Registered users receive a variety of benefits including the ability to customize email alerts, create favorite journals list, and save searches.
Please note that a BioOne web account does not automatically grant access to full-text content. An institutional or society member subscription is required to view non-Open Access content.
Contact helpdesk@bioone.org with any questions.
The Svalbard population of pink-footed geese Anser brachyrhynchus is concentrated in western Jutland, Denmark, from early March to early May. During spring, the geese shift feeding habitat from grasslands and stubble fields to new-sown fields. To avoid crop damage, grain bait is provided at five sites. The aim of this study was to quantify the exposure of geese to, and the ingestion rates of, pesticide-treated seeds, and to evaluate the potential effects at the individual and the population level. During spring 1994, approximately 7% and 1 % of the total number of goose-days were spent on new-sown cereal fields and new-sown pea fields, respectively. After the commencement of sowing, about 25% of all goose-days were spent in new-sown fields. Late-departing individually marked geese made more frequent use of new-sown fields than early-departing individuals (P < 0.001). Geese foraged intensively in new-sown fields early in the morning and sometimes late in the evening. Due to high feeding profitability of the new-sown grain compared to grass, the geese obtained half or more of their daily energy intake by feeding on new-sown cereal fields, even where bait grain was provided. Spring-sown barley is treated with the fungicide Imazalil and peas are usually treated with Thiram. The daily Imazalil ingestion rate by an 'average' goose was estimated at 9–15 mg active ingredient (a.i.), or 3–-5 mg a.i./kg body mass, which is two orders of magnitude below reported LD50 values for various species of test birds. Imazalil may have sub-lethal effects, especially on geese using the new-sown cereal fields for consecutive days, but the low toxicity and high mobility of the compound suggest that effects are minor and short-lived. The daily Thiram ingestion rate by the geese was not quantified, but it is calculated that a goose would have to eat about 100 g of peas to reach a level of Thiram ingestion (200 mg/kg diet), which could have sub-lethal effects on reproductive parameters. A goose foraging on new-sown peas can accomplish this within less than one hour. Special management precautions should be taken to deter geese from exploiting new-sown pea fields.
A recent increase in the area open to hunters in the Swedish mountains has directed attention to the possibility of overharvesting and greater wildlife disturbance. Using radio-telemetry, the movements of willow grouse Lagopus lagopus in a heavily hunted area were compared to movements in areas where hunting was prohibited. Although hunter density was higher than the regional average, no significant differences in movements, measured as rate or distance, between grouse in hunted and unhunted areas were found. Willow grouse did not move out of the hunted area, a common belief amongst many hunters. Seasonal migration was not induced by deliberate human disturbance. It is suggested that grouse reduce the risk of being killed by habitually moving within a familiar area with known escape sites (cover). Neither hunting, deliberate flushing or catch and release caused a change in the movement patterns of willow grouse. It is suggested that such disturbances were perceived as part of a naturally unpredictable predator environment, and not sufficient to alter grouse movements.
Environmental monitoring programmes are often confined by limited funds. By use of Monte Carlo simulations and GLM procedures, it is examined to what extent trends documented for some Norwegian seabird populations could have been obtained with less field effort. Changes in both breeding and wintering numbers are analysed. To minimise bias from merging different populations, only regional trends are considered. The results strongly suggest that some populations can be monitored adequately by less effort than that applied, i.e. still ensuring that the counts will reveal the various sources of variation in reliable proportions to the total variance in bird numbers. This may be achieved either by reducing the number of plots or by counting them less frequently, for example in alternate years only. General advise with respect to what changes deserve special attention from conservation authorities, and a discussion of the principles and considerations which should be taken into account when designing monitoring programmes for seabirds are presented.
