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We examined age-related changes and consistency in physical and behavioural traits of 20 male grey seals ( Halichoerus grypus (Fabricius, 1791)) and implications for a proxy of mating success (number of oestrous females attended) over four successive breeding seasons on Sable Island, Canada. Across the study, young males (10–15 years) gained body mass, while old males (23–31 years) lost body mass. Body length was an important determinant of tenure (time spent at a site among females) and males of all ages exhibited a high level of consistency in duration of tenure (r = 0.40–0.50). In young males, our proxy of success showed a strong relationship with arrival body mass and also exhibited a high level of consistency (r = 0.50). None of the physical traits measured explained variation in success by exhibiting mating tactics that did not involve tenure, which is likely due to the opportunistic nature of those tactics. Whereas young male grey seals exhibited age-dependent improvements in success owing to changes in their physical state, later in life physical traits were less influential and suggest that nonphysical traits may compensate for a deteriorating physical state and its impact on male success.

Wecomparedthebehaviorsofprimiparousandmultiparousgrayseal(Halichoerus grypus) females over the course of lactation to examine whether poorly developed maternal behaviors may play a role in the reduced lactation performance observed in primiparous females. Overall, primiparous females spent as much time interacting with their pups as multiparous females. The proportion of time spent nursing their pup increased significantly between early and peak lactation in both primiparous and multiparous females. Although there was no significant difference in the duration of nursing bouts as a function of reproductive status, primiparous females nursed significantly more frequently (bouts/hour) and, therefore, spent a significantly greater proportion of time nursing than multiparous females throughout lactation. Primiparous gray seal females were also significantly more active than multiparous females, however, the difference in activity represented only a small proportion of the overall time budget. We conclude that poorly developed maternal

At the Gannet Islands, Labrador, sympatric thick-billed murres ( Uria lomvia (L., 1758)) and razorbills ( Alca torda L., 1758) are slightly sexually dimorphic and have similar intersexual differences in parental roles; females are the main meal providers and males are mostly involved in brooding and chick defence at the breeding site and at sea. The question is whether differences in parental roles influence the foraging behaviour patterns of males and females. Murre females foraged during twilight periods and dived shallower than males. In razorbills, although sex differences were not as clear, females also tended to dive shallower (

Studies on primates and other taxa have shown that the physiological response of an individual to stress reflects their social status. We combined behavioral observations with measures of stress to test the hypothesis that stress is an important physiological determinant of mating behavior and success in the male grey seal. Known-age males (N=19) were studied during the breeding seasons of 2004 and 2005 at Sable Island, Canada. The stressor was a capture and restraint period of 35 min and serial samples of cortisol and testosterone were taken as measures of stress. The mean baseline concentrations of cortisol and testosterone were 9.7+/-0.5 ug/dl and 6.2+/-0.6 ng/mL, respectively. The baseline cortisol concentration was negatively correlated with the duration of time a male spent at a site (r=-0.507, P=0.027), which was a strong correlate of mating success (r=0.659, P=0.002). All males experienced an increase in the concentration of cortisol during the restraint period (79.1+/-8.4%; CV=46.1%). The percentage rise in cortisol during restraint was correlated with the mean duration of time spent at a site (r=0.544, P=0.016) and thus success. The concentration of testosterone also increased during the restraint period (32.8+/-9.7%). This might be an adaptive response to maintaining the ability to reproduce while under stress. Our study indicates that stress is an important determinant of success in male grey seals. More successful males might exhibit an adaptive response to stress by maintaining low concentrations of cortisol during breeding.

Our best understanding of marine mammal mating systems comes from land-mating pinnipeds. Logistical problems of observing behavior at sea have limited our ability to make inferences about species with aquatic-mating systems, which comprise over half the pinnipeds. The mating systems of these species likely involve different mating tactics than land-mating species. We used several methods in combination (e.g., animal-borne cameras, radio telemetry, time-depth recorders, and DNA paternity assessment) to provide a comprehensive study of the aquatic-mating tactics of harbor seal males. Males decreased time offshore (26.0 vs 14.8%) and increased time near shore (33.8 vs 43.7%) between premating and mating periods, respectively. Concomitantly, males reduced foraging effort and increased activities associated with competition for females (e.g., visual/vocal displays and threats). As females come into estrus near the end of lactation and spend more time at sea, males reduced their near-shore ranges (4.2 vs 1.0 km2), which were clustered within 1–1.5 km of the beach where females attended their pups. Body mass of males was not a major factor affecting their reproductive behavior. From a small number of paternity assignments to study males, it appears that females select males. These combined results are more consistent with a lek-type mating system than with the territorial or female defense systems characteristic of land-mating pinnipeds.

Summary 1 We studied feeding frequency in free-ranging grey seals using stomach temperature telemetry to test if previously reported sex differences in the diving, movement and diet were reflected in the temporal pattern of foraging success. 2 Data were retrieved from 21 of 32 grey seals from 1999 to 2001, totalling 343 days and 555 feeding events, with individual record length varying from 2 to 40 days (mean: 16·33 ± 2·67 days/seal). 3 Seals fed on 57·8 ± 6·46% of days sampled and had an average of 1·7 ± 0·26 meals per day, but individual variability was apparent in the temporal distribution of feeding as evidenced by high coefficients of variation (coefficient of variation = 69·0%). 4 Bout analysis of non-feeding intervals of six grey seals suggests that feeding intervals of individuals were varied and probably reflect differences in prey availability. Grey seals tended to have many single feeding events with long periods separating each event, as would be expected for a large carnivore with a batch-reactor digestive system. 5 We found significant sex differences in the temporal distribution of feeding. The number of feeding events per day was greater in males (2·2 ± 0·4 vs. 1·0 ± 0·2), as was time associated with feeding per day (56·6 ± 5·8 min vs. 43·9 ± 9·4 min). 6 The number of feeding events varied with time of day with the least number occurring during dawn. Feeding event size differed significantly by time of day, with greater meal sizes during the dawn and the smallest meals during the night. 7 The length of time between meals increased with the size of the previous meal, and was significantly less in males (541·4 ± 63·5 min) than in females (1092·6 ± 169·9 min). 8 These results provide new insight into the basis of sex differences in diving and diet in this large size-dimorphic marine predator.

