Timing of births and juvenile mortality in the South American fur seal in Peru

In most species, synchronous, seasonal reproduction is usually associated with higher offspring survival in animals giving birth around the peak, relative to those breeding at the extremes of the reproductive season. In contrast, in the South American fur seal ( Arctocephalus australis ) at Punta San Juan, Peru, females pupping around the peak of births had a greater probability of losing their pups and/or tended to lose them at an earlier age than females breeding early or late in the season. However, the timing of breeding in this population varies little between years and is consistently synchronous. Individual females maintained their relative breeding times in consecutive years, regardless of whether or not they lost their pup the previous year. Thus, pup mortality seems to have no effect on the timing of reproduction in this population.
High breeding densities and the consequent high pup mortality in the S. American fur seal in Peru may have resulted from intense poaching outside protected areas and are of recent origin. The reproductive synchrony in this population could have originally evolved as a response to seasonal variations in food availability and weather conditions, differences in female or pup body condition, predation pressure, sexual selection and/or harassment avoidance, but at the present high density levels has become maladaptive.     

Causes of mortality in South American fur seal pups (Arctophoca australis gracilis) at Guafo Island,southern Chile (2004–2008)

As part of population dynamics studies of the South American fur seal (Arctophoca australis gracilis) rookery at Punta Weather in Guafo Island (43°36'S, 74°43’W), the causes and extent of pup mortality were monitored. During four breeding seasons, daily counts of live and dead pups were carried out to determine pup production and pup mortality. Dead pups were retrieved from the rookery to perform necropsies. The mean pup production was 1,735.5 ± 336 pups and the mean pup mortality up to 12 wk old was 6.0%± 2.6%. The major causes of death were enteritis with microscopic lesions of bacteremia (28.4%), starvation (23.5%), drowning (21%), trauma (19.8%), and stillbirths (2.5%). Enteritis with microscopic lesions of bacteremia, and starvation had higher incidence during January (beginning and middle of the breeding season) while most trauma and drowning occurred during February (end of the breeding season). In the 2006–2007 breeding season there was an increase in mortality due to starvation and trauma. Most pup deaths at Guafo Island are generated by extrinsic factors; therefore, additional studies that assess the impact of environmental changes and fishing activities, are needed in order to determine the exact causes of the decline of this species along Chilean coasts.     

Distribution, pup production and mortality of New Zealand sea lion

Surveys were undertaken at Campbell Island / Motu Ihupuku during January and February 2008, to determine the distribution and pup production of New Zealand sea lions (NZ sea lion; Phocarctos hookeri). In addition, necropsies were performed at the main breeding site of Davis Point to determine the principal causes of early mortality for NZ sea lion pups. In total, 397 pups were tagged and 186 untagged pups were found dead, giving a minimum pup production of 583 pups and a one month of age mortality estimate of 40%. This represents a higher pup production than previous estimates from Campbell Island (although survey techniques are not comparable), and equates to 21% of the total pup production for NZ sea lions in the 2007/08 season. Early pup mortality was high (40%) at Campbell Island, with trauma, starvation, and drowning in rock pools and peat mires the major causes of death. Pups were concentrated in two colonial breeding sites: Davis Point on the north shore of Perseverance Harbour (76%) and a newly recorded breeding site (Paradise Point) on the southern shore of Perseverance Harbour (21%). Non-colonial breeding or single pups occurred around the southern parts of the island from sea level to 400 m; however, these only contributed 3% of the known pup production.     

Factors affecting early mortality in the South American fur seal (Arctocephalus australis) in Peru: density-related effects and predation

Early mortality in the South American fur seal ( Arctocephatus australis ) in Peru is considerably higher than that seen in any other population of fur seal; 31–49% in the first month as opposed to a maximum of 20% in other populations. In 1987 and 1988, pup mortality was found to be enhanced by density-related effects and predation on pups by the southern sea-lion ( Olaria byronia ). At a high density beach, where 60% of the fur seals bred, mortality correlated with the number of females ashore as did aggression. Female aggression was driven to high levels by a combination of high density and movement within the colony to thermoregulate. However, even at a low density, beach mortality remained high due to a high level of predation by male southern sea-lions (low density beach 5·0–8·3% of all pups; high density beach 0·2%). Predation rates were lower at the high density beach because male fur seals expelled most attacking sea-lions during the breeding season (low density beach 10·0% of attacking sea-lions expelled; high density beach 58·8%).     

