It is an axiom in ecology that knowing the sheer number of individuals in a population is of very little help if the objective is to understand future and past changes in population size. Yet, this is exactly how migratory European ducks are monitored, many of which are important quarry species in several countries. We argue that present monitoring is insufficient to address objectives of wise use andsustainabilitysuchasthoseemphasisedinrecentmanagementdirectivesand multilateral international agreements. The two main problems are the almost total lack of reliable data on recruitment and mortality. We advocate a pan-European monitoring system based on undisputed scientific principles; i.e. a long-term, coordinated and standardised scheme that produces data about vital rates of duck populations as well as about harvest size. Data from such a scheme can be used by game biologists to produce predictive tools, thus providing a functional basis for management decisions for adaptive harvesting and conservation alike.

Increasing populations of cervids in Europe and North America have made the issue of overgrazing relevant outside areas with domestic or semi-domestic herbivores. Over grazing is defined depending on management objectives. I focus on challenges related to implementing a ‘range ecologist’ baseline, defining overgrazing as situations when ‘forage species are not able to maintain themselves over time due to an excess of herbivory or related processes’. Herbivores may be naturally regulated at ecological carrying capacity (K) with no overgrazing, but overgrazing may occur below K. Rare, preferred plant species can decline in density due to a ‘herbivore pit’ created by generalist herbivores, without having much effect on K. The concept of overgrazing is almost meaningless unless the issue of spatial scale is considered, and the extent to which preferred plant species decline in coverage. Herbivore population instability increases with increased population growth rate, but overgrazing depends also on the tolerance to grazing of the forage used by a given herbivore, which is closely related to functional plant traits. Ecosystem factors such as soil quality and slope also affect the likelihood that overgrazing will occur. Currently we can only qualitatively identify some important factors to consider. A better understanding of the sequence of events happening to performance of both animals and plants over time when a herbivore population increases provides a very useful approach until tools are developed to measure overgrazing quantitatively. More detailed knowledge about grazing effects on biodiversity is necessary to implement a broader ecosystem perspective of overgrazing.

Population control of great cormorants Phalacrocorax carbo sinensis has been suggested as a tool to mitigate fish losses by cormorants foraging in pound nets, gill nets and fykes. The objective of our study was to quantify the difference between first-year birds and older birds in the risk of drowning in fishing gear, and to explore the influence of population size on the proportion of individuals drowning. An index of the proportion of first-year birds and older birds that drowned was obtained for cormorants ringed in the Danish Vorsø colony using resightings of colour-ringed individuals and ring recoveries of individuals found dead. First-year birds were approximately 10 times more likely to drown than older birds. We used ring recoveries of cormorants ringed in Denmark and found dead in Denmark, North Germany and South Sweden (i.e. in the main post-breeding area) to reveal changes over a 25-year period in the proportion drowned among those recovered. Among first-year birds the proportion drowned declined from 66% in 1978–1984 to 24% in 2000–2002, and among older birds the proportion declined from 46% in 1978–1984 to 26% in 1999–2002. During 1978–2000, breeding numbers in Denmark increased from 1,400 to 42,500 nests, and the proportion of cormorants drowned among those recovered was significantly negatively correlated with population size. This suggests that the proportion of the population foraging in nets declined as the population increased. The damage caused by cormorants foraging in pound nets is, therefore, unlikely to decrease in proportion to reductions in population size reached through population control.

We examined 70 years (1931–2000) of black brant Branta bernicla nigricans abundance on Humboldt Bay, California. We used linear regression to convert count data to a standard variable (use-days) for evaluating hypotheses that explain temporal trends in brant use. Winter and spring brant-days on Humboldt Bay declined sharply in the mid-1950s and continued to decline through the mid-1980s, but have since increased. Evidence suggests that this trend may have been driven largely by changes in temporal patterns of hunting pressure on Humboldt Bay. We found little convincing support for alternative hypotheses such as changes in eelgrass Zostera marina condition over time, effects of non-hunting disturbance, and correlation with trends in abundance at the flyway level. Our study affirms the appropriateness of current hunting regulations for brant in California, but poses a challenge to wildlife managers who wish to provide hunting opportunities without displacing brant from important staging and wintering areas.

