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Explanations for the coexistence of migratory and sedentary (resident) birds are much debated: some authors have suggested that migrants make use of surplus resources not exploited by residents, whereas others have recorded ecological shifts in residents during periods when migrants are present. These shifts have been ascribed to the presence of migrants but could equally reflect seasonal variation in the distribution of resources required by sedentary species. Here we assess how the abundance of migrants affects the territorial behaviour and habitat use of resident Sardinian Warblers Sylvia melanocephala at a stop-over site on the Rock of Gibraltar. There was a significant positive relationship between the abundance of migrants and the distances moved, time spent calling and the species and functional diversity of plants used by Sardinian Warblers on a daily basis, suggesting that migrants have a significant impact on residents. [ABSTRACT FROM AUTHOR]

This paper describes a method of scoring the neck pattern of reticulated giraffes as a simple code that can be searched for in an Excel spreadsheet. This enables several hundred individual giraffe to be recognized and repeatedly found within a database. Possible sources of error are described and quantified. Data on group size, dispersal within groups and social network patterns are described. The latter is facilitated using Ucinet 6.85 for Windows, a software package that helps to visualize and analyse such networks. [ABSTRACT FROM AUTHOR]

This study compares two methods of estimating the density of three ungulate species: Kirk’s dik-dik, impala and common zebra, in a dry savannah ecosystem. Fixed strip width and distance sampling involving direct animal counts were used in parallel, and tested for bias and precision in two habitats. Distance sampling was the method that achieved a better balance between accuracy and precision. The differences in sightability of ungulates, according to body size, colour and habitat characteristics, are taken into account by the distance sampling method, but not by the strip method, which produced, what we suspect are, underestimates of animal density. [ABSTRACT FROM AUTHOR]

One of the advantages of living in groups is that individuals may need to be less vigilant, allowing them more time for other important activities, such as foraging. This relationship between group size and per cent time spent being vigilant was investigated by observing impala in Nairobi National Park, Kenya. Three types of individual were observed: females, territorial males and bachelor males. Only females showed the predicted negative relationship between per cent vigilance and herd size. Both types of male showed no significant change of vigilance with increasing group size. There was no difference in levels of vigilance in open or closed habitats and no difference in vigilance between herds‘alone’ and herds with other species that might have provided‘extra eyes’. [ABSTRACT FROM AUTHOR]

Summary Measurements of the density of an upland population of the spittlebug Neophilaenus lineatus (L.) (Homoptera, Auchenorrhyncha) were made from 1961 to 1997. Population change from year to year is shown to be largely density-independent. Analyses of meteorological records over the 37-year period showed that the weather variable with the highest correlation with population change was mean minimum temperature in September. A simple model was constructed relating numerical changes from 1961 to 1992 to temperature, and this was found to explain 75% of the change in this population. The model was used to predict numerical change from 1993 to 1997 over which period it explained 70% of the change. The model predicts that a projected rise in mean temperature of 1°C would increase the mean population density of N. lineatus by 50%. Experimental cloches at the upland site which raised mean temperature by 1°C, had N. lineatus densities which were 157% higher than in adjacent control quadrats. An experimental raising of field temperature at a lowland site where population change had been shown to be density dependent did not result in density changes, although dates of hatching were earlier. [ABSTRACT FROM AUTHOR]

Examines the aggregation and interspecific abundance and occupancy relationship of species of organisms. Effect of spatial distribution of individuals; Exhibition of aggregation of species; Complexity of the relationship between aggregation and density.

Summary We investigated cohort differences in the lifetime breeding success and survival of male red deer Cervus elaphus L. in an increasing population on the Isle of Rum, Scotland. There were significant differences in survival through different stages of the life span between 15 cohorts of males, ranging between: 0.26–1.00, calf survival through first winter; 0.56–1.00, yearling survival; 0.44–0.94, adult survival. This variation in survival was related to environmental conditions in the cohorts' year of birth, whilst controlling for annual effects. For 10 cohorts of males with complete lifetime data, mean breeding success also varied significantly, between 0.83 and 3.86. This variation, too, was associated with environmental conditions in the cohorts' year of birth. Since in many sexually dimorphic mammals, the growth and survival of males is more strongly affected by adverse environmental conditions than that of females, we expected that cohort variation would be more extreme amongst males than females. This was true, for both cohort survival and reproduction. We expected to observe selection on cohort adult body size, related to survival or reproduction. However, there was no evidence of variation in adult body size between cohorts, nor for relationships between differences in body size between cohorts and measures of survival or breeding success. Cohorts which underwent high intial mortality subsequently experienced higher adult survival than cohorts not subjected to high density-related selection early in life. [ABSTRACT FROM AUTHOR]

