Rates of predation on mammals by gombe chimpanzees, 1972–1975

Rates of chimpanzee predation on mammals are calculated using data on 75 kills recorded during focal observation in Gombe National Park, Tanzania, from January 1972 to April 1975. The chimpanzees were members of two study communities (Kanyawara, or Northern, and Kahama, or Southern, community), and were observed as focal individuals for 14,583 hr by more than 30 researchers and field assistants working in pairs. The rate of predation by females was too low to allow reasonable estimates. For males, the mean rate of killing during the study period was 0.31 kills per male per 100 hr (N=17 males), or 4.65 kills per 100 hr in the two communities. In contrast to results from Mahale Mountains, there was no difference in predation rate between wet and dry seasons. However, predation rates varied over time, increasing by four times between the first three and last four seasons of the sample period. In an average year the 15 adult and subadult male chimpanzees are calculated to have killed 204 prey per year in an area of 16 km², varying between 99 and 420 prey per year in periods of low and high predation rate. Red colobus were the most frequent prey, followed by bushpig and bushbuck. Predation rates varied greatly on different prey species, and were not related to either the proportion of time spent within 200 m of male chimpanzees, or to their population densities. In relation to encounter rates and population density, baboons, blue monkeys, and redtail monkeys were killed at a fraction of the rate of red colobus monkeys, which suffered severe mortality from chimpanzee predation. Predation on bushpig and bushbuck also appears to have been high in relation to population density. The amount of food provided by predation is estimated to have averaged 600 kg per year for chimpanzees in the two communities (totalling 14–17 adult or subadult males, 18–20 adult of subadult females, and about 19 infants or juveniles). This suggests that adult males consumed around 25 kg of meat per year, although any average figure undoubtedly masks considerable individual variation. Present data suggest that chimpanzees in Gombe and Tai National Park, Ivory Coast, prey on mammals at rates higher than other populations.     

Dynamics of long-leaved sundew Drosera intermedia populations at two extremes of a hydrological gradient

Densities of Drosera intermedia were low in two studied habitats (10–25 ramets m⁻¹), a path through a wet heath (short inundation in spring, low soil moisture in summer) and a pool edge (longlasting inundation, high soil moisture in summer). The low densities could be explained by the observed low recruitment and high adult mortality.
The low recruitment resulted from: (1) a high first year mortality of the large number of seedlings that emerged each year in the path population, caused by summer drought and cover with algae after heavy rainfall; (2) the absence in two years out of three of seedling emergence at the pool edge, due to the longlasting inundation. In neither population any seedlings survived to flower; (3) low vegetative reproduction rate.
Adult mortality during the growing season was caused by drought, which did not occur at the pool edge. Rapid senescence in autumn, caused by summer drought on the path and by a rapid submersion after heavy rainfall at the pool edge, was associated with a high winter mortality.     

AGE- AND SEX-SPECIFIC MORTALITY AND POPULATION STRUCTURE IN SEA OTTERS

We used 742 beach-cast carcasses to characterize age- and sex-specific sea otter mortality during the winter of 1990-1991 at Bering Island, Russia. We also examined 363 carcasses recovered after the 1989 grounding of the T/V Exxon Valdez , to characterize age and sex composition in the living western Prince William Sound (WPWS) sea otter population. At Bering Island, mortality was male-biased (81%), and 75% were adults. The WPWS population was female-biased (59%) and most animals were subadult (79% of the males and 45% of the females). In the decade prior to 1990-1991 we found increasing sea otter densities (particularly among males), declining prey resources, and declining weights in adult male sea otters at Bering Island. Our findings suggest the increased mortality at Bering Island in 1990-1991 was a density-dependent population response. We propose male-maintained breeding territories and exclusion of juvenile females by adult females, providing a mechanism for maintaining densities in female areas below densities in male areas and for potentially moderating the effects of prey reductions on the female population. Increased adult male mortality at Bering Island in 1990-1991 likely modified the sex and age class structure there toward that observed in Prince William Sound.     

