Reproductive Ecology and Cub Survival of Florida Black Bears

Abstract: We investigated reproductive ecology and cub survival of Florida black bears (Ursus americanus floridanus) in Ocala National Forest and the adjacent residential area of Lynne, Florida, USA, 1999-2003. We documented production of 81 cubs from 39 litters. Average litter size was 2.08 ± 0.11 (SE) cubs. The mean age of first reproduction was 3.25 ± 0.27 years. Excluding females that reproduced in consecutive years due to litter loss, interlitter interval was 2.11 ± 0.11 years. The mean annual fecundity rate was 0.57 ± 0.06. We used expandable radiocollars to monitor the fate of 41 bear cubs. The probability of cubs surviving to 9 months of age was 0.46 ± 0.09 and did not differ between cohorts or study locations. The most important causes of cub mortality included infanticide and mortality caused directly or indirectly by collisions with vehicles. Our results indicate that reproductive rates of female black bears in the Ocala study area are comparable to those reported for other black bear populations from eastern United States, but cub survival rates are lower than those reported for most black bear populations. Management of Florida black bears should emphasize strategies to reduce the mortality of cubs.     

Behavioural Differences between Single Scandinavian Brown Bears (Ursus arctos) and Females with Dependent Young When Experimentally Approached by Humans

Carnivore-human encounters that result in human injury present a conservation and management challenge and it is therefore important to understand under what conditions such incidents occur. Females with cubs are often involved when humans are injured by brown bears Ursus arctos. In Scandinavia, this is particularly true for unarmed recreational forest users. Our aim was to document behavioural differences between single bears and females with cubs in order to develop recommendations to minimize the risk of injuries to recreational forest users. We documented the reactions of GPS-collared females with cubs and single brown bears to experimental approaches by humans to 50 m from the bear on 42 and 108 occasions, respectively. The majority of females with cubs (95%) and single bears (89%) left when approached. Bears that left were passed at shorter distances and were in more open areas than those that stayed. Both groups had similar flight initiation distances, which were longer for bears that were active at the time of the disturbance. Females with cubs selected more open habitat than single bears, also for the new site they selected following disturbance. Females with cubs, particularly active females with cubs of the year, moved greater distances and spent more time active following the approach. Females with cubs and single bears were seen or heard in 26% and 14% of the approaches, respectively. None of the bears displayed any aggressive behaviour during the approaches. Females with cubs selected more open habitat, perhaps predisposing them to encountering people that are not involved in hunting activities, which might be the primary explanation why females with cubs are most frequently involved when unarmed people are injured by bears in Scandinavia. To mitigate injury risks, one must consider factors that bring bears closer to human activity in the first place.     

Reconstructing the reproductive history of female polar bears using cementum patterns of premolar teeth

Premolar teeth collected from 220 adult female polar bears (Ursus maritimus) from western Hudson Bay, Canada, were examined to determine whether past reproductive events are recorded in cementum. The widths of annular cementum growth layer groups (GLGs) were measured and compared as proportional width index (PWI) values to correct for age and body size bias. Known reproductive states (pregnant, with cubs, or with yearlings) were used to confirm and calibrate cementum annuli. Significant differences in PWI were observed between GLGs formed the year females were pregnant versus when accompanied by cubs or yearlings. The probability of a female having produced a cub in adulthood was determined by fitting a logistic regression model between the ΔPWI of females when pregnant and with their cubs. Logistic regression of ΔPWI (β₀ = −0.229, β₁ = −13.465, G ² = 46.55, df = 1, P < 0.001) correctly classified the presence or absence of cubs in 72% of GLGs. Cementum width did not vary between different litter sizes. Observations of females with early litter loss suggests that longer periods of lactation contributes to decreased cementum width and therefore cementum may record a minimum age of litter survival. Predictions of litter production rate (0.43 litters/female/year) derived from cementum were similar to field observations; however, age at first parturition was underestimated by 1 year. We conclude that patterns of cementum deposition may be useful to determine individual reproductive histories and establish course estimates of reproductive parameters when regular field observations are not feasible. We also conclude that reproductive parameters derived from cementum are not adequate on their own for monitoring populations which are in decline or under stress and field observation should not be replaced under these conditions.     

