Seasonal variation in the activity patterns of the Orkney vole Microtus arvalis orcadensis

In captivity, Orkney voles Microtus uruulis orcudensis show an activity pattern that consists of regularly alternating periods of rest and activity with a periodicity of about 2.8 hours. Captive voles kept under ambient conditions are equally active day and night at all times of the year. Free-living voles also show a regular short-term rhythm of activity but in addition the partition of activity between day and night varies seasonally. At two sites on Orkney Mainland cyclic variation in diurnality with a period of 12 months were recorded. Although surface activity occurred during both the day and night throughout the year, day activity predominated, particularly during the winter months. The cycle appeared to be synchronous at the two study sites.
Seasonal variation in diurnality appeared to be associated with population density and due largely to the proportion of juveniles in the population. Given the 12-month cycle of diurnality found in the Orkney vole, phase relationships with photoperiod are likely to be consistent between years. This may explain why populations of this subspecies do not appear to undergo multi-annual population cycles.
Despite intense levels of predation by raptors, including the short-eared owl which switches between nocturnal and diurnal hunting, Orkney voles exhibit a relatively simple and highly predictable cycle of diurnality. This cycle is unlikely therefore to have evolved as a means of preventing predator specialization with respect to time of day, season or year.     

Feedback structures of northern small rodent populations

Regular oscillations of northern small rodents (lemmings, voles and mice) have fascinated ecologists for decades. In particular, cycles exhibited by Fennoscandian voles have inspired population ecologists to propose several hypotheses for their underlying causes. Although there is now some agreement that the interaction with specialist predators is involved, many aspects remain enigmatic, one being the precise ecological mechanism involved in the first-order feedback effect (i.e. direct density dependence). In this paper we evaluate the relative importance of first and second-order negative feedback on small rodent dynamics in 64 data sets, assess the evidence of non-linearity in the feedback structure, and look for similarities and/or differences between species and places. A clear feature of our analysis was the highly consistent pattern of first-order dynamics across species and locations, suggesting the importance of intra-specific interactions independent of local environmental conditions. Second-order feedback generally showed a large degree of variation and appears to be strongly dependent on environmental conditions and locality. There seems to be no consistent latitudinal pattern or non-linearity in the feedback responses. We conclude that northern small rodent populations are basically regulated by both highly consistent first-order feedback (e.g. intra-specific competition, functional responses of generalist predators) and less consistent, site-specific second-order effects (e.g. numerical responses of specialist predators or food plants).     

Breeding suppression in free-ranging grey-sided voles under the influence of predator odour

The breeding suppression hypothesis predicts that females of certain small mammal species will reduce reproduction as a response to the odour of a specialised mammalian predator. This was tested in a field experiment with grey-sided voles ( Clethrionomys rufocanus) during three summer seasons (1997–1999) in the subalpine tundra of northern Norway, which is a natural habitat of this species. In a first phase free-ranging voles in six unfenced 1-ha plots were monitored by live-trapping from June to August each year. In a second phase from August to September, three of the plots were sprayed with weasel ( Mustela nivalis) odour to simulate increased apparent predation risk, while the remaining three plots served as untreated controls. On all plots voles were individually marked with ear tattoos and were regularly live-trapped during the whole breeding season to follow their performance. On the treatment plots the recruitment rate of juveniles did not increase in late summer as it did on the control plots. The proportion of reproductively non-active adult females was significantly higher on the treatment plots for both old and young females. Our results thus verify the breeding suppression hypothesis for the first time under natural conditions. However, the response in overwintered females is in conflict with the original hypothesis because the assumed fitness benefits from breeding delayed until the next season are inaccessible to them. As an alternative explanation we propose a short-term response of reduced activity and interrupted breeding until the predator has exploited and left the feeding patch. Such a duck and cover strategy would increase the fitness of females of all age classes when prey habitats are patchy.     

