Establishment of vocal communication and discrimination between ewes and their lamb in the first two days after parturition

Puppy whines mediate maternal behavior in domestic dogs

In mammals, offspring vocalizations typically encode information about identity and body condition, allowing parents to limit alloparenting and adjust care. But how do these vocalizations mediate parental behavior in species faced with the problem of rearing not one, but multiple offspring, such as domestic dogs? Comprehensive acoustic analyses of 4,400 whines recorded from 220 Beagle puppies in 40 litters revealed litter and individual (within litter) differences in call acoustic structure. By then playing resynthesized whines to mothers, we showed that they provided more care to their litters, and were more likely to carry the emitting loudspeaker to the nest, in response to whine variants derived from their own puppies than from strangers. Importantly, care provisioning was attenuated by experimentally moving the fundamental frequency (fo, perceived as pitch) of their own puppies' whines outside their litter-specific range. Within most litters, we found a negative relationship between puppies' whine fo and body weight. Consistent with this, playbacks showed that maternal care was stronger in response to high-pitched whine variants simulating relatively small offspring within their own litter's range compared to lower-pitched variants simulating larger offspring. We thus show that maternal care in a litter-rearing species relies on a dual assessment of offspring identity and condition, largely based on level-specific inter- and intra-litter variation in offspring call fo. This dual encoding system highlights how, even in a long-domesticated species, vocalizations reflect selective pressures to meet species-specific needs. Comparative work should now investigate whether similar communication systems have convergently evolved in other litter-rearing species.

Selection signature analysis reveals RDH5 performed key function in vision during sheep domestication process

Abstract. As one of the most successful domesticated animals in the Neolithic age, sheep gradually migrated all over the world with human activities. During the domestication process, remarkable changes have taken place in morphology, physiology, and behavior, resulting in different breeds with different characters via artificial and natural selection. However, the genetic background responsible for these phenotypic variations remains largely unclear. Here, we used whole genome resequencing technology to compare and analyze the genome differences between Asiatic mouflon wild sheep (Ovis orientalis) and Hu sheep (Ovis aries). A total of 755 genes were positively selected in the process of domestication and selection, and the genes related to sensory perception had directional evolution in the autosomal region, such as OPRL1, LEF1, TAS1R3, ATF6, VSX2, MYO1A, RDH5, and some novel genes. A missense mutation of c.T722C/p.M241T in exon 4 of RDH5 existing in sheep were found, and the T allele was completely fixed in Hu sheep. In addition, the mutation with the C allele reduced the retinol dehydrogenase activity encoding by RDH5, which can impair retinoic acid metabolism and further influenced the visual cycle. Overall, our results showed significant enrichment for positively selected genes involved in sensory perception development during sheep domestication; RDH5 and its variants may be related to the retinal degeneration in sheep. We infer that the wild sheep ancestors with weaker visual sensitivity were weeded out by humans, and the mutation was selective, swept by the dual pressures of natural and artificial selection.

Ovine vocal individuality expression by ewes and lambs at a late (40 days) post-partum time point

Recognizing the identity of conspecifics is important for survival and social interactions. In sheep, vocal individuality enhances postnatal recognition and strengthens the mother-offspring bond. Although previous studies report vocal individuality in an early postnatal period (3-15 days of life), scarce information exists on whether individuality occurs at a later postnatal time point. The aim of the study was to identify whether individuality in acoustic cues is expressed in ewes' and their lambs' bleats at 40 days post-partum. Dairy ewes (N = 21) and their suckling offspring (n = 30) were isolated separately without hearing or seeing each other, and vocalizations were recorded. Different approaches for estimating individuality on 18 determined acoustic parameters were implemented. All parameters showed individuality, but higher individuality appeared in those related with source and spectral characteristics. A discriminant function analysis showed similar levels of individuality between ewes and lambs, but lower than that reported in an earlier postnatal time, suggesting that ewes and lambs do not need strong individualized cues at the examined time point. In both cases, jitter was the only common parameter, suggesting its importance. Distinctive cues were noted between siblings. Ewes displayed vocal individuality at their dry season (a later time point than suckling period), which was based on amplitude-related acoustic parameters.

Early onset of postnatal individual vocal recognition in a highly colonial mammal species

Mother-young vocal recognition is widespread in mammals. The features of vocal recognition are known to be shaped by the ecological constraints faced by each species. In some species, a rapid establishment of mother-young vocal recognition is crucial for offspring's survival. However, knowledge of the precise features of this recognition system, especially the timing of the onset in the first hours after birth, is often lacking. Here we show that Cape fur seal females can recognize their pup's voice 2-4 h after parturition and that pups develop this aptitude 4-6 h after birth. This study is the first to investigate this mechanism in a wild and free-ranging mammal from only 2 h after birth. We report the fastest establishment of mother-young vocal recognition for any mammalian species, including humans, described to date. Such early vocal identification in pups suggests an in utero vocal imprinting. These findings highlight the synergistic role of environmental constraints and biological traits in optimizing the timing of individual vocal recognition onset in vertebrates.

