bluuebunny/crossref_metadata_2025 huggingface dataset:
Delayed maturation in female bank voles: optimal decision or social constraint?
Authors: Prévot‐Julliard Anne‐Caroline , Henttonen Heikki , Yoccoz Nigel G. , Stenseth Nils ChR.
Published: March 2003

1. Density, maturation and survival of female bank vole (Clethrionomys glareolus) in the northern taiga of Finnish Lapland were studied using long‐term capture–mark–recapture data from two large grids, one food‐addition grid and one control grid, in 1982–94.

2. The density on the food grid was consistently higher than the density on the control grid.

3. Females born early in the breeding season usually matured, except at very high densities. Those born later in the summer season commonly delayed maturation to the following spring.

4. Winter survival of sub‐adult (having delayed maturation) females was significantly higher than survival of adult (breeding) females. However, empirical values of sub‐adult and adult survival, as well as difference between them, were not consistent with survival values assumed in theoretical models on optimal deferred breeding.

5. There was a density‐dependent relationship between the maturation rate of young voles and the density of already established breeding females (both bank voles and all Clethrionomys together; C. rutilus and C. rufocanus occasionally occurred on the study grids). This density dependence was different for the two grids (weaker on the food‐addition grid).

6. These findings are discussed within an evolutionary context: we have, on the basis of these findings, no evidence suggesting that the observed delayed maturation represents an evolutionary optimal strategy. Rather, there is evidence suggesting that the delay is due to social constraints.
Effects of breeding pond isolation on the spatial and temporal dynamics of pond use by the tungara frog,Physalaemus pustulosus
Authors: Marsh David M. , Fegraus EriC. H. , Harrison Susan
Published: March 2003

1.Recent theoretical and empirical research has shown that habitat isolation can have strong effects on patterns of abundance and population dynamics of animals. Effects of habitat patch isolation may be particularly strong in taxa such as amphibians, which may have limited dispersal abilities and yet rely on breeding habitats that are variable in space and time.

2.We manipulated the distribution of replicated artificial ponds in order to determine the effects of breeding pond isolation on the spatial and temporal dynamics of pond use by the tungara frog (Physalaemus pustulosusLynch), on Barro Colorado Island (BCI), Panama. Our principal objectives were to determine whether pond isolation affects if, when, and how much a pond will be used, and to determine the spatial scale over which isolation effects are likely to be important.

3.We used three sets of experimental ponds: ponds placed at distances from 1 to 200 m from active natural breeding sites; ponds placed at these same distances from recently abandoned breeding sites; and ponds placed among different terrestrial habitat types and at least 200 m from any known breeding sites (‘sampling ponds’).

4.We found that time to pond use increased with pond isolation, and that ponds near active sites were used more quickly than ponds near abandoned sites. The number of egg masses per pond decreased with pond isolation and was significantly lower near abandoned sites. Ponds near active breeding sites were more likely to be used by tungara frogs than both ponds near abandoned sites and sampling ponds.

5.Used sampling ponds were clumped at spatial scales less than 200 m, and mark–recapture data suggest that tungara frogs routinely move between ponds over these distances.

6.We conclude that breeding pond isolation is a primary determinant of the temporal and spatial dynamics of pond use by tungara frogs, and can result in spatial patterns in pond use that are independent of pond quality. These isolation effects are, however, unrelated to metapopulation processes, as most turnover in pond use is probably a result of dispersal and breeding site selection by individuals, and not resulting from the extinction of local populations.
Seasonal declines in replacement egg‐layings in a long‐lived, Arctic seabird: costs of late breeding or variation in female quality?
Authors: Hipfner J. Mark , Gaston Anthony J. , Martin Debbie L. , Jones Ian L.
Published: March 2003

1. In many species of birds, the proportion of females that relays after losing their first clutch varies. Replacement clutches can make important contributions to an individual's lifetime reproductive success, so the decision on whether or not to relay may have significant consequences for fitness.

2. Many studies report that female birds of ‘high quality’ (e.g. older and more experienced) were more likely to relay following clutch loss, and that the proportion of females that relaid declined as the breeding season progressed. High quality females tend to nest early, and may be less likely to lose their clutches. As a result, it is unclear whether few females relay late in the season because there are prohibitive costs associated with late breeding, or because those females that lay and lose their eggs late are of low quality, and therefore incapable of relaying.

3. We examined the roles of date and quality in causing seasonal declines in replacement layings in Brünnich's guillemot [Uria lomvia (Linnaeus)], a long‐lived, Arctic marine bird that lays a one‐egg clutch. At two low‐Arctic colonies in eastern Canada in 1996 and 1997, the single egg was experimentally removed from samples of early‐laying pairs (presumably those of high quality) at 3‐day intervals beginning on the median laying date and ending 12 days later.