We studied female and male parental roles in two sympatric auks, thick-billed murre (Uria lomvia) and razorbill (Alca torda), with initial biparental care at the breeding site and later exclusively paternal care at sea. Our study addressed the following two questions: Why do males accompany chicks to sea?, and How do the sexes allocate parental effort at the breeding site before parental care at sea begins? We tested the hypothesis that males care for chicks at sea because they are in better condition at the time of chick departure as a result of femalebiased parental effort at the breeding site (‘nest’). Breeding success and duration of chickrearing did not differ between the two study years in either species at the Gannet Islands, Labrador. At the breeding colonies, females of both species provided more food (murres: 2.84 ± 0.18 loads day−1; razorbills: 2.02 ± 0.11 loads day−1) to their chicks than males (murres: 2.26±0.12 loads day−1; razorbills: 1.42±0.09 loads day−1), and males spent more time brooding the chicks. These differences were chick-age dependent in both species, with females providing more meals to chicks older than two weeks. Razorbill males spent more time with chicks greater than two weeks old, while murre male’s attentiveness of brooding did not vary with chick age. In both species, males (murres: 3.04 ± 0.3 h day−1; razorbill: 3.30±0.2 h day−1) performed longer foraging trips with meal delivery than females (murres: 1.23 ± 0.4 h/day; razorbill: 2.50 ± 0.4 h day−1). Thick-billed murres showed a consistent diurnal pattern of egg and chick attendance: females were usually found at the breeding site during the day whereas males were found there early in the morning and at night. In contrast, razorbill’s timing of attendance was much more variable and did not differ between sexes. Despite these differences in timing of breeding site attendance between species, males of both species spent twice as much time as females engaged in the defence of the egg or chick at the breeding site, which suggest male-biased capability of protecting the chick at departure. Overall our data indicated different female and male parental roles at the breeding site but not a female-biased allocation of time, energy and risk as predicted. In fact, males seem to provide equal if not more parental effort than females prior to the time of colony departure. We propose that the patterns of parental roles found between sexes is the result of a chain of events favouring male involvement in chick brooding and care at sea.

The purpose of this study was to examine the importance of body size and body composition as determinants of conditional mating tactics exhibited in male grey seals. We combined behavioral observations with measures of energy expenditure and success on 42 known-age individuals during the breeding seasons of 1997–2001 at Sable Island, Canada. Males with a large body mass arrived at the breeding grounds with more body fat and body energy and catabolized less body protein than smaller males. Males consumed 1.9 6 0.2 MJ day � 1 , and those with a smaller percentage of body fat had higher rates of food energy intake. The amount of body energy on arrival was positively correlated with the duration of the breeding period. Males that exhibited the primary mating tactic of consortship were heavier, had absolutely more body fat and body energy, and sustained breeding longer than those males that did not exhibit the primary tactic. Amongst all males, body mass showed a quadratic relationship with the number of female consorts mated and the estimated number of pups sired. Thus, intermediate-sized males mated with the most consorts and achieved the highest success. Intermediate body size may be optimal during breeding due to greater agility in male combat. Body size was an important determinant of mating tactics used by male grey seals. A large body size provided an energetic advantage of greater endurance while an intermediate body size may provide greater competitive ability in acquiring consortships. Key words: body size, conditional mating tactics, endurance rivalry, energetics, Halichoerus grypus, pinnipeds, reproductive behavior. [Behav Ecol]

Theoretical models predict that in species with obligate biparental care, individuals will partially compensate for decreased parental effort by their partners as a stable evolutionary strategy. Full compensation may occur when breeding success is an accelerating function of parental effort, especially in long-lived bird species. We experimentally examined the effect of time-depth recorders (TDRs) on body mass and parental behaviour of thick-billed murres, Uria lomvia, and evaluated the effect of TDRs as handicaps to test whether individuals compensate for decreased partner effort and whether compensation is sex biased. Compared with control birds, TDR-equipped birds had reduced body mass, offspring attendance, number of foraging trips and feeding rates, and males had increased foraging trip duration. In general, males lost mass at a higher rate and made longer foraging trips than females. Partners of TDR-equipped birds compensated for their mates' reduced parental effort by increasing offspring attendance and by increasing chick provisioning above average rates of control birds. Although partners of TDR-equipped birds fully compensated for their mates' reduced offspring attendance (i.e. chicks were never observed to be left unattended), total provisioning rates of pairs with a TDR-equipped bird ( X ¯ ± SE = 4.38 ± 0.26 meals / day ) were significantly lower than those of control pairs (5.74 ± 0.31 meals/day). However, fledgling success of control and TDR-equipped birds did not differ between reproductive seasons. TDR-equipped birds also had a significantly lower rate of return to breed than their non-TDR-equipped partners or control birds, and those that did return the following season were more likely to change mates (32%) compared with controls (0%). Taken together, our results underline the need to quantify the effects of monitoring equipment used to measure seabirds' activities, and indicate the ability of female and male thick-billed murres to compensate for reduced partner effort due to handicapping. Compensatory behaviour seems to be a necessary response of this single-brooded species to ensure current breeding success; however, it may affect the stability of pair bonds in some individuals.

Studies using molecular markers have shown that some grey seal males may be gaining success through exhibiting alternative mating tactics. We estimated the probability of fertilization success of grey seal males exhibiting the primary tactic of female defence and one alternative tactic of mating with departing females on Sable Island, Nova Scotia, Canada, during the breeding seasons of 1997-2002. Although the fertilization rate of the primary tactic (27-43%) was greater than that of the alternative tactic (10-12%), these low rates indicate the potential fitness value of alternative mating tactics in this size-dimorphic pinniped species.

Annual censuses of the number of harbour seal Phoca vitulina pups born on Sable Island Canada showed an increasing trend during the 1980s, but a rapid decline through the 1990s from 625 pups in 1989 to only 32 by 1997. Weekly surveys of the North Beach of the island during the 1991–98 breeding seasons showed that the number of adults and juveniles also declined during the 1990s. Despite the dramatic demographic changes, maternal postpartum mass, pup birth mass, relative birth mass, lactation duration, pup weaning mass and relative weaning mass showed no significant trends during 1987–96. However, two traits did change. The age structure of parturient females increased significantly, indicating reduced recruitment to the breeding population. Mean birth date increased by 7 days during the early 1990s, suggesting nutritional stress of females and later implantation dates. This nutritional stress may in turn have been caused by increased competition from the rapidly increasing grey seal population on Sable Island. Although minimum estimates of shark-inflicted mortality can account for much of the decline, evidence suggests that food shortage arising from interspecific competition may have also played a role in causing the decline of the population through effects on fecundity and juvenile survival.

We examined the diving behaviour of breeding male grey seals (Halichoerus grypus) at Sable Island, Nova Scotia, from 1997 to 2001. The proportion of time spent at sea varied between 0 and 78% (N = 30). Males engaged in deep (43.4 ± 3.3 m (mean ± SE), N = 27) diving, and these dives were clustered into bouts, which mostly occurred during long trips (62.2 ± 14.7 h). We suggest that males spent time foraging during deep dives. Shallow diving (5.9 ± 0.1 m, N = 27) accounted for 40.8% of dives, which were also clustered into bouts that mostly occurred during short trips (2.1 ± 0.37 h). We suggest that shallow diving comprised a suite of behaviours, but included little foraging behaviour. Phenotypic traits had little influence on diving behaviour. Further work is required to understand the extent to which foraging behaviour enhances reproductive success, and whether shallow diving is a component of the mating tactics of male grey seals at Sable Island.