Reproductive parameters of the common genet <Emphasis Type="Italic">Genetta genetta</Emphasis> (Linnaeus, 1758) in Southwest Europe

We used information from 148 litters belonging to 119 different wild and captive female common genets (Genetta genetta) in SW Europe over a period of almost 50 years to study certain reproductive parameters. Data were obtained from a combination of sources including carcasses, live captures, telemetry-based studies, captive genets, and reports in the literature. The circannual pattern of breeding was fairly similar in both wild and captive genets, with births occurring in all months except December, albeit with a large peak in spring and a secondary peak in autumn. The sex ratio at birth was near to 1:1, and mean litter size was 2.16 ± 0.76 cubs/litter with a range of 1–5 cubs. Litters of two cubs were the most frequent both in wild and captive settings. In captivity, we have observed the births of replacement litters and double litters; however, we did not find evidence of wild females that having two litters in the same year. We conclude that the possibility of breeding at any time of the year is facilitated by the continuous spermatogenesis of the males and by the ability of females to enter into estrus after losing a litter prematurely and to breed twice in the same year.     

Space Use,Survival, Movements,and Reproduction of Reintroduced Louisiana Black Bears

ABSTRACT Studies of reintroduced animals are beneficial to evaluate the success of reintroduction programs and to understand factors influencing fitness of reintroduced individuals. The geographic distribution of the federally threatened Louisiana black bear (Ursus americanus luteolus) has been reduced to 3 isolated populations due to habitat loss and excessive harvest. We reintroduced 23 adult female Louisiana black bears and their cubs to east-central Louisiana, USA, and documented postrelease space use, survival, movements, and reproduction. Individual females used larger home ranges after reintroduction than they had in the source population (P = 0.037). Spring ranges of reintroduced females were smaller than summer, autumn, and annual ranges (all P < 0.09), which did not differ from each other (all P > 0.60). Survival of reintroduced females did not differ between their first (S = 0.933) and second (S = 1.00) year after release or from annual survival of females in the source population (S = 0.964–1.00). Mean straight-line distance traveled by females from their release sites to the center of established home ranges or last recorded locations was 22.7 km. Six females reproduced after reintroduction and produced 15 cubs. Mean postrelease litter size of parturient reintroduced females (2.5) was similar to reported mean litter size of females in the source population (2.4). Our results suggest that the Louisiana reintroduction program is proceeding favorably; however, future studies should continue to monitor survival and reproduction of reintroduced females in Louisiana. Additional demographic parameters (i.e., cub survival) should be estimated to allow for population viability analysis to determine if the new population is self-sustaining.     

Litter loss triggers estrus in a nonsocial seasonal breeder

Sexually selected infanticide (SSI) is often presumed to be rare among seasonal breeders, because it would require a near immediate return to estrus after the loss of an entire litter during the mating season. We evaluated changes in reproductive strategies and the reproductive fate of females that experienced litter loss during the mating season in a seasonal breeder with strong evidence for SSI, the brown bear. First, we used a long‐term demographic dataset (1986–2011) to document that a large majority of females (>91%) that lose their entire litter during the mating season in fact do enter estrus, mate, and give birth during the subsequent birthing season. Second, we used high‐resolution movement data (2005–2011) to evaluate how females changed reproductive strategies after losing their entire litter during the mating season. We hypothesized that females would shift from the sedentary lifestyle typical for females with cubs‐of‐the‐year to a roam‐to‐mate behavior typical for receptive females in no more than a few (~3) days after litter loss. We found that females with cubs‐of‐the‐year moved at about 1/3 of the rate and in a less bimodal diurnal pattern than receptive females during the mating season. The probability of litter loss was positively related with movement rate, suggesting that being elusive and sedentary is a strategy to enhance cub survival rather than a relic of cub mobility itself. The movement patterns of receptive females and females after litter loss were indistinguishable within 1–2 days after the litter loss, and we illustrate that SSI can significantly reduce the female interbirth interval (50–85%). Our results suggest that SSI can also be advantageous for males in seasonally breeding mammals. We propose that infanticide as a male reproductive strategy is more prevalent among mammals with reproductive seasonality than observed or reported.     