4. In the general population, the proportion of pairs that relaid following natural egg loss declined with the date of loss. In contrast, the proportion of experimental pairs that relaid remained high irrespective of the date their egg was removed. These results support the quality hypothesis, but not the date hypothesis. We conclude that seasonal declines in replacement layings occurred primarily because increasing proportions of low quality females lost eggs as the season advanced.

5. The experimental pairs also suffered no overt reduction in reproductive success as a result of the delay, at least up to the time that their chicks departed to sea. This suggests that timing of breeding had little effect on the immediate success of more capable pairs.

6. Our results may have important implications about the seasonality of low‐Arctic marine environments, and the life histories of birds that inhabit them.
Differential response by males and females to manipulation of partner contribution in the great tit (Parus major)
Authors: Sanz Juan J. , Kranenbarg Sander , Tinbergen Joost M.
Published: March 2003

1. In birds with bi‐parental care, handicapping is often assumed to decrease the amount of parental care of the handicapped partner. We discuss how handicapping could alter the shape of the handicapped bird's survival–effort curve (theoretical curve relating the survival of a parent to its effort) and show that the optimal response could yield a decrease, no response or even an increase in effort of the handicapped bird.

2. Male or female great tits Parus major (L.) were handicapped during the nestling period by clipping a number of feathers in order to study the effects on parental care and body condition.

3. Handicapped males significantly decreased their feeding rates, while handicapped females did not. Condition of handicapped females significantly deteriorated, while condition of handicapped males did not change during the experiment. Females with a handicapped partner fully compensated for their partner's decrease in work rate, while males with a handicapped partner did not show any compensation and even tended to decrease their feeding rates.

4. Using an inverse optimality approach, we reconstructed the theoretical curve relating the survival of a parent to its effort on the basis of the experimental effects. The handicapped male's survival–effort curve appeared to be slightly steeper than that of handicapped females. This suggests that handicapped males suffer more from an increase in effort than handicapped females.
Reproductive consequences of egg‐laying decisions in snow geese
Authors: Lepage Denis , Gauthier Gilles , Menu Stéphane
Published: March 2003

1. Even though feeding conditions typically improve over time during the laying period, clutch size decreases over the course of the nesting period in most bird species. We examined whether seasonal decrease in offspring value could explain the seasonal decline in clutch size in arctic‐nesting greater snow geese (Anser caerulescens atlanticusL.).

2. Nesting was synchronized within a year, with more than 90% of the nests being initiated within about 8 days. Despite this high synchrony, there was a steep seasonal decline in clutch size in each of the 7 years of the study, from about five eggs in early clutches to three in late ones (−0·20 egg day−1).

3. Late parents performed more poorly than early parents in most components of reproductive success. The relationship between laying date and nesting success was curvilinear, early and late nests having a higher failure rate than those initiated near the median. Prefledging survival decreased by about 50% over the season, although the earliest hatched goslings also tended to have a reduced survival. The postfledging survival showed the strongest seasonal decline, as survival probability of late‐hatched birds was about five times lower than in early‐hatched ones.

4. Overall reproductive success showed a very steep seasonal decline as the number of young surviving to the first winter was about eight times lower in late‐nesting birds than in early‐nesting ones. Reproductive success declined slightly in the earliest‐nesting birds, suggesting a cost to nesting too early.

5. The observed clutch size generally matched the clutch size that yielded the highest reproductive success for each laying date, except in earliest‐nesting birds which should have done better by slightly delaying nesting. Our data suggest that trading off additional eggs for earlier nesting to increase reproductive success is an option in geese. Consequently, the seasonal decline in clutch size may be an adaptive response to seasonally declining survival prospects of offspring.
Food‐supplementation does not override the effect of egg mass on fitness‐related traits of nestling house wrens
Authors: Styrsky John D. , Dobbs Robert C. , Thompson Charles F.
Published: March 2003

1. Cross‐fostering experiments have shown that egg massper sepositively affects post‐hatching growth and development in passerine birds. In most studies, however, the initial influence of egg mass was not sustained, leading to questions about the importance of egg mass relative to the cumulative effects of environmental factors during the period of post‐hatching care.

2. In house wrens,Troglodytes aedonVieillot, evidence from cross‐fostering experiments suggests that food availability mitigates the influence of egg mass on posthatching growth: early in the season, when food was putatively abundant, the initial effect of egg mass was lost as nestlings aged; however, later, when food was putatively scarcer, the effect of egg mass persisted until nestlings left the nest.

3. We tested the hypothesis that abundant food for provisioning nestlings can decouple the relationship between fitness‐related traits of nestlings and the mass of the eggs from which they hatch (‘egg‐mass override hypothesis’) by providing daily mealworm supplements to broods of house wrens.

4. The food supplements did not increase final nestling mass, final nestling tarsus length, growth rate, or survival until nest‐leaving in late‐season broods, when the hypothesis of food limitation predicts that there should be such an effect. Instead, the food supplements significantly, but only slightly, increased final nestling mass in early‐season broods, when food is putatively abundant.

