Winter Severity Index Research Articles

Solar forcing on the ice winter severity index in the western Baltic region

The Sun is the fundamental energy source of the Earth's climate and therefore its variations can contribute to natural climate variations. In the present work we study the variability of ice winter severity index in the Baltic Sea since the 15th century and its possible connection with solar activity. Based on a new method for finding and measuring amplitude–phase cross-frequency coupling in time series with a low signal/noise ratio, we suggest that the ice winter severity index in the Baltic Sea is modulated by solar activity and solar motion in several frequency bands during the last 500 years. According to our model a strong coupling between the decadal periodicity in the ice winter severity index time series and the secular periodicity of solar activity is present. We found that the ice winter severity index is strongly modulated by solar activity at the decadal periodicity. We also found that the 180 year periodicity of the Barycentre motion modulates the amplitudes of the decadal periodicity of solar activity and the ice winter severity index. This method represents a useful tool to study the solar–terrestrial relationship.

Winter severity index using widely available weather information

Context Changes in global climate and evidence of species’ responses to these changes have increased interest in relationships between climate variables and species demography and distributions. Although an important tool for many ecological questions, large-scale climate indices fail to provide the spatial resolution necessary to investigate drivers of change across small spatial scales. Climate variables that describe yearly climate variation at large spatial extents and small spatial grain are needed. Aim Here we develop a model for snow depth using snow water equivalent (SWE) data, which are readily available in a number of formats, to be included in a more general climate index. We use an existing winter severity index (WSI) for white-tailed deer to test the performance of the model. Methods We obtained data for 13 weather stations from north-western Canada, reporting both SWE and snow depth. We accumulated a snowpack from daily SWE of snowfall and then tested two methods for converting the SWE of the snowpack into the snow portion of the WSI. We then generalised the model for application to the northwest forest climate region. Key results Coefficients of determination (R2) relating the actual and predicted snow depth portion of the WSI ranged from 0.41 to 0.78, with only three stations being below 0.50. Coefficients of determination (R2) relating the actual and predicted WSI for the northwest climate region ranged from 0.58 to 0.88. Conclusions The SWE model predicts the snow portion of the WSI well for most stations and, when incorporated into the full WSI, provides a good measure of relative winter severity across space and time for most stations. Implications The method developed here could be applied elsewhere, where snow depth is an important factor in species ecology. The benefit of this approach is a comparatively simple method that maximises the use of widely available SWE data in place of snow-depth data.

Socioeconomic and ecological correlates of bobcat harvest in Minnesota

AbstractManagement of game animals requires understanding of factors that affect harvest levels. Although influenced by international law, bobcat (Lynx rufus) management is the responsibility of state or provincial agencies, and jurisdictional environmental, ecological, and regulatory differences may alter which variables influence harvest. Consequently, our understanding of the factors driving bobcat harvest should be at a scale similar to that at which they are managed. We associated 32 years of bobcat harvest data from Minnesota with socioeconomic (e.g., pelt prices, license sales) and ecological variables (e.g., prey abundance, bobcat‐specific index of winter severity) to determine what variables most strongly influenced annual bobcat harvest. We constructed candidate negative binomial generalized linear models based on an information–theoretic approach and used quasi‐likelihood Akaike's Information Criterion adjusted for small sample size to assess the relative performance of each model. Our best model suggested that annual bobcat harvest in Minnesota was positively related to the proportion of scent stations visited by bobcats and season length, and negatively related to the proportion of days when the maximum temperature did not exceed the bobcat's lower critical temperature. Our results differ from those of other studies examining factors influencing furbearer harvest that have suggested furbearer harvest is driven primarily by pelt price, and suggest that managers can influence the annual harvest of bobcats by changing season length. © 2011 The Wildlife Society.