Detection of pregnancy in a hibernator based on activity data

Pregnancy and parturition are often difficult to detect in wild-living animals, especially in species that give birth to altricial young in burrows or caves. Current methods to detect pregnancy and birth in hibernating animals often entail disturbances that can affect the animals' reproductive success. We developed a new method to confirm pregnancy and parturition in hibernating brown bears (Ursus arctos) using activity data recorded in dual-axis motion sensors mounted on GPS–GSM neck collars on 30 brown bears during 52 hibernation seasons in Sweden. We adjusted recorded activity to the individual basal activity level for each bear. Pregnant females showed characteristic activity patterns during the period of pregnancy, with significantly higher daily activity levels and frequency of active periods during pregnancy than nonpregnant bears. Pregnant females were active on average 2.20 times more often during the pregnancy period than during the postpartum period, compared with 0.97 times for nonpregnant females. A pregnancy index was defined as the average of the proportion of mean daily activity levels and the proportion of activity events during the pregnancy period compared with the postpartum period. It averaged 2.61?±?1.73 (SD) for pregnant females and 0.94?±?0.24 for nonpregnant females. Using this method, we evaluated a group of adult females that had an unverified reproductive status but were classified as not pregnant because no cubs had been observed after den emergence. The results suggested that 35 % of those females had, in fact, been pregnant.     

Factors Affecting Date of Implantation,Parturition, and Den Entry Estimated from Activity and Body Temperature in Free-Ranging Brown Bears

Knowledge of factors influencing the timing of reproduction is important for animal conservation and management. Brown bears (Ursus arctos) are able to vary the birth date of their cubs in response to their fat stores, but little information is available about the timing of implantation and parturition in free-ranging brown bears. Body temperature and activity of pregnant brown bears is higher during the gestation period than during the rest of hibernation and drops at parturition. We compared mean daily body temperature and activity levels of pregnant and nonpregnant females during preimplantation, gestation, and lactation. Additionally we tested whether age, litter size, primiparity, environmental conditions, and the start of hibernation influence the timing of parturition. The mean date of implantation was 1 December (SD = 12), the mean date of parturition was 26 January (SD = 12), and the mean duration of the gestation period was 56 days (SD = 2). The body temperature of pregnant females was higher during the gestation and lactation periods than that of nonpregnant bears. The body temperature of pregnant females decreased during the gestation period. Activity recordings were also used to determine the date of parturition. The parturition dates calculated with activity and body temperature data did not differ significantly and were the same in 50% of the females. Older females started hibernation earlier. The start of hibernation was earlier during years with favorable environmental conditions. Dates of parturition were later during years with good environmental conditions which was unexpected. We suggest that free-ranging pregnant brown bears in areas with high levels of human activities at the beginning of the denning period, as in our study area, might prioritize investing energy in early denning than in early parturition during years with favorable environmental conditions, as a strategy to prevent disturbances caused by human.     

Grizzly bear population vital rates and trend in the Northern Continental Divide Ecosystem,Montana

We estimated grizzly bear (Ursus arctos) population vital rates and trend for the Northern Continental Divide Ecosystem (NCDE), Montana, between 2004 and 2009 by following radio-collared females and observing their fate and reproductive performance. Our estimates of dependent cub and yearling survival were 0.612 (95% CI = 0.300–0.818) and 0.682 (95% CI = 0.258–0.898). Our estimates of subadult and adult female survival were 0.852 (95% CI = 0.628–0.951) and 0.952 (95% CI = 0.892–0.980). From visual observations, we estimated a mean litter size of 2.00 cubs/litter. Accounting for cub mortality prior to the first observations of litters in spring, our adjusted mean litter size was 2.27 cubs/litter. We estimated the probabilities of females transitioning from one reproductive state to another between years. Using the stable state probability of 0.322 (95% CI = 0.262–0.382) for females with cub litters, our adjusted fecundity estimate (m_x) was 0.367 (95% CI = 0.273–0.461). Using our derived rates, we estimated that the population grew at a mean annual rate of approximately 3% (λ = 1.0306, 95% CI = 0.928–1.102), and 71.5% of 10,000 Monte Carlo simulations produced estimates of λ > 1.0. Our results indicate an increasing population trend of grizzly bears in the NCDE. Coupled with concurrent studies of population size, we estimate that over 1,000 grizzly bears reside in and adjacent to this recovery area. We suggest that monitoring of population trend and other vital rates using radioed females be continued. © 2011 The Wildlife Society.     

