Great spotted woodpeckers Dendrocopos major exert multiple forms of phenotypic selection on Scots pine Pinus sylvestris

Relatively few animal species extract seeds from closed conifer cones because of the forces required to spread apart or penetrate the woody scales. Those species that forage on seeds in closed cones tend to forage selectively, and therefore act as selective agents on cone structure. However, little is known about the foraging preferences and thus phenotypic selection that is exerted on conifers by many species that forage extensively on seeds in closed cones, including especially woodpeckers (Picidae). Great spotted woodpeckers Dendrocopos major are one of the main predators of seeds in closed cones of Scots pine Pinus sylvestris in central and eastern Europe. To estimate the cone preferences of these woodpeckers foraging on Scots pine, we contrasted traits of cones that were and were not foraged on by woodpeckers. Woodpeckers preferred to forage on shorter cones when scales were thin (smaller apophyses) but preferred cones of intermediate length when scales were thicker, providing evidence for correlational selection. The preference for intermediate‐sized cones indicates that woodpeckers exert disruptive selection on cone length when cones have thicker scales, but the overall selection on cone length across all scale types indicates directional favoring the evolution of longer cones. Woodpeckers avoided cones with thicker scales, which would lead to directional selection favoring the evolution of thicker scales. Preferences for intermediate‐sized cones have been found in tree squirrels and directional selection favoring the evolution of cones with thicker scales may be a common outcome of the foraging behavior of birds.     

Age composition of winter irruptive Snowy Owls in North America

Patterns of winter irruptions in several owl species apparently follow the ‘lack of food’ hypothesis, which predicts that individuals leave their breeding grounds in search of food when prey populations do not allow breeding and are too small to ensure survival. Recent analyses, however, suggest an alternative mechanism dubbed the ‘breeding success’ hypothesis, which predicts that winter irruptions might instead be the result of a very successful breeding season, with a large pool of young birds subsequently migrating south from the breeding grounds. Here we assessed age‐class (juvenile vs. non‐juvenile) composition of winter irruptive Snowy Owls Bubo scandiacus over a 25‐year period (winter 1991–1992 to 2015–2016) between regular (North American Prairies and Great Plains) and irregular wintering areas (northeastern North America) using live‐trapped individuals and high‐resolution images of individual owls. Our results show that the proportion of juveniles (birds less than 1 year of age) varies considerably annually but is positively correlated with irruption intensity in both regions. In irregular wintering areas, it can constitute the majority (up to more than 90%) of winter irruptive Snowy Owls over a large geographical area. These results are consistent with the idea that large winter irruptions at temperate latitudes are not the result of adults massively leaving the Arctic in search of food after a breeding failure but are more likely to be a consequence of good reproductive conditions in the Arctic that create a large pool of winter migrants.     

Host-plant influence on the population ecology of the jack pine budworm, Choristoneura pinus (Lepidoptera: Tortricidae)

Abstract.

• 1 Newly-emerged, second-instar jack pine budworm (Choristoneura pinus Freeman) establish spring feeding sites preferentially in the pollen cones of their host tree, Pinus banksiana Lamb.
• 2 Laboratory studies showed that the rate of establishment and survival of jack pine budworm on pollen cones was high throughout the entire spring emergence period of the insect.
• 3 In contrast, the rate of establishment and survival of jack pine budworm on vegetative buds was very poor early in the spring. Vegetative buds were only acceptable as feeding sites to the jack pine budworm for a relatively brief period in late spring.
• 4 Field studies showed that the change in population density of jack pine budworm during the spring emergence stage, as expressed by k-values, was a function of the abundance of pollen cones in the stand. Population reduction was greatest in those stands with the fewest pollen cones.
• 5 Direct measurement of spring dispersal by jack pine budworm showed that dispersal and consequent losses to the budworm population were greatest in stands with the fewest pollen cones.
• 6 We conclude that changes in the density of jack pine budworm are strongly influenced by production of pollen cones in the host stand. Because pollen cone production is related to previous years of defoliation by the jack pine budworm, we propose that pollen cones act as a density-dependent factor governing the density of early-stage jack pine budworm.
• 7 The resulting dynamics are compared to those of other budworm species and used to explain observed regional and temporal patterns of jack pine budworm outbreaks.