5. The effect of the food supplements on final nestling mass was independent of egg mass. Nestling survival in early‐season broods, and final nestling mass and tarsus length in both early and late‐season broods significantly increased with increasing egg mass in both experimental and control broods.

6. We propose that food was not limiting during the course of the experiments and that final nestling mass and tarsus length remained positively related to egg mass because nestling growth and development in house wrens is ‘predetermined’ by some component or property of eggs that covaries with egg mass.
The effect of helpers on reproductive success in the laughing kookaburra
Authors: Legge Sarah
Published: March 2003

1. In co‐operatively breeding birds and mammals that live in family groups, helpers may gain indirect fitness benefits by increasing the number of breeding attempts in a season, by increasing the success of each nesting attempt, and by increasing the survivorship of related breeders.

2. The effects of helpers were examined in an analysis of reproductive success in the laughing kookaburra (Dacelo novaeguineae), where a monogamously breeding pair is assisted by offspring of both sexes.

3. Helpers could not increase the number of attempts in a season, because kookaburras are single‐brooded.

4. In a paired analysis controlling for pair and territory quality, increases in group size were not matched by increases in the number or weight of fledglings in each breeding attempt, even though brood reduction was the major source of productivity loss. This concurs with previous results showing that group size does not affect overall provisioning levels to broods, because all group members reduced their provisioning effort as group size increased.

5. Because kookaburras prefer to reduce workloads during breeding rather than raise larger broods, the costs of caring for young must be high. Thus breeders with helpers may enjoy energetic savings and enhanced survivorship.

6. Helpers had different effects on nest success depending on their sex. Whereas male helpers had a neutral effect on fledging success and fledgling weight, additional female helpers reduced fledging success. Females are relatively poor helpers, and other group members may not properly compensate for the female's ‘inadequate’ help.

7. High‐quality kookaburra pairs, or pairs on good territories, were more likely to be in larger groups because they produced more potential recruits for their groups than relatively ‘poor’ performers. This was demonstrated by comparing the results of the paired comparisons with those of a correlational analysis that showed that in groups of two to six birds, group size was positively correlated with fledging success and fledgling weight (which affects the probability of juvenile survival).

8. However, unusually large groups of seven or more birds suffered drastically reduced nest success because eggs were damaged during incubation.
A quantitative analysis of fishing impacts on shelf‐sea benthos
Authors: Collie Jeremy S. , Hall Stephen J. , Kaiser Michel J. , Poiner Ian R.
Published: March 2003

1. The effects of towed bottom‐fishing gear on benthic communities is the subject of heated debate, but the generality of trawl effects with respect to gear and habitat types is poorly understood. To address this deficiency we undertook a meta‐analysis of 39 published fishing impact studies.

2. Our analysis shows that inter‐tidal dredging and scallop dredging have the greatest initial effects on benthic biota, while trawling has less effect. Fauna in stable gravel, mud and biogenic habitats are more adversely affected than those in less consolidated coarse sediments.

3. Recovery rate appears most rapid in these less physically stable habitats, which are generally inhabited by more opportunistic species. However, defined areas that are fished in excess of three times per year (as occurs in parts of the North Sea and Georges Bank) are likely to be maintained in a permanently altered state.

4. We conclude that intuition about how fishing ought to affect benthic communities is generally supported, but that there are substantial gaps in the available data, which urgently need to be filled. In particular, data on impacts and recovery of epifaunal structure‐forming benthic communities are badly needed.
Size matters: competition between male and female great tit offspring
Authors: Oddie Kate R.
Published: March 2003

1. Studies of sex allocation in birds have traditionally centred on Fisher's (1930) theory of equal parental investment in male and female offspring. They concentrate particularly on sexually dimorphic species, where costs of rearing offspring are assumed to vary between male and female young because of body size differences.

2. Higher mortality of the larger sex (males), particularly in poorer conditions, is expected to result in female‐biased sex ratios in the great tit, Parus major. Several studies have found the contrary, reporting male‐biased fledging and recruiting sex ratios when conditions are poor. One reason why this may be the case is that males can gain more food resources than their sisters because of the competitive advantage afforded by their larger size. They may thus suffer less mortality in the nest or fledge in better condition, thereby enhancing their survival prospects.

3. This study investigates the importance of size in competitive interactions between nestlings of different sexes. A cross‐fostering design was employed to create broods of mixed size through swapping half a brood of 2‐day‐old ‘small’ and half a brood of 4‐day‐old ‘large’ nestlings. Nestling morphometrics and mortality were measured during the nestling period. Nestlings were sexed by PCR amplification of sex‐linked genes. To test for a male advantage in competitive environments, size and mortality measures were compared between ‘small’ males and females, and ‘large’ males and females (i.e. the interaction term ‘size treatment’ and ‘sex’).