Grey seal (Halichoerus grypus) pup production at North Rona: A study of birth and survival statistics collected in 1972

The Grey seal breeding assembly on North Rona was studied throughout autumn 1972. Weekly censuses provided data on birth rate and mortality. It is estimated that 1736 pups were born in 1972. This is about 500 less than the mean production estimate for this assembly during the period 1959–71, possibly a result of disturbance of the breeding site by the expedition. About 600 of the pups died before putting to sea. The mean date of birth and the duration of the pupping season agree closely with earlier work on North Rona, although the mean daily birth rate curve is somewhat irregular, perhaps because there was an unusually dry spell of weather at a critical time in the pupping season. An improved estimate of mortality at this assembly showed a relationship with pup density similar to that observed at the Fame Islands. Techniques for estimating pup production (and consequently total population), though not reliable for determining absolute values, are useful for indicating trends and they suggest a stable population of 8000–9000 animals at North Rona. Such estimates might be improved by the use of better methods of aerial photography.     

BREEDING BIOLOGY OF SOUTHERN ELEPHANT SEALS IN PATAGONIA

Abstract: Elephant seals breed in Patagonia (Península Valdés, Argentina) from late August to early November, reaching peak numbers during the first week in October. Observations of this population over the past ten years yielded similar results. Eighty percent of the pups were born by 2 October. Most (96%) of 663 females marked during three breeding seasons gave birth to a pup. Females stayed on land a mean of 28 d, gave birth 6 d after arrival, nursed their pups for 22 d, and copulated a mean of 2.5 times 20 d after parturition and 2 d before departure. Copulations peaked during the third week in October. Males spent 57–80 d on land fasting and defending harems of up to 134 females (median 11–13 females, depending on year). Most (96%) marked females that gave birth ( n = 636) also weaned their pups successfully. Pup sex ratio was unity. Harems were smaller and breeding occurred about three weeks earlier in Patagonia than in other colonies. Thermal conditions, day length and food availability may explain clines in the timing of breeding events between populations, Other parameters of the breeding season for the expanding Patagonia colony are similar to those for declining southern elephant seal populations elsewhere.     

Effects of maternal age and condition on parturition and the perinatal period of Antarctic fur seals

The effect of maternal age and condition on the date of parturition and the duration of the perinatal period of Antarctic fur seals at Bird Island, South Georgia, were investigated over three consecutive breeding seasons. Females rear young during a four-month lactation period in a highly seasonal but predictable environment. Although females may first pup at three years of age, they did not attain full adult size until six years of age; older females (≥ 6 years) tended to be heavier, longer, and in better condition than younger females (3–5 years). Older females returned to breeding beaches earlier and could occupy the most suitable pupping sites, and gave birth when densities of animals on the beaches were low (i.e. more favourable for pup survival). Females that arrived earlier were able to remain ashore longer with their pups prior to departing on their first foraging trips but this was unrelated to either maternal age or condition. Younger females returned later in the pupping season, possibly as a result of late implantation due to smaller energy reserves than older and larger females. In 1990 all females arrived late, were in poorer condition, gave birth to lighter pups, and had shorter perinatal periods. This suggests that not only was implantation late but that females returned to an area of low food availability prior to parturition.     

Field metabolic rate of lactating female Galápagos fur seals (Arctocephalus galapagoensis): the influence of offspring age and environment.