The policy of the European Commission prohibits hunting of migratory birds while they travel to their breeding grounds. To date, spring migration dates of ducks have mainly been determined using bird counts, but the validity of this sometimes disputed method has never been tested. We used ring-recovery data from close to 9,000 teal Anas crecca ringed in the Camargue, southern France, to determine the onset of spring migration. This method makes it possible to avoid potential biases linked to duck counts, and was used to test the validity of spring migration dates inferred from such counts. Depending on the type of analysis (intra- or inter-annual recoveries), teal appeared to start migrating from the Camargue during the first or second 10-day period of January, with no significant differences between years, and no effect of the bird's age or sex. However, when taking potential winter dispersion into account, we suggest that a conservative estimate for the onset of spring migration is the first 10-day period of February. Migration dates inferred from ring-recovery analyses were consistent with earlier results from duck counts, and provide a firm basis for policy making related to hunting. Though ringing data should be preferred when available, our study suggests that determining migration dates from bird counts may be a reliable method for teal, and potentially for other dabbling and diving ducks as well.

In 1992–1993 we replicated a mourning dove Zenaida macroura marginella study conducted in 1951–1952 near Fillmore, Utah, to document differences in nesting activity between time periods. Nests along irrigation canals averaged 6.8 nests/km in 1993 vs 36.9 nests/km in 1952. Dove production was 2.4 offspring per pair in 1993 vs 3.9 offspring per pair in 1952, and nest abandonment was higher: 12.9 vs 6.2%, respectively. No differences occurred in nest success (57.1 vs 57.4%) or nest predation (35.7 vs 29.6%). The breeding season was 80 days in 1952, 75 days in 1992, and 70 days in 1993. Nest height was lower in 1992–1993 than in 1951–1952, and nest frequency by vegetation type changed from predominately willow Salix spp. to a broader distribution of nests among available vegetation types. Two distinct riparian habitats existed in both time periods: a natural creek and man-made irrigation canals. The highest nest density occurred in riparian areas during both time periods, but the relative number of nests within these riparian habitats differed, with the highest number of nets occurring along the creek in 1992–1993 and along the irrigation canals in 1951–1952. The highest predation rates occurred in creek habitat during 1992–1993.

Numbers of European hares Lepus europaeus have declined throughout Europe due to agricultural intensification. However, hares are more common in intensive arable areas than in pastural areas. To identify factors limiting populations, functional explanations for differences in density of hares were sought. We compared demography (litter size, prenatal mortality and participation in breeding by females), body condition (urinary and serum nitrogen, kidney fat, bone marrow fat, skeletal size and body weight), and dietary quality of hares from parts of England and Wales where they are present at relatively high densities (arable habitats) and at relatively low densities (pastural habitats). In pastural areas a lower proportion of adult females were lactating in late winter than in arable areas. Recruitment was therefore lower in pastural than in arable habitats. Hares from pastural areas were smaller, lighter and had less fat than those from arable areas, but dietary quality was similar. Thus hares in low-density populations from pastural areas were able to obtain a good-quality diet, but expended more energy and were unable to maintain body condition as well as those from arable areas. Pastural habitat, which in England and Wales is relatively warm and wet, is suboptimal for hares. The reduced recruitment and chance of survival of hares in the pastural habitats we describe may explain the differences in density of hares in arable and pastural habitats. Efforts to conserve the hare should focus on the reduction of predation and exposure to unfavourable weather by the provision of year-round vegetative cover (such as fallow land, rough grassland and shelterbelts), to increase the chances of survival of leverets and adult hares.

The marine otter Lontra felina lives along the Pacific coast of South America from 6°S to 56°S. A method for estimating marine otter abundance is described and a comparison of the characteristics of the terrestrial habitat of this species in southern Chile is made. From June 1999 to June 2000, we conducted eight hours of observations on one day each month at four study sites. An average of 3.8 observable otters/km were recorded, with significant differences between sites but no systematic trends with regard to season. Observable pups were recorded year-round. Otters spent 80% of their time out of view, engaged in behaviours other than feeding; observable otters were mostly seen feeding. The methodology described is effective for indexing abundances at small geographic scales. The marine otter needs both an aquatic habitat for foraging and a terrestrial habitat with an abundance of safe shelters, which, in turn, could limit the distribution of the species when human settlers and domestic dogs utilise the terrestrial habitats.

