THE LIFE HISTORY OF FREE-RANGING ATLANTIC SPOTTED DOLPHINS (STENELLA FRONTALIS): AGE CLASSES, COLOR PHASES, AND FEMALE REPRODUCTION

Atlantic spotted dolphins (Stenella frontalis) were observed underwater and from the surface from 1985 to 1996 and photographed through successive years. Individuals were categorized into age classes by their degree of spotting and color phases. Dolphins spent an average of 3 yr in the two-tone color phase, 5 yr in the speckled phase, 7 yr in the mottled phase and up to 10 yr or more in the fused phase.
Sex ratios were close to parity, with old adults skewed towards females and juveniles and young adults skewed towards males. The average calving interval for 24 females was 2.96 years with a range of 1–5 yr. Females whose calves survived the first year had a significantly longer calving interval (3.56 years). The ages of first parturition for five females were estimated to be 10–12 yr. The age at sexual maturation was estimated to range from 8 to 15 yr.
Pregnancy rate fluctuated annually, with an average rate of 0.25 (range 0.07–0.57). Annual average birth rate was 0.08 (range 0.07–0.14), average calf production was 0.33 (range 0.06–0.52), average fecundity was 0.23 (range 0.13–0.30), and average recruitment was 0.06 (range 0.03–0.08). Most females who lost a calf conceived the same or following year.
Lactation lasted up to 5 yr, and 45% of visibly pregnant females were also lactating. Age of first parturition was associated with the mottled color phase. Average first-year mortality rate of calves was 0.24.     

Elk survival and mortality causes in the Blue Mountains of Washington

We studied survival of elk (Cervus elaphus) ≥1 yr old and quantified mortality sources in the Blue Mountains of Washington, 2003–2006, following a period of extensive poaching. The population was managed under a spike-only general hunting season, with limited permits for larger males and for females. We radiomarked 190 elk (82 males and 39 females >1 yr old and 65 males 11 months old), most with rumen transmitters and neck radiocollars; 60 elk only received rumen transmitters. We estimated annual survival using known fate models and explored survival differences among sex and age classes and in 2 potentially different vulnerability zones for males. We found little support for differences in survival between younger (2–3-yr old) and older (≥4-yr old) branch-antlered males or zone differences for yearling males. A model with zone differences for branch-antlered males was the second ranked model and accounted for 14% of the available model weight. From the best-supported models, we estimated annual survival for yearling males at 0.41 (95% CI: 0.29–0.53). We estimated pooled adult female survival at 0.80 (95% CI: 0.64–0.93); when an age-class effect was included, point estimates were higher for prime-aged females (2–11 yr: S = 0.81 [0.70–0.88]) than for older females (≥12 yr: S = 0.72 [0.56–0.83]), but confidence intervals broadly overlapped. Only 1 of 7 models with a female age effect on survival was among the competitive models. For branch-antlered males, survival ranged 0.80–0.85, depending on whether zone variation was modeled. We recorded 78 deaths of radiomarked elk. Human-caused deaths (n = 55) predominated among causes and most were of yearling males killed during state-sanctioned hunts (n = 28). Most subadult male deaths were from tribal hunting (n = 5), and most mature males died from natural causes (n = 6) and tribal hunting (n = 5). We detected few illegal kills (n = 4). Our results suggest that increased enforcement effectively reduced poaching, that unreported tribal harvest was not a trivial source of mortality, and that spike-only general seasons were effective in recruiting branch-antlered males. © 2011 The Wildlife Society.     

AGE, GROWTH, AND REPRODUCTION IN NEW ZEALAND FUR SEALS

Growth and reproductive biology of New Zealand fur seals ( Arctocephalus forsteri ) were studied by examining 127 seals (57 females, 64 males) killed incidentally in fishing gear in New Zealand waters in 1996. Tooth sections were used to age the animals, and male and female reproductive organs were examined macroscopically and histologically. The maximum age observed was 22 yr for females and 12 yr for males. Males were significantly larger than females, but growth was similar up to 5 yr. Males reached sexual maturity between 5 and 9 yr of age, whereas females did so between 4 and 6 yr. The mean pregnancy rate in females was 0.69 (95% CI = 0.54–0.81).     

Influences of stress, age and sex on serum growth hormone and free fatty acid levels in cattle.

