VOCAL INDIVIDUALITY OF IN-AIR WEDDELL SEAL (LEPTONYCHOTES WEDDELLII) PUP "PRIMARY" CALLS

As a result of selective pressures faced during lactation, vocal recognition may play a crucial role in maintaining the phocid mother–pup bond during the period of dependence. To investigate this possibility, we examined whether Weddell seal ( Leptonychotes weddellii ) pups produce individually distinctive "primary" calls. One temporal, nine fundamental frequency features, and two spectral characteristics were measured. A discriminant function analysis (DFA) of 15 Vestfold Hills pups correctly classified 52% of calls, while the cross-validation procedure classified 29% of calls to the correct pup. A second DFA of 10 known-age McMurdo Sound pups correctly classified 44% of "test" calls. For novel calls, the probabilities of attaining such classification rates by chance are low. The relationship between age and call stereotypy indicated that pups 2 wk and older may be more vocally distinctive. Overall, findings suggest that Weddell seal pup "primary" calls are moderately distinctive and only exhibit sufficient stereotypy to aid maternal recognition by approximately two weeks of age.     

Age-related changes in hematocrit in the Galápagos sea lion (Zalophus wollebaeki) and the Weddell seal (Leptonychotes weddellii)

In mammals, hematocrit (Hct) is optimized between the divergent requirements of blood flow characteristics and oxygen transport and storage capacity. This trade‐off plays a particularly major role in marine mammals, in which oxygen demand during sustained diving requires high Hct levels. Galápagos sea lions (Zalophus wollebaeki) need a long time after birth to develop from terrestrial life to the state of an independent forager at sea. We here show that pups were born with high Hct of 45%, then reduced Hct during the first 40 d of life to 31% while they remain constantly ashore, and increased Hct again until the adult level (57%) is reached at 1 yr of age when they begin to dive for foraging at sea. A similar, but much more rapidly changing pattern is seen in Weddell seal pups, but not in northern elephant seals, where no reduction in Hct is seen after birth. These and similarly changing patterns in terrestrial mammals likely reflect species specific functional adjustments during development due to a trade‐off between the costs of circulation and the changing need to store and transport oxygen.     

Sex‐related differences in the postmolt distribution of Weddell seals (Leptonychotes weddellii) in the southern Weddell Sea

The population of Weddell seals (Leptonychotes weddellii) in the southern Weddell Sea is in a unique position on the continental shelf edge, with vast shelf waters to the south, and deep Southern Ocean to the north. We describe sex‐related differences in the winter distribution of this population, from data collected by 20 conductivity‐temperature‐depth satellite relay data loggers deployed in February 2011 at the end of the annual molt. The regional daily speed was calculated, and a state‐space model was used to estimate behavioral states to positions along individuals’ tracks. GLMMs estimated that males and smaller individuals, diving in shallower water, traveled less far per day of deployment (males 14.6 ± 2.26 km/d, females 18.9 ± 2.42 km/d), and males were estimated to dive in shallower water (males 604 ± 382 m, females 1,875 ± 1,458 m). Males and smaller individuals were also estimated to be more resident; males spent an average 83.4% ± 7.7% of their time in a resident behavioral state, compared to females at 74.1% ± 7.1%. This evidence that male and female Weddell seals in the southern Weddell Sea are adopting different strategies has not been shown elsewhere along their circumpolar distribution.     

Influence of maternal mass and condition on energy transfer in Weddell seals

1. Environmental variation influences food abundance and availability, which is reflected in the reproductive success of top predators. We examined maternal expenditure, offspring mass and condition for Weddell seals in 2 years when individuals exhibited marked differences in these traits. 2. For females weighing > or = 355 kg there was a positive relationship between maternal post-partum mass (MPPM) and lactation length, but below this there was no relationship, suggesting that heavier females were able to increase lactation length but lighter females were restricted to a minimum lactation period of 33 days. 3. Overall, females were heavier in 2002, but in 2003 shorter females were lighter than similar-sized females in 2002 suggesting that the effects of environmental variability on foraging success and condition are more pronounced in smaller individuals. 4. There was no relationship between MPPM and pup birth mass, indicating pre-partum investment did not differ between years. However, there was a positive relationship between MPPM and pup mass gain. Mass and energy transfer efficiency were 10.2 and 5.4% higher in 2002 than 2003, which suggests costs associated with a putatively poor-resource year were delayed until lactation. 5. Heavier females lost a higher proportion of mass during lactation in both years, so smaller females may not have been able to provide more to their offspring to wean a pup of similar size to larger females. 6. MPPM had only a small influence on total body lipid; therefore, regardless of mass, females had the same relative body composition. Females with male pups lost a higher percentage of lipid than those with female pups, but by the end of lactation female pups had 4.5% higher lipid content than males. 7. It appears that for Weddell seals the consequences of environmentally induced variation in food availability are manifested in differences in maternal mass and expenditure during lactation. These differences translate to changes in pup mass and condition at weaning with potential consequences for future survival and recruitment.     