What Do We Know and Need to Know About Weaning in Sheep? An Overview of Weaning Practises, Stress and Welfare

Artificial weaning is the separation of the mother and her lamb, involving the forced ending of suckling and milk supply by the ewes to their lambs. Artificial weaning time varies depending on the purpose of each sheep farm and the characteristics of the lambs, including age and weight of the lambs, and their ability to eat solid food. Artificial weaning is performed from 24 h postpartum until around the age of natural weaning (up to 12 mo of age). Artificial weaning results in the breaking of the ewe-lamb bond, the end of suckling and the complete replacement of milk by solid food, frequently added to changes in both the physical and social environment. It triggers behavioural, physiological and immunological changes that generate negative consequences on the health of both ewes and lambs, as well as on the growth of the lambs, rising animal welfare concerns. As artificial weaning is considered one of the most stressful situations in the life of farm mammals, it is important to consider the factors involved in those responses to develop adequate strategies and improve sheep welfare at weaning. The most frequently used method is the abrupt separation of the ewes and their lambs. However, the adaptation of the animals after weaning can be improved by alternative weaning methods (e.g., progressive, two-steps weaning and mixed regimes), hormonal treatments (e.g., administration of progesterone), and pre- and postweaning management (e.g., the use of creeping feeding, and the presence of conspecifics or humans after weaning). This review presents and summarises information on the stress response and animal welfare issues at artificial weaning in sheep and some management practises that can be used to reduce these problems. The major points included are the ewe-lamb bond at birth and during the lactation period; the stress response at weaning; the factors involved in the stress response at weaning; the different types and weaning methods and their repercussions on animal welfare; and some strategies that can be used to improve sheep welfare at weaning. Lastly, we propose directions for research needed to develop practical alternatives to minimise sheep's stress response at weaning.

The Onset of Maternal Behavior in Sheep and Goats: Endocrine, Sensory, Neural, and Experiential Mechanisms

In sheep and goats, the onset of maternal behavior at parturition is characterized by a first phase called maternal responsiveness during which the mother is attracted to any newborn. In a second phase, called maternal selectivity, the mother establishes a selective bond with her young so that she only accepts it at suckling. After a description of the behavioral expression of both phases, this chapter reviews the physiological, sensory, and neural mechanisms involved. These two behavioral processes are synchronized with parturition by the vaginocervical stimulation induced by the expulsion of the newborn. Olfactory cues provided by the neonate are involved in maternal responsiveness and selectivity. Oxytocin supported by estrogens is the key factor for maternal responsiveness. The neural network involved in maternal responsiveness is mainly hypothalamic and is different from the circuitry involved in selectivity, which mainly concerns olfactory processing regions. Visual and auditory cues are necessary for offspring recognition at a distance. This multisensory recognition suggests that mothers form a mental image of their young. Maternal experience renders mothers more responsive to maternally relevant physiology and to young-related sensory inputs.

A Non-Invasive Millimetre-Wave Radar Sensor for Automated Behavioural Tracking in Precision Farming-Application to Sheep Husbandry

The automated quantification of the behaviour of freely moving animals is increasingly needed in applied ethology. State-of-the-art approaches often require tags to identify animals, high computational power for data collection and processing, and are sensitive to environmental conditions, which limits their large-scale utilization, for instance in genetic selection programs of animal breeding. Here we introduce a new automated tracking system based on millimetre-wave radars for real time robust and high precision monitoring of untagged animals. In contrast to conventional video tracking systems, radar tracking requires low processing power, is independent on light variations and has more accurate estimations of animal positions due to a lower misdetection rate. To validate our approach, we monitored the movements of 58 sheep in a standard indoor behavioural test used for assessing social motivation. We derived new estimators from the radar data that can be used to improve the behavioural phenotyping of the sheep. We then showed how radars can be used for movement tracking at larger spatial scales, in the field, by adjusting operating frequency and radiated electromagnetic power. Millimetre-wave radars thus hold considerable promises precision farming through high-throughput recording of the behaviour of untagged animals in different types of environments.

Maternal responses to pup calls in a high-cost lactation species

Bonding between mothers and their young is fundamental to mammalian reproductive behaviour and individual fitness. In social systems where the risk of confusing filial and non-filial offspring is high, mothers should demonstrate early, strong and consistent responses to their kin throughout the period of offspring dependence, irrespective of maternal traits. We tested this hypothesis through playback experiments in the northern elephant seal Mirounga angustirostris, a phocid species that breeds in high-density colonies. We found that mothers recognized their offspring throughout lactation and as early as 1-2 days after parturition. Measures of experience (age) and temperament (aggressivity) did not predict their response strength to filial playback treatments, nor did pup age or sex. Some mothers showed great consistency in behavioural responses throughout the lactation period, while others were less predictable. The strength of a female's response did not influence her pup's weaning weight; however, more consistent females weaned pups of higher mass. This is a rare demonstration of individual recognition among phocid mothers and their offspring, and suggests that consistency in maternal responsiveness may be an important social factor influencing the pup's growth and survival.