Summary Juvenile flying animals, including bats, often cease increasing, or even decrease in body mass after the onset of flight. The low body mass of juvenile bats may be a result of stresses associated with the initiation of flight, or may be an adaptation to reduce flight costs. To test these hypotheses, the body masses of adults and unknown aged juvenile big brown bats (Eptesicus fuscus ) were separately compared in August 1990 through to 1995. It was hypothesized that there should be little variation in the body mass of juveniles from year to year if low body mass is an adaption to reduce flight costs. The foraging behaviour and body masses of bats of known or estimated age were also compared in 1994 and 1995. Ambient temperature at sunset was greater in 1994 than in 1995. It was assumed that prey density and predictability increased with temperature, and hypothesized that if low body mass results from energetic stress, then this should be more apparent in 1995. Using radiotelemetry, the foraging behaviour of juvenile, yearling and adult E. fuscus was compared in 1994 and 1995 to determine whether young bats attempt to compensate for energetic shortfalls by foraging for longer, or emerging earlier, than adults. Unknown-aged juveniles did not differ significantly in body mass in August from 1990 through to 1995. Adults were significantly heavier in August in 1990 and 1994 than in 1991, 1993 and 1995. Known-aged juveniles had lower body mass than adults in 1994, and lower wing loading than adults in 1995. Known-aged juveniles did not differ in mass between 1994 and 1995, while adults were heavier in 1994. The foraging times for juvenile and adult bats were both significantly related to ambient temperature. However, the slope of this relationship was steeper for weaned juveniles than for adults. The foraging times of yearling and adults bats were not significantly different. The emergence times of juvenile and adult bats did not differ, nor did the emergence... [ABSTRACT FROM AUTHOR]

Summary Pre-breeding survival, i.e. survival from fledging up to the third winter, of barnacle geese (Branta leucopsis) was analysed by using more than 45000 resightings of 1302 individually marked birds. Since observations from the wintering areas only were used, the survival estimates obtained were not confounded by natal dispersal. Post-fledging survival, i.e. survival from fledging to the start of the first winter, differed significantly among the 10 cohorts analysed. These differences were related to the mean body weight and mean tarsus length of cohorts just before fledging. In further analyses, when data from all cohorts were combined, body weight and tarsus length of individuals just before fledging were found to be positively related to Post-fledging survival. Post-fledging survival rates were, on average, lower than survival rates after the first winter. This age effect was largest in cohorts with low mean body weight at capture and was absent in cohorts with high mean body weight at capture. The age effect on survival could only partly be explained by individuals with low body weight having lower survival and successively disappearing from the cohort. It was therefore concluded that other factors must have contributed to the age effect as well. It is hypothesized that lightweight birds are more vulnerable to, for example, diseases, parasites and predation during the first months of their life. Once they have survived this critical period, the effects of characters related to low body weight at capture seem to disappear. Body size of juveniles just before fledging has previously been found to be greatly affected by weather factors and the availability of high quality food during the growth period. Hence, a considerable part of the observed variation in Pre-breeding survival appears to be outside the individual's control. [ABSTRACT FROM AUTHOR]