4. There was greater sexual dimorphism between small nestlings than large nestlings at fledging. This is interpreted as revealing enhanced competitive ability of male offspring under stressful conditions. Offspring from the ‘large’ group suffered lower mortality, but there was no difference in mortality according to sex, and no significant size*sex interaction. Similarly, no difference in recruitment was found, although this may be due to the small overall proportion of birds recruiting (3·1%).

5. The study suggests that male biased fledging/recruitment sex ratios in great tits may be explained by enhanced competitive ability of male nestlings in poor rearing environments.
Trawling disturbance can modify benthic production processes
Authors: Jennings Simon , Dinmore Tracy A. , Duplisea Daniel E. , Warr Karema J. , Lancaster John E.
Published: March 2003

Trawling disturbance has wide‐ranging impacts on the marine environment and is well known to modify benthic habitat and community structure. This has led to speculation about the positive and negative impacts of trawling on ecosystem processes such as production.

 Existing theory suggests that frequent trawling disturbance may lead to the proliferation of smaller benthic species, with faster life histories, because they can withstand the mortality imposed by trawling and benefit from reduced competition or predation as populations of larger species are depleted. Since smaller species are more productive, trawling disturbance may ‘farm the sea’, with knock‐on benefits for consumers, including fish populations.

 We conducted the first large‐scale studies of trawling effects on benthic production across quantified gradients of trawling disturbance on real fishing grounds in two regions (Silver Pit and Hills) of the North Sea. There were 27‐ and 10‐fold differences in levels of beam trawl disturbance among the Silver Pit and Hills sites, respectively.

 Size structure was described using normalized size‐spectra, and the slopes and intercepts of these spectra were related to levels of trawling disturbance. Production was estimated from the size spectra, using a new allometric relationship between body mass and the production to biomass (P:B) ratio of marine invertebrates. The general validity of the relationship was confirmed using a phylogenetic comparative approach.

 In the Silver Pit region, trawling led to significant decreases in infaunal biomass and production. The abundance of larger individuals was depleted more than smaller ones, as reflected by the positive relationship between the slope of the normalized size spectra and trawling disturbance. The effects of trawling disturbance were not significant in the epifaunal community. In the Hills region, where the range of trawling disturbance was lower, trawling disturbance did not have significant effects on biomass or production.

 In the Silver Pit, relative infaunal production (production per unit biomass) rose with increased trawling disturbance. This was attributable largely to the dominance of smaller animals in the disturbed communities. The increase in relative production did not compensate for the loss of total production that resulted from the depletion of large individuals. There was some evidence for the proliferation of small polychaetes at moderate levels of disturbance, but at higher levels of disturbance their biomass and production fell.

 We conclude that reported increases in the biomass and production of small infaunal invertebrates in the North Sea are attributable largely to recent increases in primary production that were driven by climate change, and not to the effects of trawling disturbance.
Variation in survivorship of a migratory songbird throughout its annual cycle
Authors: Sillett T. Scott , Holmes Richard T.
Published: March 2003

Demographic data from both breeding and non‐breeding periods are needed to manage populations of migratory birds, many of which are declining in abundance and are of conservation concern. Although habitat associations, and to a lesser extent, reproductive biology, are known for many migratory species, few studies have measured survival rates of these birds at different parts of their annual cycle.

Cormack–Jolly–Seber models and Akaike’s information criterion model selection were used to investigate seasonal variation in survival of a Nearctic – Neotropical migrant songbird, the black‐throated blue warbler,Dendroica caerulescens. Seasonal and annual survival were estimated from resightings of colour‐ringed individuals on breeding grounds in New Hampshire, USA from 1986 to 2000 and on winter quarters in Jamaica, West Indies from 1986 to 1999. Warblers were studied each year during the May–August breeding period in New Hampshire and during the October–March overwinter period in Jamaica.

In New Hampshire, males had higher annual survival (0·51 ± 0·03) and recapture probabilities (0·93 ± 0·03) than did females (survival: 0·40 ± 0·04; recapture: 0·87 ± 0·06). In Jamaica, annual survival (0·43 ± 0·03) and recapture (0·95 ± 0·04) probabilities did not differ between sexes. Annual survival and recapture probabilities of young birds (i.e. yearlings in New Hampshire and hatch‐year birds in Jamaica) did not differ from adults, indicating that from the time hatch‐year individuals acquire territories on winter quarters in mid‐October, they survive as well as adults within the same habitat.

Monthly survival probabilities during the summer (May–August) and winter (October–March) stationary periods were high: 1·0 for males in New Hampshire, and 0·99 ± 0·01 for males in Jamaica and for females in both locations.

These annual and seasonal survival estimates were used to calculate warbler survival for the migratory periods. Monthly survival probability during migration ranged from 0·77 to 0·81 ± 0·02. Thus, apparent mortality rates were at least 15 times higher during migration compared to that in the stationary periods, and more than 85% of apparent annual mortality ofD. caerulescensoccurred during migration.