Neurophysiological Mechanisms of Mother-Young Bonding in Buffalo and Other Farm Animals

Simple Summary

The present paper reviews the importance of bonding for the survival and well-being in the cow–calf relationship. The review focuses on buffaloes and information from other species is used for comparison or to find more general patterns in the absence of specific sources. Differences between several farm species are also described, focusing on the role played by the sensory stimuli during the sensitive period after birth. How bonding can be classified according to the predominant senses used by different species, the importance of learning (i.e., imprinting) in the development of mother–young relationship, and the neurobiological mechanisms involved are also delineated. Finally, some examples of the main factors that can affect the mother–young relationship in the field are given. By understanding the imprinting at brain level, as well as the relationship with behavior, we gain a deeper insight into the critical role that experience, and environmental factors play in shaping the development of the mother–offspring bond.

Abstract

In buffaloes and other mammalian farm species, the mother provides food and protection to the young, but she is also the main source of behavioral and social learning for the offspring. It is important that mother and young establish a bond based on a learning mechanism defined as “imprinting” early after parturition during the sensitive period, on which the welfare and survival of the offspring will depend. This review aims to summarize and discuss current knowledge regarding the imprinting process, the neurobiological pathways that are triggered during this sensitive period, and the development of the cow–calf bond. Touch, hearing, vision, and smell seem to be the predominant senses involved during imprinting in buffaloes and other mammalian farm species. In buffalo, bonding is very particular due to the expression of specific behaviors, such as allo-suckling and communal rearing. In general, imprinting and the subsequent bond may be affected by the lack of experience of the mothers or dystocic parturitions, which occur most frequently with male calves and in primiparous dams. The main problems in the development of this process include lack of seeking a protected and isolated place to give birth; moving from the birth-site after parturition; insufficient postpartum care; aversion or aggressiveness towards the newborn, or abandonment of the newborn. The process can develop differently according to the species. However, the correct development of the cow–calf relationship represents, regardless of the species, a key factor for their fitness.

An acute dose of intranasal oxytocin rapidly increases maternal communication and maintains maternal care in primiparous postpartum California mice

Maternal-offspring communication and care are essential for offspring survival. Oxytocin (OXT) is known for its role in initiation of maternal care, but whether OXT can rapidly influence maternal behavior or ultrasonic vocalizations (USVs; above 50 kHz) has not been examined. To test for rapid effects of OXT, California mouse mothers were administered an acute intranasal (IN) dose of OXT (0.8 IU/kg) or saline followed by a separation test with three phases: habituation with pups in a new testing chamber, separation via a wire mesh, and finally reunion with pups. We measured maternal care, maternal USVs, and pup USVs. In mothers, we primarily observed simple sweep USVs, a short downward sweeping call around 50 kHz, and in pups we only observed pup whines, a long call with multiple harmonics ranging from 20 kHz to 50 kHz. We found that IN OXT rapidly and selectively enhanced the normal increase in maternal simple sweep USVs when mothers had physical access to pups (habituation and reunion), but not when mothers were physically separated from pups. Frequency of mothers’ and pups’ USVs were correlated upon reunion, but IN OXT did not influence this correlation. Finally, mothers given IN OXT showed more efficient pup retrieval/carrying and greater total maternal care upon reunion. Behavioral changes were specific to maternal behaviors (e.g. retrievals) as mothers given IN OXT did not differ from controls in stress-related behaviors (e.g. freezing). Overall, these findings highlight the rapid effects and context-dependent effect a single treatment with IN OXT has on both maternal USV production and offspring care.

Dam parity and calf sex affect maternal and neonatal behaviors during the first week postpartum in stabled Maghrebi dairy camels

Currently, a trend toward the commercialization of dromedary milk associated with recent intensive rearing systems has starting worldwide which impose constraints on animals affecting their behavioral repertoires and welfare status. The aim of this study was to investigate the effects of dam parity and calf sex on parturition, neonatal, and maternal behaviors in stabled Maghrebi dairy camels (Camelus dromedarius). Thirty-six (primiparas N = 10; multiparas N = 26) periparturient females were kept under video surveillance using a digital IR camera and 24-h sessions were chosen to assess calving, maternal, and neonatal behaviors in calving pens. Duration of restlessness, process of giving birth, and expulsion of fetal membranes were assessed. After first suckling, dams and their calves were moved into an individual enclosure to assess maternal behavior at 12 h, 24 h, 48 h, 72 h, and 7d postpartum. Behavior was assessed using a camcorder for 30 min after 1 h of young separation in an adjacent enclosure. Results showed an effect of parity on the duration of the birth process which was longer for primiparous than multiparous camels (P = 0.034). During this stage, primiparous females tended to raise their tails more often (P = 0.054) and spent more time standing (P = 0.001) than multiparous camels. Neonatal behavior was affected by calf sex. Female newborns took less time to raise their heads (P = 0.041) and to stand up (P = 0.048) for the first time and were the earliest to suckle their dams (P = 0.032). Multiparous dams stood up sooner (P = 0.019) after calving and suckled their calves earlier (P = 0.043) than primiparous dams. They emitted more bleats and exhibited more sniffing during the first week postpartum than primiparas. During the first postpartum week, both primiparas and multiparas showed a decrease in the total number of bleats (P < 0.001), low-pitch bleats (P < 0.001), and high-pitch bleats (P < 0.001), in sniffing frequency (P < 0.001) and sniffing duration (P < 0.001). This is the first study to describe in detail the calving, maternal, and neonatal behaviors of dromedary camels and to show the influence of parity and calf sex. Maternal care toward the newborn calf exhibited by a high level of bleating and sniffing activities in the first 2 days suggest that they play an important role in the establishment of mother-young relationship.