Galápagos fur seals, Arctocephalus galapagoensis, live in a seasonal environment which varies strongly in productivity from year to year. We measured how the field metabolic rates (FMR) of lactating females varied with season, pup age and year. Energy expenditure was measured using doubly labeled water (DLW) during the cold seasons of 1984 and 1985 in 9 mothers of 1-3-month-old pups and 5 mothers of yearlings, and during the 1986 warm season in 8 mothers of 6-month-old pups. Young pups gained 0.84% mass/day during the cold season, but larger pups during the warm season lost 1.25% mass/day. During the warm season, females had lower relative total body water than during the cold season suggesting higher fat content during the warm, less productive season, but the effect was even more marked when comparing different years of the study: fat content was high in 1984 and 1986 and low in 1985. The FMR of mothers varied from 134 to 167 W but did not show significant differences between any of the pup age-groups. Among the years of the study, FMR showed only a trend towards low energy expenditure of mothers of young pups in 1984. The mean FMR was lower than for other otariids. Mothers may limit energy expenditure independent of pup age and season to minimize their own risk of starvation in an environment of comparatively low productivity, varying unpredictably due to frequent El Ni?o events.     

Grey seal, Halichoerus grypus, energetics: females invest more in male offspring

Grey seal females transfer large amounts of energy to their pups during the brief lactation period. The costs of lactation have been measured using weight changes of mother and pup pairs. Large females come ashore to give birth earlier in the season and lose weight more rapidly than smaller females. The sex ratio of Grey seal pups born is skewed towards males in the early part of the breeding season. Male pups are larger at birth and gain weight more rapidly than female pups, and their mothers show a correspondingly faster rate of weight loss than mothers of female pups. The energy costs of gestation and lactation to a Grey seal mother are 31 GJ for male pups and2–8 GJ for female pups. Males are therefore 10% more costly in energy terms to raise to weaning. Because, on average, large females arrive at breeding sites before smaller animals, biased results on weight changes would be obtained from methods which do not use repeated weighings. We suggest that the high efficiencies of lactation estimated for Harp seals compared with other phocid seals could be accounted for by such a bias.     

Large Forest Patches Promote Breeding Success of a Terrestrial Mammal in Urban Landscapes

Despite a marked increase in the focus toward biodiversity conservation in fragmented landscapes, studies that confirm species breeding success are scarce and limited. In this paper, we asked whether local (area of forest patches) and landscape (amount of suitable habitat surrounding of focal patches) factors affect the breeding success of raccoon dogs (Nyctereutes procyonoides) in Tokyo, Central Japan. The breeding success of raccoon dogs is easy to judge as adults travel with pups during the breeding season. We selected 21 forest patches (3.3–797.8 ha) as study sites. In each forest patch, we used infra-red-triggered cameras for a total of 60 camera days per site. We inspected each photo to determine whether it was of an adult or a pup. Although we found adult raccoon dogs in all 21 forest patches, pups were found only in 13 patches. To estimate probability of occurrence and detection for raccoon in 21 forest fragments, we used single season site occupancy models in PRESENCE program. Model selection based on AIC and model averaging showed that the occupancy probability of pups was positively affected by patch area. This result suggests that large forests improve breeding success of raccoon dogs. A major reason for the low habitat value of small, isolated patches may be the low availability of food sources and the high risk of being killed on the roads in such areas. Understanding the effects of local and landscape parameters on species breeding success may help us to devise and implement effective long-term conservation and management plans.     

Annual variation in the timing of reproduction in Antarctic fur seals, Arctocephalus gazella, at Bird Island, South Georgia

The arrival of Antarctic fur seals at a breeding beach on Bird Island, South Georgia, was studied over five consecutive breeding seasons, 1983 to 1987. Experienced bulls arrived first and established breeding territories on the beaches in anticipation of the arrival of the cows. Male arrival, which is less synchronous within years than female arrival, was significantly later in 1987 than in any other year. Female arrival, estimated by pup birth date where necessary, was highly synchronous; it usually started when 80% or more of potential territory sites were occupied by males. Cows arrived significantly later in 1984 and 1987 than in 1983, 1985 or 1986. The late arrival of both males and females in 1987 is attributed to unusually severe climatic conditions during the preceding winter. The late arrival and reduced fecundity of females in 1984 is attributed to markedly reduced food availability during the austral winter and summer of 1983. Males were not affected in 1984 because they could move away from the area of reduced food availability earlier than females and because they have a more varied diet. Factors influencing the winter distribution, the timing and pattern of arrival and the breeding of male and female Antarctic fur seals are discussed.     

