The demography of a high-density badger (Meles meles) population in the west of England

Data from the longest running capture-mark-recapture study of Eurasian badgers, in an undisturbed wild population at Woodchester Park in Gloucestershire, were used to investigate population dynamics. Twenty-one social groups of badgers occupying an area of 7.3km² were studied from 1978-1993. The density increased steadily over the study period, reaching the highest published density known anywhere at 25.3 adults per km² in 1993, and the average social group size increased to 8.8 adults (S.E. ± 0.85) in 1993. By 1993, 97% of the population trapped was of known age and overall the population consisted of 27% cubs and 73% adults. In addition, the results supported previous studies in that the population had an equal sex ratio as cubs, but became increasingly female biased with age. There was high juvenile mortality, nearly 50% dying in their first year. Between 58 and 90.2% of adult females did not breed each year.     

The biology of the stoat (Mustela erminea) in the National Parks of New Zealand IV. Reproduction

Abstract

The gonads of 528 female and 821 male stoats were examined. The weights of ovaries and testes in adults peaked simultaneously in October, the season of births and of post-partum oestrus. Of 73 females, 78% had even numbers of nipples, mostly 8 or 10. The mean number of embryos in 13 pregnancies was 8.8 (6–13), and embryo weights ranged from 0.005 g to 2.9 g. Of 11 pregnant females, 8 contained fewer embryos than corpora lutea, and there was evidence of transuterine migration of blastocysts in 6. All but 2 of 451 females caught in December–July inclusive carried corpora lutea of delay. Few adult and no young females were found in oestrus in September–October, though adult males were fertile from August to February (no first-year males were fertile). There was some evidence that the breeding season started later at more southerly latitudes in both males and females. The mean number of corpora lutea per female was 9.7 (n = 439), and there was a significant inverse correlation between counts for the 2 ovaries of one individual. There was generally no significant variation in fecundity of females with age, body weight, or year. Of 11 females which were considered to have lost their litters, 10 were collected in beech (Nothofagus) forests. Four females and 9 males had abnormal gonads; the most severe abnormality was an ovarian teratoma of unknown pathology.     

To breed or not to breed: an analysis of the social and density-dependent constraints on the fecundity of female badgers (Meles meles).

Data from post-mortem examinations, population density estimates and long term capture-mark-recapture studies have been combined to look at the pattern of reproductive behaviour and the social factors leading to reproductive failure in badgers in Britain. The results are used to evaluate whether the hypothesis that the defence of oestrous females (as opposed to defence of food resources) best explains territorial behaviour and the social organization of badgers. Badgers in Britain have two peaks of reproductive activity, one immediately post partum and one in the summer/autumn. These coincide with two peaks of ovulation, and in the late winter/spring there is a steep rise in the number of sows carrying blastocysts, to reach an asymptote in June for yearling sows and April in older sows. Measured by their contribution to overall productivity, winter/spring matings were much more important than summer/autumn matings, contributing 65% of total autumn blastocysts in yearling sows and 71% of autumn blastocysts in older sows. The relative importance of the two mating periods is reflected in the seasonal pattern of bite wounding in adult male badgers; minor bite wounding in January-March was 2.3 times as frequent as in August-October, and moderate-extensive bite wounding was 3.1 times more frequent. In the populations studied, pre- and post-natal losses were high, with reproductive failure occurring at all stages of the breeding cycle, so that less than 30% of potential productivity was achieved. Indeed 22% of sows failed to develop blastocysts; these had a lower body mass, less body fat, larger adrenal glands, poorer health and higher bite wound scores than sows with blastocysts. Only 44% of adult sows implanted their blastocysts and proceeded to the end of pregnancy. However, it was less easy to identify features characteristic of sows that did or did not go on to implant their blastocysts. Finally, 35% of sows that produced cubs ceased lactation early, and this loss of entire litters was thought to be due to infanticide by dominant sows. The presence of annexe setts correlates with increased productivity in younger sows, and this is thought to be because annexe setts enable younger sows and their cubs to avoid the aggression of older, more dominant sows. Living in large social groups has no net reproductive gain for adult males or females, and there was a decline in productivity (per adult) with increasing group size.(ABSTRACT TRUNCATED AT 400 WORDS)     

Hyperglycemia-induced apoptosis affects sex ratio of bovine and murine preimplantation embryos