Neonatal Suckling, Oxytocin, and Early Infant Attachment to the Mother

The neuropeptide oxytocin (OT) promotes maternal care and social affiliation in adults but its importance in infant attachment still remains unknown. True animal models of infant attachment are extremely rare, and the sheep (in complement to non-human primates) is one of the few that provides the opportunity to investigate its neuroendocrinological basis. In the lamb, access to the udder has strong rewarding properties for the establishment of a preferential relationship with the mother. Therefore, the present study explored the possible involvement of OT through its release during close social contacts with the mother. The first experiment revealed that lambs having free access to the udder from birth onward developed, by 12 h of age, a clear preference for their mothers over another maternal ewe. Delaying access to the udder for six, four or even only 2 h starting at birth, by covering the ewe's udder, resulted in the lack of such a preference without affecting general activity. These effects persisted in most cases at 24 h but by 72 h of age a bond with the mother was clearly expressed. Experiment two showed that social interactions with the mother were followed by a release of OT in the plasma when lambs had the possibility to suckle. Non-nutritive interactions were without effects. Preliminary data on two subjects suggested that OT might also increase in the cerebrospinal fluid after suckling. Finally, in the third experiment, oral administration of a non-peptide OT receptor antagonist (L-368-899, Merck) over the first 4 h after birth led to decreased exploration of the mother's body compared to lambs receiving saline, and impaired the expression of a preference for the mother at 24 h. The effects were no longer observed at 48 h. Our findings demonstrate that both delayed access to the mother's udder and OT receptor antagonist alter the onset of mother preference in newborn lambs. This suggests that central OT facilitates the development of filial attachment through its release during suckling.

Does lambing season affect mother-young relationships and lamb vigor in D'man sheep reared in oases?

Although sheep are known to be seasonal breeders and give birth in winter, not all of them follow this trend. A few breeds can be mated and give birth all year round, meaning that mothers and neonates will have to face contrasting climatic conditions. The aim of this study was to test whether lambing season affects maternal and neonatal behaviors in D'man sheep. During four different lambing seasons (winter, autumn, summer and spring), periparturient ewes (n = 111) and their lambs (n = 213) were kept under 24-h-video surveillance in order to record postpartum behaviors. Mother-young preference was tested around 48 h after parturition. Lamb vigor was studied by the determination of birth weight, early postnatal behavior and rectal temperature at birth and 48 h later. Litter expulsion time was not affected by lambing season, but birth weight was biased against summer and winter born lambs. Ewes provided a higher intensity of care to their offspring in winter: latency for grooming was shorter and time spent grooming was longer compared to lambing in spring and summer (P = 0.01 in all cases). On the other hand, lambs were the most active in spring as they were faster to extend their hind legs (P = 0.01), stand up (P = 0.04) and reach the udder (P = 0.04). Rectal temperature at 48 h was affected by season of birth (P < 0.001) with higher values observed in summer. Glycemia variation between birth and 48 h was the lowest in spring born lambs and plasma levels increased less in spring born lambs than in winter (P < 0.0001), autumn (P < 0.0001) and summer born lambs (P < 0.0001). In the choice test, mothers clearly preferred their own young and no season effect was detected except that in the first minute of the test they spent less time near their own young in winter than in the other seasons (P = 0.04). Lambs also chose their mother successfully without any major effect of the season however, but winter born lambs were the least vocal (P = 0.01). Overall, this study show that maternal care, lamb behavior and vigor vary lightly according to seasons, albeit not in a consistent manner. In conclusion, a season is no more detrimental than another for the onset of mother-young relationships.

Genetic parameters estimates for ewes' behavioural reactivity towards their litter after lambing

In livestock, improving maternal reactivity towards the litter is an important issue in breeding strategies to promote production and animal welfare. As of yet, no studies have investigated the within-breed genetic variation of maternal reactivity in sheep. The objective of this study was to estimate the genetic parameters of maternal reactivity traits. A total of 1,095 primiparous and 1,441 multiparous Romane ewes were phenotyped 24 hr postlambing using a behavioural test (arena test, AT) over a 10-year experimental period. The test consisted of three successive phases evaluating the ewe's attraction to her litter, reactivity to separation from her litter, and reactivity to a conflict between attraction to her litter and avoidance of a motionless human. The ewes were reared exclusively on rangelands (South of France) and lambed outdoors in the spring. High-pitched bleating and low-pitched bleating in the AT were mostly highly heritable (0.39-0.46). Heritabilities were moderate for proximity to the litter in the presence of a human (0.27) and low for locomotion and vigilance in the AT (0.09-0.15). The measurements of a given behaviour in the three phases of the AT were highly genetically correlated. Few genetic correlations were found between the different behavioural traits in the AT, the highest correlations being between high-pitched bleating and low-pitched bleating (-0.43 to -0.77). In conclusion, our findings demonstrate moderate-to-high heritability for maternal reactivity traits. These traits could be included in genetic selection schemes to enhance maternal attachment provided there is no unfavourable link with other production traits.