Southern fur seals Arctocephalus australis in Peru have declined gradually over the past decade, and declined dramatically (72%) as a result of low food availability during the severe El Nino in 1997–98. In 1999, seals abandoned some historically important breeding sites. This is particularly alarming because new sites were not colonized. Our objective was to examine how habitat features and human disturbance influenced whether sites were currently used, abandoned or apparently not used in the past by fur seals for breeding. Data were collected on 14 variables at 70 potential breeding sites at three guano reserves in Peru. Discriminant analysis revealed significant multivariate differences among sites currently used for breeding, abandoned sites and unused sites (F=5.97, P

We studied the foraging behaviour of endangered Humboldt penguins (Spheniscus humboldti) to examine general foraging patterns, sex differences in foraging behaviour, and the reasons for incidental catches in fishing nets. Humboldt penguins foraged diurnally and typically made short, shallow dives within 30 m of the surface. Males and females made overnight (lasting 25.8 ± 3.4 h; mean ± SD) and day (10.4 ± 2.0 h) trips when they departed the colony to forage. Overnight trips were more common (68.2% of all trips) and were associated with a significantly greater amount of foraging time. Males dived to greater maximum depths than females but did not differ in other diving parameters, including foraging time, foraging effort, and proportions of day and overnight trips made. Adults may maintain their body condition during chick rearing by making a mixture of overnight and day trips. The two foraging periods observed during overnight trips may function to feed both the adults and the chicks, whereas the single period observed during day trips may function to accommodate the rate of provisioning required by the chicks. We suggest that both males and females would be protected from incidental catches in fishing nets if commercial fisheries avoided setting surface nets at night and setting nets between 0 and 30 m depth during the day in areas where penguins forage and transit.

Predators face decisions about which prey to include in their diet in order to maximize fitness. The foraging tactics used to capture prey and the resulting profitability of prey influence these decisions. We present the first evidence of prey-dependent foraging tactics and prey profitabil- ity in a free-ranging pinniped. We studied 39 adult male harbour seals Phoca vitulina at Sable Island, Nova Scotia using an animal-borne video system. Each male wore the camera system for 3 d during which 10 min video samples were recorded every 45 min from 06:00 h, resulting in approximately 3 h of videotape per male and a total of 1094 capture attempts of identified prey. Males foraged mainly on sand lance Ammodytes dubius and flounders (Pleuronectids), but salmonid and gadoid fishes were occasionally pursued. Foraging tactics differed among and within prey types based on differ- ences in prey behaviour. Sand lance was both a cryptic prey, when in the bottom substrate, and a con- spicuous schooling prey. Seal swimming speed, handling time and capture success differed between cryptic and conspicuous sand lance. The highest capture success and handling time was recorded for flounders. Estimated profitability, i.e. net energy intake per unit time, also differed with prey type and prey size. Our results suggest that diet selection may have important implications on the foraging energetics of pinnipeds.

We analyzed patterns of egg laying and breeding frequency of Humboldt Penguins (Spheniscus humboldti) between 1993 and 1997 at Punta San Juan, Peru. Egg-laying extended from mid-March to the first week of December, showing two well-defined peaks in April and August–September. The extended breeding period of these birds was the result of individuals having a second clutch. About half of the females (n =189) had two clutches per year, most of which were double broods (73%). The date of completion and outcome of reproduction, or whether a change of mates occurred from the previous year, did not affect timing of egg laying. The majority of first clutches (62%) were laid in April each year. Two-clutch breeders that started laying eggs early in April had a higher breeding success than those starting in late April, and double brooders had greater success than single brooders. Two-clutch breeders started to lay eggs earlier than single-clutch breeders. Taking into account that a penguin breeding cycle (from egg laying to fledging) lasts ∼4 months, laying eggs early in April increases the chance of rearing two successful broods per year. During three consecutive years, females tended to have two clutches instead of only one clutch and an average breeding success of 4.54 fledglings over 3 years. Having as many clutches as possible when conditions are favorable appears to be a strategy used by Humboldt Penguins to maximize their lifetime reproductive success within a productive but unpredictable environment.

Marine animals equipped with data recording devices sometimes show changes in their foraging behaviour, which can indicate an adverse effect of the instrument. We attached time-depth recorders (TDRs) and radio-transmitters to study foraging behaviour in Humboldt Penguins Spheniscus humboldti and observed an increase in the duration of foraging trips. We suggest that further tagging of this endangered species be approached with caution since this increase in trip duration may negatively affect reproductive and foraging success.

Studies of the grey seal Halichoerus grypus mating system, using focal animal sampling constrained by study site location and size, limit the measurement of variation in male mating tactics and success. Using this method, the mating tactics of grey seal males have been classified as either ‘tenured’ or ‘transient’. Preliminary evidence is presented of wider variation in male mating tactics and success using mobile focal-animal techniques that are not constrained by site, and of the effects of age on behaviour when accounting for body mass. The study was conducted during the breeding seasons of 1997 and 1998 at Sable Island, Nova Scotia. Six young (11–12 years) and five old (20–25 years) males were captured at the beginning of the breeding season, weighed and fitted with a VHF transmitter and time-depth recorder. Each male was located daily, and a count of late-lactating females within a 10 m radius recorded as a measure of mating potential. Female guarding and observed copulatory attempts were used as a measure of mating success. Mean initial body mass of young males and old males was similar, 291 ± 13 kg and 298 ± 14 kg, respectively. All males changed location during the study period. Young males changed sites more often and moved shorter distances between sites than old males. Estimated mating success varied from probably no matings to a minimum of seven; there were no differences between young and old males. Maximum duration of stay at a site and the number of late-lactating females at a site significantly influenced mating success. All the males except for two young males departed on diving excursions during the breeding season and engaged in deep diving behaviour. Diving behaviour did not differ between the age classes. Our results indicate that the current classification of mating tactics in grey seal males is an oversimplification. Preliminary data show that age may account for some of the variation in male behaviour on land and mating success, but not for behaviour at sea.

Summary 1. Female mammals increase energy expenditure during lactation to support the high cost of milk production. The extent to which lactation in a small phocid species, the Harbour Seal Phoca vitulina L., was fuelled by food vs body stores, how this allocation varied with maternal body mass and the consequences of maternal expenditure on offspring growth were studied. 2. The proportional body composition of 30 females was independent of initial postpartum body mass, but larger females had absolutely more stored energy than smaller ones. 3. Females lost 32% of postpartum body mass and 62% of body energy by late lactation; 97% of energy loss was derived from body fat. Percentage loss of body energy was independent of initial body mass, indicating that females limit their allocation of body stores to offspring by expending a constant proportion of stores rather than a constant amount. 4. Females spent more time diving and individual dives were deeper and longer as lactation progressed. By late lactation, these characteristics of diving were inversely proportional with initial postpartum mass. 5. During early lactation, female expenditures were covered mainly by a reduction in body energy stores. By late lactation, food intake increased six-fold but the extent of this increase varied inversely with postpartum mass. 6. Pup growth rate and weaning mass were positively related to postpartum mass and total daily energy expenditure of females, but were independent of the source of energy used by females during lactation. Pups of heavy females had higher survival than pups of light females. 7. Our results support the hypothesis that maternal body mass is an important determinant of lactation strategies in pinnipeds.