Physiological and behavioral determinants of the aerobic dive limit in Weddell seal (Leptonychotes weddellii) Pups

The aerobic dive limit, as defined by an increase in plasma lactate levels following dives, has to date only been determined in adult and juvenile Weddell seals (Leptonychotes weddellii). However, theoretical aerobic dive limits based on calculated total body oxygen stores, estimated metabolic rates, and dive duration frequencies have been published for several species. Using data collected over the past 3 years in McMurdo Sound. Antarctica, the aerobic dive limit of Weddell seal pups was determined by both the physiological and modeling methods. Time-depth diving recorders deployed on 36 pups between 2 and 14 weeks of age allowed the aerobic dive limit to be predicted from duration-frequency histograms. The aerobic dive limit was also calculated from estimates of total body oxygen stores and predicted diving metabolic rates. Finally, these two estimates were compared with aerobic dive limits determined from post-dive lactate levels in three pups between 5 and 7 weeks old. The aerobic dive limits of pups increased with age, but pup aerobic dive limits were still significantly shorter than those of yearlings and adults. In addition, the aerobic dive limits determined by the three methods were not equivalent for pups, yearlings, or adults, and indicate that care should be taken when modeling methods are used to estimate the aerobic dive limit in other species. Changes in hematocrit, plasma glucose, and plasma lactate levels during and between rest, diving, and recovery in pups were compared to known values for juveniles and adults. Plasma metabolite levels were more highly regulated in older pups, and together with the increasing aerobic dive limit, suggest that Weddell seal pups are not refined divers until after they are weaned, and that their diving ability continues to develop over several years.     

Variations in underwater vocalizations of Weddell seals (Leptonychotes weddelli) at the Vestfold Hills as a measure of breeding population discreteness

Weddell seal vocalizations from Davis Station showed similarities to those from McMurdo Sound and Palmer Peninsula, but none were identical. One vocalization, DD1, was unique to Davis Station. At all sites trills, or territorial defense calls, were the most common and had more types than other calls. Chugs, an aggressive sound, were common at all sites. Weddell seal calls from Davis Station showed similarities to sounds from McMurdo by sharing the use of prefixes and suffixes. Sounds from Davis Station shared the use of both ascending and descending trills and whistles with calls from Palmer Peninsula.Commonalities in underwater vocalizations may indicate the degree of mixing between breeding populations, in which case, Weddell seals in the Davis area probably are from a breeding population distinct from those at either McMurdo Sound or Palmer Peninsula.     

Influence of age and individual identity in the use of breeding colony habitat by male Weddell seals in Erebus Bay,Antarctica

Male–male contest behavior can contribute to spatial distributions of male pinnipeds during breeding seasons. To maximize breeding opportunities, the most competitive males would be expected to be surrounded by the highest numbers of reproductive-age females. As information regarding fine-scale spatial ecology of Weddell seals is lacking, we performed an exploratory study using kernel density analyses to evaluate age-specific habitat use of male Weddell seals in Erebus Bay, Antarctica. Additionally, we investigated the relationship between age and number of surrounding reproductive-age females using a competing set of regression models in a Bayesian framework that considered different functional forms of age while incorporating individual heterogeneity. As male adult Weddell seals aged, to at least 20 years, they were more likely to be found in areas associated with the greatest densities of reproductive-age females, but individual heterogeneity also influenced the number of reproductive-age female neighbors. The youngest males tended to haul out in offshore areas associated with better hunting, and older males tended to settle in more nearshore areas associated with more pup production. Our findings from this preliminary investigation indicate that male Weddell seal spatial behavior during the breeding season varies with age and individual and might be related to reproductive activity.     