Summary We used path analysis to investigate the causal relationships between Iberian lynx and Egyptian mongoose track numbers, and to estimate the direct effect of the former on the latter in the Doñana area (2750 km2 ), south-western Spain. Relative abundance of rabbits, shrub cover and protection level were also considered in the path analysis. An observational study consisting of a repeated track survey with a split-plot design was also carried out between 1990 and 1996 to independently test the results obtained by path analysis. Maximum likelihood ratio tests of the goodness-of-fit of the model to the data and other indices used all indicated that the proposed theoretical model depicting the relationships among variables was adequate. Egyptian mongooses suffered a significant direct negative effect from lynx, and rabbits and protection level positively, and significantly affected lynx track abundance; rabbits were also significantly affected by shrub cover (all these standardized partial correlation coefficients ranged from 0.34 to 0.41). Shrub cover did not directly affect either lynx or mongoose tracks. Relatively important indirect effects were found between shrubs and lynx (0.12), and between rabbits and mongooses (-0.14), and protection and mongooses (-0.17). The two latter non-intuitive indirect effects were through the lynx path, as a consequence of the negative direct influence of lynx on mongooses. The repeated track censuses confirmed that lynx presence significantly affects number of mongoose tracks. In areas without lynx, mean number of mongoose tracks were 3.6 times higher than in areas with lynx. It remains an interesting question which of several proposed hypotheses explains co-existence of both species in south-western Spain. [ABSTRACT FROM AUTHOR]

Summary The population dynamics of two moth species, Plodia interpunctella (Hübner) and Ephestia kuehniella Zeller in the presence of their shared parasitoid, Venturia canescens (Gravenhorst), were studied in well replicated time series experiments. Moths were prevented from competing for resources and could therefore only interact via the shared parasitoid. This study examines the consequences of apparent competition on the population dynamics of a simple laboratory insect assemblage. Ephestia kuehniella suffers severly in the presence of the shared parasitoid. In all eight replicates, this moth species is eliminated. Time series analysis reveals that the E. kuehniella populations show divergent oscillations. Plodia interpunctella and V. canescens populations show persistent populations. Time series analysis reveals that there is a delayed density dependence acting on these populations and the dynamics are either stable equilibrium or damped oscillations. Repeated-measures analysis of the strength of the indirect interaction reveals that the effects of apparent competition before E. kuehniella is lost are amensal. The indirect interaction between E. kuehniella and P. interpunctella is [–, 0] rather than [–, –]. [ABSTRACT FROM AUTHOR]

Summary Many hypotheses for hatching asynchrony within avian clutches centre around food supply during the laying or nestling periods, but food is measured in few studies. Patterns of clutch size and hatching asynchrony were analysed in the Eurasian kestrel [Falco tinnunculus (Linnaeus)] breeding in Finland, where small mammal populations show dramatic 3-year cycles. Data collected over 12 years showed that clutches were larger when food was more abundant in spring. While controlling for clutch size, hatching was more synchronous in the low phase of the vole cycle compared to the increase phase, contrary to conventional interpretation of the brood reduction hypothesis. The age of the female, but not the age of the male was associated with the degree of asynchrony. Paradoxically, numbers of voles were most stable in the ‘low’ phase, which may lead to a unique situation, where food is more predictable when scarce. Kestrels have small, synchronous clutches in the ‘low’ phase and large asynchronous clutches in the ‘increase’ phase. Based on results of this study, it is suggested that it is important to consider the predictability of food, and not only the mean abundance of food when evaluating hypotheses for hatching asynchrony. Patterns of clutch size and hatching asynchrony at the population level can be used to evaluate current energy-related hypotheses for asynchrony. [ABSTRACT FROM AUTHOR]

Summary The effects of human-caused fragmentation of boreal forest on the abundance of red fox Vulpes vulpes L. and pine marten Martes martes L. were studied by combining the Finnish wildlife-triangle snow-track data (1990–94) with land-use and forest resources data employing the GIS. Two study areas (each 45 000 km2 ) located in northern and southern Finland were selected for the investigation. The extent of landscape that best explained predator abundance (tracks per 10 km 24 h-1 ) was the same (about 100 km2 ) in both species and study areas. The decreasing proportion of older forest and the increasing proportions of young forest and agricultural land in the landscape positively affected track density of red fox. The relationship between agricultural land and fox abundance, however, was characterized by a convex curve peaking at 20–30% of agricultural land. With the habitat classification used, landscape composition explained 26% and 11% of the spatial variation in fox abundance in the northern and southern study area, respectively. The relationship between landscape composition and pine marten abundance was not as clear as in that of red fox. Landscape composition explained 10% and 6% of spatial variation in pine marten abundance in the northern and southern study area, respectively. In both areas a positive impact occurred with the increasing proposition of young forest in the landscape, but in the northern area the negative effect of increasing proportion of agricultural land was dominant. The abundances of red fox and pine marten were not negatively correlated, indicating that competition or intraguild predation by red fox do not determine abundance of pine marten on a landscape scale. A general increase in predation pressure by generalist predators in fragmented forest landscapes has been an intensively discussed conservation problem during recent years. We conclude that the red fox is a species potentially... [ABSTRACT FROM AUTHOR]