Additional data from multiple species, especially measures of habitat‐specific demography and dispersal, will improve our understanding of the relative impacts of the breeding, migratory, and winter periods on population dynamics of migratory birds and thus enhance future conservation efforts.
The population response to environmental noise: population size, variance and correlation in an experimental system
Authors: Benton T. G. , Lapsley C. T. , Beckerman A. P.
Published: March 2003

summary

 Variation in an organism’s environment can influence its life history and therefore its population size. Understanding the interplay between noise and population dynamics is of considerable importance, especially for prescribing management of economically important or threatened species. The impact of noise on population biology has been the subject of frequent theoretical investigations and discussed in posthoc analyses of time‐series. However, there is a dearth of experimental investigations.

 Here we report results from a replicated laboratory study of soil mites, Sancassania berlesei, kept in controlled environments but with food supplied randomly, with different synchrony and variances, while maintaining the same mean rate.

 Increasing environmental variance increases population variance, but decreases mean population size, therefore changing the observed shape of the distribution of population sizes: the shape becomes more skewed with more environmental variance.

 The distribution of population sizes are best described by negative binomial or gamma distributions. Log‐normal and normal distributions rarely fit and Poisson distributions never fit.

 The correlation between populations is sensitive to the correlation in environmental noise but insensitive to its variance.

 Different life stages (eggs, juveniles and adults) respond differently to noise, in that there are significant differences in the way that environmental variation changes the mean, variance, shape of distribution and relationship between environmental and population synchrony.
Variability in interaction strength and implications for biodiversity
Authors: Kokkoris Giorgos D. , Jansen Vincent A. A. , Loreau Michel , Troumbis Andreas Y.
Published: March 2003

We examined the species richness of theoretical communities in relation to interaction strength between species.

To do so, we used randomly constructed interaction matrices for competitive systems. To determine co‐existence, we tested for local stability and equilibrium feasibility of these theoretical assemblages.

As expected, we found that a low mean species interaction strength could allow for many species to co‐exist. However, variance in the interaction strengths may alter previous results; two systems with the same mean interaction strength show markedly different diversity depending critically on the magnitude of the variance. If species are similar enough then many can co‐exist, even if they compete strongly.

In addition we found that the species richness of a competitive community can greatly depend on the correlation between interaction strengths, an issue that so far has gone unreported. This correlation, a result of trade‐offs between species’ characteristics, may profoundly increase the potential for stable co‐existence of a highly species‐rich community.

Competition may not be an anathema to diversity. Statistical properties of species’ interactions may be critical factors that contribute to the explanation of species diversity in natural communities.
Factors affecting pup growth and survival in co‐operatively breeding meerkats Suricata suricatta
Authors: Russell A. F. , Clutton‐Brock T. H. , Brotherton P. N. M. , Sharpe L. L. , Mcilrath G. M. , Dalerum F. D. , Cameron E. Z. , Barnard J. A.
Published: March 2003

We examined the relative importance of maternal, environmental and social factors for post‐weaning pup growth and survival in a co‐operatively breeding mammal, the meerkat Suricata suricatta .

Pup daily weight gain was primarily influenced by the number of carers per pup and the daily weight gain of those carers. Rainfall and daily temperatures had additional positive and negative effects, respectively, on weight gain of pups born to subordinates.

Pup overnight weight loss was primarily influenced by the amount of weight pups gained during the day, and their age. However, pups also lost considerably more weight overnight when temperatures were cold, although such effects were less in large groups.

Pup growth rates were positively influenced by the number of carers per pup and carer condition, and negatively influenced by high daytime temperatures.

Pup weight at independence was positively associated with weight at emergence and pup weight gain during provisioning, but negatively associated with the extent of overnight weight loss.

Pup survival between emergence and independence was related to maternal status, pup sex and overnight weight loss, as well as to group size, daytime temperature and monthly rainfall.

Thus, in meerkats, social factors largely, but not wholly, replace the importance of maternal factors that are commonly found to govern reproductive success in non‐co‐operatively breeding social vertebrates.
The impact of gastrointestinal nematodes on wild reindeer: experimental and cross‐sectional studies
Authors: Stien A. , Irvine R. J. , Ropstad E. , Halvorsen O. , Langvatn R. , Albon S. D.
Published: March 2003

It is well known that gastrointestinal nematodes can have a significant impact on the growth of farmed ruminants. The clinical signs of these parasites are often subtle, with production losses mainly due to reductions in host appetite and gut function. However, little is known about the impact of this widespread group of parasites on wild ruminants. We use experiments and cross‐sectional data to investigate the effects of gastrointestinal nematodes on a wild host, the Svalbard reindeer.