The effect of glucose in the medium used during in vitro culture on both cell death by apoptosis and the sex ratio of bovine blastocysts derived from in vitro-matured and in vitro-fertilized oocytes was evaluated. Oocytes were matured, inseminated, and cultured in vitro in mSOF medium with 10% FCS with or without glucose supplementation. Exposure to high concentrations of glucose (10, 20, and 30 mM) during bovine embryo development in vitro from zygote to blastocyst resulted in a decrease in the number of cells per embryo and an increase in the frequency of apoptotic cells. A significantly higher proportion of females was found among those embryos that developed under hyperglycemic conditions in vitro. Moreover, both murine and bovine blastocysts incubated for 6 hr in 20 mM glucose had a significantly higher number of apoptotic cells in comparison to control. In this study, we also determined whether blastocyst production of the X-linked inhibitor of apoptosis protein (XIAP) differs between the sexes. Our results show that female bovine blastocysts produce significantly higher amounts of XIAP mRNA than males and this could be crucial in explaining the higher proportion of female blastocysts observed following in vitro culture under hyperglycemic conditions which induce apoptosis. Moreover, a higher proportion of female murine blastocysts cultured under hyperglycemic conditions were implanted in the uterus (65.3 of implantations from embryos cultured with 20 mM of glucose are females vs. 49% in control). This mechanism provides an explanation for the significant reduction of male children born to diabetic mothers.     

Fertilization rates and embryonic development in CD-1 mice fed fungal endophyte-infected tall fescue seed

The objective of this study was to assess the effects of endophyte-infected tall fescue (KY-31) seed (80% infected, containing Acremonium coenophialum ) on the fertilization rates and embryonic development of CD-1 mice. Twenty-four pairs of mature CD-1 mice were randomly allocated to two dietary treatments containing 40% mouse chow and 1) 60% noninfected tall fescue seed or 2) 60% infected tall fescue seed (w/w). The mice were preconditioned on their respective diets for 60 d prior to 96 h of cohabitation between pairs of males and females. Following the removal of the males, equal numbers of females (n = 4) from each dietary treatment were sacrificed at 80 h, 6 and 10 d after vaginal plug establishment. The female reproductive tracts were excised and flushed to recover eggs and embryos or dissected to identify the number and status of the implanted fetuses. The number of eggs-embryos and/or fetuses per mouse present at the time of sacrifice were 9.8, 8.8 and 11.5 vs 8.2, 5.3 and 4.8 for the mice fed the noninfected and infected fescue seeds, respectively. Similarly, the conception rates (%) were 100, 100 and 100 vs 73, 50 and 50 for the two treatments. The mice sacrificed at 80 h and fed the noninfected fescue had 9.8 expanded blastocysts per animal, whereas those fed the infected fescue had only 4.0 expanded blastocysts. The results suggest that the infected fescue seed consumed by these mice had a significant effect on fertilization rates. More importantly, the infected fescue seed influenced negatively the development of these embryos during the embryonic-preimplantation period.     

REPRODUCTIVE CHARACTERISTICS OF FEMALE SEA OTTERS

Abstract: Several important aspects of reproduction in the female sea otter, such as gestation, pupping frequency, period of pup dependency, and annual pupping rate, were unclear when this study was begun. We present data from 75 tagged adult females that indicate gestation is variable, but on average is about 6 months, the length of pup dependency is 6 mo, thus the pupping interval is usually 12–13 mo. Most females breed for the first time in their fifth year of life. About 85–90% of adult females pup in a given year.     

Group living, breeding behaviour and territoriality in the Subdesert Mesite Monias benschi

In 1997–2000 we studied a population of Subdesert Mesites Monias benschi consisting of 35–68 adults comprising 32 groups of two to nine birds (modal group size of four). The study population was significantly male-biased in 1999 but not in 1997 or 1998. Overall, both sexes were philopatric, but when dispersal (or eviction) occurred, it appeared to be female-biased. Over 40% of groups contained more than two adult males, whilst < 15% contained more than two adult females. Whilst there was no evidence of behavioural dominance by females, intrasexual aggression within groups was observed only amongst females. In contrast to other birds occupying the same habitat, breeding in mesites was not tied to rainfall, and occurred throughout the year. Each breeding unit constructed several nests every year, only one of which was used. All adult males and at least one adult female co-operated to raise one or two clutches of one or two eggs per year. Males and females contributed equally to incubation. Chick production and chick survival were not related to group size or territory size. Groups defended large, permanent, and multipurpose territories and all group members contributed to territory defence. Territory size was positively correlated with the number of males in groups, but not with overall group size. Territories were tightly packed with very few areas unoccupied. Transect surveys conducted throughout the narrow geographical range of this species revealed its presence in a range of semi-arid habitat types. Small groups were more likely to be detected in intact, high-stature forest, whilst large groups were more likely to be detected in low-stature forest containing numerous spiny, xerophytic trees Didierea madagascariensis .     