Birth Timing for Mountain Lions (Puma concolor); Testing the Prey Availability Hypothesis

We investigated potential advantages in birth timing for mountain lion (Puma concolor) cubs. We examined cub body mass, survival, and age of natal dispersal in relation to specific timing of birth. We also investigated the role of maternal age relative to timing of births. We captured mountain lion cubs while in the natal den to determine birth date, which allowed for precise estimates of the population birth pulse and age of natal dispersal. A birth pulse occurred during June–August. Body mass of cubs was related to litter size and timing of birth; heaviest cubs occurred in litters of 2, and those born after 1 July. Cubs born within pulse months exhibited similar survival to those born out of the pulse. We found that cubs born April–June dispersed at younger ages than those born after 1 July. There was less variation in birth timing for 1^st litters of females than older females. We hypothesize that cubs born after the peak in births of neonate prey are advantaged by the abundance of vulnerable prey and those cubs and mothers realize an evolutionary advantage.     

GRIZZLY BEAR DEMOGRAPHICS IN AND AROUND BANFF NATIONAL PARK AND KANANASKIS COUNTRY,ALBERTA

Abstract: The area in and around Banff National Park (BNP) in southwestern Alberta, Canada, is 1 of the most heavily used and developed areas where grizzly bears (Ursus arctos) still exist. During 1994–2002, we radiomarked and monitored 37 female and 34 male bears in this area to estimate rates of survival, reproduction, and population growth. Annual survival rates of bears other than dependent young averaged 95% for females and 81–85% for males. Although this area was largely unhunted, humans caused 75% of female mortality and 86% of male mortality. Females produced their first surviving litter at 6–12 years of age (x̄ = 8.4 years). Litters averaged 1.84 cubs spaced at 4.4-year intervals. Adult (≥6-years-old) females produced 0.24 female cubs per year and were expected to produce an average of 1.7 female cubs in their lifetime, based on rates of reproduction and survival. Cub survival was 79%, yearling survival was 91%, and survival through independence at 2.5–5.5 years of age was 72%, as no dependent young older than yearlings died. Although this is the slowest-reproducing grizzly bear population yet studied, high rates of survival seem to have enabled positive population growth (Λ = 1.04, 95% CI = 0.99–1.09), based on analyses using Leslie matrices. Current management practices, instituted in the late 1980s, focus on alleviating human-caused bear mortality. If the 1970–1980s style of management had continued, we estimated that an average of 1 more radiomarked female would have been killed each year, reducing female survival to the point that the population would have declined.     

Polar bear (Ursus maritimus) cub mortality at a den site in northern Alaska

In March 2009, we documented the death of one member of a triplet polar bear (Ursus maritimus) litter at its den site in the southern Beaufort Sea (SBS) of Alaska. We used a self-contained video camera unit to document activity between den emergence and departure. All three cubs showed low activity levels relative to other cubs observed, and one died within one week of den emergence. Necropsy confirmed that the dead cub had a low body weight and was malnourished. Capture later confirmed that the two surviving cubs were also undersized. Polar bear cub survival is influenced by many factors including litter size and sea ice conditions. Triplet litters are often smaller and suffer higher mortality rates than singletons and twins. This cub was not only a triplet but also born following 2 years of record minimum sea ice extent, both of which may have played a role in this cub’s demise.     

Reproductive Ecology of American Black Bears in the Alleghany Mountains of Virginia,USA

We studied reproduction of American black bears (Ursus americanus) in western Virginia from 1994 to 2003. We handled 326 ≥2-year-old female black bears 672 times during summer trapping and followed 176 of these individuals through 424 winter den seasons. We examined 183 litters consisting of 455 cubs. Primiparity occurred at mean and modal ages of 3.8 and 3 years, respectively. Composite mean litter size was 2.49 (SE = 0.06) cubs/litter; 3- and 4-year-olds had smaller litters than older bears. We tracked reproductive synchrony using 5 indices and documented a resetting of this synchrony, likely in response to hard-mast failure. The amplitude of oscillations in synchrony indices dampened through time after the synchronizing events. Documentation and quantification of relationships between nutrient availability, reproduction and population dynamics can be used to inform population modeling efforts and more accurately forecast harvest. © 2011 The Wildlife Society.     