In order to estimate the potential importance of each of the demographic traits egg, chick, and apparent winter survival on willow grouse Lagopus lagopus population dynamics, a sensitivity/elasticity analysis on a general model for the growth rate of breeding hen willow grouse numbers was performed. The demographic parameters used were taken from a 21-year study of willow grouse population dynamics on a Norwegian island. The growth rate of breeding hen numbers may be sensitive to changes in a parameter either because of the structure of the model or because of a substantial between year variation in the parameter. Therefore, three measures of parameter importance were used: sensitivity, elasticity and an actual elasticity coefficient (AE-coefficient). Sensitivity is an unsealed measure of the impact of a parameter, and thus cannot be used for comparisons between different parameters. Elasticity is a scaled measure of sensitivity allowing direct comparison between effects of different parameters on the growth rate (λ). To interpret the true effect of a demographic parameter on λ, between year variations in the parameter must be accounted for. The actual elasticity coefficient of each parameter is the product of the elasticity coefficient and the coefficient of variation, CV, for the demographic parameter in question. Sensitivity, elasticity and AE-coefficients showed that apparent winter survival of juveniles had the largest potential impact on changes in X, followed by egg survival, chick survival and adult apparent winter survival. Considering elasticity coefficients alone, apparent winter survival compared to survival from egg laying to four weeks after hatching had 2.3 times the impact on X. However, between year variation in apparent winter survival was far less than between year variation in survival from egg laying to four weeks after hatching, which leads to them both having a similar impact on X. Management efforts on willow grouse have largely been devoted to enhancing survival from egg laying to four weeks after hatching which was believed to be the single most important factor determining population size. The results presented suggest that equal attention should be paid to winter survival. One cause of reduced winter survival may be hunting. A model incorporating the area specific survival and chick production resulted in λ = 1, when chick production was 1.8 chicks per adult and when there was no hunting. The model suggested that grouse could not be hunted in four of the 21 years without reducing the population size on the island and in many years only a modest harvest could be recommended.
Six scat-analysis methods were compared and tested for differential assessment of a wolf Canis lupus diet in the Northern Apennine Mountains, Italy. A sample of 217 wolf scats was analysed using standardised laboratory techniques, and the recovered undigested remains were quantified according to the following diet measurements: frequency of occurrence, dry weight (estimated and measured), relative volume, and biomass ingested (two methods). With the exception of one of the biomass methods, there was no significant disagreement between the procedures examined. However, some discrepancies between rankings from different methods indicated the sources of bias that should be accounted for to avoid misleading conclusions. Frequency data can be corrected to reduce some of the associated forms of bias, whereas rankings by weight and volume appear affected by the structure of undigested remains. Although to different extents, all the methods which rank food items according to direct measures of the undigested remains, i.e. by frequency, weight, and volume, suffer from the surface to volume ratio bias of varying prey sizes. Linear-regression biomass models correct for the surface/volume bias, but there are some drawbacks when applying them, and they are limited to mammalian prey. Applicability of the biomass models should be evaluated on the basis of diet composition and prey sizes, and results carefully interpreted in concert with other field-collected information. Interpretation of scat-analysis data in order to assess the diet of wolves, as well as of other carnivores, would be greatly enhanced by comparing results obtained with two or more methods.
Radio-marked female ruffed grouse Bonasa umbellus were monitored in central Wisconsin, USA, during 1983–1988 to estimate nesting rates (the percentage of hens that initiate a clutch), clutch size, nest success, and the prevalence and success of renests. All 23 radio-marked females initiated a clutch, 22 completed a first clutch; the remaining hen was killed by a predator during laying. Mean clutch size of first nests was 11.0 ± 0.5 eggs (range = 7–13). Five of nine (56%) hens attempted to renest with a mean clutch size of 7.4 ± 1.3 eggs (range = 6–9). Mean nest success was 46%; 43% for yearlings and 60% for adults. First nests produced the large majority of eggs that hatched (86.1%) compared to renests (13.9%). Productivity was estimated at 5.8 chicks hatched for each hen alive on 20 April, the mean date of the first egg laid.
Weighing large animals in the field is often labourious and expensive. Alternative methods which replace direct measurements of body mass are, therefore, of practical value. In order to predict body mass in moose Alces alces, an allometric model based on chest circumference, sex, age and population was applied. A model to predict body mass based on chest circumference and a truncated age measurement is suggested. Impact of sex and population was weak. The ability to predict body mass was mostly influenced by chest circumference. The proportion of carcass mass to total body mass varied between 45% and 51 % among age-classes. In addition, there was a slight effect of sex on this variation, males having a proportionally larger carcass mass than females. The model's predictions of body mass are adequate for describing the distribution of body mass in moose populations and for comparing moose populations.
This article is only available to subscribers. It is not available for individual sale.
Access to the requested content is limited to institutions that have
purchased or subscribe to this BioOne eBook Collection. You are receiving
this notice because your organization may not have this eBook access.*
*Shibboleth/Open Athens users-please
sign in
to access your institution's subscriptions.
Additional information about institution subscriptions can be foundhere