The serum growth hormone (BGH) and free fatty acid (FFA) concentrations of large groups of calves (male and female ranging in age from 8 to 14 days and from 3 to 6 months old), bulls, oxen, heifers and cows under normal conditions were compared with the serum BGH and FFA values of corresponding large groups of animals under stress conditions. Stress was caused by transport, as it routinely occurs, and was further reinforced by a stay of several hours in unfamiliar surroundings. Stress provokes a significant increase in serum FFA in all groups and induced a significant decrease in serum BGH in all groups, with the exception of the non-pregnant heifers. The male and female calves which were 8 to 14 days old, had significantly higher BGH levels than the older animals. The female calves from 3 to 6 months of age, and the heifers had significantly lower BGH levels than the cows. The males had higher serum BGH values than the females, but a significant difference could be demonstrated only between the male and female calves of both age-groups. The oxen, which were 1 to 3 years old, had significantly higher BGH levels than the non-pregnant heifers of the same age. It appeared that gestation had no influence on the serum BGH and FFA levels of both heifers and cows.     

Occurrence of neonatal and postnatal mortality in range beef cattle. I. Calf loss incidence from birth to weaning, backward and breech presentations and effects of calf loss on subsequent pregnancy rate of dams

Data from 13,296 calvings collected over a 15-yr period indicated 893 calves died from birth to weaning for an average loss of 6.7%. Calves lost from birth through Day 3 postcalving accounted for a 4.6% loss with an additional 2.1% loss from Day 4 through weaning. Calf deaths from primiparous 2- and 3-yr-old dams accounted for 41.0% of total mortality. Losses within groups were primiparous 2-yr-olds, 10.9%; primiparous 3-yr-olds, 8.7%; second-calf 3-yr-olds, 4.1%; second-calf 4-yr-olds, 8.3%; multiparous 4-yr-olds, 4.8%; and dams 5 yr and older, 5.3%. The majority of calf deaths (57.4%) occurred within the first 24 h postpartum with 75% of the total occurring Days 0 through 7. This loss was similar among all dam age and parity groups. Calf death due to dystocia accounted for the single largest loss category through the first 96 h postpartum, resulting in 69.6, 39.6, 30.8 and 33.3% of the loss incidence for Day 0, 1, 2 and 3 postpartum, respectively. More (P < 0.01) male calves (510, 57.6%) died than females (376, 42.4%). Backward presentations occurred more frequently (P < 0.01) than breech (1.6 vs 0.6% of all births, respectively). Incidence of backward presentation was 2.3%, 5.6% and 0.9% for primiparous 2-yr-old, 3-yr-old and multiparous dams, respectively (P < 0.01); 64.2% of the backward calves were males and 35.8% females (P < 0.01). Survival of calves in backward presentation exceeded (P < 0.01) that of breech calves (70.7 vs 32.9%). Fall pregnancy rate of dams that lost calves and reentered the breeding herd that same year was 72.4% compared to 79.4% (P < 0.01) for contemporary females that did not lose calves. The depression in pregnancy rate was not specifically due to dystocia but apparently to some general effect of calf loss.     

Age-dependent changes in sperm production, semen quality, and testicular volume in the black-footed ferret (Mustela nigripes)

The black-footed ferret (Mustela nigripes), which was extirpated from its native North American prairie habitat during the 1980s, is being reintroduced to the wild because of a successful captive-breeding program. To enhance propagation, the reproductive biology of this endangered species is being studied intensively. The typical life span of the black-footed ferret is approximately 7 yr. Female fecundity declines after 3 yr of age, but the influence of age on male reproduction is unknown. In this study, testis volume, seminal traits, sperm morphology, and serum testosterone were compared in 116 males from 1 to 7 yr of age living in captivity. Results demonstrated that testes volume during the peak breeding season was similar (P > 0.05) among males 1 to 5 yr of age, reduced (P < 0.05) among males 6 yr of age, and further reduced (P < 0.05) among males 7 yr of age. Motile sperm/ejaculate was similar in males 1 to 6 yr of age but diminished (P < 0.05) in those 7 yr of age. Males at 6 and 7 yr of age produced fewer (P < 0.05) structurally normal sperm than younger counterparts; however, serum testosterone concentrations were not reduced (P > 0.05) in older males. Histological comparison of testicular/epididymal tissue from 5- and 7-yr-old black-footed ferrets confirmed that the interval between these two ages may represent a transitional period to reproductive senescence. In summary, functional reproductive capacity of male black-footed ferrets exceeds that of females by at least 2 yr. Testes and seminal quality are indistinguishable among males 1 to 5 yr of age, with progressive reproductive aging occurring thereafter.     