Longevity and survival of female pipistrelle bats (Pipistrellus pipistrellus) on the Vale of York, England

Female pipistrelle bats ( Pipistrellus pipistrellus Schreber) form large nursery colonies in summer. Between 1977 and 1984, around York in the north of England, 1328 pipistrelle bats were ringed. Ninety adult females were ringed in 1977, and from capture, release and recapture data life tables for an unaged female cohort were constructed. Age-specific survival rate for adult females on the Vale of York was 0–64 per year. Three bats from the original 1977 cohort were recaptured in 1984 and are likely to have been at least eight years old. Juvenile female pipistrelles appear to survive less well than adults.     

Reproductive performance of the wild white-lipped peccary (<Emphasis Type="Italic">Tayassu pecari</Emphasis>) female in the Peruvian Amazon

The ability of any species to support high hunting pressures depends on its reproductive efficiency. Based on the gross anatomic examination of 208 adult female reproductive tracts, we characterised the reproductive biology of the wild white-lipped peccary in the northeastern Peruvian Amazon. White-lipped peccary apparently bred year round in the northeastern Peruvian Amazon, and the number of pregnant females was 80 (38.4%). Mean ovulation rate was 2.09 ± 0.47 CLs, and litter size was 1.60 ± 0.49 embryos or foetuses per pregnant female. A phenomenon of embryo migration was observed in the 27.5% of pregnant females. Estimations suggest 0.89 births per year and a yearly reproductive production of 1.42 piglets per pregnant female. Females in the late pregnancy stage showed a higher hunting vulnerability that could be an important restrictive factor for the reproductive efficiency of the wild white-lipped peccary populations in the Peruvian Amazon.     

Comparison of hybrid and purebred in vitro-derived cattle embryos during in vitro culture

Frozen-thawed spermatozoa collected from a beef bull (Japanese Black) were used for in vitro fertilization (IVF) of matured oocytes obtained from dairy (Holstein) and beef (Japanese Black) females. Embryos were examined for fertilization, cleavage rate, interval between insemination and blastocyst production (experiment I), total cell number per embryo and sex ratio during blastocyst formation (experiment II), and blastocyst production rate of zygotes that developed to 2-, 4-, and 8-cell stages at 48h post-fertilization (experiment III). Fertilized oocytes were cultured in vitro on a cumulus cell co-culture system. The fertilization and cleavage rate of oocytes groups were similar, however, the blastocyst production rate was greater (P<0.05) in hybrid than from purebred embryos (27% versus 20%). Development of blastocysts produced from hybrid embryos developed at a faster rate than blastocysts produced from the straightbred embryos. In hybrid embryos, blastocyst production was significantly greater on day 7 (56%) and gradually decreased from 20% on day 8 to 17% on day 9. In contrast, blastocyst production rate from the purebred embryos was lower on day 7 (17%), increasing on day 8 to 59% and then decreased on day 9 to 24%. The total number of cells per embryo and sex ratio of in vitro-produced blastocysts were not different between hybrid and purebred embryos. The number of blastocysts obtained from embryos at the 8-cell stage of development by 48h post-fertilization (94%) was greater (P<0.01) than the number of zygotes producing blastocysts that had developed to the 4-cell stage (4%) and the 2-cell stage (2%) during the same interval. These results show that the blastocyst production rate and developmental rate to the blastocyst stage were different between hybrid and purebred embryos, and that almost all of the in vitro-produced blastocysts were obtained from zygotes that had developed to the 8-cell stage 48h post-fertilization.     