Baby cry recognition is independent of motherhood but improved by experience and exposure

Neurobiological changes affecting new mothers are known to support the development of the mother-infant relationship (the 'maternal brain'). However, which aspects of parenting are actually mother-specific and which rely on general cognitive abilities remains debated. For example, refuting earlier findings, a recent study demonstrated that fathers identify their own baby from their cries just as well as mothers. Here we show that this performance is independent not only of sex, but also of parenthood status. We found that mothers' ability to recognize their newborn from their cries increased rapidly within few days postpartum, with highly multiparous mothers performing better. However, both male and female non-parents could similarly recognize an assigned baby, even after a very short exposure. As in mothers, both the initial amount of experimental exposure to the baby's cries (learning opportunity) and prior experience of caring for infants (auditory expertise) affected participants' performance. We thus suggest that, rather than being female-specific or motherhood-dependent, the ability to recognize a baby from their cries derives from general auditory and learning skills. By being available to non-parents of both sexes, it may contribute to the caregiving flexibility required for efficient cooperative breeding in humans.

Mother-young recognition in goitered gazelle during hiding period

The mother-young recognition process is crucial for the growth and survival of progeny. In "follower" ungulate species, vocal and visual cues have been found to play a leading role in the mother-young identification process from the first days postpartum, with olfactory cues also important in establishing the initial selective mother-young bond immediately after birth. In "hider" species, however, much less has been documented of mother-young recognition behaviors, especially in their natural habitat. In this paper, we investigated this process in goitered gazelle (Gazella subgutturosa), a typical hider species, in its native environment in Kazakhstan. Over the course of our study period, we investigated the behaviors of 257 females with twins and 158 females with singles through visual observations. We found that within the first month after birth, when females spend only a short time with their young, mothers recognized their fawns using mostly olfactory cues, while vision was used to locate their hiding offspring. Fawns vocalized very rarely, producing only distress calls that did not seem intended for individual identification. Licking of young by their mothers was observed frequently, not only during the first week after birth, when this action was very important for fawn stimulation for a number of physiological functions, but for several weeks after (until one month of age), when licking lost its physiological importance and likely became more of a recognition procedure. Fawns did not recognize their mothers at all, either through vision or vocalizations, since during their first weeks after birth, they responded to any gazelle that approached their hiding area. By a month after birth, when mothers and fawns began to stay together for longer periods of time, their recognition process became more enhanced, and in addition to olfactory cues, the mother and her young began to use more and more visual cues for longer distance identification, as well as vocalizations for shorter distances. Similar dynamics are likely typical for most hiding species, although information for wild ungulates is still very limited, especially for those with strong hider behaviors.

Distress vocalization delay in the neonate lamb as a neurobehavioral assessment tool

Acoustic features of infant distress vocalizations including latency and rate of emission are used as indices of neurological deficit and integrity in human and rodent neonates. This paper investigates the relationship between temporal characteristics of distress calls, elicited by an isolation stimulus, and indicators of neurobehavioral development over 12 hr postpartum in the neonate lamb. Delayed vocalization initiation was found to be associated with poor locomotor and orientation behavior reflecting the capacity of the lamb to reunite with and follow its dam, and a lowered rate of signal emission following commencement of vocalization. Animals demonstrating delayed vocalization initiation also appeared more likely to be of a birth weight predisposed to fetal distress, and to urinate when exposed to a novel environment. Based on these preliminary studies, we propose that compromised emission of vocal signals is indicative of neurobehavioral deficit in the neonate lamb.

Remarkable vocal identity in wild-living mother and neonate saiga antelopes: a specialization for breeding in huge aggregations?

Saiga antelopes Saiga tatarica tatarica give birth in large aggregations, and offspring follow the herd soon after birth. Herding is advantageous as anti-predator strategy; however, communication between mothers and neonates is strongly complicated in large aggregations. Individual series of nasal and oral contact calls of mother and neonate saiga antelopes were selected from recordings made with automated recording systems placed near the hiding neonates on the saiga breeding grounds in Northern Kazakhstan during synchronized parturitions of 30,000 calving females. We used for comparison of the acoustic structure of nasal and oral contact calls 168 nasal calls of 18 mothers, 192 oral calls of 21 mothers, 78 nasal calls of 16 neonates, and 197 oral calls of 22 neonates. In the oral calls of either mothers or neonates, formant frequencies were higher and the duration was longer than in the nasal calls, whereas fundamental frequencies did not differ between oral and nasal calls. Discriminant function analysis (DFA) based on six acoustic variables, accurately classified individual identity for 99.4% of oral calls of 18 mothers, for 89.3% of nasal calls of 18 mothers, and for 94.4% of oral calls of 18 neonates. The average value of correct classification to individual was higher in mother oral than in mother nasal calls and in mother oral calls than in neonate oral calls; no significant difference was observed between mother nasal and neonate oral calls. Variables mainly responsible for vocal identity were the fundamental frequency and the second and third formants in either mothers or neonates, and in either nasal or oral calls. The high vocal identity of mothers and neonates suggests a powerful potential for the mutual mother-offspring recognition in dense aggregations of saiga antelopes as an important component of their survival strategy.