     

Seasonal pre‐migratory fattening and increased activity in a nomadic and irruptive migrant,the Red Crossbill Loxia curvirostra

It is well documented that irruptive and nomadic migrants move in response to resources that are distributed unpredictably in space, time or both. Increasing evidence, however, suggests that irruptive and nomadic species may use seasonal timing mechanisms to prepare for migrations, despite the more facultative nature of their movements. Here we use data from free‐living and captive Red Crossbills Loxia curvirostra, a typical irruptive nomad, to examine three hypotheses regarding control of facultative migration: (1) the facultative migration hypothesis, which states that both preparation and departure decisions are regulated by resource availability; (2) the seasonal preparation hypothesis, which states that preparation is initiated by seasonal factors (i.e. endogenous rhythms and/or photoperiod) but that departure decisions are dependent on local resource availability; and (3) the seasonal migration hypothesis, which states that both preparation and departure decisions are initiated by seasonal mechanisms and are independent of local food resources. Red Crossbills in North America are thought to make temporally consistent spring migrations in anticipation of conifer cone maturation. In this study, fat deposits of free‐living Red Crossbills peaked in May and June, exceeding even winter deposits. In agreement with the field data, captive birds on a natural photoperiod with constant food and temperature showed a peak in fat deposition and activity levels in June. These findings are consistent with the seasonal preparation and the seasonal migration hypotheses and contribute to a growing literature that suggests that facultative migrants may prepare for movements in similar ways to seasonal migrants.     

Between-species correlations in the number of migrants at Ulmeth?chi (Switzerland)

We analysed the number of autumn migrants at a bird ringing station over 41 years in the Jura mountains of Switzerland. For 12 irruptive or potentially irruptive bird species, the correlations between their numbers per year were calculated and the species were clustered accordingly. We found high correlations in the number of migrants between the Coal Tit Periparus ater, Great Tit Parus major and Blue Tit Cyanistes caeruleus. Most correlations of passage number between species pairs changed dramatically over time. Only Blue Tit and Coal Tit showed continuously high correlation in this respect. The variation and changes over time in between-species correlations in the number of migrants needs more attention.     

Positive and negative density-dependence and boom-bust dynamics in enemy-victim populations: a mountain pine beetle case study

Negative density-dependent population regulation in exploitative species is well studied. Positive density-dependence can arise if exploiters must cooperate to obtain access to well-defended resources. Most studies, however, focus on the first type of density-dependence at the expense of the other. Using a parasitoid-host model, we explored how positive density-dependence driven by host defenses in combination with negative density-dependence due to competition for resources impact transient population dynamics. Inspired by interactions between the mountain pine beetle and its pine hosts, we formulated a model of enemy-victim interactions in discrete-time in which the victim is capable of deadly self-defense against exploitation. We fitted the model to data and then analyzed its non-equilibrium dynamics to determine what conditions promote boom-bust dynamics. When present together, strong Allee effects and overcompensating competition for resources among exploiters can cause their populations to irrupt and then crash even though many exploitable resources remain. Accelerating population irruptions followed by precipitous collapse occur for realistic parameter values of our model of mountain pine beetle dynamics. Insect dynamics are often dominated by sudden irruptions and collapses on short time scales. Population crashes in exploitative species often happen enigmatically even when exploitable resources are not depleted. Herein, we argue that strong Allee effects in combination with overcompensation provide a plausible explanation for these boom-bust dynamics in some species.     

Performance of the fir coneworm Dioryctria abietivorella (Grote) as affected by host species and presence or absence of seed cones

1 Larval performance of Dioryctria abietivorella (Grote) (Lepidoptera: Pyralidae) was compared when insects were reared in white spruce, black spruce and Jack pine seed orchards. For each species, half of the insects developed in the presence of cones, while the other half was maintained on branches without cones. 2 Significantly faster development rates were observed on spruce species when compared to Jack pine. Significant differences in survival were also recorded between the different feeding treatments. 3 The presence of seed cones on spruce species significantly increased insect mean weight compared with branches without cones, but no significant differences were noticed between the different tree species with cones. 4 White spruce is the most suitable host tree for fir coneworm feeding and the availability of seed cones plays an important role in determining D. abietivorella larval performance.     

Effect of increased food abundance near forest edges on flocking patterns of Coal Tit Parus ater winter groups in mountain coniferous forests

CapsuleIndividuals concentrated near forest edges in bigger social groups than in forest interiors and foraged more on pine cones which were more abundant there.

