s penis into the vaginal slit of a female. The penis may be inserted partially or completely; however, little is known whether there is a difference in fertilization success rate for partial versus full intromission (Lünen 2020). Intromission is considered a reproductive act if the function is to fertilize an ovulating female. Despite the prevalence and extended duration of many odontocete sexual interactions, intromission itself is rarely observed in either free-ranging or captive settings (reviewed by Schaeff 2007; Orbach 2019), primarily due to the speed at which it occurs (Table 9.1). Whether it is a killer whale, a bottlenose dolphin, Pacific white-sided dolphin, coastal tucuxi (Sotalia fluviatilis guianensis), or beluga whale, the entire act of copulation appears to occur in seconds to no more than a minute (Tavolga and Essapian 1957; Puente and Dewsbury 1976; Terry 1984; Schaeff 2007; Muraco and Kuczaj 2015). Apparent successful copulation has been described for some baleen whales, including male orgasm in southern right whales, Eubalaena australis (Würsig 2000).

Often short intromissions, along with the difficulty in determining estrous state and the propensity of many odontocetes to engage in high levels of sociosexual behavior, make the act of copulation difficult to study systematically. Female receptivity is key to successful copulation attempts, regardless of coercive tactics used by some populations of bottlenose dolphins (e.g., in Shark Bay, Australia, Connor et al. 1992; Connor and Krützen 2015). Many descriptions of copulation attempts or completions commonly report the importance of females presenting their ventrum to the male of interest within close proximity (Table 9.1, Fig. 9.1, also reviewed by Schaeff 2007; Orbach 2019). Without this cooperation, males appear to be unsuccessful in their attempts to copulate (e.g., Terry 1984). Other behaviors reported in Table 9.1 that warrant further systematic investigation are the specific vocalizations associated with copulation, spasms (which could be similar to orgasms), and object carrying. Among odontocetes, female choice, male competition, and courtship behaviors are important driving forces in mating behaviors.

Fig. 9.1
An underwater photo of 2 whales. One whale swims over the other whale forming an S-shape.

After the adult male beluga whale (on left) displayed an s-posture, the adult female beluga whale (on right) swam over to the adult male and positioned herself, ventrum up, next to the adult male. Image taken from video footage collected by H. Manitzas Hill

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9.3 Non-conceptive Sexual Behavior

One common form of behavior observed in odontocetes is non-conceptive sexual behavior or actions where conception is not possible. This may include behaviors between two animals of the same sex, two different species, sexually immature and mature animals, or masturbation. Often characterized as sociosexual behavior (when exhibited within a social domain), these behaviors are frequently observed in animals in managed care facilities and nature. For beluga whales, a well-documented species, this behavior is exhibited from a young age and develops slowly (Glabicky et al. 2010; Hill et al. 2015; Lilley et al. 2020; Ham et al. 2022). As male beluga whales approach adulthood, they engage in sociosexual behavior relatively frequently, making up around 5–10% of their time budget (when considering “solo,” “affiliative,” “agonistic,” and “sociosexual” behavior, Lilley et al. 2020). Though studied systematically in a few species, most reports of non-conceptive sexual behavior are anecdotal; but together, these studies suggest there are multiple functions and types of non-conceptive sexual behavior in Odontoceti. Ham et al. (2023, this book) review what is known about cetacean non-conceptive sexual behavior.

9.3.1 Development

One suggested function of non-conceptive sexual behavior in odontocetes is that such activities contribute to the development and practice of reproductively functional behavior (Mann 2006; Bailey and Zuk 2009; Lilley et al. 2020). Sociosexual behavior, which is often similar to copulatory behavior (Hill et al. 2015), may be repeated or practiced before sexual maturity and may even require repeated practice to develop full copulatory behavior patterns (Ham et al. 2022). Sociosexual behavior is common among young male bottlenose dolphins beginning with neonates and has been reported in both managed care and nature (e.g., Connor et al. 2006; Sakai et al. 2006; Dudzinski and Ribic 2017; all chapter coauthors, personal observations, Table 9.1). The extent to which sexual behavior is innate or learned is not known. Some courtship- and reproductive-specific behaviors likely emerge innately (e.g., genital stimulation for both sexes or erections in males); however, there is a growing body of evidence that observational learning and direct mentoring may improve reproductive success (Dudzinski et al. 2022; Ham et al. 2022; Hill et al. 2022; Table 9.1; see Fig. 9.2). Even if mentors or role models are not crucial, conspecific partners may provide opportunities for sociosexual behavior exchanges during which motor skills are developed.