Ice winter severity in the western Baltic Sea in the period of 1301–1500: comparison with other relevant data

AbstractA 700‐year time series of ice winter severity index (referred to as Ice Index in this contribution) which additionally includes the period from 1301 to 1500 is now available for the region of the western Baltic. It is compared with air temperature time series, NAO, and other relevant indices. As expected for a regional time series, agreement with larger‐scale northern hemisphere temperature variations is found only on longer time scales. Very good correspondence, even on shorter time scales, is obtained using a geographically close time series of annual mean air temperatures for the Low Countries (The Netherlands and Belgium). Although the data basis for the additionally included 1301–1500 period is quite sparse, there is also very good correspondence in this period. Correlation with the NAO Winter Index is generally negative, but the correlation is not significant for earlier periods. Copyright © 2011 Royal Meteorological Society

Grouse dynamics and harvesting in Kainuu, northeastern Finland

We study the dynamics of the capercaillie, black grouse, hazel grouse and willow grouse in Kainuu game management district in northeastern Finland in the years 1989 – 2004. It appears that the 6 – 7 year periodicity that prevailed in this region from 1960s up to 1980s has now vanished in all species. Th e grouse data are modelled using a linear autoregressive model with lag terms for population dynamics including grouse harvest as annual bag and an index of winter severity (winter-time area of Baltic Sea ice cover). We use the Akaike information criterion for selecting the best model for each species; fi rst order lag is forced to the models. It turns out that a term is needed for harvesting (with a negative coeffi cient) in models for all species. For the capercaillie and the hazel grouse second order lag was included, for the black grouse and the willow grouse fi rst order lag suffi ces. Th e willow grouse is the only species where the index of winter strength (with a negative coeffi cient) is needed in the model.

Relationship between winter severity and survival of mule deer fawns in the Peace Region of British Columbia

This extension note summarizes results of an ongoing study to measure the survival of mule deer ( Odocoileus hemionus) fawns through their first winter in the Peace Region of British Columbia. Each spring since 1991, mule deer were counted and classified by sex and age by driving along roads that go through areas known for providing good winter range. Seven transects were driven for a total distance of 205.3 km. The number of fawns observed is expressed as a ratio of fawns per 100 does. Average monthly air temperature and total monthly snowfall data from November to the following April from 1991 through 2008 were obtained from Environment Canada’s website. A winter severity index (WSI) integrating temperature and snowfall data was calculated and correlated to the observed fawn-to-doe ratio. A statistically significant relationship between this ratio and the WSI was obtained through regression analysis. Resulting data confirms previous research that showed survival of fawns through their first winter is higher in milder winters. For the same time period, we also compared WSI values for the Peace Region with those from three other areas in British Columbia. Results indicate that, on average, the Peace Region experienced harsher winter conditions than the other regions. The variation of the WSI was also much greater in the Peace Region. These results have implications for mule deer management in this region.

Survival, Birth Characteristics, and Cause‐Specific Mortality of White‐Tailed Deer Neonates

ABSTRACT Understanding survival of and factors that may predispose newborn deer (Odocoileus spp.) to mortality contribute to improved understanding of population dynamics. We captured free‐ranging white‐tailed deer neonates (n = 66) of radiocollared females that survived severe (Winter Severity Index [WSI] = 153) and mild (WSI = 45) winters 2000–2001 and 2001–2002. Mean dates of birth (26 May ± 1.7 [SE] days and 26 May ± 1.3 days) and estimated birth‐masses of 2.8 ± 0.1 kg and 3.0 ± 0.1 kg were similar between springs 2001 (n = 31) and 2002 (n = 35), respectively. Neonate survival was similar between years; pooled mortality rates of neonates were 0.14, 0.11, and 0.20 at 0–1 weeks, 2–4 weeks, and 5–12 weeks of age, respectively, and overall survival rate for neonates to 12 weeks of age was 0.47. Predation accounted for 86% of mortality; the remaining 14% of deaths were attributed to unknown causes. Black bears (Ursus americanus) were responsible for 57% and 38% of predation of neonates in springs 2001 and 2002, respectively, whereas bobcats (Felis rufus) accounted for 50% in 2002. Wolves (Canis lupus) accounted for only 5% of predator‐related deaths. Low birth‐mass, smaller body size, and elevated concentrations of serum urea nitrogen (26.1 ± 2.6 mg/dL vs 19.3 ± 0.8 mg/dL) and tumor necrosis factor‐α (82.6 ± 78.6 pg/mL vs. 2.3 ± 0.5 pg/mL) were associated with neonates that died within 1 week of birth. Even though we did not detect a direct relation between winter severity and birth or blood characteristics of neonates, evidence suggests that birth‐mass and key serum indices of neonate nutrition were associated with their early mortality. Thus, managers can make more informed predictions regarding survival and cause‐specific mortality of fawns and adjust management strategies to better control deer population goals.