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%).     

Gender performance in a cultivated cohort of the cycad Zamia integrifolia (Zamiaceae)

A progeny of the native Florida cycad Zamia integrifolia grown from seeds planted in 1986 was monitored until 1995 to record mortality and the nature and time of expression of primary and secondary sex characters. In addition to gender-specific cone morphologies, males and females differed in secondary sex characters such as age at first cone production, frequency of cone production, mean cone numbers in second and later coning episodes, and, in older plants, mean leaf and branch numbers. Gender differences expressed themselves at different stages in the life history: their nature and extent varied during the years following sexual maturation. By 1995, 46% of the plants in the progeny had died, most of them before producing cones. Prior to 1988 the mean leaf number of plants that died did not differ from that of survivors, but the mean leaf number of plants dying between 1988 and 1989 was 0.4 times that of the survivors during that period, suggesting reduced vigor prior to death. Mean age at first cone production was 5.8 yr for males and 6.6 yr for females. Mean dry masses of individual male cones increased between the first and second coning episodes, but not between the second and third coning episodes. Mean dry masses of the entire cone crop of individual males increased through the third coning episode due to an increase in mean cone number per episode, but mean cone number was unchanged between the third and fourth coning episodes. Mean dry mass of unpollinated female cones did not change between the first and second coning episodes; mean cone numbers did not change between the first and third coning episodes. After the first coning episode, males produced higher mean cone numbers than females. By 1995, the mean dry mass of an individual male's cone crop was greater than that of a female. Coning frequency of males was 1.7 times greater than that of unpollinated females, suggesting a gender difference in the genetic control of coning frequency. Coning frequency of females pollinated 1 or 2 yr previously was reduced compared with that of unpollinated females. Cone production did not affect subsequent leaf production by either gender. Mean leaf numbers increased in some years and not in others. Mean leaf numbers of males and females did not differ prior to cone production. After cone production mean leaf numbers of males were greater than of females. Mean age of males producing first branches was 6.3 yr, with a mean of 2.5 first branches per plant. Mean age of females producing first branches was 7.7 yr, with a mean of 2.5 first branches per plant. By 1995 the mean branch number of males was 5.7 per plant and of females was 2.7 per plant. Between 1993 and 1995 the mean branch number of males and females increased incrementally, but mean leaf numbers did not change. In early years of branching, leaf number increased with branch number; higher mean leaf numbers of males of an age class thus reflected their earlier branching. Males produced first cones earlier than females. Since branch production was associated with cone production, higher branch numbers of males in an age class reflected their earlier first cone production. In 1995 the sex ratio of known males and females in the progeny was 1:1, with a few individuals not having produced cones by that year.     

Marrow fat content, sex and age of red deer killed by wolves in winter in the Carpathian Mountains

Age, sex and legbone marrow fat content of 90 red deer Cervus elaphus killed by wolves Canis lupus in winter in southeastern Poland were examined 1984–1988. The majority of kills were calves (44%) and hinds (40%); stags formed only 16%. The average age of hinds was 7.2 yr compared to 5.3 yr in stags. Animals older than 10 yr comprised only 13% of prey. Adults showed high femoral fat content (> 80%) throughout the winter (76% in early winter and 52% in late winter). Among calves femur marrow fat varied through the winter. In early winter 70% of calves had a high fat content (> 80%), though by late winter only 20% had such a high fat content, whilst 43% had low fat content (< 20%).     