Reproductive life history of South African cheetahs (Acynonyx jubatus jubatus) at the San Diego Zoo Wild Animal Park, 1970–2005

We analyzed 35 years of data from a captive breeding program of cheetahs to determine basic reproductive life history characteristics of females. Breeding females ranged in age from 2.7–10.5 years. Sixteen females and over 13 males produced 129 cubs in 36 litters, with an average litter size of 3.6. Older females produced significantly fewer cubs per litter than younger females, but cub survivorship was comparable across female ages. Sex ratio was balanced at birth and 71% of infants survived the weaning period. Given that the reproductive output of captive cheetahs in our study is similar to that in other zoologic institutions and to cheetahs in the wild, we suggest that reproductive deficits in captive cheetahs arise from the inability of some pairs to breed, due to a lack of mating preference, rather than from a species‐wide problem. Zoo Biol 0:1–8, 2006. © 2006 Wiley‐Liss, Inc.     

Split parturition observed in a captive North American brown bear (Ursus arctos)

Reproductive physiology in North American ursids is characterized by mating from spring to early summer, delayed implantation, and birth during hibernation. During spring 2008, a captive adult female brown bear was mated with two adult males. Pregnancy was determined by elevated progesterone concentrations during late fall before hibernation. Two male cubs were born on December 31, 2008, and a third female cub was born 17 days later on January 16. All were successfully raised and all were confirmed to have identical paternity. When normalized to age, cub growth rates did not differ. To our knowledge, this is the first documented case of markedly different birth dates in a single litter of brown bear cubs.     

Influence of Female Copulation Calls on Male Sexual Behavior in Captive Macaca fascicularis

We investigated the function of copulation calls—vocalizations by females during mating—in captive groups of long-tailed macaques. We tested predictions of the contest-competition, sperm competition, synchronized orgasms, mate again, alpha-male notification and graded-signal hypotheses. We observed 371 copulations of 36 females wherein the presence or absence of a copulation call was clear. Females call equally often with different males and shortly after ejaculation. Copulation calls occurred equally with copulations with and without ejaculation. Calls did not incite disruptions of the mating. Following calls females mated again, more often than expected, with their mating partner. Both pregnant and fertile females uttered copulation calls. Two females conceived and mated mainly with the alpha male then. We conclude that copulation calls do not incite male contest competition for sexual access to females and that it is unlikely that calls synchronize male and female orgasms. Several hypotheses remain plausible, but not all predictions are borne out unequivocably. This alerts us to the possibility that the calls could have multiple beneficial effects; natural selection might strike a compromise among functions. Investigation of the mate again, sperm competition and alpha-male notification hypotheses, and of hypotheses not tested in our study concerning female breeding overlap and female-female agonism, is required.     

Age-specific reproductive performance of female polar bears (Ursus maritimus)

Age-specific patterns of maternal weight, litter size, litter weight and reproductive effort were investigated for polar bears ( Ursus maritimus ) from western Hudson Bay. Most relationships were described by quadratic equations. Maternal weight in spring and autumn increased until 17 and 15 years of age, respectively, and then declined. Age-related increases in maternal weight were thought to be associated with improving hunting skills. The relationships between age and litter size, litter weight and reproductive effort, in both the spring and autumn, increased until 14 to 16 years, followed by a decline. We speculate that age-related decreases in reproductive performance are due to undetennined processes associated with ageing that impair the accumulation of fat stores necessary for reproduction. Pregnant females lost an average of 127 kg overwinter which represented an average of 43.5% of their autumn weight. Fat stores remaining after the overwinter fast may be critical for maintaining an energy supply to cubs once they return to the sea ice where the distribution and abundance of their prey is unpredictable. We suggest that maternal condition is an important factor contributing to lifetime reproductive success in polar bears.     