Control of a coypu Myocastor coypus population in northern Italy and management implications

The effects of removal on the structure of a coypu population were investigated during a three‐year trapping program in the Val Campotto wetlands (northern Italy). The investigation was conducted on 267 specimens collected from March to December 1996. Winter severity index values indicated a sequence of cold winters, which may explain the unusual lack of individuals in the 0–4 months age class. Nevertheless, the demographic changes due to cold winters were counterbalanced by a high birth rate, the presence of pregnant females throughout the year and a low rate of embryo resorption (suggesting a high recruitment rate). Despite the intensive trapping campaign from 1994 to 1996 (8600 animals removed), no reduction of coypus was observed. Control campaigns and cold winters temporarily affected the sex ratio and age structure of the population, but did not limit coypu abundance. These results were compared with data collected during similar coypu control programs carried out in Italy and abroad.

Ice Bridges on the St. Lawrence River as an Index of Winter Severity from 1620 to 1910

Abstract Temperature reconstruction of the last thousand years suggests that an unprecedented warming (+0.6°C) occurred over the globe in the last century. However, regional variations in climate are not resolved by Northern Hemisphere reconstructions. In northeastern North America, past climate and, particularly, past winter variations are poorly known. Here, the authors report on the variation of a winter temperature index during the 1620–1910 period, based on the ice bridge formation (IBF) rate on the Saint Lawrence River at Québec City (Canada), combined with instrumental data (1876–2000). During this 300-yr period, the IBF rate shows that winters in the seventeenth and eighteenth centuries were warmer than those in the nineteenth century. In particular, the IBF rate suggests that winter severity culminated in the 1850–1900 period, while very few ice bridges were reported between 1620 and 1740, presumably because of warmer temperatures and the relative scarcity of historical documents for the 1680–1740 period. These data suggest that winter temperature, particularly between ∼1800 and 1910, was 2.4° to 4.0°C colder than the last 30-yr average. Major volcanic eruptions had a significant positive impact on IBF rates, which is consistent with their role as important climate-forcing events.

Development and evaluation of an accounting model for estimating deer population sizes

We developed a deterministic population model to simulate dynamics of the white-tailed deer ( Odocoileus virginianus) herd in the Mille Lacs Wildlife Management Area, Minnesota. The model was driven by three primary parameters representing reproduction, harvest, and natural mortality. Reproductive rates were age-specific, while harvest and natural mortality rates were age- and sex-specific. Natural mortality rates were estimated using survival data collected from 81 radio-collared female deer during 1996–2000. Minimal variation was observed in annual summer survival rates (range = 96–100%), but annual winter survival rates varied (range = 76–96%) and were related to winter severity indices ( P = 0.02). Deer herd dynamics were simulated from 1990 to 2001 and population estimates derived from aerial surveys conducted in 1997 and 2001 were used to validate simulated model estimates. Sensitivity analyses were performed to identify important model parameters and quantify error in model estimates caused by inaccurate input data used during deterministic simulations. Model estimates were most sensitive to biased summer survival, winter survival, and productivity rates of adult females. High variance in model estimates was caused by annual variability in adult female winter survival, adult female productivity, and fawn female summer survival. We recommend collecting data for sensitive model parameters to improve model accuracy. A stochastic model was used to simulate herd sizes that could have occurred in the real population and these population estimates were compared to simulated estimates derived from the deterministic model to assess model performance. This analysis indicated that population estimates produced by the deterministic model would be reasonably accurate for up to 4 years. However, accuracy in modeled estimates declined overtime which suggested that accounting models should not be used exclusively as long-term population monitoring devices for deer management. Additionally, we developed an individual-based population model to examine the effect demographic stochasticity had on error in model estimates for small deer herds. The relative variation in model output decreased in a curvilinear fashion as the number of adult females in the initial population increased. Our findings indicate that while deterministic accounting models are useful to guide research activities and assess potential consequences of proposed management strategies, they are not designed to monitor deer abundance over an extended period of time.