Lifetime Sex-Specific Moose Mortality During an Intentional Population Reduction

Where elevated harvest of ungulates is a priority, managers benefit by understanding how various sources of mortality affect the age and sex structure and trend of ungulate populations. Prior studies reported a long period (1997–2014) of moose (Alces alces gigas) nutritional stress from overabundance in our study area, an intentional 31% reduction in moose numbers using liberal harvests of females (2004–2012), and low bear (Ursus spp.) predation and high moose harvest densities relative to other largely roadless systems with moose, bears, and wolves (Canis lupus). In this paper, we detailed management findings after describing causes and rates of mortality from 226 female and 164 male moose radio-collared at 9 months of age (1997–2008) and followed through life (1997–2019) and throughout the population reduction. We listened for mortality signals on radio-collars 1–2 times/month when snow cover was complete and 2–4 times/month when snow cover was incomplete. Upon hearing a mortality signal, we investigated mortality sites usually within 24 hours via helicopter. Excluding hunter-caused mortality, we estimated 28% annual mortality for male yearlings versus 17% for female yearlings, then low annual mortality rates (0–4%) to 84 months of age for males and 96 months of age for females, and gradually increasing annual mortality rates thereafter. Most (83%) male moose ≥24 months of age died from hunters; minor causes included wolves (8%), malnutrition or disease (5%), grizzly bears (U. arctos; 2%), and accidents (2%). Most female moose ≥24 months of age died from wolves (37%) or hunters (33%); minor causes included malnutrition or disease (15%), grizzly bears (10%), and accidents (5%). The proportion of radio-collared females killed by hunters varied depending on numbers of permits issued to hunters; the kill rate of females ≥24 months of age was 58% during the initial 4 years of the 9-year reduction, moderated at 29% during the final 5 years of the reduction, and was only 7% for all other study years. We attributed 32% of hunter kills to illegal harvest and unrecovered hunter kills. Hunters played a key role in the intentional population reduction by harvesting prime-age and near prime-age male and female moose that rarely died from other sources of mortality compared with calf, yearling, and older moose. Restricting general season hunters to primarily harvesting prime-age and older male moose with antler spreads ≥127 cm did not appreciably reduce harvest of adult males. Male moose 2.0–5.3 years of age rarely died from non-hunter causes and were largely harvested at older, prime ages (5.3–8.3 yr of age). Yearling moose of both sexes died primarily from wolves, with wolves selecting more for males. By using liberal harvests of female moose to reduce the population, managers improved moose nutrition and reproduction, met mandates for elevated harvests, and may have avoided a reoccurrence of a previous precipitous decline in moose numbers that was initiated by overabundance and extreme snow depths. © 2019 The Wildlife Society.     

Distribution, movements, and mortality of anadromous arctic char, Salvelinus alpinus L., in the Cumberland Sound area of Baffin Island

During 1972 the downstream movement of anadromous artic char, Salvelinus alpinus L., from two rivers flowing into Cumberland Sound, Baffin Island, began during the middle of May and was completed within 2 weeks. This movement took place during both the day and night. Upon reaching saltwater, many char older than 9 years (longer than 20 cm) began to migrate along the shore of the Sound at a rate of 0–6–0-9 km/day with the result that the average maximum distance travelled from the natal river was 40–50 km. Char 6–9 years old, 10–20 cm in length, remained much closer to the rivers while those younger than 5 years never entered saltwater. During the period of saltwater residence, the fish frequently moved into the intertidal zone and freshwater. Maturing fish of both sexes were occasionally found in saltwater. The upstream migration to the lakes began during the second week of August and was completed within 5–6 weeks. Females tended to ascend the rivers before males, although fish of all different size and age migrated upstream simultaneously. Migration occurred during both the day and night. The maximum distance anadromous char moved from saltwater was 40 km. The char were found only in freshwater between May and September and were normally located near the bottom of lakes at a depth of 15–40 m. During this period, large scale movements were probably very limited. Average annual mortality was estimated at 16.0% per year with the highest rates (25–30%) occurring at ages 10 and 15–17 years. Many fish probably died of old age but physical deterioration during and after spawning was also an important cause of death.     

Chillingham Cattle: Dominance and Affinities and Access to Supplementary Food

A herd of cattle of natural sex ratio and age distribution, inhabiting a 134-ha park in northern England, was studied during supplementary feeding in 4 winters. Interactions could be summarised by conventional dominance hierarchies, more strictly linear and less stable among males than among females. Personal associations among individuals were not important, but affinities among social classes were, in determining the composition of feeding groups. Dominant males often fed in the same groups as dominant females. Dominant animals were less often seen to feed alone, implying that social dominance did not confer exclusive access to food. Cattle often fed in groups of two or three; certain combinations (notably those including two males, or one male and one female, or three calves) were stable, others unstable, notably combinations of females and calves, or of two or three females. This implies that females may defend resources more vigorously against other females than males do against other males.     