Fig. 9.2
An underwater photo of 2 whales. One whale swims over the other whale. Sub-adult male Beluga exhibiting an s-posture and erection, displaying social behavior towards a juvenile male Beluga.

A subadult male beluga whale displaying an s-posture and erection toward a juvenile male beluga whale. This image was taken from a bout of sociosexual behavior that lasted several minutes with the two male beluga whales taking turns reciprocating the behavior. Image taken from video footage collected by H. Manitzas Hill

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9.3.2 Social Bonds

Non-conceptive sexual behavior may aid in bond formation and bond maintenance (Connor et al. 1992, 2001, 2006; Dudzinski and Ribic 2017; Lilley et al. 2020) and likely also serves as a form of tactile communication (Gaskin 1982; Dudzinski and Ribic 2017; Tyack 2019). For example, in bottlenose dolphins living in Shark Bay, Australia, same-sex sexual interactions between sexually immature males seem to facilitate, at least in part, bond and alliance formations (Connor et al. 1992, 2001, 2006); these interactions have been documented for bottlenose dolphins in managed care facilities with similar behaviors and functions confirmed (Dudzinski and Ribic 2017; Table 9.1). Indeed, young male bottlenose dolphins likely exchange these sociosexual behaviors (e.g., mounting peers, rubbing body and erections on peers, etc.) when establishing their bonds with other males. Connor et al. (1992) and Dudzinski and Ribic (2017) suggest that sociosexual exchanges in which three to four young males (sexually immature) take turns in active and passive roles that include much body contact, rubbing peers with erect penises, active rubbing of body parts, and whistle and squawk vocals may be critical in establishing bonds and maintaining those relationships into adulthood. These actions serve to signal to close affiliates that the individuals have a tight bond and to let others in a group know that those particular individuals are associated. Similar non-conceptive sexual functions have been suggested for beluga whales and killer whales in managed care facilities and nature (Sánchez-Hernández et al. 2019; Lilley et al. 2020; Sanvito and Galimberti 2022).

9.3.3 Masturbation and Sexual Object Play

Many species of odontocetes in managed care facilities rub their ventrums and more specifically their genitals, on the environment in which they are housed, as well as on conspecifics, non-reciprocating species (e.g., turtles, sharks, fish), and/or items found within their environment (Table 9.1). These behaviors, though not functionally reproductive, likely provide some form of sexual tension relief or physical pleasure (Dudzinski et al. 2012). With increased research on the genitals of both female and male odontocetes (Orbach et al. 2019), it is becoming clear that odontocetes have functional anatomy for feeling sensations (Brennan et al. 2022). However, for males, ejaculation is rarely observed in nonreproductive sexual behavior (Table 9.1). As part of masturbation, odontocetes sometimes engage in playful sexual behavior with objects (Burghardt 2005; Greene et al. 2011; Hill et al. 2016, 2017), using their genitals to move or manipulate objects (Table 9.1). For males, this may mean thrusting toward an environmental enrichment device (e.g., buoy, hose, towel, pipe) with an erect penis. Females may rub their genitals on objects such that the object externally rubs the genital slit or penetrates the slit. In both sexes, it is likely that this rubbing is pleasurable in a sexual (Brennan et al. 2022) and playful domain (Kuczaj and Eskelinen 2014).

9.3.4 Same-Sex Sexual Interactions

One of the most commonly described non-conceptive sexual behavior in odontocetes is same-sex non-conceptive behavior (Ham et al. 2023, this book). This may occur between two females or between two males (Table 9.1), but in either case it is very clearly not reproductively functional. Same-sex sexual interactions are sometimes described as playful and often occur between same-aged individuals. This behavior likely functions in a multitude of facets from practice (Mann 2006; Lilley et al. 2020) to managing social relations (Dudzinski and Ribic 2017; Harvey et al. 2017; Lilley et al. 2020, 2022a, b). As noted in Table 9.1, many same-sex sexual interactions often involve more than two individuals, which can take the form of all behaviors directed toward one recipient or can involve group members being both an initiator and recipient (sometimes simultaneously) of sexual behavior. These triads or larger groups are sometimes referred to as “group social balls” (Miller et al. 2010, 2021; Fig. 9.3). Once thought to be rare among nonhuman animals or only found in highly socially complex species (Furuichi et al. 2014), same-sex interactions are becoming increasingly well-documented across taxa, including cetaceans.

Fig. 9.3
3 photos taken underwater exhibit a group social ball among bottlenose dolphins. Multiple angles capture sociosexual behaviors primarily performed by male dolphins towards one or more recipients within the group.