Aims To evaluate differences in food distribution between forest edges and forest interiors and their effects on the non-breeding flocking patterns of Coal Tit populations inhabiting mountain coniferous forests.

Methods We collected cone production data at forests edges and interiors in mountain pine forests located in the Pyrenees (northeast Iberian peninsula). At the same sites, we also quantified Coal Tit abundance, flocking patterns and foraging behaviour by means of paired bird surveys during autumn and early winter.

Results We recorded a larger abundance of pine cones available on trees along forest edges compared with forest interiors. Coal Tit groups were of bigger size along forest edges, although the number of social groups detected did not differ from forest interiors. Our observations on foraging behaviour supported the hypothesis that differences in flock sizes and overall abundances associated with distance to the edge are due to differences in the availability of pine cones and to the heavier use of these foraging substrates by birds along forest edges.

Conclusions Our results suggest that by changing food distribution, edge effects on pine cone production may be significantly involved in local changes in the social structure of the Coal Tit. An increase in resource heterogeneity and local population density may have important implications at a population level, such as favouring mobility of individuals searching for food resources and thus a transient life, and increasing the costs of territory defence to resident individuals.     

Stable isotope evidence for different regional source areas of common crossbill Loxia curvirostra irruptions into Britain

We used the stable isotope composition of body feathers to show the extraordinarily varying regional provenance of an irruptive conifer seed specialist, the common crossbill Loxia curvirostra . In the boreal region of the western Palearctic, this species specialises on the seeds of Norway spruce Picea abies . The patterns of deuterium in the feathers of migrant common crossbills collected in Britain suggested that irruptions in different years originated in widely separated regions of the Palearctic boreal forest. The birds from some irruptions were relatively narrow-billed compared with those from others, but bill width was not correlated with deuterium values. However, deuterium values did co-vary with the dates that the irruptions reached Britain, with the lowest deuterium levels in years with the latest arrivals. This finding was consistent with the idea that birds with low values came further, from regions far to the northeast. This pattern was very different from that found in irruptive northern bullfinches Pyrrhula p. pyrrhula which had larger variation in deuterium values within an irruption, suggestive of a much more widespread provenance. It is argued that the difference between species is the result of their differing foraging ecology. Bullfinches have a varied summer diet and, unlike common crossbills, do not concentrate regionally to breed where a single type of food is available that year.     

Influence of host log age and refuge from natural enemies on colonization and survival of Phoracantha semipunctata

The pine cone weevil, Pissodes validirostris Gyll. (Coleoptera: Curculionidae), attacks seed cones of most Eurasian pine species, except these of Swiss stone pine (Pinus cembra L.). Behavioural responses of adult weevils to cone volatile emissions of Swiss stone pine and to those of a common host, mountain pine (Pinus uncinata Ram.), were compared in an olfactometer. Weevils were significantly attracted by the volatile blend emitted by mountain pine, but Swiss stone pine volatiles elicited an inverse response, with most weevils moving in the opposite direction to the odour source. However, the majority of second instar weevil larvae that were extracted from mountain pine cones and transferred into Swiss stone pine cones were capable of developing to the adult stage. This suggests that Swiss stone pine cones do not contain strong feeding deterrents that could prevent larval development. The possible factors involved in the absence of colonization of Swiss stone pine cones by cone weevils are discussed.     

Mechanisms of population dynamics in trans-Saharan migrant birds: A review

Modern views on the mechanisms of population dynamics in Palearctic birds wintering in tropical Africa are discussed with regard to the distribution of migrants on the African continent and the influence of external factors on conditions of bird wintering. The data on long-term bird trapping at ten ornithological stations in Europe are analyzed. Among 142 long-term trends in the population dynamics of 18 bird species, 34% are negative, 11% are positive, and the remaining trends lack statistical significance. The proportion of negative trends in each species negatively correlates with the number of birds: the more abundant the species, the lower the probability of its long-term population decline. Population dynamics may largely be determined by environmental conditions in wintering regions. Population studies on ten Palearctic species showed that drastic population declines and even local extinction of birds in recent decades resulted from the dramatic decrease in their survival on African wintering grounds because of insufficient precipitation and, in particular, severe droughts in the Sahel.     