The influence of increasing density on body weight, kid production, home range and winter grouping in roe deer (Capreolus capreolus)

In this paper, we present an analysis of the consequences of increasing density, over a period of nine years (from 1980 to 1988), on the dynamics, and the social and spatial organization of a forest roe deer population. Hunting of this population ceased in 1979, after which time there was a significant increase in population density, with three distinct periods easily identified: 1980–1983 (PI), immediately following cessation of hunting, characterized by a relatively low density (d = 5–7 animals/100 ha), 1984–1985 (P2), a period of rapid population growth, and 1986–88 (P3), a period of high density (d = 25 animals/100 ha). During PI, the population was irregularly distributed across the study site but, as density increased, distribution became more uniform, and eventually covered the whole of the available area. Home-range structure and shape remained unchanged from PI to P3 but, by the end of the study, average range size was 30% lower for adult males only, and the period prior to subadult males, but not females, establishing a permanent home range had increased from c. 18 month to c. 30 months. Winter group size increased overall from PI to P3 with, for the first time, observations of groups of five or more animals and a reduction in the frequency of observations of solitary females, with does more commonly observed in pairs or small groups; the proportion of solitary males, however, did not change between the two periods. The mean number of kids per female declined significantly from PI to P3 and body weights recorded for juveniles of both sexes and for adult males were also significantly lower during the period of relatively high density (P3). However, for adult females, absolutely no body weight change was observed. This divergence between the sexes of response to increasing density is discussed.     

Adult survival and numbers in a coastal breeding population of Redshank Tringa totanus in northwest England

The results of a long-term capture-mark-recapture ringing programme carried out on a coastal population of breeding Redshanks Tringa totanus between 1974 and 1988 are presented.
Both sexes were equally likely to be recaptured in subsequent years, as were birds captured for the first time compared with those that had been captured previously. Older birds were more frequently recaptured than were young birds. There was no significant difference in male and female adult survival rates, with a mean of 72% of females and 75% of males surviving each year.
The breeding population fluctuated annually with estimated breeding densities of 122–285 pairs per km². Variation in breeding numbers (males), but not survival, was partially attributable to winter air temperature.     

Recruitment in the swash zone – temporal variations in juvenile recruitment of an exposed sand beach surf clam

This study examined factors affecting juvenile recruitment in the tuatua Paphies donacinaon an exposed surf beach in Pegasus Bay, South Island New Zealand between October 1994 and April 1997. Tuatua recruitment followed female gonad maturation with a delay of approximately 2 months. Juveniles (1–10 mm shell length) occurred throughout the study except during June and July 1995 (winter). Average densities (m^–2 ) were 28 in winter, 230 in spring, 174 in summer and 108 in autumn. There was high juvenile mortality and/or emigration and the maximum average density of (741m^–2 ) was recorded in November 1996. Recruit densities were similar between years except during winter. Adult tuatua populations were dominated by modal shell lengths greater than 70 mm.There was no significant relationship between adult and juvenile recruit length. Recruit length decreased with recruit density suggesting density dependent competition for space or food resources. Juvenile density increased following increases in food availability (chlorophyll a concentration) but average length of juveniles did not correlate directly with any of the environmental variables. Recruit density decreased as the modal adult length increased and recruit length reduced when adult populations had a high condition index. Because larvae, juveniles and adult are mobile the beach population is characteristic of an open system with adults and juveniles from the resident population affecting post-settlement density- dependent processes.     

Population dynamics of the bearded vulture Gypaetus barbatus in southern Africa

The essential features of mortality and survivorship of bearded vultures Gypaetus barbatus in southern Africa were deduced from age class plumage characteristics. The population consisted of about 204 adult pairs within a breeding range of about 35,000 sq km. Pairs bred every year and produced, on average, about 0·9 young per pair per year. Young birds made up about 37% of the population, subadults 3·5% and adults 60%. About 182 fledged young were recruited to the population each year. The proportion of young birds in the population in different areas was inversely related to the breeding density of adult birds (range 24–47%). Young bird mortality over the four years to subadult age was 87%, the survival rate of adults was 94% and the mean lifespan of birds surviving to adulthood was 21·4 years. This study demonstrates the need to understand the relationship between adult breeding density and young bird numbers in different parts of their range to accurately deduce population dynamics characteristics.     

Sex ratio in the spider Pityohyphantes phrygianus affected by winter severity

The sex ratio of subadult Pityohyphantes phrygianus was recorded before and after five winters in a natural population in coniferous forest in south-west Sweden. In autumn, the proportion of males was on average 33–8% (range 28–7–40–1) and the proportion of females was 66–2% (59–9–71–3). In each of the winters 1981 82, 1982–83, 1984–5, the proportion of males decreased significantly. The proportion of males decreased more the lower the February mean temperature. Field experiments showed that low ambient temperature in winter caused high mortality among spiders. Experimental data also suggest that males are more vulnerable to low winter temperatures than are females. Indirect evidence indicates that neither predation pressure nor starvation alone are likely to cause the observed changes in sex ratio in the three winters. However, the combined effect of sex differences in predation by birds and cold-induced mortality may explain why males disappear faster than females in certain winters.     