During observations at a breeding colony of Humboldt Penguins (Spheniscus humboldti), we noted five male penguins enter nests occupied by breeding pairs and engage in aggressive interactions with the resident adult. These nest intrusions resulted in egg loss or infanticide, and accounted for 11.1% of breeding failure in the colony. Two intruder males ultimately mated with respective resident females. This behavior had not been observed previously in Humboldt Penguins and we suggest that it may occur when males are unable to obtain mates through advertising at the nest. Intrusion behavior may slow down population recovery in this endangered species.

We studied effects of maternal age, body mass, and parturition date on birth mass and stage of development at birth in harbor seals (Phoca vitulina) on Sable Island, Nova Scotia, over a 10-year period. As predicted, effects of maternal mass and age on pup traits varied with maternal age. Premature pups, characterized by extensive fetal pelage termed lanugo, weighed 20% less than newborns without lanugo and were born early in the season to lowbody-mass females 4‐6 years of age. Among intermediate-age females (7‐10 years old), percentage of lanugo on pups was correlated negatively with female postpartum body mass but not with female age. Thus, maternal condition rather than age had stronger effects on stage of development of offspring at birth. Overall, maternal age explained 54% of the variance in birth mass, whereas postpartum mass of females explained only 20% of the variance. These relationships did not differ with sex of the pup, although male pups were 3.7% heavier than female pups. Effects of maternal age were strongest among young females; however, reproductive parity was more important than age itself in determining offspring birth mass.

Parental recognition of offspring would be expected to evolve among densely populated species in which parental investment is large, and separations of the mother–pup pair are frequent. Although otariids present a well-developed system of mutual vocal recognition, evidence in phocids is weak. Furthermore, allo-suckling is prevalent in some species and may reflect confusion over the identity of pups. The vocalizations of grey seal Halichoerus grypus pups have been found to be stereotyped and individually distinctive on the Isle of May, Scotland. However, playback experiments showed that mothers fail to discriminate between the vocalizations of their pup and a non-filial pup. Moreover, widespread allo-suckling was observed. In contrast, grey seals on Sable Island, Nova Scotia, a population reproductively isolated from that of the Isle of May, show very little allo-suckling. This may reflect the presence of a recognition system that does not seem to be present on the Isle of May. During the 1999 breeding season on Sable Island, vocalizations of grey seal pups were recorded and playback experiments carried out to determine whether female grey seals respond differently to the playback of vocalizations of their own pup, a familiar pup and an unfamiliar pup. Grey seal mothers were found to make significantly more head turns and body movements towards the loudspeaker during the playback of their own pup call than during the playback of a familiar or unfamiliar pup call. In addition, there was no evidence of an effect of pup age. This suggests that female grey seals can discriminate between pup calls using the stereotyped and individually distinctive vocalizations of their pup, and that different selective pressures may be in operation between the Sable Island and Isle of May colonies.

Female harbour seals (Phoca vitulina) undertake foraging trips during mid to late lactation. We show that they are accompanied by their pup during many of these foraging trips. Time-depth recorder data were obtained from 20 lactating females and 14 of their pups in 1995 and 1996 at Sable Island, Nova Scotia. Overall, females spent 55.4 ± 4.68% (mean ± SE) of their time at sea compared with 39.8 ± 2.29% for pups. Like those of their mothers, pups' dives occurred in clusters or bouts: 71.4 ± 4.4 dives, 2.5 ± 0.15 h in duration. Bouts of diving by females and pups began 0-3 days post partum. Mean dive duration of pups increased from about 1 to 1.5 min over the course of lactation, but was still shorter than that of adult females (1.5-2.25 min). Both females and pups appeared to dive within their theoretical aerobic dive limits (TADL) of 8.9 and 2.6-3.1 min, respectively. Up to 3.6% of dives by some pups may have exceeded their TADL. Pups appeared to compensate for their lesser diving ability by making more and shorter dives per bout than females, particularly during early lactation.

Michael K. Schwartz,a,b Daryl J. Boness,a Catherine M. Schaeff,b Patricia Majluf,c Elizabeth A. Perry,a and Robert C. Fleischera aDepartment of Zoological Research, National Zoological Park, Smithsonian Institution, Washington, DC 20008, USA, bDepartment of Biology, American University, 4400 Massachusetts Avenue, Washington, DC 20016, USA, and cWildlife Conservation Society, Paul de Beaudiez 520, Lima 27, Peru

When closely related species breed in sympatry, and where hybrids have lower fitness, reinforcement theory predicts that selection should favour mechanisms that reduce the probability of interspecific matings. If this situation arises among species that exhibit resource defence polygyny where males and females of different species reside in the same territories, there may be some conflict between mate choice based on territory-holding ability (sexual selection) and mate choice for correct species. We investigated this in a population of fur seals where three species are sympatric and where some females breed in the territories of heterospecific males, and where interspecific matings and hybrid pups are observed. The territorial status of males and the birthing sites of females were determined during daily observations, as were the movements of males and females, the location of matings and mating partners. DNA extracted from skin samples was used to determine paternities using DNA fingerprinting and the mtDNA genotype of individuals. Individuals were also classed on the basis of species-typical phenotype. We found that extra-territory inseminations (ETIs) were significantly more prevalent (67%) when territorial males and resident females were of different phenotype than when of similar phenotype (27%), but mtDNA genotype had no effect on the rate of ETIs. ETIs were probably by males with the same phenotype, as pups born to these females in the following season had the same phenotype as their mothers, suggesting they were not hybrids. These results suggest that within the resource defence polygynous mating system of these sympatric fur seals, female mate choice is more influenced by male phenotype than genotype. Contrary to our predictions, our study indicates that potential conflict between mate choice based on sexual selection and species recognition is unlikely, because females have some capacity to discriminate between males both within and between species on phenotypic traits additional to those under sexual selection. Although at least 25% of the pups born in this study were hybrid, this study can only support reinforcement theory if hybrids have reduced fitness. The fitness of hybrids among the species studied is currently unknown.

We evaluated bioelectrical impedance analysis (BIA) as a means of rapidly and inexpensively estimating total body water (TBW) of harbor seals (Phoca vitulina). Deuterium oxide dilution was used to estimate TBW in 17 adult females and 16 of their pups between birth and late lactation. Isotope dilution was also used to determine TBW in 12 adult males early and 10 of these males late in the breeding season. At the same time, resistance (Rs) and reactance (Xc) measurements were taken using a tetrapolar, impedance plethysmograph (Model 101 A, RJL Systems). Seals were sedated with diazepam prior to taking BIA measurements. Within-day duplicate RJ measurements on pups and adults, taken 2-240 min apart, differed by an average of 3.0% & 1.4% (n = 42, CV = 102%). Movement of the seal during BIA measurements caused variability in both Rs and Xc values. BIA measurements were generally poor predictors of TBW. Rs was significantly correlated with TBW in pups only (Rs = 0.93, P = 0.001, n = 11). Bioelectrical conductor volume (length2/Rs) was significantly correlated with TBW only in adult females (Rs = 0.63, P = 0.02, n = 14). We conclude that BIA is not a reliable method of estimating TBW in wild harbor seals.