Individually marked reindeer were treated for parasites. Their body mass, back fat depth and fecundity were compared with the control group one year later. The effect of treatment on worm burdens was investigated in a subsample of animals that were culled 3 and 6 months after treatment. Also, the relationship between the intensity of infection and body mass, back fat depth and host pregnancy rates was investigated in cross‐sectional data from culled reindeer.

The anthelmintic treatment caused an increase in the body mass, back fat depth and fecundity of the reindeer. Treatment depressed the abundance of adult parasites ofOstertagia gruehnerifor at least 6 months, but had no significant effect on the abundance of adults of the other dominant parasite species,Marshallagi marshalli, or the abundance of larval stages of either species.

In the cross‐sectional study, the probability of a reindeer being pregnant in late winter was negatively related to the abundance of adultO. gruehneriwhen controlling for host body mass. However, no clear evidence were found for an effect of parasitism on host condition in the cross‐sectional study.

Our experimental results show for the first time in a natural ruminant host population that gastrointestinal nematodes can have a significant effect on host condition and fecundity. However, effects of infection on host condition was not detectable in the cross‐sectional study. Also, we show that the experimental effects on host condition and fecundity is most likely to be due to a negative effect ofO. gruehneri, while the experimental design did not allow detection of potential negative effects ofM. marshalli.
North Atlantic Oscillation timing of long‐ and short‐distance migration
Authors: Forchhammer Mads C. , Post Eric , Stenseth Nils CHR.
Published: March 2003

The timing of migration is associated with survival and reproductive risks of migrating species. Hence, variation in factors influencing this timing, such as climate, may have significant life history consequences for migrating species.

Using an autoregressive phenological model, we analysed and contrasted the effects of climate (the North Atlantic Oscillation, NAO) and temporal dependence on the long‐term (1928–77) dynamics of springtime arrival in three long‐distance (83 populations) and three short‐distance (52 populations) migratory bird species breeding throughout Norway.

Following high NAO winters both long‐ and short‐distance migrants arrived earlier than after low NAO winters. For long‐distance migrants, the effect of high NAO winters was probably indirect through improved forage conditions in winter quarters, whereas the effect on short‐distance migrants may be related both to improved forage and weather conditions during their northward spring migration. The NAO explained on average 13% (0–46%) and 18% (0–43%) of the interannual variation in arrival dates of long‐ and short‐distance migrants, respectively.

For both migrant types, long‐term variability in springtime arrival increased with increasing strength of the influence of the NAO on timing of migration. In contrast, the strength of temporal dependence was unrelated to variability in long‐term springtime arrival.
Effects of sociality on short‐distance, female‐biased dispersal in tropical wrens
Authors: Yáber María Carolina , Rabenold Kerry N.
Published: March 2003

Dispersal from the natal area, or between breeding sites, marks a critical transition for individual animals, and a fundamental demographic and genetic process. Limitations on dispersal in natural populations are important in predicting population dynamics and structure. Tropical habitats that can be naturally patchy are also being fragmented rapidly, and these habitats harbour many social species.

We studied dispersal in cooperatively breeding stripe‐backed wrens (Campylorhynchus nuchalis) in the Venezuelan savanna, using 20 years of data from marked populations over 40 km2. We test the hypotheses that dispersal is limited by competition for social position and that such limitation is sex‐specific.

Dispersal is strongly female‐biased, and results mainly in attainment of breeding status in neighbouring groups. Reproductive success is determined by the structure of the breeding group, and is concentrated in a small minority of individuals.

Natal dispersal is delayed, and represents a dramatic shift from indirect contribution to kin production (helping) to the direct approach of breeding. Monogamy limits breeding opportunities, compared to other social species, and both natal and breeding dispersal are constrained to short distances, particularly when compared to non‐cooperative breeders.

Males are more philopatric compared to females, for which more frequent and distant dispersal leads to greater reproductive success. Competition for breeding status in an established social order impedes dispersal, in part because experience and previous familiarity are important, particularly in males that rarely disperse to productive large groups.

Diverse patterns of sex bias in dispersal among cooperatively breeding birds can be explained by the comparative diversity of reproductive alternatives available to males and females. A ‘breeding diversity’ hypothesis is illustrated by comparison with male‐biased dispersal in brown jays.

Social resistance to movement establishes a brake on gene flow and demographic interaction among populations that has important implications for population viability.
Trends in the abundance of farmland birds: a quantitative comparison of smoothed Common Birds Census indices
Authors: Siriwardena Gavin M. , Baillie Stephen R. , Buckland Stephen T. , Fewster Rachel M. , Marchant John H. , Wilson Jeremy D.
Published: March 2003

1.  Widespread declines in the populations of many British farmland birds have occurred since the early 1970s. We must understand the causes of these declines tomake recommendations about conservation and agricultural management, andthis can be approached by investigating the relationships, across species, betweenabundance and agricultural change. We describe novel, quantitative approaches to the interpretation of abundance indices from which reliable inferences about conservation status can be made.