Early embryonic development and in vitro culture of in vivo produced embryos in the farmed European polecat (Mustela putorius)

Early embryonic development and in vitro culture of in vivo produced embryos in the farmed European polecat (Mustela putorius) was investigated as a part of an ex situ conservation program of the endangered European mink (Mustela lutreola), using the European polecat as a model species. The oestrus cycles of 34 yearling polecat females were monitored by visual examination of the vulval swelling and, to induce ovulation, the females were mated once daily on two consecutive days. Sixteen yearling males were used for mating. The females were humanely killed 3-14 days after the first mating and the uteri and oviducts were collected for embryo recovery. Uterine and oviductal flushings yielded a total number of 295 embryos, representing developmental stages from the 1-cell stage to large expanded and hatched blastocysts. On Day 3 after the first mating, only 1-16-cell stage embryos were recovered. Between Days 4 and 6 after the first mating, 1-16-cell stage embryos and morulae were found. The first blastocysts were recovered on Day 7 after the first mating. The first implanted blastocysts were detected on Day 11 after the first mating. A total number of 85 embryos were in vitro cultured after recovery. Blastocyst production rates for in vitro cultured 1-16-cell stage embryos and for morulae/compact morulae were 68 and 84%, respectively. For all cultured embryos, the hatching rate was 15%. The in vitro culture requirements for the preimplantation embryos of the farmed European polecat remain to be determined before further utilization of the technique.     

Age, sex, and condition as predictors of moult and the efficacy of a novel fur-clip technique for individual marking of the European badger (Meles meles)

The European badger ( Meles meles ) moults once a year. In our study site in lowland England, pelage replacement of the guard hairs and a protracted period of fur growth (follicular anagen) occur between May and early November, with a peak in July. The precise timing of the moult depends on the age and condition of the badger. Yearling badgers undergo moult significantly earlier than adults. Adult females that have lactated, moult significantly later than other classes of adult, delaying the moult until autumn which corresponds to an annual period of food abundance. Lactation was significantly associated with poor condition in these badgers. It was not possible to determine whether delayed moult was due to poor condition per se , or due to some other physiological consequence of lactation, e.g. hormonal changes. We hypothesize that delay of moult in laclating/poor condition individuals has the adaptive consequence of delaying the metabolic costs of pelage replacement from a time of energy deficit until a time of relative plenty.
These findings are of practical importance to a novel solution to the problem of individually marking badgers during observational studies. The technique involves clipping the dark band near the tips of the badger's guard hairs to reveal the white under-fur and produce patterning of the coat. The highly contrasting marks were well suited to visual identification during observations under low light and infra-red illumination, and they allowed a large number of individuals (over 80 in our study) to be distinctively marked. The mark persists until the badger undergoes its single annual moult, or until three months of the active phase of fur growth have passed. Clip marks on adults made in late August had the greatest longevity, with 80% still visible after nine months. Though clipping had no significant effect on body condition in our study site, it should be cautiously applied with individuals in poor condition or in cold climates.     

Prepubertal goat oocytes from large follicles result in similar blastocyst production and embryo ploidy than those from adult goats

Developmental competence of oocytes from prepubertal females is lower than those from adult females. Oocyte development competence is positively related to follicular diameter. Most of the follicles of prepubertal goat ovaries are smaller than 3 mm. The aim of this study was to compare oocytes of two follicle sizes (< 3 mm and ≥ 3 mm) from prepubertal goats with oocytes from adult goats in relation to their in vitro production and quality of blastocysts. Oocytes from prepubertal goats were obtained from slaughterhouse ovaries and selected according to the follicle diameter whereas oocytes from adult goats were recovered in vivo by LOPU technique without prior selection of follicle size. COCs were IVM for 27 h, IVF at the conventional conditions with fresh semen and presumptive zygotes were cultured in SOF medium for 8 days. Blastocysts obtained were vitrified and after warming their blastocoele re-expansion and the ploidy by FISH technique were assessed. We found significant differences between blastocysts yield of oocytes recovered from follicles smaller than 3 mm of prepubertal goats compared to those from adult goats (5.45% vs 20. 83%, respectively) however, these differences disappear if oocytes were recovered form large follicles (18.07%). A total of 28 blastocysts were analysed and 96.43% showed mixoploidy. Age did not affect the number of embryos with abnormal ploidy or blastocyst re-expansion after warming. Furthermore, the percentage of diploid blastomeres per embryo was similar in the 3 groups studied, adult, prepubertal from follicles ≥ 3 mm and < 3 mm (68.6%, 80.8% and 73.6%, respectively). In conclusion, IVP of blastocysts coming from follicles larger than 3 mm of goats 45 days old were not different to the blastocysts produced from adult goats, both in terms of quantity and quality.     