Microscopic anatomy of the eye of the deep-diving Antarctic Weddell seal (Leptonychotes weddellii)

The microscopic anatomy of the eye of the Weddell seal was studied with various light and electron microscopic methods with a view to correlating morphological findings with the biology of this seal which is adapted to the extremes of the Antarctic environment and to extreme diving excursions into the lightless depths of the sea. In the retina an area centralis was found but no fovea centralis. The densely packed photoreceptors consist exclusively of highly differentiated rods, which in primates detect light at low intensity but have rather poor image discrimination. The ganglion cells are relatively scarce, suggesting a high degree of convergence of the light-sensitive cells on the ganglion cells. The pigment epithelium is almost devoid of pigment granules. The extensive tapetum lucidum is about 400-500 microm thick and is composed of about 30 layers of specialized cells. The cornea is 650 (center) to 800-900 (periphery) microm thick. Its structure and glycosaminoglycan histochemistry correspond to that of other mammals. The iridocorneal angle is unusually deep and pervaded by an elaborate trabecular meshwork, which together with a complex canal of Schlemm can be correlated with the ability to absorb large amounts of fluid. The ciliary muscle and its antagonist, the membrane of Bruch, are poorly developed, suggesting relatively poor abilities of accommodation. The combination of a well-developed tapetum lucidum, an unpigmented pigment epithelium, well-developed rods, and a high number of rods converging on only few ganglion cells is obviously an adaptation to an extreme light sensitivity, enabling the animals to make use of the little light available in the deep sea.     

Variation of annual apparent survival and detection rates with age,year and individual identity in male Weddell seals (Leptonychotes weddellii) from long-term mark-recapture data

Exploring age- and sex-specific survival rates provides insight regarding population behavior and life-history trait evolution. However, our understanding of how age-specific patterns of survival, including actuarial senescence, compare between the sexes remains inadequate. Using 36 years of mark-recapture data for 7,516 male Weddell seals (Leptonychotes weddellii) born in Erebus Bay, Antarctica, we estimated age-specific annual survival rates using a hierarchical model for mark-recapture data in a Bayesian framework. Our male survival estimates were moderate for pups and yearlings, highest for 2-year-olds, and gradually declined with age thereafter such that the oldest animals observed had the lowest rates of any age. Reports of senescence in other wildlife populations of species with similar longevity occurred at older ages than those presented here. When compared to recently published estimates for reproductive Weddell seal females, we found that peak survival rates were similar (males: 0.94, 95% CI = 0.92–0.96; females: 0.92, 95% CI = 0.93–0.95), but survival rates at older ages were lower in males. Age-specific male Weddell seal survival rates varied across years and individuals, with greater variation occurring across years. Similar studies on a broad range of species are needed to contextualize these results for a better understanding of the variation in senescence patterns between the sexes of the same species, but our study adds information for a marine mammal species to a research topic dominated by avian and ungulate species.     

Geographic variation of Weddell seal (<Emphasis Type="Italic">Leptonychotes weddellii</Emphasis>) airborne mother–pup vocalisations

Geographic variation of vocal behaviour may be reflective of genetic, cultural and ecological differences between locations. Such differences have been previously reported in six pinnipeds, including Weddell seals (Leptonychotes weddellii). This study investigated whether the acoustic characteristics of airborne Weddell seal mother and pup ‘contact’ calls vary geographically between the Vestfold Hills and McMurdo Sound. From each location, 72 mother and 120 pup calls were analysed, with 11 acoustic characteristics measured. MANOVA and Discriminant function analysis (DFA) identified significant differences in several fundamental frequency characteristics. The cross-validated DFA classified greater than 60% of mother and pup vocalisations to the correct location. For novel calls, the probabilities of correctly classifying these percentages by chance are low. Additionally, ordinal logistic regression identified significant differences in the maximum energy distribution of mother and pup vocalisations. For pups, this variation is likely the result of genetic differences between the two populations. Nevertheless, results support suggestions that, when compared with underwater repertoire differences, airborne within-call differences are less efficient at identifying Weddell seal breeding populations.     

Satellite imagery can be used to detect variation in abundance of Weddell seals (Leptonychotes weddellii) in Erebus Bay, Antarctica

The Weddell seal population in Erebus Bay, Antarctica, represents one of the best-studied marine mammal populations in the world, providing an ideal test for the efficacy of satellite imagery to inform about seal abundance and population trends. Using high-resolution (0.6 m) satellite imagery, we compared counts from imagery to ground counts of adult Weddell seals and determined temporal trends in Erebus Bay during November 2004–2006 and 2009, and December 2007. Seals were counted from QuickBird-2 and WorldView-1 images, and these counts were compared with ground counts at overlapping locations within Erebus Bay during the same time. Counts were compared across years and within individual haul-out locations. We counted a total of 1,000 adult Weddell seals from five images across all years (for a total of 21 satellite-to-ground count comparisons), approximately 72% of the total counted on the ground at overlapping locations. We accurately detected an increase in abundance during 2004–2009. There was a strong, positive correlation (r = 0.98, df = 3, P < 0.003) between ground counts and counts derived from the imagery. The correlation between counts at individual haul-out locations was also strong (r = 0.80, df = 19, P < 0.001). Detection rates ranged from 30 to 88%. Overall, our results showed the utility of high-resolution imagery to provide an accurate way to detect the presence and variation in abundance of Weddell seals. Our methods may be applied to other species in polar regions, such as walruses or polar bears, particularly in areas where little is known about population status.     