Inter-sexual differences in Antarctic fur seal pup growth rates: evidence of environmental regulation?

We investigated the variation of Antarctic fur seal (Arctocephalus gazella) pup growth rates in response to sex, breeding season and duration of both maternal foraging trip and attendance bouts. Data were collected during five consecutive rearing seasons at Cape Shirreff, the most important breeding colony in the South Shetland Islands, Antarctica. Our results showed significant interannual and sexual variations in pup growth rates. Male pups grew significantly faster than female pups during 2000, 2001, 2002 and 2004 seasons, whilst during 2003 no difference was found. The interannual variation in pup growth rates was correlated with the interannual fluctuation in maternal foraging trip and attendance bouts. There was a significant effect of pup sex and maternal foraging trip duration on pup growth rates, which varied between years having foraging trip duration a major effect during 2003, when females spent more time at sea and interestingly on that year there were no sexual differences in pup growth rates. The effect of attendance bout on pup growth rates was not significant. Diet analysis showed that Antarctic krill (Euphausia superba) was the most frequent prey item during the study period. Analysis of krill size distribution showed a significant difference in krill length, during 2003, when A. gazella preyed upon the smallest sizes of krill. In this study, sex was the most important factor on pup growth rates, but when prey availability seemed more limited, there are longer foraging trips and shorter attendance bouts the sex factor became less significant.     

Growth and survival of New Zealand sea lions, <Emphasis Type="Italic">Phocarctos hookeri:</Emphasis> birth to 3 months

Offspring birth mass and growth rate represent important life history traits, which influence many vital population and individual characteristics, while offspring survival is a key factor in variation in female reproductive success. For a threatened population of pinnipeds, such as New Zealand sea lions, Phocarctos hookeri, (Grey, 1844, NZ sea lions), understanding individual life history parameters and population dynamics is vital for their management and conservation. This is the first study of the behaviour of females during parturition, pup birth mass and growth, and pre-weaning survival of NZ sea lions, Enderby Island, Auckland Islands during austral summer breeding seasons, 2001/2002 to 2003/2004. Pregnant females arrived ashore 2.1 ± 0.16 days prior to giving birth. After parturition, mothers suckled their pups for 8.6 ± 0.16 days before leaving on their first foraging trip. Male pups were born significantly heavier than female (males 10.6 ± 1.4 kg, females 9.7 ± 0.9 kg). Pups lost on average 48 ± 0.14 g per day mass during the early postpartum period (between birth and mothers first foraging trip). Pup mortality did not vary by pup sex, birth mass, date of birth or any maternal characteristics however it varied significantly between years due to a bacterial infection epidemic (Pup mortality at 60 days: 2001 32%; 2002 21%; 2003 12%). The absolute growth rate per day for pups was 151 g/day over all years. Pup growth rate measured as the slope of linear line fitted to pup mass by age was consistently higher for pups with heavier birth mass, male pups and during the 2002 season. High offspring mortality and slow growth rates coupled with maternal foraging behaviour at their physiological limits may reflect a threatened species which has limited ability for population growth in an environment which is at the extreme of their historical range and impacted upon by fisheries.     