Abundance of two threatened woodpecker species in relation to the proportion of spruce plantations in native pine forests of western Norway

In a comparative study we investigated woodpecker abundance in forest landscapes with different proportion of native pine forest and spruce plantations in western Norway. In 100 circular study plots of 100ha each we recorded 38 white-backed –Dendrocopos leucotos, 22 grey-headed –Picus canus, 13 great spotted –Dendrocopos major, 6 green –Picus viridis, and 2 lesser spotted –Dendrocopos minor woodpeckers in the breeding season. The mean number of recorded woodpecker species peaked at 20–40% spruce plantations. The two most common species in the study, the white-backed and the grey-headed woodpeckers are both Red-listed species in Norway and among the rarest woodpeckers in Europe. The white-backed woodpecker preferred plots with higher than average proportions of standing dead trees and deciduous trees, and low proportions of spruce plantations in the plots. The grey-headed woodpecker preferred plots in the western (coastal) parts of the study area with presence of large aspen Populus tremula trees. Logistic regression models did not reveal any clear threshold values with respect to proportion of spruce plantations in plots, although both woodpecker species were extremely rare in plots with >60% spruce plantations. We recommend spruce plantations to be kept at moderate levels to ensure viable populations of woodpeckers in western Norway.     

Prescribed Fire Effects on Wintering,Bark-Foraging Birds in Northern Arizona

ABSTRACT We examined effects of prescribed fire on 3 wintering, bark-foraging birds, hairy woodpeckers (Picoides villosus), pygmy nuthatches (Sitta pygmaea), and white-breasted nuthatches (S. carolinensis), in ponderosa pine (Pinus ponderosa) forests of northern Arizona, USA. During winters of 2004–2006, we compared bird density, foraging behavior, and bark beetle activity among burned treatment and unburned control units. Hairy woodpecker density was 5 times greater in burn units, whereas white-breasted nuthatches and pygmy nuthatches had similar densities between treatments. Compared to available trees, trees used by foraging hairy woodpeckers had 9 times greater odds of having bark beetles in control units and 12 times greater odds in burn units. Tree diameter appeared to be the main factor bark-foraging birds used in selecting winter foraging trees. Our results suggest that forest managers can use prescribed fire treatments without detrimental effects to wintering nuthatches, while providing additional food to hairy woodpeckers.     

同域分布3种啄木鸟冬季取食的生态位差异

为了掌握黑啄木鸟、三趾啄木鸟和大斑啄木鸟的冬季取食行为特征,特别是三者之间取食生态位的差异,于2016年1月5-13日,在黑龙江省凉水国家级自然保护区以样线法结合样方法对3种啄木鸟的取食生境和取食行为进行了系统调查,收集了15个生境和行为特征变量数据。共布设45条样线,484个对照样方,收集312组啄木鸟取食数据,其中黑啄木鸟73组,三趾啄木鸟97组,大斑啄木鸟142组。多变量回归树和多分类逻辑斯谛分析结果显示,3种啄木鸟在所调查的15项特征上存在显著分异。采用基于利用-可利用方法的Bailey''s方法和双因子方差分析,分别对3种啄木鸟的生境选择和行为特征进行分析,结果显示：黑啄木鸟和三趾啄木鸟偏好在郁闭度较高的原始云、冷杉林中取食,而大斑啄木鸟则随机地在各种林型、生境中取食。黑啄木鸟、三趾啄木鸟多在树干取食,黑啄木鸟更常在倒木上取食,而大斑啄木鸟则多在树冠层取食。黑啄木鸟基本只在主干上凿洞,其他两种特别是大斑啄木鸟则可以在侧枝上取食。与黑啄木鸟和大斑啄木鸟凿洞取食昆虫不同,三趾啄木鸟多通过扒去树皮获得食物。黑啄木鸟的取食树基本为死树,单树取食时间最长,大斑啄木鸟多在活树上取食,单树取食时间最短,经常更换取食树,而三趾啄木鸟的取食树则死活参半,单树取食时间也较长。黑啄木鸟的冬季取食行为节律表现为双峰形,日出后和日落前各有一个活动高峰,其他两种则于白天持续取食。3种啄木鸟取食生境和行为生态位的差异,使它们能够更有效地利用有限的食物资源,共存于同一森林。     

Mitochondrial haplotypic diversity of pine cone beetles (Scolytinae: Conophthorus) collected on food sources