THE POPULATION DYNAMICS OF NORTHERN SEA LIONS, 1975-1985

Abstract: Populations of northern sea lions ( Eumetopias jubatus ) in the vicinity of Marmot Island, Alaska declined during 1975–1985 at about 5% per year (Merrick et al. 1987). The cause of this decline is not known. A life table for the northern sea lion was calculated assuming that life spans follow a Weibull distribution. Samples of northern sea lions taken in the vicinity of Marmot Island, Alaska during 1975–1978 and 1985–1986 indicate that the average age of females older than 3 yr increased about 1.55 yr (SD = 0.35 yr) while the population was declining at about 5% per year. Fecundity rates decreased by 10% over the same period, but the decrease was not statistically significant (Calkins and Goodwin 1988). Possible causes of the population decline and the change in age structure were examined by writing the Leslie matrix population equation in terms of changes in juvenile and adult survival rates and fecundity, and examining the short–term behavior of the trajectories of the average age of adult females, total number of females, and total number of pups with respect to those changes in the vital parameters. From the observed rate of declines of adults and the changes in average age of adult females and fecundity, estimates of the changes in adult and juvenile survival were calculated; estimates of the standard deviations of these changes were estimated via a bootstrap procedure. One purpose of this exercise is to aid in setting priorities for research for determining the cause of the decline. An explanation for the observed declines in numbers of adult sea lions consistent with the observed fecundity rates, a rate of decrease of 5% in the number of adults, and the corresponding increase in average age (of females age 3 yr and older) was a 10%–20% decrease in the survival of juveniles (age 0-3 yr) coupled with an insignificant change in adult survival (0.03%, SD = 1%).     

Body weight as an indication of density-dependent population regulation in badgers (Meles meles) at Woodchester Park, Gloucestershire

The body weights of badgers were examined to look for density-dependent effects of the increase in group size at Woodchester Park, Gloucestershire. The weight of badgers in 21 groups were studied from 1978–1993. A significant negative relationship was found between weight and group size in breeding adult females in autumn and winter, and adult males in summer, such that increase in group size caused a decrease in weight. However, these relationships were affected by year-to-year changes and random variation, and overall there was no downward trend in body weight. The existence of density-dependent effects on badger populations at high density was consistent with previous findings     

Reproductive variables of Urotrygon rogersi (Batoidea: Urotrygonidae): a species with a triannual reproductive cycle in the eastern tropical Pacific Ocean

Reproductive aspects of the round ray Urotrygon rogersi were studied based on 2005 specimens obtained in the artisanal shrimp fishery operating on the Colombian Pacific coast. Females reached greater maximum total length (L(T) ), disc width (W(D) ) and mass (M) (38·0 cm, 19·9 cm and 348 g) than males (32·5 cm, 17·0 cm and 165 g). Sex ratio of juveniles and adults was 1:1. Clasper length increased rapidly between 10·0 and 12·5 cm W(D) . The smallest mature male measured 10·5 cm W(D) and the largest immature individual 13·7 cm W(D) . Male first maturity was reached at 61·8% of maximum W(D) , and estimated W(D50) was between 11·5 and 11·8 cm. The smallest mature female measured 10·5 cm W(D) ; the size at first maturity was 52·8% of maximum W(D) , and estimated W(D50) was between 11·8 and 12·3 cm. Embryos were found in females ≥ 10·5 cm W(D) and maximum fecundity was three embryos per female (mode = 1) and varied with maternal size. Embryos were found in all months, but three birthing peaks per year were identified and a gestation period of 4-5 months estimated. Based on ovulation time, embryonic growth and parturition dates, a triannual reproductive cycle was inferred for this species, with overlapping ovarian and uterine cycles. These results suggest that U. rogersi has a reproductive strategy based on low fecundity, a rapid reproductive cycle (short ovulation and gestation time), three birth peaks per year and large embryos. This strategy probably allows U. rogersi to withstand the fishing pressure they are subject to on the Colombian Pacific coast. The results also suggest that the study area is an important nursery and reproductive area for this species.     

Reproductive performance of the wild collared peccary (Tayassu tajacu) female in the Peruvian Amazon

Based on the gross anatomic examination of 218 adult female reproductive tracts, we characterised the reproductive biology of the wild collared peccary in the Northeastern Peruvian Amazon. Collared peccary apparently breed year round in the Northeastern Peruvian Amazon and the number of pregnant females was 92 (42.2%). Estimations suggest 1.12 births/year and a yearly reproductive production of 1.98 piglets per pregnant female. Collared peccary females presented a mean ovulation rate of 2.25 ± 0.58 CLs, a litter size of 1.77 ± 0.48 embryos or foetuses and a reproductive wastage of 0.45 ± 0.65 (21.3%) oocytes or embryos per pregnant female. A phenomenon of embryo migration was observed in 31.8% of pregnant females. This study provides reproductive information that should be taken into account in management plans.     