2.  We calculated farmland Common Birds Census indices for 42 species, smoothed the series to reveal underlying trends and estimated confidence intervals for the changes in abundance.

3.  Between 1968 and 1995, the abundance of 12 species declined significantly andthat of 14 species increased.

4.  Specialization was the only significant determinant of changes in abundance (of 10 tests against species characteristics): 13 farmland specialists declined, on average, by 30%, whilst 29 more generalist species underwent an average increase of 23%, confirming that farmland birds should engender conservation concern.

5.  Smoothed abundance curves, transformed to emphasize trend direction and timing, were then compared quantitatively to identify whether groups of species had shared common trends.

6.  Species tended not to be strongly grouped, but small groups of species with common trends were identified. Similarities in ecology among grouped species clarify the possible environmental causes of their population trends, indicating future research priorities.

7.  The groups identified included: one group consisting of three thrush species Turdus and the skylark Alauda arvensis L. which all declined from the mid‐1970s after being stable previously; one group comprising three trans‐Saharan migrant warblers (Sylvidae), whose abundance fell in the early 1970s and later increased; and a diverse group of six smoothly increasing species.

8.  Turning points were identified as where each species’ population trend turned significantly, revealing critical periods during which populations are likely to have been affected by environmental change.

9.  Three collections of downward turning points were found, including one in the mid‐1970s when many farmland bird declines began. Four other periods each included many upturns. The groups of turning points should facilitate the identification of environmental changes which have had widespread effects. Management prescriptions can then be designed to reverse or to mirror such key changes and thereby focus conservation effort effectively.
Examining threats faced by island birds: a population viability analysis on the Capricorn silvereye using long‐term data
Authors: BROOK BARRY W. , KIKKAWA JIRO
Published: March 2003

Population viability analysis (PVA) is widely used for assessing the extinction risk faced by endangered species and for evaluating the effects of potential management strategies. However, most PVAs are done in urgency and with limited data.

It is therefore important to know how the amount and quality of available ecological data affect the predictions of PVA. How can PVA results be interpreted when we have reliable, long‐term population data? When a species is endangered on islands, as are many endemic bird species, what are the likely causes of the decline, and what is the probable impact of new threats? This paper investigates these issues by modelling 26 years of monitoring data on the population of Capricorn silvereyes Zosterops lateralis chlorocephala Campbell & White of Heron Island on the Great Barrier Reef. Australia.

A PVA with parameters estimated from a relatively short (5‐year) period of data collection produced very different predictions of extinction risk compared with a PVA based on more comprehensive ecological data spanning 15–25 years. This indicates that caution should be exercised when using PVA as an indicator of absolute extinction risk.

Despite remaining viable over the past 26 years, the Heron Island silvereye population is predicted to be at risk of extinction within the next 100 years, with the magnitude of risk depending on the severity of impact of a range of potentially threatening factors. Increased mortality due to the introduction of new predators or diseases, inbreeding depression or frequent severe storms greatly increased the extinction risk. Habitat reduction, if not very severe, is unlikely to have a large impact. Similar threats and impacts may apply to other island bird populations.

Movement or dispersal between neighbouring islands had a mitigating effect on extinction probability and allowed extinct island populations to be re‐established. However, very small islands could only support sink populations that quickly became extinct and required an unrealistically high immigration rate to remain viable in the long term.
Temporal patterns of crop‐raiding by primates: linking food availability in croplands and adjacent forest
Authors: NAUGHTON‐TREVES LISA , TREVES ADRIAN , CHAPMAN COLIN , WRANGHAM RICHARD
Published: March 2003

Primates dominate lists of pests that damage crops around African parks and reserves. Beyond creating management problems, crop foraging is integral to the ecology of primates inhabiting forest—agriculture ecotones.

Twenty‐three months of data from four villages around Kibale National Park, Uganda, revealed that redtail monkeysCercopithecus ascanius, olive baboonsPapio cynocephalusand chimpanzeesPan troglodytesselected different crops or plant parts. Baboons took root and tuber crops ignored by other primates, and fed on the greatest variety of crops. All three species preferred maize and/or bananas. Redtails ate only banana fruit, baboons ate banana fruit more frequently than pith, and chimpanzees raided pith and fruit in equal proportions.

Each primate showed a distinct monthly pattern of crop foraging, significantly non‐random for baboons and redtail monkeys, weakly for chimpanzees. Large inter‐monthly variation was observed for all three primates, but was least pronounced in redtails.

Raiding frequency on maize peaked approximately 8 weeks after the onset of rains and was strongly correlated between the three primate species. Abundant forest fruit did not diminish primate appetite for maize.

Raiding frequency on bananas varied considerably despite continuous availability of fruit and pith. Peaks in banana consumption were unrelated to rainfall or maize raiding, but were associated instead with forest fruit shortages, specificallyMimusops bagshawei.