Previous studies of fur seals suggest that the attendance patterns and consequent temporal patterning of energy transfer from mother to pup follows a latitudinal cline. While data from subpolar, tropical, and some temperate latitude species support the postulated cline, data for the temperate latitude Juan Fernandez fur seal do not. Maternal foraging trips and associated visits ashore were the longest of all otariids studied to date. The first foraging trip postpartum averaged 10.2 d (n= 51 females, range 1–22.5), foraging trips combined averaged 12.3 d (n= 100, range 1.0-25.0), and visits ashore averaged 5.3 d (n= 91, range 0.3-15.8) over the three seasons of study. Only duration of lactation was intermediate between subpolar and tropical strategies as predicted. Dive records suggest that these females feed almost exclusively at night at depths of less than 10 m and at distances of more than 500 km offshore. The prey species of this fur seal, primarily myctophids and squid, migrate to the surface at night and are patchily distributed. Foraging trip length varied between years in conjunction with shifts in seasurface temperature and type of prey consumed. We suggest that distribution of prey, irrespective of latitude, dictates foraging patterns of fur seals and leads to the exceptionally long foraging trips and visits ashore observed in this species.

The energy expenditure of breeding male harbour seals, Phoca vitulina, on Sable Island, Nova Scotia, was investigated by measuring changes in body mass, body composition, and water flux using isotope dilution. Seals lost 0.47% +/- 0.04% (n = 34) of their initial mass per day during the breeding season (4 wk), and fat, water, and protein accounted for 64.3% +/- 4.8%, 27.8% +/- 3.3%, and 6.9% +/- 1.4% of this mass loss, respectively (n = 31). Total energy expenditure was estimated as 33.3 +/- 1.9 MJ d(-1), or 3.9 +/- 0.2 W kg(-1) (n = 17), similar to rates measured in terrestrially mating pinniped species. However, unlike terrestrially mating pinnipeds, male harbour seals did not fast during the breeding season, and energy intake from foraging accounted for 61.8% +/- 4.0% of the total energy expended. Males derived most of their expended energy from food intake early in the breeding season. However, as oestrus females became increasingly available, reduced rates of food intake in males were coupled with increased rates of total energy expenditure. Larger males expended significantly more energy from body stores and more total energy than smaller males. Male harbour seals appeared to balance the energetic costs of reproduction against the constraints of small body size by foraging during deep-diving trips before the appearance of oestrus females and by opportunistic feeding throughout the breeding season while at sea. We suggest that size dimorphism may be less pronounced in aquatically mating pinnipeds partly because the temporal and spatial separation of foraging and reproduction is less distinct than it is for terrestrially breeding pinnipeds.

The objectives of this study were to establish body mass at birth, postnatal growth rate, and the factors that influence these parameters for the Juan Fernández fur seal, Arctocephalus philippii. Females of this species have an unusual attendance pattern in which foraging trips and shore visits last, on average, 12.3 and 5.3 days, respectively. Pup mass was obtained from cohorts born during the reproductive seasons in 1988 through 1992. Birth masses of male and female pups were significantly different, averaging 6.1 and 5.5 kg, respectively (F = 13.2, P < 0.0003, n = 238). Birth masses also differed among cohorts, being lowest in 1992 and highest in 1990. During the first 2 months of life, male and female pups grew at the same rate (79 ± 61.5 g · day-1 (mean ± SD); F[1] = 0.03, P = 0.8562). Interannual differences in growth rate during the first month were significant (F[4] = 8.14, P < 0.0001), as was the interaction between month and year effects (F[2] = 6.81, P = 0.0012). Growth rates for the 1990 cohort were lower than those in all other years except 1992. Birth masses and postnatal growth rates of Juan Fernández fur seal pups are comparable to those of other otariid species.

We tested the hypothesis that kin selection may play a role in fostering behaviour in grey seals. Fostering frequency varied among three colonies, ranging from 3% to 28%. Band-sharing coefficients (S) of DNA fingerprints, from two multilocus probes, were used to predict relatedness (r). Mean r did not differ between foster mother-pup pairs and the expected r = 0 for presumed unrelated female-pup pairs. Likewise, mean r between fostered and filial pups compared to r between presumed unrelated pups within the same beaches did not differ. Mean S values of presumed unrelated pups on different beaches within the two smallest colonies were indistinguishable, indicating that there is not increased variation in relatedness in small colonies. These results suggest that kin selection does not play a significant role in the maintenance of grey seal fostering behaviour.

Aquatically mating male harbour seals, Phoca vitulinamust balance the competing demands of foraging and reproduction while at sea during the breeding season. Time-depth recorders (TDRs) were attached to 31 adult male harbour seals to investigate changes in diving behaviour at Sable Island, Nova Scotia, during the 1992-1994 breeding seasons. Male seals were captured, fitted with TDRs and weighed at the beginning of the season in late May, then recaptured for TDR removal and reweighing at the end of June. Males made deep dives (to maximum depths20 m) more frequently early in the breeding season, then switched to shallow (/=20 m) diving later during the mating period. Deep dives (38.8plusmn;2.2 m; 4.6plusmn;0.1 min) were fairly uniform in shape, appearing flat-bottomed with rapid rates of descent and ascent and long bottom time, but shallow dives (10.5plusmn;0.5 m; 3.0plusmn;0.1 min) were more variable in shape. Rates of mass loss varied inversely with time spent in deep dives, indicating that deep diving behaviour reflects foraging activity. Males lost mass while making shallow dives associated with mating behaviour later in the breeding season. Deep diving occurred more frequently during daylight hours. Shallow dives were predominant at twilight and at night when females are likely to be departing and returning to the island from foraging trips in late lactation. At Sable Island, males may maximize their encounter rates with oestrous females by ceasing to make offshore foraging trips, and increasing the time spent patrolling home ranges and displaying in shallow water near the breeding colony in late lactation. Relatively larger males may have a competitive advantage since they can afford to spend less time making foraging trips away from the concentration of females and more time displaying in shallow water near the shore.1997The Association for the Study of Animal Behaviour