Sexual dimorphism in interferon-tau production by in vivo-derived bovine embryos

Interferon-tau (IFN-tau) is an anti-luteolytic factor responsible for preventing regression of the maternal corpus luteum (CL) during early pregnancy of cattle. In vitro-produced (IVP) bovine embryos first produce IFN-tau as blastocysts. In the present study, we have examined whether sexually dimorphic production of IFN-tau, which is observed among IVP blastocysts, also occurs among in vivo-produced blastocysts, and whether this difference between the sexes persists to day 14 when silencing of one of the X-chromosomes in the trophectoderm is complete. Embryos were flushed from cattle that had been superovulated and bred by AI. Blastocysts (63 male, 62 female) recovered between days 8.5 and 9.5 of pregnancy, were cultured individually. No differences were observed between males and females in either their developmental stage or quality at the beginning, during, and at the end of culture. Female embryos produced more IFN-tau than males by 24 hr (mean values, males: 16.6 +/- 3.7, females: 49.4 +/- 9.0 pg per embryo; P < 0.05) and 48 hr (male: 189.8 +/- 37.1, female: 410.9 +/- 66.6 pg per embryo; P < 0.05). However, the variability in IFN-tau production between individual blastocysts was so great that IFN-tau secretion is unlikely to be of value as a non-invasive means to predict embryo sex. When conceptuses were recovered at day 14, elongating males (n = 25) and females (n = 24) were similar in dimension and did not differ in their IFN-tau production after 4.5 hr (male: 2,550 +/- 607, female: 2,376 +/- 772 ng per conceptus) and 24 hr (male: 12,056 +/- 2,438, female: 8,447 +/- 1,630 ng per conceptus) of culture. Thus, sexual dimorphism in IFN-tau production is observed in both IVP and in vivo-produced expanded blastocysts, but is lost by day 14 of in vivo development.     

Movement of badgers (Meles meles) in a high-density population: individual,population and disease effects.

The movement of 1763 badgers trapped between 36 social groups in Woodchester Park, Gloucestershire, over 18 years was analysed to determine the frequency and duration of moves, the factors associated with a predisposition to move and the spatial pattern of movements. Of those badgers whose capture history could be categorized, nearly half had moved. Of these, 73.1% were classified as ''occasional movers'', 22.1% as ''permanent movers'' and 4.8% as ''frequent movers''. Most adult badgers that moved made occasional moves (78.8%, n = 67). Cubs made all types of move including permanent moves (29%, n = 10). Seventy per cent of females were non-movers compared with 37% of males. Badgers were significantly more likely to move to smaller groups, whereas male badgers were significantly more likely to move to groups with a greater proportion of females. The spatial pattern of movement differed from the distribution of groups with bovine tuberculosis in the study area. However, temporal changes in movement were significantly related to the incidence of Mycobacterium bovis infection in the following year, indicating that as the movement of badgers between groups varies so does the incidence of bovine tuberculosis in the population. This finding is of central importance in the formulation of badger control policy.     

Reproductive Biology Including Evidence for Superfetation in the European Badger Meles meles (Carnivora: Mustelidae)

The reproductive biology of the European badger (Meles meles) is of wide interest because it is one of the few mammal species that show delayed implantation and one of only five which are suggested to show superfetation as a reproductive strategy. This study aimed to describe the reproductive biology of female Irish badgers with a view to increasing our understanding of the process of delayed implantation and superfetation. We carried out a detailed histological examination of the reproductive tract of 264 female badgers taken from sites across 20 of the 26 counties in the Republic of Ireland. The key results show evidence of multiple blastocysts at different stages of development present simultaneously in the same female, supporting the view that superfetation is relatively common in this population of badgers. In addition we present strong evidence that the breeding rate in Irish badgers is limited by failure to conceive, rather than failure at any other stages of the breeding cycle. We show few effects of age on breeding success, suggesting no breeding suppression by adult females in this population. The study sheds new light on this unusual breeding strategy of delayed implantation and superfetation, and highlights a number of significant differences between the reproductive biology of female Irish badgers and those of Great Britain and Swedish populations.