Chimpanzees consumed banana pith more frequently when forest fruits were scarce, whereas baboons targeted more banana fruits. The use of banana pith by chimpanzees supports the suggestion that energy‐rich pith is crucial to chimpanzees during fruit scarcity.

Conservation ofMimusops bagshaweiand other key forest fruit trees may lessen primate raiding intensity on perennial crops, e.g. bananas. Maize raiding appears unaffected by forest fruit abundance. Such highly palatable crops are best planted > 500 m from the forest edge.

Planting agroforestry buffers along park edges creates ideal habitat for crop‐raiders. This management strategy is appropriate where human population density is low and crop raiding species are legal game. When dangerous or destructive wildlife species forage amidst densely settled subsistence farmland, managers are challenged to separate forests from agriculture using non‐palatable plant barriers or electric fences.
Squid stock fluctuations and water temperature: temporal analysis of English Channel Loliginidae
Authors: Robin J. ‐P. , Denis V.
Published: March 2003

1. Monthly series of abundance indexes for the English Channel squid stock, based on fishery statistics of the United Kingdom (1980–93) and France (1986–96), were compared with water temperature data. The two objectives of the study were to test empirical predictive models and to analyse the stock–environment relationship at various time scales; both correlation and time‐series statistical techniques were applied. Sea surface temperature (SST) showed inter‐annual fluctuations and month‐to‐month auto‐correlation in addition to the annual cycle.

2. Trends in squid landings and temperature at the annual scale were found to be related, whatever the statistical method used (moving averages, cumulative functions or regression using averaged data).

3. Variable selection applied in a ‘multi‐month’ model suggested that fishing season indexes could be predicted from temperatures observed in the previous winter. The link between mild winter conditions and cohort success in winter/spring spawning species suggested that early life survival (and/or growth) was involved. This empirical model is a first step in the development of environment‐predicted recruitment indexes useful for management advice.

4. Seasonal decomposition was performed on both the squid resource data and SST data in search of short‐term relationships. In spite of the flexibility of the loliginid life‐cycle, no significant relationship was found between squid seasonally adjusted indexes and temperature anomalies in the previous months. This underlined the conclusion that temperature effect on cohort success was not constant throughout the year.
Densities of mammals in partially protected areas: the Katavi ecosystem of western Tanzania
Authors: Caro T. M.
Published: March 2003

1.In Africa the majority of conservation areas sanction some sort of human activities within their borders but few of them are part of community‐based conservation schemes. The effectiveness of these state‐owned, partially protected areas in conserving mammalian fauna is largely unknown.

2.Large and medium‐sized mammal densities in three different sorts of partially protected area were compared to mammal densities in an adjacent national park in western Tanzania by driving 2953 km of strip transects over a 14‐month period.

3.In a Game Controlled Area that permitted temporary settlement, cattle grazing and tourist big game hunting, mammal diversity and mammal densities were relatively high. In a Forest Reserve that permitted limited hardwood extraction and resident hunting, most large species were absent. In a third, Open Area that allowed settlement, cattle grazing, firewood collection and beekeeping activities, mammal diversity and densities were again low but some large ungulates still used the area seasonally.

4.The chief factors responsible for lowered mammal densities outside the Park were illegal hunting, especially in close proximity to town, and to a lesser extent, resident hunting quotas that were too high.

5.These data suggest that state‐owned conservation areas permitting human activities within their borders cannot be relied upon as a means of conserving large and middle‐sized mammals in Africa.

6.Two methods are being employed to ameliorate this problem in Africa: excluding people from conservation areas while upgrading ground protection effort, and initiation of community‐based conservation schemes. As yet, however, very few quantitative data are available to evaluate the efficacy of these methods in enhancing mammal populations.
On rate of increase (r): patterns of variation in Australian mammals and the implications for wildlife management
Authors: Hone* Jim
Published: March 2003

1. The annual rate of increase of a wildlife population is the change in abundance or density from one year to the next. This paper compares the expected and observed means and frequency distributions of annual instantaneous rates of increase (r) for unmanipulated field populations of the European rabbitOryctolagus cuniculus, red foxVulpes vulpesand house mouseMus domesticusin Australia.

2. The observed meanrwas not significantly different from zero, the expected value, for each species, and the observed frequency distributions were not significantly different from the expected normal distributions.

3. The observed distributions were used to estimate the threshold proportions of pests that need to be killed, harvested or sterilized to stop population growth. To stop maximum population growth, as can occur after large population reductions, the proportion to kill, harvest or sterilize ranged from 0·65 year–1for foxes to 0·97 year–1for house mice. It is recommended that the estimates are tested experimentally.

4. The estimated proportions of pests to control were compared with extensive field data detailing attempts to control the pests. Estimated required levels of fox control were often less than observed levels of control. The required levels of rabbit and house mouse control could be higher than observed levels.