Species of the suborder Pinnipedia belong to three families (Phocidae-true seals; Otariidae­ fur seals and sea lions; and Odo­ benidae-walruses) and are distinc­ tive ~mong mammals in that they are neither exclusively land dwelling nor excl,usively ocean dwelling. Pinni­ peds spend the majority of their time at sea foraging; however, with the exception of the walrus, they appear to require land (or sea ice) on which to give birth and nurse their young (Bonner 1984, Oftedal et a1. 1987a). Consequently, nursing of young and foraging for food must be spatially and temporally separated. Although pinniped, females and males aggre­ gate during the breeding season, fe­ male pinnipeds, unlike many other carnivores, are the sole providers of nutritional resources to the young; there is no male assistance or ex­ tended social group that assists the

Harp seals (Phoca groenlandica) give birth on pack ice and nurse their pups for about 13 d. We hypothesized that lactating females would transfer milk and energy to pups at a high rate to compensate for the brevity of lactation. To test this hypothesis, the milk intake of five pups was measured over a 6-8-d period after administration of deuterium oxide; the initial age of pups was estimated to range from 0 to 5 d postpartum. Body water content of 17 pups was also measured by isotope dilution, and body composition of 12 pups was determined by chemical analysis. The proximate composition of harp seal milk (n = 21) was also assayed. Harp seal pups contained little fat (3%) at birth, but 61% of the increase in body mass (average 2.3 kg/d) was fat, with the result that fat accounted for 47% of body mass at weaning. Body water estimated by isotope dilution was not significantly different from that measured directly (n = 9 paired samples); water composed 72% of lean body mass. From birth to weaning, milk lipid ...

Proximal mechanisms underlying a faster growth rate in male compared to female California sea lion pups were investigated. Males are significantly larger at birth than females. Specifically, we asked if differential maternal investment contributed to enhanced male growth via: (1) larger mothers having disproportionately more male pups, (2) more time and energy put into foraging by mothers of male pups, and (3) greater milk production in mothers of male pups. We also considered four aspects of differential energy utilization and acquisition by male and female pups: (1) male pups attempting to save energy for growth by changes in behavior, (2) longer suckling bouts with mother and more sneak suckling of non-filial females by male pups, (3) lower maintenance costs in males via a lowered resting metabolic rate, and (4) increased assimilation efficiency in males. Our study showed that there are no differences in the size of females or length of foraging trips for mothers of male and female pups. Male pups received more milk from their mothers, but the difference was no longer significant when the larger body size of males was considered. There were no differences in either the activity budgets or suckling behavior of male and female pups. Male pups, however, did have lower resting metabolic rates than females. We conclude that enhanced male perinatal growth is a consequence of a larger size at birth, proportionally more milk from mothers to support the greater demands of larger body size, and lower maintenance costs due to a lower resting metabolic rate.

Vocalizations of individual Hawaiian monk seal pups, Monachus schauinslandi, do not have unique attributes that enable females to recognize their own offspring. Despite low aggregation density during pupping, aggressive encounters are common between females with pups. Fostering is prevalent and may reflect confusion over the identity of pups following aggressive encounters between females. All pup vocalizations were simple in structure and contained true harmonics. The coefficients of variation revealed considerable variance in vocalization structure within pups. Controlling for age, multivariate analyses of variance revealed significant differences among pups in vocalization attributes. Significant developmental changes occurred in vocalization structure for some pups but not for others. Discriminant function analysis suggested that it would be difficult for females to distinguish between the vocalizations of pups. The results of experiments conducted in the field showed that females did not discriminate between filial and alien pups by voice. In addition, females tended not to foster pups that had vocalizations similar to those of their own offspring. Thus, females seem to be unable to recognize their pups by voice. The apparent lack of vocal recognition of pups may contribute to the high frequency of fostering in this species.

Unlike most mammals, hooded seal (Cystophora cristata) pups are born with a substantial layer of adipose tissue. Subsequently, during the brief lactation period of only 4 days, fasting mothers mobilize enormous amounts of lipid from blubber and secrete milk (60% fat) at rates of 10 kg.day-1. Pups gain 7 kg.day-1 due primarily to the deposition of fat in blubber. We measured blubber content and fatty acid composition of blubber and milk in hooded seal mother-pup pairs at birth and over the 4-day lactation period to examine the nature and source of fetal lipids, the incorporation of maternal blubber fatty acids into milk lipid, and patterns of fatty acid deposition in suckling young. The fatty acid composition of the blubber of the newborn was notably different from that of its mother. Fetal deposition was likely due to a combination of both fetal synthesis and direct placental transfer of maternal circulating fatty acids. The blubber of the newborn was characterized by high levels (> 90% of total fatty acids) of saturated and monounsaturated fatty acids of primarily endogenous origin. In particular, the fetus appeared to have high delta-9 desaturase activity as evidenced by the large amounts of 14:1n-5 (4.2%) and 16:1n-7 (37.0%) in newborn blubber compared to maternal blubber (0.2% and 14.1%, respectively). Nevertheless, essential and long-chain polyunsaturated fatty acids of the n-3 and n-6 families, which could only have originated by direct transfer from the mother, comprised > 7% of pup blubber fatty acids and indicated greater rates of placental transfer than found in humans. In hooded seal mothers, rapid lipid transfer during the brief lactation period appeared to be facilitated by direct incorporation of mobilized fatty acids into milk. Although some differences in proportions of specific fatty acids were found between milk and maternal blubber, most of these differences declined over the course of lactation. However, selective mobilization of 20:5n-3 from maternal blubber into milk was apparent throughout lactation and resulted in elevated levels in pup blubber at weaning compared to maternal blubber. Ingested fatty acids were deposited directly and without modification into the blubber of pups, and by 4 days the fatty acid composition of pup blubber was virtually identical to that of the milk consumed.

We investigated the possibility that male harassment of lactating females differed in relation to time of birth in the grey seal, Halichoerus grypus, on Sable Island, Nova Scotia. This was done by comparing the frequency of male disturbances, maternal performance and pup growth for females that either gave birth during the peak of the pupping season or after the peak. Of the females, 58% gave birth in a 7-day period near the beginning of the pupping period, when the operational sex ratio was 2–4 females per male. Late in the pupping period the operational sex ratio reversed to about 1 female for every 2 males. The relative frequency of disturbances by males was significantly greater for late-pupping mothers than for peak-pupping ones (1.9 vs. 1.4 encounters/h). Females that gave birth late also were disturbed by males 3 times more often than females that gave birth during the peak (3.4 vs. 1.1 % of observation time). Late-pupping mothers spent 22% less time suckling (4.0 vs. 5.1 % of observation time), had 30% slower growing pups (1.7 vs. 2.4 kg/d), and weaned pups that were 16% lighter (45.6 vs. 54.0 kg). The effect of birth time on pup mass gain and weaning mass was not attributable to factors such as maternal mass, pup birth mass or pup sex. We conclude that the reduced maternal performance is likely the result of the increased male harassment. As reduced weaning mass can lead to reduced juvenile survival, male harassment may have contributed to the enhanced reproductive synchrony in this species.