Conophthorus Hopkins attack, oviposit, and feed in immature cones of many pine (Pinus) species. They are a serious pest of pine seed orchards and can destroy up to 100% of the cone crop. Beetles can plague orchards over many years because emerging beetles tend to attack cones of the same or a nearby tree. However, fluctuating pine cone production suggests that beetles may disperse from their natal tree stand to find second-year cones for oviposition. These dispersal behaviors may influence population level genetic diversity, that is, populations may exhibit low or high diversity. In this study, we assess the mitochondrial haplotypic diversity among 10 populations of Conophthorus representing four species. Furthermore, the haplotypic diversities are compared with published haplotypic diversities of other scolytine species to assess the influence of fluctuating food resources on Conophthorus haplotype diversity. Conophthorus haplotypic diversity ranged between 13 and 70%, which was similar to population level haplotypic diversities of other scolytines. The tendency of the emerging brood to reinfest the same tree has little influence on haplotype composition of populations and haplotype diversity is likely more influenced by beetles in search of pine cones.     

Discrimination among pinyon pine trees by Clark's Nutcrackers: effects of cone crop size and cone characters

Summary The influences of Colorado pinyon pine (Pinus edulis) cone crop size, cone and seed weight, cone length, number of seeds per cone, number of viable seeds, and percent viable seeds on the foraging behavior of avian seed dispersal agents were examined in field and laboratory settings. In the field, there was a significant positive relationship between cone number per tree and both the absolute number of cones and the percentage of the cone crop from which seeds were harvested. Cone weight and the number of viable seeds were also significantly related to seed harvest intensity. Laboratory experiments examined the relationship between crop size and cone characters on seed harvest by 18 Clark's Nutcrackers (Nucifraga columbiana). Nutcrackers were offered a choice of two tree types: one with 20 cones attached, and another with 10 cones attached. Significantly more birds chose to remove seeds first from the tree with 20 cones than the tree with 10 cones. In timed trials, they also harvested seeds from significantly more cones on the tree with the higher cone density. In the laboratory, cones chosen for seed removal by the nutcrackers had significantly more viable seeds, more seeds, and were longer compared to cones that were not chosen. Such discriminatory foraging behavior may increase avian foraging efficiency and result in differential reproductive success of pinyon pines. This behavior may therefore influence the evolution of pinyon pine reproductive traits.     

Oribatid Mites (Acariformes, Oribatei) as an Index of Postpyrogenous Changes in Podzol and Peat Soils of Boreal Forests

Population changes of oribatid mites were studied in a bilberry-moss spruce stand and shrub-peat moss pine stand caused by ground fire. The fire resulted in a drop of population density and changes in the species composition of mites in both forest types. In the case of the spruce stand, the restoration of species composition proceeded parallel to the formation of a bilberry-moss cover and litter and became distinct four years after the fire. In the case of pine stand, the fire enveloped only the peripheral region. After the sphagnum cover burned out, the moor dehydration began and the mineralized organogenic substrate emerged. Here, the oribatid complex was significantly rearranged and the previously dominating moisture-loving species were replaced by the mesophilous-xerophilous species typical predominantly for mineralized soils. This explains why the oribatid species composition in the burned pine stand is more similar to that in the control spruce stand than to that in the control pine stand.     

Cones structure and seed traits of four species of large‐seeded pines: Adaptation to animal‐mediated dispersal

Seed dispersal selection pressures may cause morphological differences in cone structure and seed traits of large‐seeded pine trees. We investigated the cone, seed, and scale traits of four species of animal‐dispersed pine trees to explore the adaptations of morphological structures to different dispersers. The four focal pines analyzed in this study were Chinese white pine (Pinus armandi), Korean pine (P. koraiensis), Siberian dwarf pine (P. pumila), and Dabieshan white pine (P. dabeshanensis). There are significant differences in the traits of the cones and seeds of these four animal‐dispersed pines. The scales of Korean pine and Siberian dwarf pine are somewhat opened after cone maturity, the seeds are closely combined with scales, and the seed coat and scales are thick. The cones of Chinese white pine and Dabieshan white pine are open after ripening, the seeds fall easily from the cones, and the seed coat and seed scales are relatively thin. The results showed that the cone structure of Chinese white pine is similar to that of Dabieshan white pine, whereas Korean pine and Siberian dwarf pine are significantly different from the other two pines and vary significantly from each other. This suggests that species with similar seed dispersal strategies exhibit similar morphological adaptions. Accordingly, we predicted three possible seed dispersal paradigms for animal‐dispersed pines: the first, as represented by Chinese white pine and Dabieshan white pine, relies upon small forest rodents for seed dispersal; the second, represented by Korean pine, relies primarily on birds and squirrels to disperse the seeds; and the third, represented by Siberian dwarf pine, relies primarily on birds for seed dispersal. Our study highlights the significance of animal seed dispersal in shaping cone morphology, and our predictions provide a theoretical framework for research investigating the coevolution of large‐seeded pines and their seed dispersers.     