Optimal foraging theory predicts that an animal should optimize its time spent in food patches based on resource levels and, if preyed on by another species, predation risk. In large mammal predator-prey systems, previous studies have suggested that prey do consider predation risk when foraging and tend to avoid high-risk areas. In contrast, if large mammalian predators are trying to optimize their foraging, we predict that they should select these high-risk areas because such areas represent higher predation success. For pumas Puma concolor in southeastern Idaho, previous work showed that edges of forests were the most successful hunting areas for mule deer Odocoileus hemionus compared to open and forest areas. We tested the prediction that pumas should optimize their foraging strategies by selecting edge areas during periods of movement. We followed puma tracks in the snow and recorded for every 20 m whether the pumas had been in an edge, open or forest area. We used a resource selection function and composition analysis to test if pumas were preferentially selecting edge areas over open or forested areas. Based on the resource selection function, pumas were four times more likely to use edge than open areas, but used edge and forest areas equally. Results of the composition analysis indicated that pumas also used edge areas significantly more than open but similar to forest areas. As pumas were selecting edge areas and avoiding open areas to forage, these results indicated that pumas may be foraging optimally. However, the equal use of edge and forest areas did not support our predictions, and we discuss possible explanations of these results.

Sika deer Cervus nippon populations in eastern Hokkaido, Japan, increased rapidly during 1990–1998. This increase appeared to have halted in 1999–2000, probably due to increased hunting and nuisance control. The period of rapid increase was associated with a disproportionately rapid increase in compensation paid for deer damage to crops. We studied changes in diet during 1990–2000, as reflected by stable isotope ratios of C and N in tooth collagen. We hypothesised that isotope ratios would demonstrate dietary shifts related to population levels and/or time, and that shifts in isotope ratios would be consistent with increasing individual consumption of pasture grasses at higher population levels. δ¹³C isotope ratios of tooth collagen in 3-year-old sika indicated a diet dominated by C3 plants throughout the period, and that forage species other than pasture grasses and dwarf bamboo Sasa nipponica (the main crop and woodland understory plants, respectively) were important elements. There was a significant decline in the δ¹³C isotope ratio during 1990–2000 in both males and females. δ¹⁵N values showed no trend with time for males, but increased over time in females. Indices of population (Sightings per Unit Effort, SPUE) were negatively correlated with female δ¹³C, and positively correlated with female δ¹⁵N, values, indicating a shift in diet over the period, especially among females. This shift may be related to population and/or offtake levels, in particular the rapid increase in female offtake for nuisance control and hunting during the period. The data are consistent with a relative increase in pasture grass consumption per individual at higher population levels; however, other explanations of the data are equally plausible. Possible dietary changes, and other factors, influencing the observed shift in isotope ratios are discussed. Although statistically significant, the magnitude of dietary shifts nevertheless appeared small, and did not provide evidence which would justify modifying the current policy, of limiting crop damage through managed population reduction to about 25% of peak levels.

To examine how endogenous reserves may influence avian life history, it is often necessary to quantify carcass composition. However, proximate analyses are expensive, time-consuming and difficult to perform under field conditions. Consequently, carcass composition is often estimated from easily measured data. We evaluate methods of estimating carcass composition of the common eider duck Somateria mollissima. We measured, dissected and completed proximate analyses of 92 eiders. Predictive models were derived using multiple regressions of 70 birds, while the remaining 22 were used as an independent test of the models. Each model's accuracy was evaluated by comparing estimates against known values of protein and lipids, using root mean square error (RMSE). Abdominal and leg fat pad mass were highly correlated with total lipid (r = 0.92), and body mass was highly correlated with total protein (r = 0.80). Models that used body mass, fat depots and/or muscle group data were the most accurate (lipids adjusted R² = 0.93, RMSE = 14.60; protein adjusted R² = 0.74, RMSE = 11.14). By using these equations it is possible, using dissection data, to accurately estimate carcass composition of eiders. If dissection data are not available, one can still estimate carcass composition using equations that require only morphometrics although in our lipid analysis such equations had relatively low accuracy (lipids adjusted R² = 0.54, RMSE = 32.74).

We radio-tagged and tracked 22 hen and three cock capercaillie Tetrao urogallus in northeast Scotland during 1989–1995. Natal dispersal distances of 13 first-year hens ranged within 1–30 km (median: 11 km). There were two main periods of dispersal, autumn and spring, with much individual variation. Some hens dispersed in autumn, some in spring, some in autumn and again in spring, and some moved little. Of 10 hens that nested, seven did so in their first year, two not until their second and one in her third year. After their first year, hens were quite sedentary, but some showed increased movement in April as they attended leks. Capercaillie in Scotland live in fragmented woodlands. How far they disperse is an important consideration when managing woods for their benefit.