Effects of population structure and density on calf sex ratio in red deer (<Emphasis Type="Italic">Cervus elaphus</Emphasis>)—implications for management

There is ongoing interest to assess what factors affect offspring sex ratio, especially in ungulates. Wildlife managers might be interested in influencing this sex ratio for two reasons: either in order to limit population growth more effectively by reducing the proportion of females born or to increase revenues by a higher proportion of trophy bearing males in the population. While previous studies mostly focused on how maternal traits affect offspring sex ratio, we included here also male traits in our analysis. We achieved this by investigating data from 30 areas covering entire Lower Austria, collected over the past 12 years from both hunted red deer and those killed in road accidents. We focused our analyses on parameters that can be easily assessed by managers on the population and individual level, i.e. the numbers of animals culled in different age/sex classes and their body mass. We found that the proportion of females among calves increased with population density. Furthermore, we found that calf sex ratio (i.e. the proportion males among calves aged between 2 and 7 months) increased with increasing proportions of adult females and males older than 10 years, independent of the density effect. We conclude that wildlife managers interested in the effective reduction of red deer abundance and/or increasing the proportion of males among offspring should select a culling regime leading to a low population density dominated by adult, prime-aged females and males. This can be achieved by over-proportional removal of young females and warranting that a high number of strong males reach an age of at least 10 years.     

Abortion and Calf Mortality in Danish Cattle Herds

The aetiology of abortions and calf mortality in 65 Danish cattle herds consisting of both dairy and beef breeds during a 1-year period is described. All observed aborted foetuses, stillborn calves, and calves dying before 6 months of age were necropsied, and relevant microbiological examinations were performed. A total of 240 calves and 66 abortions were submitted corresponding to a calf mortality rate of 7%. The abortion frequency could not be calculated. 43% of the calves died at day 0, while 22% were aborted, 15% died during the first week of life, 9% died from 1 to 4 weeks of age, and 11% died at the age of 1 to 6 months. The most common cause was neonatal pulmonic atelectasis (stillbirth) followed by foetal infections, pneumonia, and septicaemia.     

Genetic analysis of the growth rate of Israeli Holstein calves

Weight of male and female Israeli Holstein calves and yearling gain were analyzed on 285 800 records from 105 935 animals from 458 herds recorded between 1994 and 2007. The difference between the sexes increased until around 400 days, at which point the difference between males and females was 110 kg. Yearling gain, defined as 365 × (weight - 35)/age + 35, was greatest for males at approximately 300 days and for females at 225 days. Yearling gain of male and female calves were highly correlated genetically; thus records from both sexes were combined into a joint genetic analysis. Heritability and repeatability were 0.33 and 0.73 in the analysis of both sexes, and similar in the single-sex analyses. Yearling gain is also highly correlated genetically with various measures of mature cow size. Yearling gain was positively correlated with milk, fat, protein production and somatic cell score, but negatively correlated with fertility and cow survival. Yearling gain was also positively correlated with both the sire and maternal grandsire effects on dystocia, but not with calf mortality. The genetic trend for yearling gain was 0.16 kg/year, while phenotypic trends for first and last weighings were both negative.     

Young Bighorn (Ovis canadensis) Males: can they Successfully Woo Females?

Mating by young males or low male‐to‐female ratios can decrease pregnancy rates and postpone birthdates in ungulates, thereby hindering population growth. Young (2.5–3.5 yr old) male bighorn (Ovis canadensis) behave differently than older males, and age, horn size, mating behavior, and social rank help determine reproductive success. We estimated birthdates in two populations of bighorn sheep in Utah, USA, to determine if mating by young males or low male‐to‐female ratios resulted in fewer young born per female, a shift in mean timing of births, or asynchronous births. When reintroduced, the Rock Canyon population consisted of four males (two each of 2.5 yr old and 1.5 yr old) and a 1 to 7.5 ratio of males (>2 yr old) to adult females (≥3.5 yr old); the Mount Nebo population consisted of four males ≤1.5 yr old and a 0 to 12 ratio of males to adult females. For both populations, the number of young born per female did not differ between the first parturition period after reintroduction (where females were impregnated by males from their source populations) and the second period of parturition (where females were impregnated by young, reintroduced males). Mean birthdates and synchrony (SD) of births did not differ for Rock Canyon (May 12, 2001 ± 4.5 d, May 14, 2002 ± 3.2 d) or Mount Nebo (May 23, 2005 ± 8.1 d, May 22, 2006 ± 10.2 d) between the first and second years following reintroduction. Mating by young males or low male‐to‐female ratios had no demonstrable effect on the number of young born per female or timing and synchrony of births in these populations.     