贵州地区黑线姬鼠种群繁殖特征

黑线姬鼠(Apodemus agrarius)是贵州地区分布广泛的主要农田害鼠之一,掌握其种群繁殖特征可为种群动态的预测预报提供基础资料。1984~2014年间,采用夹夜法逐月调查了贵州省余庆县8个县(市)监测点黑线姬鼠种群动态数据,分析了其种群性比、雌鼠怀孕率和平均胎仔数、雄鼠睾丸下降率等主要繁殖生物学指标及其地理差异和季节性变动规律,明确了贵州地区黑线姬鼠种群的繁殖特征。共捕获黑线姬鼠20 113只,不同地区种群间,除平均胎仔数有显著差异外(χ~2=36.503,df=7,P0.01),其他繁殖特征值均没有差异。从时间序列看,种群中雌鼠怀孕率和雄鼠睾丸下降率的季节性变化均表现为春季(4~5月)及夏末秋初(8~9月)达到高峰的双峰型。雌鼠产仔数一般2~10只,4~7只最为常见(占93.87%)。不同季节平均胎仔数差异不大。贵州地区黑线姬鼠繁殖的总体特点为全年繁殖,春秋两季为繁殖的高峰期,冬季(12月份和翌年1、2月份)繁殖强度明显低于其他季节(F_(11,84)=61.92,P0.01),但种群密度表现为6月达到最高点的单峰型特点。     

The Impact of Roads on the Demography of Grizzly Bears in Alberta

One of the principal factors that have reduced grizzly bear populations has been the creation of human access into grizzly bear habitat by roads built for resource extraction. Past studies have documented mortality and distributional changes of bears relative to roads but none have attempted to estimate the direct demographic impact of roads in terms of both survival rates, reproductive rates, and the interaction of reproductive state of female bears with survival rate. We applied a combination of survival and reproductive models to estimate demographic parameters for threatened grizzly bear populations in Alberta. Instead of attempting to estimate mean trend we explored factors which caused biological and spatial variation in population trend. We found that sex and age class survival was related to road density with subadult bears being most vulnerable to road-based mortality. A multi-state reproduction model found that females accompanied by cubs of the year and/or yearling cubs had lower survival rates compared to females with two year olds or no cubs. A demographic model found strong spatial gradients in population trend based upon road density. Threshold road densities needed to ensure population stability were estimated to further refine targets for population recovery of grizzly bears in Alberta. Models that considered lowered survival of females with dependant offspring resulted in lower road density thresholds to ensure stable bear populations. Our results demonstrate likely spatial variation in population trend and provide an example how demographic analysis can be used to refine and direct conservation measures for threatened species.     

Short-term behavioural response of polar bears (<Emphasis Type="Italic">Ursus maritimus</Emphasis>) to snowmobile disturbance

In this study the distance, at which polar bears detected and actively responded to approaching snowmobiles was measured and the behavioural response was recorded. The study was performed on Svalbard, an arctic island where human traffic has increased substantially in recent years. Fieldwork was conduced in April and/or May during the years 2003–2005. Polar bears were observed on ice with telescopes and binoculars. Undisturbed polar bears were observed continuously and their behaviours recorded, during the time when two snowmobiles moved toward the bear(s). Distances between the bear, the observer, and the approaching snowmobiles were measured using GPS positions taken on the track towards the bear. Data on the behavioural response of 20 encounters with bears were collected. On average, bears were alerted to the snowmobiles at 1,164 m. Mean distance at which the locomotive response occurred was 843 m, and there was a statistical significant difference in distance between sex and age classes [326 m (95% CI = 138–496 m) for adult males; 1,534 m (95% CI = 508–2,768 m) for adult females with cubs; 164 m (95% CI = 49–543 m) for two adult females without cubs; and 1,160 m (95% CI = 375–1,353 m) for single medium sized bears]. The responses of the polar bears to the snowmobiles were categorized according to intensity and persistence of reactions. Females with cubs and single medium sized bears tended to show more intense responses than adult males and lone adult females. Wind direction affects sound and odour transmission, and although an effect on response distance was not found, the response intensity was affected by wind direction. We conclude that female polar bears with small cubs in particular may have a greater risk to be disturbed, since they react at greater distances with amplified reactions; thus, users of snowmobiles should take particular care in areas where females with cubs are present.