Elk exposure to arsenic in geothermal watersheds of Yellowstone National Park, USA.

Geothermal activity in Yellowstone National Park (WY, USA) (YNP) results in elevated levels of arsenic in surface waters, aquatic vegetation, and sediments in the Upper Madison River Basin. This study was conducted to determine concentrations of arsenic in the tissues, feces, and rumen contents of elk (Cervus elaphus) residing in the Madison-Firehole (MF) River basin, and to evaluate potential arsenic exposure pathways. Concentrations of total arsenic in MF elk were significantly higher than in control elk populations, and analysis of arsenic in surface waters, elk forage, sediments, and soils suggests that the predominant arsenic exposure pathways are forage species found in aquatic and riparian habitats. Analysis of arsenic species in selected plant and elk samples indicated that the ingested forms of arsenic are predominantly inorganic, while the appearance of dimethylarsonate in elk rumen and feces suggests that arsenic is subject to methylation reactions after ingestion, potentially contributing to arsenic detoxification. Arsenic:creatinine ratios of elk urine samples analyzed across three different winters increased during winter progression and were correlated with total snow water equivalent as an index of winter severity. Exposure to arsenic and other trace elements (fluorine) may contribute to the previously observed decreased life expectancy of MF elk relative to control populations.

Winter severity in the Great Lakes region: a tale of two oscillations

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 24:19-31 (2003) - doi:10.3354/cr024019 Winter severity in the Great Lakes region: a tale of two oscillations Sergei Rodionov1, Raymond A. Assel2,* 1Department of Computer Science, Campus Box 430, University of Colorado, Boulder, Colorado 80309-0430, USA 2National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory, Ann Arbor, Michigan 48105-2945, USA *Corresponding author. Email: assel@glerl.noaa.gov ABSTRACT: The effects of Pacific Decadal Oscillation (PDO) and the El Niño-Southern Oscillation (ENSO) on Laurentian Great Lakes regional winter air temperature and, more generally, surface-air temperatures (SAT) over North America are examined. The relationship between ENSO and winter severity in the Great Lakes is highly nonlinear and depends on the strength of El Niño events. Significant positive correlation between the winter severity and ENSO indices noted in earlier works is limited to strong El Niño events and is associated with an expansion of positive temperature anomalies in NW North America inland toward the Great Lakes. Although both ENSO and PDO are positively correlated with the Pacific-North American (PNA) teleconnection index, a closer look at the large-scale atmospheric circulation associated with the 2 oscillations reveals a substantial difference. During warm PDO phases (not coincident with strong El Niño events), atmospheric circulation resembles the classical PNA pattern, with a strong Aleutian Low at the surface and amplified ridges and troughs in the mid-troposphere. During strong El Niño events the Aleutian Low is also stronger than normal, but shifted eastward, to the Gulf of Alaska. Over North America, an upper atmospheric ridge on the west is not accompanied with a deep trough on the east as in the classical PNA pattern. As a result, outbreaks of cold Arctic air over the eastern US are rare and winters in the Great Lakes region are abnormally mild. KEY WORDS: Great Lakes · Pacific Decadal Oscillation · El Niño-Southern Oscillation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 24, No. 1. Online publication date: June 10, 2003 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2003 Inter-Research.