Causes and predictors of nest mortality in a European rabbit population

We conducted a study on nest mortality of an individually marked population of European rabbits (Oryctolagus cuniculus L., 1758) living in a field enclosure. Over 4 years, we determined maternities and quantified pup mortality during the nest period of 703 pups born in subterranean breeding burrows. Overall, pup mortality occurred in 42.7% of the litters, whereas 32.4% of all born pups were affected. Mortality was highest during the first few postnatal days. In about 50% of the cases, we managed to quantify different causes of mortality such as malnutrition, flooding, cooling of the pups, infanticide, or predation. The pups’ body mass on postnatal day 1, the thermal environment and the number of litter mates were the most important predictors of nest mortality. Litter mortality risk decreased with increasing soil temperature around the subterranean nests. A comparatively higher average pup body mass lowered the nest mortality risk of a litter, whereas this effect was more pronounced when soil temperatures were low. Furthermore, mortality was lowest in medium-sized litters, most probably due to the balance between the thermal benefits of huddling with litter siblings and the costs of having them due to the lower share of milk obtained by the individual pups in larger litters. In addition, nest mortality depended on characteristics of the mother; mortality was increased in litters of low-ranking females and of mothers with lower body mass. In conclusion, our study highlights multiple causes and the effects of different environmental and social factors on nest mortality of this small mammal.     

DEMOGRAPHY AND BREEDING BIOLOGY OF A SMALL,LOCALIZED POPULATION OF SOUTHERN ELEPHANT SEALS (MIROUNGA LEONINA)

Southern elephant seals have been studied in depth in most of their breeding range. One notable exception is the Falkland Islands population. We present data on demography and breeding biology of elephant seals of Sea Lion Island, the main breeding site of this species in the Falklands. Sea Lion Island shelters a small, localized population of southern elephant seals (516 breeding females in 1995 and 518 in 1996). Comparison with the few available census data collected prior to our study suggests that the population has been stable in the short term (1989-1996). Females produced pups at maximum rate and pup mortality was low (2.13%). Breeding sex ratio was strongly unbalanced, with about 14 females per breeding male and 47 females per harem-holding male at peak haul-out. Survival rate between breeding seasons was 67.4% for females and 50% for males. Timing of the breeding season was very similar to that recorded in other populations and was in accordance with clinal variation with latitude. Sex ratio at birth was balanced, and no significant weight dimorphism at weaning between sexes was detected (males: 135.4 kg; females: 132.0 kg). Weaning weight was correlated with size class of the mother.     

Habitat selection by dispersing yellow-headed blackbirds: evidence of prospecting and the use of public information

In migratory birds individuals may prospect for potential breeding sites months before they attempt to breed and should use the cues most predictive of future reproductive success when selecting a breeding site. However, what cues individuals use when prospecting and which cues are used in selecting a breeding site are unknown for most species. I investigated whether yellow-headed blackbirds (Xanthocephalus xanthocephalus) prospect for future breeding sites and whether they select breeding habitats based on food availability, male or female density, or the average number of young produced per female in the previous year. Although it is often assumed that migratory birds prospect for potential breeding sites at the end of the breeding season, I investigated this by recording all visits to sites early and late in the breeding season. I found that males and females who visited sites other than the site at which they bred were more likely to disperse than individuals only observed at the site where they bred, and that males and females were more likely to prospect late in the breeding season. Both food availability and density in year ^x were not predictive of the number of young per female in year ^x+1; however, the number of young produced per female at a site in year ^x was predictive of the number of young per female in year ^x+1. As expected, dispersers used the most informative cue, the number of young per female and moved to sites with a relatively high number of young per female. This study suggests that individuals prospect for potential breeding sites late in the breeding season when they can use information gathered from the reproductive success of other individuals (i.e., public information) to select a breeding site.     

Influence of the physical environment and conspecific aggression on the spatial arrangement of breeding grey seals

Understanding the habitat requirements of a species for breeding is essential for its conservation, particularly if the availability of suitable habitat is a limiting factor for population growth. This is postulated to be the case for grey seals, one of the more abundant marine apex predators in northern European waters. In common with similar studies that have investigated the habitat preferences of breeding grey seals, we use abiotic (topographical, climatological) attributes but, unlike previous work, we also incorporate behavioural variables, particularly the occurrence of aggressive interactions between females and the presence of neighbouring seals. We used two Generalized Additive Models (GAM) in a sequential and iterative fashion. The first model links the occurrence of aggression at particular points in the colony to local topography derived from a Geographical Information System (GIS), presence of neighbouring seal pups and the day of the breeding season. The output of this GAM is used as one of the explanatory variables in a GAM of daily variation in the spatial distribution of births. Although proximity of a birth site to a water source and the presence of neighbouring seal pups both had significant influences on the distribution of newborn pups over time and space, at the scale of the study site it was found that simple rules could predict pup distribution more efficiently than a complex individual-based simulation model.     