Mother-offspring recognition in the domestic cat: Kittens recognize their own mother's call

Acoustic communication can play an important part in mother-young recognition in many mammals. This, however, has still only been investigated in a small range mainly of herd- or colony-living species. Here we report on the behavioral response of kittens of the domestic cat, a typically solitary carnivore, to playbacks of "greeting chirps" and "meows" from their own versus alien mothers. We found significantly stronger responses to the chirps from kittens' own mother than to her meows or to the chirps or meows of alien mothers. Acoustic analysis revealed greater variation between vocalizations from different mothers than for vocalizations from the same mother. We conclude that chirps emitted by mother cats at the nest represent a specific form of vocal communication with their young, and that kittens learn and respond positively to these and distinguish them from chirps of other mothers and from other cat vocalizations while still in the nest. © 2016 Wiley Periodicals, Inc. Dev Psychobiol 58: 568-577, 2016.

Common and divergent psychobiological mechanisms underlying maternal behaviors in non-human and human mammals

Maternal interactions with young occupy most of the reproductive period for female mammals and are absolutely essential for offspring survival and development. The hormonal, sensory, reward-related, emotional, cognitive and neurobiological regulators of maternal caregiving behaviors have been well studied in numerous subprimate mammalian species, and some of the importance of this body of work is thought to be its relevance for understanding similar controls in humans. We here review many of the important biopsychological influences on maternal behaviors in the two best studied non-human animals, laboratory rats and sheep, and directly examine how the conceptual framework established by some of the major discoveries in these animal "models" do or do not hold for our understanding of human mothering. We also explore some of the limits for extrapolating from non-human animals to humans. We conclude that there are many similarities between non-human and human mothers in the biological and psychological factors influencing their early maternal behavior and that many of the differences are due to species-characteristic features related to the role of hormones, the relative importance of each sensory system, flexibility in what behaviors are exhibited, the presence or absence of language, and the complexity of cortical function influencing caregiving behaviors.

Survival implications of the development of behavioural responsiveness and awareness in different groups of mammalian young

This paper focuses on the development of behaviours that are critical for the survival of newborn and juvenile mammals of veterinary and wider biological interest. It provides an updated, integrated and comparative analysis of how postnatal maturation of sensory, motor and perceptual capacities support and constrain behavioural interactions between mammalian young and the mother, any littermates and the environment. Young that are neurologically exceptionally immature, moderately immature and mature at birth are compared, and include, for example, marsupial joeys, rodent pups and ruminant offspring. Mothers in these three groups exhibit distinctive patterns of birthing and postnatal care behaviours. To secure survival of the young, maternal care must compensate for behavioural inadequacies imposed by the limited sensory capacities the young possess at each stage. These sensory capacities develop in a predictable sequence in most mammals such that before birth the sequence progresses to an extent that parallels the degree of neurological maturity reached at birth. The extent of neurological maturity is likewise reflected in how long it takes after birth for the necessary brain circuit connectivity to develop sufficiently to support cortically based cognitive modulation of behaviour. This takes several months, days-to-weeks or minutes-to-hours in young that are, respectively, neurologically exceptionally immature, moderately immature, or mature at birth. Once achieved, cognitive awareness confers a high degree of behavioural flexibility that allows the young to respond more effectively to the unpredictability of their postnatal environments. It is shown that the onset of this cognitively based flexibility in the young of each group coincides with their first exposure to a variable environment that requires such behavioural flexibility.

The effects of unrelated offspring whistle calls on capybaras (Hydrochoerus hydrochaeris)

Parent-offspring vocal communication, such as the isolation call, is one of the essential adaptations in mammals that adjust parental responsiveness. Thus, our aim was to test the hypothesis that the function of the capybara infants' whistle is to attract conspecifics. We designed a playback experiment to investigate the reaction of 20 adult capybaras (seven males and 13 females) to pups' whistle calls - recorded from unrelated offspring - or to bird song, as control. The adult capybaras promptly responded to playback of unrelated pup whistles, while ignoring the bird vocalisation. The adult capybaras took, on average, 2.6 ± 2.5 seconds (s) to show a response to the whistles, with no differences between males and females. However, females look longer (17.0 ± 12.9 s) than males (3.0 ± 7.2 s) toward the sound source when playing the pups' whistle playback. The females also tended to approach the playback source, while males showed just a momentary interruption of ongoing behaviour (feeding). Our results suggest that capybara pups' whistles function as the isolation call in this species, but gender influences the intensity of the response.

The power of oral and nasal calls to discriminate individual mothers and offspring in red deer, Cervus elaphus

BACKGROUND

In most species, acoustical cues are crucial for mother-offspring recognition. Studies of a few species of ungulates showed that potential for individual recognition may differ between nasal and oral contact calls.