A Contribution to the History of European Winters: Some Climatological Proxy Data from Early-Sixteenth Century Swedish Documentary Sources

In this paper, the potential is explored for climatological information on winter weather in a hitherto largely neglected category of historical documentary sources (correspondence letters) covering two decades of the less studied intermediate stages between the proposed warm High Middle Ages and what has been termed `the Little Ice Age'. A discussion concerning some problems of interpretation is presented from a historical methodological point of view. Content analysis, with special attention paid to contemporary terms and expressions linked to transport and travel, shows that winters in Sweden during the first decades of the sixteenth century, in comparison with the average of the late twentieth century, were on the whole somewhat shorter in duration. Two of the winters studied can be said to display some extreme characteristics; one exceptionally mild, and one with an unusually early onset. On the whole, the result diverges slightly from previously published winter severity indices and confirms regional disparities in the middle phase between a possible warm High Middle Ages and the so-called `Little Ice Age'.

Atmospheric teleconnection patterns and severity of winters in the Laurentian Great Lakes basin

We analyzed the relationship between an index of Great Lakes winter severity (winters 1950–1998) and atmospheric circulation characteristics. Classification and Regression Tree analysis methods allowed us to develop a simple characterization of warm, normal and cold winters in terms of teleconnection indices and their combinations. Results are presented in the form of decision trees. The single most important classifier for warm winters was the Polar/Eurasian index (POL). A majority of warm winters (12 out of 15) occurred when this index was substantially positive (POL > 0.23). There were no cold winters when this condition was in place. Warm winters are associated with a positive phase of the Western Pacific pattern and El Niño events in the equatorial Pacific. The association between cold winters and La Niña events was much weaker. Thus, the effect of the El Niño/Southern Oscillation (ENSO) on severity of winters in the Great Lakes basin is not symmetric. The structure of the relationship between the index of winter severity and teleconnection indices is more complex for cold winters than for warm winters. It takes two or more indices to successfully classify cold winters. In general, warm winters are characterized by a predominantly zonal type of atmospheric circulation over the Northern Hemisphere (type W1). Within this type of circulation it is possible to distinguish two sub‐types, W2 and W3. Sub‐type W2 is characterized by a high‐pressure cell over North America, which is accompanied by enhanced cyclonic activity over the eastern North Pacific. Due to a broad southerly “anomalous” flow, surface air temperatures (SATs) are above normal almost everywhere over the continent. During the W3 sub‐type, the polar jet stream over North America, instead of forming a typical ridge‐trough pattern, is almost entirely zonal, thus effectively blocking an advection of cold Arctic air to the south. Cold winters tend to occur when the atmospheric circulation is more meridional (type C1). As with warm winters, there are two sub‐types of circulation, C2 and C3. In the case of C2, the jet stream loops southward over the western part of North America, but its northern excursion over the eastern part is suppressed. In this situation, the probability of a cold winter is higher for Lake Superior than for the lower Great Lakes. Sub‐type C3 is characterized by an amplification of the climatological ridge over the Rockies and the trough over the East Coast. The strongest negative SAT anomalies are located south of the Great Lakes basin, so that the probability of a cold winter is higher for the lower Great Lakes than for Lake Superior.

Density Dependence, Compensation, and Environmental Effects on Elk Calf Mortality in Yellowstone National Park

We studied survival of radiocollared elk (Cervus elaphus) calves in Yellowstone National Park from 1987 to 1990, and survival of calves computed from population estimates from 1968 to 1992. We hypothesized that summer and winter survival of elk calves and mass of neonates were inversely related to population size, measures of environmental severity, and timing of births. Herd-wide survival estimates based on winter counts, reported harvests, and herd classifications, suggested that winter survival of elk calves was related inversely to estimated size of the elk population during winter (P = 0.0002), but we found no correlation with an index of winter severity (P = 0.51). Summer survival of elk calves also was correlated inversely with the estimated size of the elk population the previous winter (P = 0.03). Summer survival of radiocollared calves averaged 0.65 (n = 127 marked calves) from 1987 to 1990, the losses mostly due to predation (22%). Winter survival of calves averaged 0.72 (n = 88 marked calves entered the winter period), with losses due mostly to malnutrition (58%). Summer survival of radiocollared calves was positively correlated with estimated birth weight (P = 0.001). Survival of radiocollared calves during winters 1987-90 was correlated positively with early calving and mildness of the winter (in contrast to herd-wide survival estimates), and was inversely correlated with estimated elk population size that winter (P = 0.006). Winter survival of radiocollared calves was lower during 1988-89 following the drought and large fires than the other 3 winters (P < 0.001). Predation on elk calves during summer doubled after the drought and fires of 1988 (13% calf losses to predation before the fires vs. 29% after the fires). Potential compensation existed between components of calf mortality: predators killed more light (P = 0.041) and more late born calves (P = 0.146); calves were born later and lighter (P = 0.048) following severe weather conditions; and heavier born calves survived at a higher rate (P = 0.006). Our results are consistent with the hypothesis that density-dependent mortality of calves during winter due to malnutrition, and summer mortality of calves due to predation were partially compensatory but severe environmental conditions produced largely additive components to both summer (increased predation) and winter (increased malnutrition) mortality.