This panel displays several angles of what is frequently labeled a group social ball. Several, usually male, bottlenose dolphins engage in sociosexual behavior with behaviors directed at one or more recipients within the group. Photo courtesy of Dolphin Communication Project

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9.3.5 Interspecies Sexual Interactions

Interspecies sexual interactions can occur when multiple species share space in nature or managed care facilities. Occurring between same-sex and mixed-sex pairings, conspecific sexual behavior may function to manage social bonds or as a way of establishing social dominance hierarchies. In some cases, these interspecies sexual interactions yield hybrid species in nature (e.g., Baird et al. 1998; Schaeff 2007; Herzing et al. 2013; Skovrind et al. 2019; K. Dudzinski, personal observation – hybrid of dusky and common dolphins confirmed morphologically) and managed care facilities (e.g., Caballero and Baker 2010). Observations of interspecific sexual exchanges have been made when mixed species are housed together; for example, immature male beluga whales have directed sexual behavior toward mature female and male Pacific white-sided dolphins who reciprocated the sexual behavior (Fig. 9.4). That is, the female Pacific white-sided dolphin exhibited a surface body spasm in response to the immature beluga whale male presents (H. Manitzas Hill and M. Lilley, personal observations). This suggests that even when individuals present to nonspecific peers, the response is behaviorally correct for the context.

Fig. 9.4
A photo of the surface of the water exhibits 3 whales engaged in sociosexual behavior.

Two male beluga whale calves and one adult female Pacific white-sided dolphin engage in sociosexual behavior. As the male calves displayed presentations of their ventrums, the adult female Pacific white-sided dolphin oriented at their genital regions, pushed them at the surface, and reciprocated with positioning her ventrum closer to the male beluga whale. Image taken from video footage collected by H. Manitzas Hill

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9.3.6 Lessons from Managed Care and Free-Ranging Populations

Studies on non-conceptive sexual behavior can yield important information on the social structure of animals (e.g., Connor et al. 2001) and how reproductive behaviors develop (e.g., Lilley et al. 2020; Ham et al. 2022) and may even provide clues on the welfare of species living in managed care and nature (Clegg and Delfour 2018; Miller et al. 2021). Given the information described above, chemical and noise pollution could impact gustatory, olfactory, and/or vocal cues for mating and impair reproduction, thus affecting not only the welfare of free-ranging odontocetes (de Vere et al. 2018) but also, potentially, their population numbers, which could be the case for the endangered Cook Inlet beluga whale population or Southern Resident killer whales off Vancouver Island. Non-conceptive sexual behavior comprises a substantial part of many odontocetes’ behavioral repertoire. Access to appropriate social partners may impact welfare in managed care settings and may also impact future reproductive success for free-ranging populations.

9.4 Future Research

Studies of the physiology and behavior of odontocetes in managed care facilities can yield unparalleled insights into their reproductive physiology and both conceptive and non-conceptive sexual behavior. Voluntary husbandry behaviors for biological samples and measurements and the opportunity for frequent behavioral observations over the lifespan of individual animals have the potential to address a number of currently unanswered questions. For example, to what extent are reproductive behaviors socially learned? Do sexually immature individuals need adult “role models” to learn the behavior? Does practicing sexual behavior in a sociosexual context either with peers or adult role models improve reproductive success later in life? In addition, questions can be answered regarding courtship displays and copulation. What are the factors involved in both female and male mate choice? How do different social group compositions affect mating systems? What role does reproductive and nonreproductive sexual behavior play in the welfare of individuals?

One question that should be investigated further is how can a male become attractive to females? This is a question that is rarely asked as most research focuses on how females make themselves more attractive to males, though, of course, both sides of the coin are important, depending on the species. No study to date provides clear evidence of a strong relationship between select behaviors and possible ovulation in females. Such studies may elucidate mechanisms of mate choice in odontocetes and thereby provide additional direction for animal management of species both in their natural habitats and in managed care facilities.

Most research on sexual behavior has centered on bottlenose dolphins, killer whales, and beluga whales. Although there is still much to learn, there are many opportunities to study the larger range of odontocete species currently living in managed care facilities by documenting sexual behavior and physiology when possible (e.g., Webber et al. 2023, this book). With advances in drone technology, behavioral observations and physiological (e.g., hormone analyses) measurements can also be conducted for free-ranging cetaceans (Ramos et al. 2023, this book). Findings from both settings can complement each other (Dudzinski 2010; Hill et al. 2021) and be used to inform best practices for conservation and welfare. As an example, the importance of role models in the development of sexual behavior and the role of mate choice in breeding success could play a crucial role for populations currently facing extinction.