Lactation strategies in the two largest families of seals have been characterized as a phylogenetic dichotomy, with sea lions and fur seals (Otariidae) exhibiting foraging cycles and true seals (Phocidae) a strategy of fasting. We show that a lactating phocid, the harbor seal, Phoca vitulina, has a foraging cycle similar to that of otariids. Time-depth recorders attached to lactating harbor seal mothers revealed that 9 of 11 females began bouts of diving, averaging 12–40 m, by mid-lactation (12 days). During the remainder of lactation, females made an average of seven diving trips, lasting about 7 h. They returned to the rookery during the interval between successive bouts to nurse their pups. Diving was more frequent during daylight than at night and diving bouts increased in duration as lactation progressed. The diving behavior of females that had weaned their pups and previously collected data from stomach lavage, suggest that the bouts of diving represent successful foraging. We propose that the lactation strategy of the harbor seal is intermediate to that of the otariids and other phocids studied. The harbor seal has a foraging cycle like the otariids, but typically resembles other phocids in length of lactation, rate of mass gain in pups, and in milk fat content. As harbor seals are among the smallest phocids, and only slightly larger than most otariids, it seems likely that maternal size constrains the amount of stored energy harbor seal females can bring to the rookery, forcing them to start feeding during the lactation period.

We studied the effects of maternal age, maternal body mass at parturition, year of birth, birth date, pup sex, and developmental stage (as indicated by the presence of a foetal pelage called lanugo) on the birth mass of harbour seals (Phoca vitulina) on Sable Island, Nova Scotia, Canada. Between 1987 and 1992, mass was obtained on 330 newborns and 259 of their mothers. Birth mass was significantly correlated with maternal mass (r = 0.42 for male pups; r = 0.32 for female pups). Among pups that had shed their lanugo, males were significantly heavier at birth (11.4 ± 0.09 kg, n = 107) than females (10.9 ± 0.09, n = 99). Birth mass increased significantly with maternal age (n = 71, range 4–12 years) even after the effects of maternal mass and pup sex were statistically removed. Mean birth mass varied significantly among years, from 10.5 to 11.5 kg. Newborns averaged 12.8% of maternal mass at parturition (84.8 ± 0.49 kg). Most (84%) pups had shed their lanugo before birth. Pups born with extensive lanugo were born earlier in the season and weighed about 20% less than pups born without lanugo. These data suggest that pups born with lanugo may be less developed than pups that had shed their foetal coat. Young mothers (4 and 5 years old) produced most of the underweight, lanugo-covered pups.

Hooded seals (Cystophora cristata) have a lactation period of 4 d. The rate of milk energy transfer must be very high to ensure that pups are weaned with sufficient energy reserves to withstand the lengthy postweaning fast. Milk energy transfer was measured by isotope dilution (n = 6), and energy deposition was assayed by chemical analysis of pups at birth (n = 4) and weaning (n = 5). Estimates of body water content obtained by isotope dilution and direct analysis were not significantly different. Water constituted only 71.7% ± 0.50% (SE) of lean body mass at birth, indicating developmental maturity. Newborn pups were also high in fat (14.0% ± 0.78%) and energy (10.1 ± 0.25 MJ/kg). Pups consumed 7.52 ± 0.469 kg/d milk containing 187 ± 11.6 MJ/d. Total milk and energy yields were estimated as 30.1 kg and 746 MJ. Pups deposited 88% of ingested fat, 41% of protein, and 84% of energy. Of the weight gain, 82% was fat. The energy content of pups increased nearly fourfold from birth to weaning, but protein conte...

In phocid species in which females fast throughout lactation, maternal energy reserves at parturition must support lactation. Thus, differences in body size and energy stores may influence the magn...

Brown, G. E., and Brown, J. A. 1992. Social dynamics in salmonid fishes: Do kin make better neighbours? Anim. Behav. In press. Burner, A. J. 195 1. Characteristics of spawning nests of Columbia River salmon. U.S. Fish Wildl. Serv. Fish. bull. 61: 97 - 1 10. Dill, P. 1977. Development of behaviour in alevins of Atlantic salmon, Salmo salar, and rainbow trout S. gairdneri. Anim. Behav. 25: 116-121. Fletcher, D. J. C. 1987. The behavioural analysis of kin recognition: perspectives on methodology and interpretation. In Kin recognition in animals. Edited by D. J. C. Fletcher and C. D. Michener. John Wiley and Sons, Toronto. pp. 19 -54. Gibson, R. J. 1978. The behaviour of juvenile Atlantic salmon (Salmo sular) and brook trout (Salvelinus fontinalis) with regard to temperature and water velocity. Trans. Am. Fish. Soc. 103: 707- 712. Grafen, A. 1990. Do animals really recognize kin? Anim. Behav. 39: 42-54. Hepper, P. G. 1986. Kin recognition: functions and mechanisms, a review. Biol. Rev. Camb. Philos. Soc. 61: 64-93. Jasienski, M. 1988. Kinship ecology of competition: size hierarchies in kin and non-kin laboratory cohorts of tadpoles. Oecologia, 77: 407-413. McKaye, K., and Barlow, G. W. 1976. Chemical recognition of young by the Midas cichlid, Cichlasoma citrinellum. Copeia, 1976: 276 -282. Michener, C. D., and Smith, B. H. 1987. Kin recognition in primi- tively eusocial insects. In Kin recognition in animals. Edited by D. J. C. Fletcher and C. D. Michener. John Wiley and Sons, Toronto. pp. 209 - 242. O'Hara, R. K., and Blaustein, A. R. 1982. Kin preference behaviour in Bufo boreas tadpoles. Behav. Ecol. Sociobiol. 11: 43 -49. Olsen, K. H. 1989. Sibling recognition in juvenile Arctic charr, Sal- velinus alpinus (L.). J. Fish Biol. 34: 571 -581. Quinn, T. P., and Busack, C. A. 1985. Chemosensory recognition of siblings in juvenile coho salmon, (Oncorhynchus kisutch). Anim. Behav. 3: 51 -56. Quinn, T. P., and Hara, T. J. 1986. Sibling recognition and olfactory sensitivity in juvenile coho salmon (Oncorhynchus kisutch). Can. J. Zool. 64: 921 -925. Scott, W. B., and Crossman, E. J. 1973. Freshwater fishes of Canada. Can. Bull. Fish. Aquat. Sci. No. 184. Scott, W. B., and Scott, M. G. 1988. Atlantic fishes of Canada. Can. Bull. Fish. Aquat. Sci. No. 218. Siegal, S. 1956. Nonparametric statistics for the behavioural sciences. McGraw-Hill, New York. Sokal, R. J., and Rohlf, F. J. 1981. Biometry. W. H. Freeman, San Francisco. Waldman, B. 1982. Sibling associations among schooling toad tad- poles: field evidence and implications. Anim. Behav. 30: 700- 713. Waldman, B., Frumhoff, P. C., and Sherman, P. W. 1988. Problems of kin recognition. Trends Ecol. Evol. 3: 8

Publisher Summary Estrus is a state of sexual receptivity during which the female will accept the male and is capable of conceiving. This behavioral state is under hormonal regulation involving the ovary and pituitary gland and precedes or coincides with ovulation. Knowledge about estrus, estrous behavior, and the estrous cycle in marine mammals is highly variable. Among cetaceans, most of it is derived from studies of the ovaries and reproductive tracts of animals killed during whaling or collected from beached and stranded specimens. The little behavioral information that is available comes mostly from studies of captive animals although some comes from observations of free-ranging animals. The hormonal cycle associated with estrus and reproduction in marine mammals appears to be similar to what happens in other mammals. High plasma concentrations of estrogens at the time of parturition decline rapidly and then begin a sharp rise again as the cells surrounding the follicle, known as the theca interna, secrete estrogen. This rise in estrogen, along with a decline in progesterone, which inhibits follicle growth, is responsible for the rapid follicular growth in the ovary and the onset of estrous behavior. At the same time the follicle grows, the epithelium of the ovary thins and eventually ruptures, marking ovulation.