Winter 1994 Weather and Ice Conditions for the Laurentian Great Lakes

The Laurentian Great Lakes developed their most extensive ice cover in over a decade during winter 1994 [December–February 1993/94 (DJF 94)]. Extensive midlake ice formation started the second half of January, about 2 weeks earlier than normal. Seasonal maximal ice extent occurred in early February, again about 2 weeks earlier than normal. Winter 1994 maximum (normal) ice coverages on the Great Lakes are Lake Superior 96% (75%), Lake Michigan 78% (45%), Lake Huron 95% (68%), Lake Erie 97% (90%), and Lake Ontario 67% (24%). Relative to the prior 31 winters (1963–93), the extent of seasonal maximal ice cover for winter 1994 for the Great Lakes taken as a unit is exceeded by only one other winter (1979); however, other winters for individual Great Lakes had similar maximal ice covers. Anomalously strong anticyclonic circulation over the central North Pacific (extending to the North Pole) and an abnormally strong polar vortex centered over northern Hudson Bay combined to produce a circulation pattern that brought frequent air masses of Arctic and polar origin to the eastern third of North America. New records were set for minimum temperatures on 19 January 1994 at many locations in the Great Lakes region. A winter severity index consisting of the average November–February air temperatures averaged over four sites on the perimeter of the Great Lakes (Duluth, Minnesota; Sault Ste. Marie, Michigan; Detroit, Michigan; and Buffalo, New York) indicates that winter 1994 was the 21st coldest since 1779. The unseasonably cold air temperatures produced much-above-normal ice cover over the Great Lakes and created problems for lake shipping. Numerous fatalities and injuries were attributed to the winter weather, which included several ice and snow storms. The much-below-normal air temperatures resulted in enhanced lake-effect snowfall along downwind lake shores, particularly during early to midwinter, prior to extensive ice formation in deeper lake areas. The low air temperatures were also responsible for record 1-day electrical usage and multimillion dollar costs associated with snow removal, U.S. and Canadian Coast Guard operational assistance to ships beset in ice, damage to ships by ice, damage to public and private property by river ice jams and associated flooding, frozen underground water pipes, and damage to fruit trees.

Effect of snow depth on wolf activity and prey selection in north central Minnesota

Wolf (Canis lupus) activity and interactions with white-tailed deer (Odocoileus virginianus) were monitored in north central Minnesota during six winters in which mean January–February snow depth alternated between shallow (19–26 cm) and relatively deep (40–47 cm) and winters (winter severity index; L. J. Verme. 1968. J. Wildl. Manage. 32: 566–574) alternated between mild (71–98) and moderately severe (126–137). Wolves traveled farther and more often and spent less time with other pack members in mild than in severe winters. Radio-marked wolves and deer used conifer cover less, and fewer deer were killed there, when snow was shallow. Similarly, fewer wolf-killed deer were found in and near deer concentration areas during mild winters. Of the 74 deer killed by wolves, the proportion that were fawns (54%) differed from the proportion of fawns in the winter population (27%), but neither varied with winter severity. Few deer killed by wolves appeared debilitated. Carcass consumption was high in all winters, regardless of their severity, but wolves scavenged less in mild than in severe winters (10 vs. 29% of deer carcasses observed). Thus, wolves changed winter activity, movement patterns, sociality, and feeding behavior in response to snow-induced changes in deer distribution and mobility.