Selectivity of wolf predation on red deer in the Bieszczady Mountains, Poland

A pattern of wolfCanis lupus Linnaeus, 1758 predation on red deerCervus elaphus Linnaeus, 1758 was studied in Bieszczady Mountains in 1991–2002. In total 324 remains of red deer > 4 months old, killed by wolves throughout the year, were found. The sex, age and bone marrow fat content of wolf kills were compared with the same characteristics within the free living red deer population. The overall contribution of calves killed by wolves (24%) in October-May was higher than in the population (17%), and decreased from autumn to spring. Adult males were more vulnerable to wolf predation than adult females: stags constituted 62% and hinds 38% of adult red deer killed by wolves, whereas in the population, the percentages were 37 and 63%, respectively. Stags killed by wolves were younger ([`(x)] = 4.1\bar x = 4.1 years old) than hinds ([`(x)] = 8.9\bar x = 8.9 years old). Wolves killed more > 8 years old hinds and < 5 years old stags than available in the population. In wolf kills, the average fat content in femur marrow was higher among hinds (84.9%) than stags (69.3%) and calves (66.1%). Only 8% of hinds had < 70% femur marrow fat content, whereas 40% of calves and 38% of stags had marrow fat values below that level. Marrow fat content showed seasonal variation and was the lowest in March among all sex-age classes. The monthly share of stags in all kills, and hinds in hind-calf part of the sample was negatively correlated with their monthly average bone marrow fat content, and monthly share of calves was positively correlated with monthly average bone marrow fat content of adults. The segregation of social units (hind-calf and stag groups), except during the rutting season, and the low fat reserves of males from midwinter until spring contribute to the high overall incidence of calves and adult males and the relatively low incidence of adult females among wolf kills.     

ASPECTS OF GROWTH IN CAPTIVE KILLER WHALES (ORCINUS ORCA)

Morphometrics from 25 captive killer whales (11 captive-born) were collected at SeaWorld parks from 1984 to 1995 to determine age-specific growth parameters. For sexes combined, the body-volume index was the most accurate predictor of body weight. However, predicting weight from total length was appropriate, although it may underestimate weight of pregnant animals. Among captive-born calves, a Gompertz model was the best predictor of weight and length at age. Estimates for length and weight at birth were done using data from in utero and neonatal calves. For ages 1-5 yr, models indicate that males grew in both weight and length at slower rates. Growth rates in males may surpass those of females at approximately 5-6 yr of age.     

Anopheles culicifacies: effects of age on the male reproductive system and mating ability of virgin adult mosquitoes

Abstract. Under controlled laboratory conditions of 28–30^oC and 16:8 L:D photoperiod, an attempt was made to develop an age-grading technique for Anopheles culicifacies males. Mating activity was maximal when females were 5–12 days old and males were 5–7 days old. The numbers of total and mature spermatocysts declined significantly with age, and the proportion of the testes occupied by the sperm reservoir increased as virgin males grew older. Mating resulted in the loss of spermatozoa and accessory gland substance from the reproductive system. Loss of mating ability of older virgin males seemed to be age-related, because the reproductive system contained ample supplies of accessory gland substance and spermatozoa. Morphological changes of the reproductive system, due to mating and age, were used to infer the age and reproductive history of unknown males in a laboratory evaluation.     

Demographic and life-history patterns in a population of ring-tailed lemurs (Lemur catta) at Beza Mahafaly Reserve,Madagascar: a 15-year perspective

Over 15 field seasons (1987-2001), we collected census and life-history data on a population of individually identified ring-tailed lemurs at the Beza Mahafaly Reserve, Madagascar. No significant difference was found in population size over the study period, though a marked decline in the population occurred following a 2-year drought. The population rebounded rapidly after the immediate postdrought period. There was nearly a complete replacement of individuals over the study period. Average group size is 11.5 animals, and adult male to female sex ratio is 0.92. Most females reproduce annually, and the average fecundity rate is 84.3%. The greatest variability in fecundity is found among old females. We suggest that ring-tailed lemur females follow an "income breeding" strategy, i.e., females use maximum resources during reproduction rather than relying on fat stores, as do "capital breeders." Infant mortality to 1 year of age in a nondrought year is 52%, higher than infant mortality in small to medium-sized anthropoids. The oldest known female was 18 years old in 2001. We suggest that 18-20 years may represent the maximum life-span for wild ring-tailed lemurs. Because males regularly emigrate from the population, we have no data regarding male life-span; however, there is some indication that males do not survive as long as females. Group fission has occurred three times: twice from one parent group living in the driest area of the reserve, with the most dispersed food resources. We suggest that the reproductive strategy that has evolved in this species, wherein females reproduce early in life and annually until old age, is a response to the unusual climate and environmental conditions under which Lemur catta has evolved.