Microgeographic variation and songs in the underwater vocalisation repertoire of the Weddell seal (Leptonychotes weddellii) from the Vestfold Hills,Antarctica

Recordings of underwater vocalisations of the Weddell seal (Leptonychotes weddellii) were made in fjords of the Vestfold Hills near Davis Station, Antarctica. The repertoire was examined for the presence of microgeographic variation. Recordings covered the period from the end of mating to the beginning of the moult in the 1989/1990 breeding season. The repertoire was classified into 44 vocalisation types using a classification method based on objective parameters. Unique vocalisations were identified at each site, with 48% exclusive to Long Fjord and 41% to Tryne Fjord. A small percentage (11%) of the repertoire was common to both fjords reflecting the limited, observed interchange of individuals between these populations due to their strong breeding site fidelity. Seven male songs are described in the present study and possibly function to maintain underwater territories.     

Early maternal recognition of offspring vocalizations in rhesus macaques (Macaca mulatta)

This study investigated the development of maternal recognition of infant calls in rhesus macaques (Macaca mulatta). Fifteen mothers and their offspring, of age ranging from several hours to 28 days, served as subjects of an experiment in which the offspring's distress vocalizations were recorded and then played back to their mothers simultaneously with those of an age-matched control infant. The proportion of time looking at, but not the proportion of orientations to the speaker playing the offspring's vocalizations increased significantly as a function of infant age. Specifically, mothers of infants older than 1 week of age responded longer to the playback of their own infant's calls than did mothers of younger infants. These findings provide the firt evidence that offspring recognition in macaques develops between the first and second week of the infant's life and are consistent with the hypothesis that mothers need to be exposed to their infants' calls in order to learn their acoustic characteristics.     

Individuality in the vocalizations of infant and adult coppery titi monkeys (Plecturocebus cupreus)

As social animals, many primates use acoustic communication to maintain relationships. Vocal individuality has been documented in a diverse range of primate species and call types, many of which have presumably different functions. Auditory recognition of one's neighbors may confer a selective advantage if identifying conspecifics decreases the need to participate in costly territorial behaviors. Alternatively, vocal individuality may be nonadaptive and the result of a unique combination of genetics and environment. Pair-bonded primates, in particular, often participate in coordinated vocal duets that can be heard over long distances by neighboring conspecifics. In contrast to adult calls, infant vocalizations are short-range and used for intragroup communication. Here, we provide two separate but complementary analyses of vocal individuality in distinct call types of coppery titi monkeys (Plecturocebus cupreus) to test whether individuality occurs in call types from animals of different age classes with presumably different functions. We analyzed 600 trill vocalizations from 30 infants and 169 pulse-chirp duet vocalizations from 30 adult titi monkeys. We predicted that duet contributions would exhibit a higher degree of individuality than infant trills, given their assumed function for long-distance, intergroup communication. We estimated 7 features from infant trills and 16 features from spectrograms of adult pulse-chirps, then used discriminant function analysis with leave-one-out cross-validation to classify individuals. We correctly classified infants with 48% accuracy and adults with 83% accuracy. To further investigate variance in call features, we used a multivariate variance components model to estimate variance partitioning in features across two levels: within- and between-individuals. Between-individual variance was the most important source of variance for all features in adults, and three of four features in infants. We show that pulse-chirps of adult titi monkey duets are individually distinct, and infant trills are less individually distinct, which may be due to the different functions of the vocalizations.     

Contexts and behavioral correlates of trill vocalizations in wild white-faced capuchin monkeys (Cebus capucinus)

Primate vocalizations that appear to occur independently of specific contexts typically are considered to be contact calls. However, results from several recent studies indicate that these calls function to facilitate social interactions. White-faced capuchin monkeys (Cebus capucinus) emit a high-frequency vocalization, termed a "trill," in social interactions and during travel. In this study, immatures emitted most trills, but adult females also trilled; by contrast, adult males rarely trilled. Infants emitted the majority of trills, and they trilled at significantly higher rates than adult females. Infants trilled most when approaching other individuals. Furthermore, infants emitted proportionately more trills than other age classes when approaching other individuals. I therefore focused on the detailed context and immediate behavioral correlates of trilling by infants. Infants that trilled when approaching others tended to interact affiliatively with them subsequently (i.e., climbing on, touching, receiving grooming, and performing food inspection) more than infants that did not trill when approaching. Therefore, infant trilling may have had an immediate effect on the recipient's behavior.