Germination Response of Artemisia tridentata (Asteraceae) to Light and Chill: Patterns of Between-Population Variation

Artemisia tridentata Nutt. is the dominant shrub over much of semiarid North America. It consists of several subspecies and includes ecotypes that occur over a range of habitats from warm desert fringes to montane forest and meadow communities. Fifteen seed collections representing the three common subspecies and a spectrum of habitats were subjected to a series of laboratory light and chill treatments. Recently harvested seeds were mostly nondormant at 15 C but required light for full germination. Removal of the pericarp, afterripening in dry storage, and short chill treatments all resulted in a reduction in light requirement. When examined on a by-collection basis, seed germination response variables were significantly correlated with each other and with mean January temperature at the seed collection site, an index of winter severity. Collections from colder sites were 16%-36% dormant in the light at 15 C and nearly 100% light-requiring, while collections from warm desert fringes were nondormant in light and only 50%-70% light-requiring. Cold winter collections required up to 98 d to germinate to 50% at 1 C in light, whereas warm winter collections germinated to 50% in as little as 16 d. There was no clear relationship between germination behavior and subspecific identity. The observed climate-correlated variation in germination response to light and chill appears to be of adaptive significance, but a genetic basis for patterns of infraspecific variation in germination response in this species has not yet been demonstrated.

Prey Selection and Fat Deposits of Bobcats (Felis rufus) during Autumn and Winter in Maine

Differences in food habits among age, sex, and weight classes of bobcats have been observed (Fritts and Sealander, 1978; Litvaitis et al., 1984). These differences may reduce intraspecific competition and influence the physical condition of bobcats, especially during periods of prey scarcity or environmental stress. Competition and environmental stress may be pronounced at the northern edge of the range of the bobcat where prey may be limited and winters are severe. The objectives of our study were to determine prey use by bobcats during autumn and winter in Maine, examine bobcat fat deposits during that period, and evaluate the relationships of those parameters to age, sex, and weight of bobcats and to winter severity. Skinned bobcat carcasses (n = 230) were obtained from trappers and hunters throughout Maine during the 1980-81 through 1983-84 harvest seasons (October-February). We recorded the sex and weight of each carcass and estimated the unskinned weight using regression equations (Miller, 1980). Carcasses were then separated into weight classes according to unskinned weights ( 12 kg). Juveniles were identified by the presence of an open apical root foramen in a lower canine. Cementum annuli counts were used to distinguish yearlings from older animals (Crowe, 1975). Visceral fat deposits, including kidney and intestinal fat, were examined to evalute physical condition of bobcats. Each carcass was assigned a numerical rank of fat abundance from 0 to 3, where 0 = no fat and 3 = large fat deposits. To reduce observer variation, the same individual examined the fat deposits of all carcasses. Gastrointestinal tracts were removed and contents separated. Prey remains were identified using a reference collection of hairs, hair scale patterns, and skulls. The frequency of occurrence of each item was based on the presence or absence of the prey item in each carcass. The numeric ranks of visceral fat abundance were compared to sex, age (juvenile, yearling, adult), and weight class. Fat abundance also was compared to a winter severity index (WSI), where:

Simulation of some strategies to reduce the effect of climatic variability on farming systems. The case of the Pyrenees mountains

Inter-annual climatic variations pose serious problems for animal breeding farms and it is important to try to reduce the effects of these variations. An investigation of how this can be done is presented here with particular reference to the Pyrenees mountains. In this case the overwintering period is particularly difficult, but the situation during this period depends on the climate throughout the year. In a previous paper, a model of the constitution and utilisation of hay-stocks was described. The model calculated an index of winter severity. In this paper various strategies aimed at reducing the variance in this index are tested. First, strategies involving changes in farm structure (harvest process, etc.) or different fixed management strategies (e.g. different lambing periods) are considered. Then, strategies involving modifications of management (fertilisation, etc.) in response to current conditions are considered. The simulation results indicate that strategies of this latter type are the more effective in reducing the variability in the index of winter severity.