RESULTS

Vocalizations of 28 hinds and 31 calves of farmed Iberian red deer (Cervus elaphus hispanicus) were examined with discriminant function analyses (DFA) to determine whether acoustic structure of their oral and nasal contact calls encodes information about the caller's identity. Contact calls were elicited by brief separation of individually identified animals by a distance over 10 m or by a bar fence. Both oral and nasal calls of both hinds and calves showed high potential to discriminate individuals. In hinds, individuality was significantly higher in the oral than in the nasal calls, whereas in calves, individuality was equally well expressed in both oral and nasal calls. For calves, the maximum fundamental frequency was higher and the duration was longer in oral calls than in nasal calls. For hinds, the maximum fundamental frequency and the duration were indistinguishable between oral and nasal calls. Compared to the pooled sample of oral and nasal calls, separate oral or nasal call samples provided better classifying accuracy to individual in either hinds or calves. Nevertheless, in both hinds and calves, even in the pooled sample of oral and nasal calls, the degree of individual identity was 2-3 times greater than expected by chance. For hinds that provided calls in both years, cross-validation of calls collected in 2012 with discriminant functions created with calls from 2011 showed a strong decrease of classifying accuracy to individual.

CONCLUSIONS

These results suggest different potentials of nasal and oral calls to allow the discrimination of individuals among hinds, but not among red deer calves. The high potential of individual recognition even with the pooled sample of oral and nasal calls allows mother and young to remember only one set of acoustic variables for mutual vocal recognition. Poor between-year stability of individual characteristics of hind oral and nasal calls would require updating keys to individual recognition each calving season.

Mother goats do not forget their kids' calls

Parent-offspring recognition is crucial for offspring survival. At long distances, this recognition is mainly based on vocalizations. Because of maturation-related changes to the structure of vocalizations, parents have to learn successive call versions produced by their offspring throughout ontogeny in order to maintain recognition. However, because of the difficulties involved in following the same individuals over years, it is not clear how long this vocal memory persists. Here, we investigated long-term vocal recognition in goats. We tested responses of mothers to their kids' calls 7-13 months after weaning. We then compared mothers' responses to calls of their previous kids with their responses to the same calls at five weeks postpartum. Subjects tended to respond more to their own kids at five weeks postpartum than 11-17 months later, but displayed stronger responses to their previous kids than to familiar kids from other females. Acoustic analyses showed that it is unlikely that mothers were responding to their previous kids simply because they confounded them with the new kids they were currently nursing. Therefore, our results provide evidence for strong, long-term vocal memory capacity in goats. The persistence of offspring vocal recognition beyond weaning could have important roles in kin social relationships and inbreeding avoidance.

Maternal behaviour and peripartum levels of oestradiol and progesterone show little difference in Merino ewes selected for calm or nervous temperament under indoor housing conditions

Temperament influences the expression of maternal behaviour in sheep under experimental field conditions. We investigated whether maternal behaviour between ewes selected for a calm or nervous temperament is independent from environmental conditions. In addition, the level of maternal behaviour expressed by mothers is correlated with the concentration of hormones during the peripartum period. Therefore, we investigated whether the selection for temperament had resulted in hormonal differences between the two lines with regard to the hormones that could be involved in the onset of maternal behaviour. Oestradiol, progesterone and cortisol concentrations from 4 days before parturition to 24 h after parturition were determined from blood samples collected from 10 calm and 12 nervous ewes. Behavioural interactions between ewe and lamb were also recorded for 2 h starting at parturition. Mothers of both temperament lines showed adequate maternal behaviour under the controlled conditions of the study. Therefore, the results of the study do not suggest that selection for a calm or nervous temperament has profoundly affected the intrinsic ability of mothers to display adequate maternal behaviour. Hormonal differences between the two temperament lines were generally small and their possible influence on the display of maternal behaviour in the two temperament lines would have to be demonstrated.

Developmental changes of nasal and oral calls in the goitred gazelle Gazella subgutturosa, a nonhuman mammal with a sexually dimorphic and descended larynx

In goitred gazelles (Gazella subgutturosa), sexual dimorphism of larynx size and position is reminiscent of the case in humans, suggesting shared features of vocal ontogenesis in both species. This study investigates the ontogeny of nasal and oral calls in 23 (10 male and 13 female) individually identified goitred gazelles from shortly after birth up to adolescence. The fundamental frequency (f0) and formants were measured as the acoustic correlates of the developing sexual dimorphism. Settings for LPC analysis of formants were based on anatomical dissections of 5 specimens. Along ontogenesis, compared to females, male f0 was consistently lower both in oral and nasal calls and male formants were lower in oral calls, whereas the first two formants of nasal calls did not differ between sexes. In goitred gazelles, significant sex differences in f0 and formants appeared as early as the second week of life, while in humans they emerge only before puberty. This result suggests different pathways of vocal ontogenesis in the goitred gazelles and in humans.

Mother-young relationships in sheep: a model for a multidisciplinary approach of the study of attachment in mammals

The onset of maternal responsiveness and the development of mother-young attachment in sheep are under the combined influence of hormonal and sensory stimulations. In the mother, the prepartum rise in oestrogen and vaginocervical stimulation caused by expulsion of the foetus act on the main olfactory system and on hypothalamic regions. This induces maternal care through the central release of oxytocin, modulated by opiates and corticotrophin-releasing hormone. In parallel, activation of the main olfactory network enables the learning of individual lamb odour and maternal attachment. In the neonate, the first suckling episodes and the concomitant activation of the cholecystokinin, opioids and oxytocin systems facilitate the development of a preference for the mother. Gastrointestinal signals activate the brain stem, the hypothalamus and the amygdala. Within 72 h of parturition, the mother-young attachment shifts from proximal to distal recognition based on visual and auditory cues after which vocal cues become more salient. Although olfaction remains a key element in the display of selective maternal nursing, maternal attachment relies on a multisensory mental image of the lamb. These findings support the view that sheep are amongst the most appropriate animal models for the study of maternal and filial attachment in mammals.