Mortality causes in British Barn Owls Tyto alba, with a discussion of aldrin-dieldrin poisoning

During 1963-89, 627 Barn Owl Tyto alba carcasses were received for autopsy and chemical analysis. Much larger numbers were received per month outside the breeding season than within it, with peaks in autumn (mainly juveniles) and late winter (adults and juveniles).
The main causes of recorded deaths were collisions (mostly with road traffic) and starvation. No great seasonal variation occurred in the main causes of recorded deaths and starved juveniles were reported even in summer. Most starved males weighed less than 240 g, and most starved females less than 250 g.
Another important cause of mortality in eastern arable counties, at least to 1977, was poisoning by organochlorine pesticides, especially aldrin/dieldrin. Levels of HEOD (the metabolized product of aldrin/dieldrin) in the livers of birds that had apparently died of aldrin/ dieldrin poisoning were in the range 6–44 ppm (geometric mean 14 ppm). Pesticide victims formed up to 40% of all dead Barn Owls obtained from some eastern counties during 1963-77. By 1987-89, HEOD levels in Barn Owls in eastern counties had fallen to less than 1.6 ppm, and no deaths from organochlorine poisoning were recorded.
Organochlorine pesticides almost certainly contributed to population decline in eastern England evident in the 1950s and 1960s, and reductions in the use of these chemicals may have allowed a subsequent increase, apparent over the last 10–15 years.     

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

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

Site tenacity and survival rates of Wrens Troglodytes troglodytes and Treecreepers Certhia familiaris in a Nottinghamshire wood

Mark-recapture data from 20 years of standardized mist-netting were used to investigate site tenacity and adult survival rates of Wrens Troglodytes troglodytes and Treecreepers Certhia familiaris in an English woodland. Within breeding seasons, a high proportion of Wren (but not Treecreeper) recaptures occurred in the same part of the wood as the original capture. Between breeding seasons, a high proportion of recaptures of adult males (but not of adult females) occurred in the same part of the wood as the original capture. Both species experienced exceptionally high mortality during the severe winters of 1978–1979 and 1985–1986, and, in the case of Wren, all or almost all birds which had previously bred in the wood probably died. Outside of these two cold winters, apparent (minimum) adult survival rates of Wrens and Treecreepers showed very different temporal patterns of variation. Wren survival rates were negatively correlated with the number of snow days in winter, whilst Treecreeper survival was negatively correlated with the amount of winter rainfall. After allowing for the influence of winter weather, apparent survival rates of adult Wrens were density dependent, indicating that either mortality or permanent emigration out of the wood was density dependent. There was some evidence from British and Irish ringing recoveries that movements of adult Wrens may be density dependent. The apparent survival rate of adult Wrens was probably an important factor determining the size of the local breeding population.     

Accounting for differential migration strategies between age groups to monitor raptor population dynamics in the eastern Black Sea flyway

Migration counts can offer a cost-effective method for monitoring the state of migrant raptor populations. However, differential migration strategies between inexperienced juveniles and experienced non-juveniles are rarely accounted for when inferring population trends from raptor migration counts. Since 2011, the Batumi Raptor Count (BRC) monitors the autumn migration of more than 1 million raptors along the eastern Black Sea coast in the Republic of Georgia. We also systematically sampled age information to assess differential migration timing between age groups and estimate age-specific linear trends in abundance between 2011 and 2018 for eight focal species. In so doing we aimed (1) to reassess the global relevance of BRC counts for each species and the potential for monitoring abundance of juveniles and non-juveniles, and (2) to identify demographic changes underlying recent trends in overall abundance. We found that the mean annual passage of non-juveniles at Batumi represents at least 1% of the estimated global breeding population of five study species. As expected, counts of juveniles were more variable than counts of non-juveniles. Yet despite our short monitoring period our models had sufficient statistical power to detect changes in abundance of 10%/year or less for at least one age group in all species except Pallid Harrier Circus macrourus. Our results indicate stable abundance and demography for half of the study species. We also found strong and significant increases in the abundance of Black Kites Milvis migrans and Short-toed Eagles Circaetus gallicus that were primarily due to increasing numbers of non-juveniles. By contrast, juvenile Montagu's Harriers Circus pygargus and Booted Eagles Hieraaetus pennatus significantly decreased in abundance. The first decade of BRC surveys offers an important benchmark for monitoring raptor populations using the eastern African–Palearctic flyway in the 21st century. We discuss possible causes of the observed trends and hope our work will stimulate demographic monitoring at migration count sites.     

