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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 (

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

To successfully transition from nursing to foraging, phocid seal pups must develop adequate diving physiology within the limited time between birth and their first independent foraging trip to sea. We studied the postpartum development of oxygen stores in gray seals (Halichoerus grypus, n=40) to better understand the ontogeny of diving capacity in phocids. Hemoglobin (Hb), hematocrit (Hct), blood volume (BV), and myoglobin (Mb) levels in newborn (3 d postpartum [DPP]) and newly weaned (17+/-0.4 DPP) pups were among the lowest measured across age classes. During the pups' terrestrial postweaning fast (PWF), Hb, Hct, mass-specific BV, and Mb increased by 28%, 21%, 13%, and 29%, respectively, resulting in a 35% increase in total body mass-specific oxygen stores and a 23% increase in calculated aerobic dive limit (CADL). Although Hb and Hct levels at the end of the PWF were nearly identical to those of yearlings, total body mass-specific oxygen stores and CADL of weaned pups departing for sea were only 66%-67% and 32%-62%, respectively, of those for yearlings and adult females. The PWF represents an integral component of the physiological development of diving capacity in phocids; however, newly independent phocids still appear to have limited diving capabilities at the onset of foraging.