Development of social familiarity in ewes

We assessed the development of individual discrimination resulting from direct contact/familiarization in ewes. Unfamiliar ewes were introduced during 6, 24 or 72 h in groups of already familiarized ewes. At the end of this contact period, the development of social recognition with the animal that has been introduced was assessed using two different types of tests: a Y-maze preference test and a delayed paired close encounters test where tested ewes are successively and randomly interacting with the familiar animal and an unfamiliar conspecific. The results of both tests showed that ewes developed a recognition of the familiar animal in comparison to a completely unfamiliar female. However, this preference was evidenced after 24 h of contact when using the paired close encounters test whereas it appears only after 72 h when using the Y-maze test, suggesting that the paired close encounters test is a more sensitive methodology to assess the development of social familiarization. The importance of estrogens, in the formation of social familiarization was also evaluated. To this end, social recognition in the paired close encounters test was compared between ovariectomized animals receiving estrogen implants or not. Despite significant high levels of estradiol in estrogen implanted females, no major differences in recognition appeared between groups, suggesting that in our conditions estrogens do not have major influence on social familiarization.

Mutual mother-offspring vocal recognition in an ungulate hider species (Capra hircus)

Parent-offspring recognition can be essential for offspring survival and important to avoid misdirected parental care when progeny mingle in large social groups. In ungulates, offspring antipredator strategies (hiding vs. following) result in differences in mother-offspring interactions, and thus different selection pressures acting on the recognition process during the first weeks of life. Hider offspring are isolated and relatively stationary and silent to avoid detection by predators, whereas follower offspring are mobile and rapidly mix in large social groups. For these reasons, hiders have been suggested to show low offspring call individuality leading to unidirectional recognition of mothers by offspring and followers high offspring call individuality and mutual recognition. We hypothesised that similar differences would exist in hider species between the hiding phase (i.e. unidirectional recognition) and the phase when offspring join social groups (i.e. mutual recognition). We tested these predictions with goats (Capra hircus), a hider species characterised by strong mother-offspring attachment. We compared the individuality of kid and mother calls, and the vocal recognition ability, during the early phase of life when kids are usually hidden and later when kids have typically joined social groups. Contrary to our predictions, we found that both kids and mothers had individualised contact calls and that mutual recognition existed even during the hiding phase. The large differences in the duration of the hiding phase and in the rate of mother-offspring interactions (possibly partially driven by domestication in some species) probably cause variations among hider species in the mother-offspring recognition process.

Challenge by a novel object does not impair the capacity of ewes and lambs selected for a nervous temperament to display early preference for each other

Novelty, a powerful fear-inducing and stressful stimulus, could be detrimental on the capacity of ewes and lambs to recognise each other. The effect of a novel object on the ability of ewes and lambs, selected for their calm or nervous temperament, to show a preference for each other was tested in a two-choice discrimination test. Both calm and nervous temperament mothers showed a preference towards their own offspring rather than the alien lambs. Nervous temperament ewes also looked at their own lamb more than the alien. In contrast, nervous lambs showed a greater preference and took less time to reach their own mother than calm lambs. Nervous temperament does not seem to impair the capacity of ewes and lambs to display an early preference for each other, and might be an advantage in some challenging postnatal situations because of the increased motivation of nervous lambs to reunite with their mother.

Rapid onset of maternal vocal recognition in a colonially breeding mammal, the Australian sea lion

BACKGROUND

In many gregarious mammals, mothers and offspring have developed the abilities to recognise each other using acoustic signals. Such capacity may develop at different rates after birth/parturition, varying between species and between the participants, i.e., mothers and young. Differences in selective pressures between species, and between mothers and offspring, are likely to drive the timing of the onset of mother-young recognition. We tested the ability of Australian sea lion mothers to identify their offspring by vocalisation, and examined the onset of this behaviour in these females. We hypothesise that a rapid onset of recognition may reflect an adaptation to a colonial lifestyle.

PRINCIPAL FINDINGS

In a playback study maternal responses to own pup and non-filial vocalisations were compared at 12, 24 and every subsequent 24 hours until the females' first departure post-partum. Mothers showed a clear ability to recognise their pup's voice by 48 hours of age. At 24 hours mothers called more, at 48 hours they called sooner and at 72 hours they looked sooner in response to their own pup's vocalisations compared to those of non-filial pups.

CONCLUSIONS

We demonstrate that Australian sea lion females can vocally identify offspring within two days of birth and before mothers leave to forage post-partum. We suggest that this rapid onset is a result of selection pressures imposed by a colonial lifestyle and may be seen in other colonial vertebrates. This is the first demonstration of the timing of the onset of maternal vocal recognition in a pinniped species.