高原鼠兔(Ochotona curzoniae)冬季自然死亡率

以耳标观察法。1985年4-7月共捕标了样地内高原鼠兔(Ochotona curzoniae)幼鼠114只。到入冬前,死亡率为50.88%。第2胎出生的鼠死亡率明显地高于第1胎的死亡率。冬季死亡率呈现波动,入冬及开春时死亡率较高。鼠兔种群进入繁殖前期死亡率趋于零。初春样区存活标志鼠6只,经夏秋冬3季总计死亡率达94.74%。如按入冬时实有标志鼠计算,冬季死亡率为91.04%。     

Distribution history and present status of the raccoon dog in Finland

The raccoon dog Nyctereutes procyonoides Gray was introduced from the Far East in several areas of the USSR, mainly the European part, in 1929–55. The first raccoon dogs were seen in Finland in the latter half of the 1930s, and by the mid-1950s, the frontier of the first regular observations had reached the most southeasterly parts of the country. Since then, the raccoon dog dispersed through southern and central Finland at an average annual rate of 20 km. The rate of population increase, as well as present density, has been highest in southern and southeastern Finland, and lowest in the northern parts of the distribution area. The northern limit of the distribution lies nowadays in southern Lapland, only a little further north than two decades earlier, when most of southern and central Finland was already inhabited.
The length of the growing season seems to explain most of the variation in the population density between the provinces. The longer the growing season, the better the raccoon dog manages; in southern Finland where the summers are longer, the juveniles have enough time to grow and gather fat reserves before hibernation. Therefore, many of them survive the winter and even breed in the following spring. In the north, in contrast, juvenile mortality is high during the first winter because of the short summer. The food availability, the yield of wild berries and the abundance of small rodents, is mostly responsible for the annual variation in the population density. Near the northern limit of the distribution, climate may also cause some of the annual variation in population density.     

Nesting densities,productivity and survival of breeding Whimbrel Numenius phaeopus in Shetland

Between 1986 and 1988 data on the nesting densities, productivity, and survival of breeding Whimbrel Numenius phaeopus were collected from 5 study sites in the Northern Isles of Shetland. Nesting densities on sites varied between 11 and 21 pairs per 100 ha. Few studies elsewhere have recorded such high densities of nesting Whimbrel as those on certain sites used in the present study. Each breeding pair produced an average of between 0.75 and 0.91 fledglings per year. Productivity varied considerably between different study sites however, primarily because of differences in the survival rate of chicks between hatching and fledging (ranging from 3% to 55% in one year). The annual survival rate of breeding adults was at least 89%. Considering adult survival in relation to overall productivity, it appears likely that the production of fledglings from study sites is in excess of that required to balance adult mortality. This result is consistent with the current increase of the Whimbrel population in Shetland.     

MOVEMENTS OF SATELLITE-TAGGED SUBADULT AND ADULT HARBOR SEALS IN PRINCE WILLIAM SOUND, ALASKA

Satellite-linked tags were attached to 49 subadult and adult harbor seals captured in Prince William Sound (PWS), Alaska, and their movements were monitored during 1992–1997. Seals were tracked for a total of 5,517 seal-days and were located on about 80% of the days that tags transmitted. Most locations were in or near PWS, but some juvenile seals moved 300–500 km east and west into the Gulf of Alaska. While several seals travelled to 50–100 km offshore, virtually all locations were in water <200 m deep. Overall, juvenile seals moved more than adults and had larger home ranges. Movements were significantly affected by month, and age by month and sex by month interactions. In all months, mean distances between successively used haulouts were <10 km for adults and <20 km for juveniles. Mean monthly home ranges varied from <100 km² to >1,500 km², and were smallest during June-July. Mean haul-out to at-sea distance was 5–10 km for adults and generally 10–25 km for juveniles. Satellite-linked tags provided an effective means of monitoring and describing the full range of harbor seal movements in this region, with the exception of late summer when tags were shed during the molt.     