Patterns of exploitation of annually varying Pinus sylvestris cone crops by seed‐eaters of differing dispersal ability

Food consumption by animals depends on functional and numerical responses, and particularly the latter for food specialists. Some birds and mammals are conifer seed specialists and are likely to exploit the varying seed production in different ways according to differences in dispersal capabilities. This in turn may determine which species is more likely to affect the evolution of cone morphology. This study examined the inter‐annual pattern of foraging on Scots pine Pinus sylvestris cones by crossbills Loxia spp. (highly dispersive) and red squirrels Sciurus vulgaris (weakly dispersive) over 16 yr in three stands of ancient native pines at Abernethy Forest in Highland Scotland. There were synchronous annual variations in cone production across the stands, and an indication of a three‐year cycle. The number of cones taken by crossbills was correlated with cone production, indicating a numerical response by the birds, up to a certain limit of cone production. By contrast, the number of cones taken by red squirrels was not correlated with cone production. Rather, the percentage of cones taken by squirrels was high when cone production was low, and low when production was high. There was also a long‐term decline in the number of cones taken by squirrels, suggesting a decline in squirrel numbers. Although a high percentage of cones was removed from some cohorts on some trees, either by crossbills (maximum of 94.8%) or red squirrels (100%), the mean percentage of cones taken by crossbills from trees was small, ranging from 3.7 to 17.1% across all cone cohorts. For red squirrels, mean values ranged from 0.1 to 46.1% across all cohorts. However, given that crossbills can track changes in cone production by rapid numerical responses (i.e. through migration), and take a larger percentage of cones from cohorts of high production (10.7%), compared with red squirrels (3.6%), crossbills may be more important in driving the evolution of cone morphology because future trees are more likely to come from cohorts of high cone production.     

Cycles in voles and small game in relation to variations in plant production indices in Northern Sweden

Population dynamics for voles (Cricetidae), Tengmalm's owl (Aegolius funereus (L.)), red fox (Vulpes vulpes (L.)) willow grouse (Lagopus lagopus (L.)), black grouse (Lyrurus tetrix (L.)), capercaillie (Tetrao urogallus L.), hazel hen (Tetrastes bonasia (L.)), mountain hare (Lepus timidus L.) and tularemia (Francisella tularensis (McCoy & Chapin)) and game bird recruitment were studied by index methods in northern Sweden. In addition contemporary temperature records and spruce (Picea abies (L.) Karst.) and pine (Pinus silvestris L.) cone crops (as indices for plant production) and the occurrence of forest damage, caused by voles eating bark, were studied.During 1970–80 two synchronous 4-year cycles were observed for voles, predators (Tengmalm's owl and red fox) and their alternative prey species (grouse and mountain hare). In grouse the change of numbers was correlated with that of recruitment. Autumn vole numbers peaked about a year before the other species and extensive forest damage occurred at winter peak densities of voles. These population fluctuations are consistent with a predator-prey model for their regulation. In short the model suggests that vole-food plant interactions trigger the cycle of voles, that voles generate the cycle of predators and that these in turn synchronize alternative prey populations to the others at vole declines.For voles, grouse and red fox the amplitude was higher in the first cycle compared to the second one whilst the opposite was true for the mountain hare. Although temperature and cone crops showed large interannual variations they still implied that herbivore food conditions were better during the former cycle. Hence, the reduction of the amplitude of the vole cycle may be explained by inter-cyclic differences in plant food conditions, implying food shortage (as indicated by bark-eating) at different population levels. The similar decrease of grouse and red fox populations may also be explained by deteriorated food conditions and/or for the fox by an outbreak of sarcoptic mange (Sarcoptes scabiae var. vulpes). The increased amplitude of the mountain hare cycle was part of a long-term rise in numbers after a tularemia epidemic in 1967. This is interpreted as a recovery, probably towards the generally higher pre-epidemic population level.