Mimicking Natural Nursing Conditions Promotes Early Pup Survival in Domestic Rabbits

In the wild rabbit, Oryctolagus cuniculus, mother–young relationships are based on restricted, once-per-day nursing interactions. Correspondingly, pups have evolved an efficient strategy of energy saving. Here we investigate under breeding conditions, whether matching or not, the once-daily nursing visit by the rabbit females has an effect on pup survival and growth. Two nursing regimen were applied to 89 primiparous (P) and to 78 multiparous (M) does: (a) one that matched the once daily nursing pattern (closed nest-box during the whole day except for a few minutes devoted to nursing) and (b) one that did not match it (24 h free nest access). In P females, the controlled nest access resulted in lower mortality between birth and weaning (8.1%) as compared to the free nest-access (18%). This effect was recorded from postnatal d 3–4 onwards. Both treatments induced different death causes (starvation (63%) in controlled-access regimen, and wounds and nest-soiling (29%) in free-access regimen). While both experimental nest-access regimens differentially affected pup survival in P or M females, they were without influence on pup growth rate in does of either parity. It is concluded that repeated nest visits by the female increase risks of injury to pups, and of out-of-time pup activation or sucking, and that, more generally, it plays against the ethophysiologigal strategy of biomass conservation evolved by rabbit newborns. The fact that the nest-access regimen no longer affected pup survival from the second parity suggests that the behaviour of multiparous does more adequately models the offspring demands.     

Factors influencing home range and activity of wild boar (Sus scrofa) in a Mediterranean coastal area

This paper analyses the temporal variation in the size of home range and activity of adult wild boar ( Sus scrofa L.). Eighteen boar were radiotracked between 1991 and 1993 in the Maremma Natural Park (Central Italy). Variations of home-range size and activity were related to sex, winter food availability and population density. The hypotheses that home-range size was inversely related to food availability and population density, and that the amount of activity was directly related to population density and inversely related to food abundance, were tested. The size of the acorn crop was used as a measure of winter resource level. No differences were found in the size of ranges, core area, and activity between males and females. In 1991–92 home-range size was larger than in 1992–93; conversely, activity increased from 1991–92 to 1992–93. Winter food availability was high in 1991–92 and low in the following year. Population density increased greatly in spring 1992 but crashed in spring and summer 1993, when a high mortality of wild boar occurred due to starvation.
The decrease in home-range size during the food shortage was explained as a possible strategy adopted by wild boar to cope with starvation. The difference in home-range size and amount of activity found between the first and the second year of study were probably influenced by differences in population density, although the individual effects of food availability and population density were not clearly separable.     

Alloparenting in Steller sea lions (<Emphasis Type="Italic">Eumetopias jubatus</Emphasis>): correlations with misdirected care and other observations

Alloparental care is rarely observed in Steller sea lions (Eumetopias jubatus) where maternal care is extended to a single pup for up to 1 year or more. However, we observed 28 allonursing events and one case of adoption at a small breeding rookery in the western Gulf of Alaska between the years 2001 and 2005. Multiparous and primiparous females were observed nursing nonfilial individuals with equal frequency, but primiparous females spent significantly more time nursing nonfilial individuals. Multiparous females allowed allonursing only while sleeping and unaware while most primiparous females were aware that they were allonursing. These results are consistent with the misdirected-care hypothesis suggesting that primiparous (presumably younger) females nurse nonfilial pups due to inexperience, whereas multiparous (presumably older) females are victims of milk stealing during times of inattentiveness. Nonfilial pups were aggressively tossed most often during the pupping season and only by multiparous females, while allonursing events occurred more frequently after the pupping season. Starveling pups were not cared for by any female, but two were attended by a single bull during separate autumn seasons.