Publisher Summary Sea lions are members of the family Otariidae. There are presently seven sea lion species in five genera. They originated in the Northeast Pacific region, sharing a common ancestor with fur seals. Although the fossil record for sea lions is poor, it appears they crossed into the Southern Hemisphere about 3 million years ago. Sea lions do tend to be larger than fur seals, with both groups exhibiting substantial differences in body mass, and smaller differences in body length, between males and females, a phenomenon known as sexual dimorphism. The ability to dive and stay underwater is an important characteristic for all marine mammals, including sea lions. Although large lung volume is important for diving animals, the lung volume for sea lions is equally proportional to their body size as to other marine mammals and even terrestrial mammals. They follow a lifestyle typical to that of all the otariids, with some characteristics common to all seals. They are long-lived, have delayed sexual maturation, and have physical and social sexual bimaturation, with males maturing more slowly than females. The status of sea lion populations is variable. The Japanese sea lion has not been sighted since the 1970s and is now considered extinct. According to the International Union for Conservation of Nature (IUCN), three species—the California, Australian, and southern sea lions—are currently considered as being at low risk of extinction. The sea lion species for which there is greatest concern at present and is listed as endangered and at high risk of extinction by the IUCN is the Steller sea lion.

Hooded and harbor seals are unique among true seals (family Phocidae) in that the lanugo (fetal pelage) is typically shed in utero. Shedding had occurred in all newborn hooded seals examined off the Labrador coast (n = 62) and in 94% of newborn harbor seals on Sable Island, Nova Scotia (n = 110), although in one-fifth of the latter the molt was incomplete. In hooded seals the shed hair in the amniotic sac was organized into tightly woven disks, whereas in harbor seals the shed hair formed a loose mat with no evident structure. We examined hair masses in the intestines of pups of both species but could find no evidence that the intestines were involved in hair disk formation. We argue that fetal shedding, like prenatal blubber deposition, is an adaptation enabling newborn pups to enter cold water without adverse consequences. This ability allows the use of pupping substrates that are unstable or regularly inundated with water.

Abstract Recent studies of fur seals and sea lions (Otariids) which are cold water adapted, indicate that social behaviour in hotter climes is constrained by the form and availability of cool substrate provided by the rookery environment. This first study of the behaviour of the Juan Fernández fur seal provides new evidence of this relationship and the extent to which thermoregultory requirements can affect social behaviour in pinnipeds. Females of this species on Alejandro Selkirk Island made daily movements from inland pupping and rest sites to the shoreline and into the water in response to rapid increases in solar radiation to levels exceeding 1.3 cal/cm2/min. Thirty percent of these females floated and groomed offshore in the afternoon in areas protected from the surf by offshore islets and rocky reefs. Males held territories on land either along the shoreline (39%) or in land-locked areas (45%) as is typical of fur seals, or held completely aquatic territories (16%) that encompassed the site where females floated. The average aquatic male, present on territory primarily during the afternoon hours when females floated offshore, achieved as many copulations as did the average land-locked or shoreline male. Land-locked males often abandoned their territories for short periods (45 minutes on average) in response to increasing solar radiation in the afternoon and at a time when female numbers on land were low. The existence of aquatic territoriality as a successful mating strategy has not yet been documented for any other otariid. The occurrence of this behavioural strategy is likely a product of the interaction of thermoregulatory constraints and topographical features which together promote predictable aggregations of females offshore. This study further substantiates that constraints on female aggregation appear to dictate the range and mode of male mating strategies in otariids.

Gray seals (Halichoerus grypus) undergo a terrestrial postweaning fast (PWF) that depletes energy reserves acquired during the suckling interval. Plasticity in PWF duration may ensure that pups of variable body condition depart for sea with adequate energy reserves. To test this hypothesis, we examined body condition of 30 gray seal pups at weaning and monitored their PWF duration. On average, fat accounted for 47.3% +/- 0.7% of their 53.2 +/- 1.3-kg weaning mass. Although fasting duration averaged 21 +/- 1.1 d (n = p28), there was considerable variation in fasting duration (9 to > 31 d) and the resulting age when pups departed to sea (26 to > 49 d). Percent fat at weaning(38.6%-54.6%) was positively correlated with fasting duration(n = 28, r = 0.376, P = 0.0489). In contrast, total body gross energy (735.3-1,447.4 MJ) and body mass (39.0-66.0 kg) were not correlated with fasting duration. Thus, body composition,not overall body reserves, predicted fasting duration, but the effect was weak, indicating that other factors also account for the observed variation in fasting duration. We speculate that pups with greater percent fat more effectively utilized lipid and conserved protein while meeting metabolic costs throughout the PWF. As a result, fatter pups extended the PWF duration,which may be critical for development of diving physiology and may have facilitated their survivorship to age 1.

Fostering behavior has been reported in a large number of mammal and bird species although the relative frequency of its occurrence in most species is unknown. A commonly held view is that fostering is costly to the parent(s) engaged in it. However, empirical studies of fostering are few, and measures of either cost or benefit are even rarer. During a study of individually marked Hawaiian monk seal mothers and pups, observed over the course of maternal care, I found that 87% of 30 females fostered pups. Females sequentially fostered an average of 2.3 pups (range: 1–5 pups) during the approximately 40-day lactation. The median proportion of lactation spent fostering was 34% (range: 5%–90%). Confusion during aggressive interactions appeared to be the major antecedent of fostering and may be understandable in terms of the spatial pattern among females. The density of females with pups was relatively low for a land-breeding seal (1.5 females per 1000 m2), and the typical spatial pattern indicated a tendency toward dispersion. Yet, movements of females and pups to and from water occasionally leave females within a meter or two of each other. Several measures of the immediate reproductive cost of fostering were obtained, including: the length of time suckled by pups, the size of pups at the end of suckling, and survivorship to 1 year of age. There was no correlation between these measures for individual pups and the extent to which their mothers fostered, indicating that the high levels of fostering may be maintained in monk seals because they are not selected against.