Ecological genetics of an island population of the House mouse (Mus musculus)

The House mouse ( Mus musculus L.) population on the small Welsh island of Skokholm was founded in the 1890s when a few animals were inadvertently introduced. It has thrived ever since. The animals breed from late March to early October, during which time the population increases 8–10 fold. Winter survival is related to temperature: the spring population can be as low as 100 individuals after a cold winter; if the winter is warm, so many animals survive that high numbers may occur in the following autumn. There are no resident predators of the mice, and no other small mammals on the island.
The population was sampled on 20 occasions between 1957 and 1972, and genetical changes measured by the incidences of non-metrical skeletal variants (which describe a substantial proportion of the genome) and (from 1968–72) by allele and genotype frequencies of electrophoretically detected genes. Two sorts of changes occurred: an irregular but increasing deviation from the genetical composition of the population at the beginning of the study period, and an annual cycle with frequencies changing in one direction during the breeding season and the opposite direction in the winter. Samples collected in the autumn were more similar to each other than spring caught samples, which conforms with independent evidence about the differing environmental contributors to death in different winters, as compared with general homogeneity of mortality factors during the summers. It is concluded that the genetical composition of the population is largely dependent on natural selection, although the agents and intensity of selection change with both seasons and years.     

Changing female spacing behaviour and demography in an enclosed breeding population of Clethrionomys glareolus

The social organization of Clethrionomys glareolus Schreber was studied by live trapping in an enclosure of 0.8 ha in Central Finland between the years 1982–1986. The enclosure consisted of three habitats: abandoned field, brushwood, and moist spruce heath forest.
The population density increased from 50 voles ha⁻¹ in 1982 and 1983 to 150 ha⁻¹ in 1984 and 1985. In the summer of 1986 the population crashed to almost zero. In the summer of 1984 after winter breeding the number of breeding females grew to 22 compared with 6–7 in previous years. In 1984 the mature females changed from territorial to group behaviour.
During the high population density in 1984 and 1985 breeding stopped already in late July – early August, thus preventing any fence effect.
The present study supports the hypothesis stating that microtine social organization is an opportunistic strategy reacting phenotypically to changing environmental – especially food – conditions.     

Co-existence of subadult males and females as alternative tactics of breeding post acquisition in a monogamous and protandrous anemonefish

Summary The monogamous and protandrous anemonefish,Amphiprion clarkii, utilizes only large host sea anemones as breeding sites. Under conditions of breeding site shortage, an important strategy for unmated fish may be to prepare themselves to enter quickly a breeding site from which a breeding male or female has recently disappeared. There are two types of subadults. Some juveniles become subadult males, which can change either to male or female afterwards, but others become subadult females, which can change only to female. Subadult females seem to acquire female posts more easily than subadult males. We develop an ESS model which evaluates the future reproductive success of subadult females and subadult males and test whether coexistence of subadult males and females can be interpreted as adaptive alternative tactics, using field data from two populations. The model predicts that if mortality does not differ between adult males and females the frequency for juveniles to become subadult females should be equal to the proportion of breeding post acquisition by subadult females among that by all subadults. The model also predicts that if mortality does not differ between subadult males and females, nor in adults, the frequency of subadult females among all subadults should be equal to the proportion of post acquisition. The model, with data from two study sites, suggests that alternative life-history pathways found inA. clarkii have evolved through adaptive tactics of breeding post acquisition.     

Demographics in an alpine reindeer herd: effects of density and winter weather

We examined how population density, winter weather, snow conditions, and 2 large-scale climatic indices (North Atlantic Oscillation, NAO, and Arctic Oscillation, AO) influenced demography (reproduction and mortality) in an alpine herd of semi-domesticated reindeer Rangifer tarandus between 1959 and 2000 in Finnish Lapland. The herd lived on heavily grazed lichen pastures, with winter densities between 0.8 and 3.9 individuals km⁻². Icing conditions occurred every 7th yr, on an average, and decreased reproductive rate (calves/females) by 49%. In general linear models icing remarkably increased the fit of snow models to reproductive rate. Incorporation of an interaction term between icing and the snow depth index provided better fit than a model without interaction. Delayed snowmelt decreased reproductive rate. For the day of snowmelt, however, the model without interaction was better than the interaction model. These 3 models provided the best fit to the data and accounted for 51–54% of the variation in reproductive rate. Winter mortality was related to density and large-scale climatic indices, but not to local winter weather except a slight increase in mortality during an icing winter. The best model for winter mortality, including reindeer density and NAO, accounted for 26% of variation in mortality. Three factors may be involved explaining weak density dependence or the lack of such dependence; climate change scenarios that predict higher winter temperature, more frequent thawing-freezing periods, and deeper snow would be expected to decrease reproductive rate and increase winter mortality of reindeer and thus to reduce profitability of reindeer husbandry. In contrast, early springs would be advantageous for reindeer in the short term.