Summary Age-specific variation in the reproductive performance of great skuas in Shetland, U.K., was investigated during a period of fluctuating sandeel availability between 1988 and 1993. Increased sandeel abundance was associated with earlier laying dates, increased clutch volumes and improved fledging success. Sandeel abundance had no effects on clutch size and hatching success. Parental age improved haying date and clutch size in a nonlinear manner. Laying date became earlier in the youngest age classes, with the effect being negligible in older birds. Clutch size increased with age up to 18 and then declined in older birds. Clutch volume increased with age and the probability of nest predation declined with age. There were no significant interactive effects of age and year on laying date nor clutch volume, indicating that birds of all ages benefited equally from increases in sandeel abundance. This suggests that lack of breeding experience rather than deficient foraging skills are responsible for young birds laying later. There was a significant interactive effect of year and age on fledging success that was associated with changes in sandeel availability. Success was uniformly low for birds of all ages in 1988–90 when sandeel abundance was low. Success increased with age in 1991 and 1992 during which time food supply improved. During 1993 food supply was abundant and fledging success was high in all age classes. Age-specific improvements in laying date, clutch size and nest predation were best explained by learning of skills associated with experience of breeding. Improvements in fledging success with age were probably best explained by the learning of skills associated with foraging. [ABSTRACT FROM AUTHOR]

Summary Using long-term data sets from two lowland floodplain forest bank vole populations in central Europe, we tested two predictions that with increasing densities: (i) proportions of nonparous females in winter populations would increase; and (ii) age of both nonparous and parous females would increase. These two predictions follow from the assumption that changes in age structure are driven by density-dependent shifts in age at first reproduction. Both populations were sampled by snap trapping between 1956 and 1976. For each year, we examined samples of animals collected between November and April for proportions of females with and without breeding experience and analysed their variation in age relative to the population density. The presence or absence of placental scars was used to discriminate between the parous and nonparous animals. Age was determined by measuring the length of the first mandibular molar (M1 ) roots. Both populations exhibited multi-annual fluctuations in numbers closely resembling those in northern Fennoscandia. The proportion of nonparous females in our total sample was 0.73, suggesting that it is uncommon for parous female bank voles to breed in two successive years and that their life histories are largely designed for breeding in one season only as a major reproductive strategy. Using a logistic-binomial regression model, we found that the probability of females being nonparous or parous at capture varied significantly with time, space and population density. The final model producing the best fit to data predicted that the proportion of nonparous females would be slightly larger over winter and substantially larger after high-density breeding seasons, which is consistent with the tested prediction. With increasing densities during the breeding seasons, both the nonparous and parous females became older at the onset of winter. Again, the field evidence was consistent with the predicted pattern. The age of parous... [ABSTRACT FROM AUTHOR]

Summary Tarsal spurs play an important role in intrasexual competition for females among male wild turkeys (Meleagris gallopavo ). Thus variation in spur development may have important fitness consequences. Fitness correlates of spur development were studied in a free-living population of wild turkeys and it was found that heavier males and males with longer beards had longer spurs. Males that had longer spurs spent more time on display areas during the breeding season and less time moving among these areas compared to males with shorter spurs, independently of their body mass. Otherwise ideally symmetrical spurs showed fluctuating asymmetry between left and right tarsi, the degree of absolute asymmetry decreased with spur length in adults, but not in subadults, and males that survived at least one winter had more symmetrical spurs compared to males that did not. We conclude that if the ability to produce symmetrical spurs has a genetic basis, then spur length and spur asymmetry could reliably indicate individual quality and that these traits are under directional selection for increased size and symmetry in wild turkeys. [ABSTRACT FROM AUTHOR]