Diet variation of common buzzards in Finland supports the alternative prey hypothesis

The regional synchrony of short-term population fluctuations of small rodents and small game has usually been explained by varying impacts of generalist predators subsisting on both voles and small game (the "alternative prey hypothesis" APH). APH says that densities of predators increase as a response to increasing vole densities and then these predators shift their diet from the main prey to the alternative prey when the main prey decline and vice versa. We studied the diet composition of breeding common buzzards Buteo buteo during 1985-92 in western Finland. Microtus voles were the main prey and water voles, shrews, forest grouse, hares and small birds the most important alternative prey. Our data from the between-year variation in the diet composition of buzzards fulfilled the main predictions of APH. The yearly proportion of main prey (Microtus voles) in the diet was higher in years of high than low vole abundance. The proportion of grouse in the diet of buzzards was negatively related to the abundance of Microtus voles in the field and was nearly independent of grouse abundance in the field. In addition, buzzards mainly took grouse chicks and young hares which is consistent with the prediction of APH. Therefore, we conclude that buzzards are able to shift their diet in the way predicted by the APH and that buzzards, together with other generalist predators, may reduce the breeding success of small game in the decline phase of the vole cycle, and thus substantially contribute to the existence of short-term population cycles of small game.     

Breeding and rearing of Japanese field voles (Microtus montebelli Milne-Edwards) and Hungarian voles (Microtus arvalis Pallas) as new herbivorous laboratory animal species

Microtus species are very useful as experimental small animals with herbivorous characteristics. In this report, to approach establishment of the use of Japanese field voles (M. montebelli) and Hungarian voles (M. arvalis) as experimental animals, the biological characteristics, breeding methods and reproductive performance of these animal species were comparatively investigated. The number of chromosomes of M. arvalis is 12n = 46, differing from those of M. montebelli, 2n = 30. The breeding and reproduction of the Microtus species were relatively easily accomplished in the laboratory, by giving high fiber-containing rations. These animals prove to be polyestrous and showed postpartum estrous on the day of parturition. In the breeding by the continuous mating of the same pair, there was little or no delay in implantation due to lactation, especially in M. arvalis resulting in continuous birth at intervals of 20 to 21 days. On examination of vaginal smears, Japanese field voles (M. montebelli) did not show any definite pattern whereas 23 out of 30 voles from Hungary (M. arvalis) examined showed 6- to 18-day cycles. There were remarkable differences between the Japanese voles and the Hungarian voles, both biologically and reproductively.     

Competition, predation and interspecific synchrony in cyclic small mammal communities

Although competition and predation are considered to be among the most important biotic processes influencing the distribution and abundance of species in space and time, the relative and interactive roles of these processes in communities comprised of cyclically fluctuating populations of small mammals are not well known. We examined these processes in and among populations of field voles, sibling voles, bank voles and common shrews in western Finland, using spatially replicated trapping data collected four times a year during two vole cycles (1987–1990 and 1997–1999). Populations of the four species exhibited relatively strong interspecific temporal synchrony in their multiannual fluctuations. During peak phases, we observed slight deviations from close temporal synchrony: field vole densities peaked at least two months earlier than those of either sibling voles or bank voles, while densities of common shrews peaked even earlier. The growth rates of all four coexisting small mammal species were best explained by their own current densities. The growth rate of bank vole populations was negatively related to increasing densities of field voles in the increase phase of the vole cycle. Apart from this, no negative effects of interspecific density, direct or delayed, were observed among the vole species. The growth rates of common shrew populations were negatively related to increasing total rodent (including water voles and harvest mice) densities in the peak phase of the vole cycle. Sibling voles appeared not to be competitively superior to field voles on a population level, as neither of these Microtus voles increased disproportionately in abundance as total rodent density increased. We suggest that interspecific competition among the vole species may occur, but only briefly, during the autumn of peak years, when the total available amount of rodent habitat becomes markedly reduced following agricultural practices. Our results nonetheless indicate that interspecific competition is not a strong determinant of the structure of communities comprised of species exhibiting cyclic dynamics. We suggest that external factors, namely predation and shortage of food, limit densities of vole populations below levels where interspecific competition occurs. Common shrews, however, appear to suffer from asymmetric space competition with rodents at peak densities of voles; this may be viewed as a synchronizing effect.     

Effects of temperature and photoperiod on thermogenesis in plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus)

We examined the effects of temperature and photoperiod on metabolic thermogenesis and the thermogenic characteristics of brown adipose tissue in plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus), the dominant species of small mammals in the alpine meadow ecosystems on the Qinghai-Tibetan Plateau. Pikas and voles were acclimated in the following groups: (1) Long day – warm temperature (16L:8D, 23 °C), (2) Long day – cold temperature (16L:8D, 5 °C), (3) short day – warm temperature (8L:16D, 23 °C), and (4) short day – cold temperature (8L:16D, 5 °C). Both temperature and photoperiod were important environmental cues for changes in thermogenesis for both species. Low temperature and short photoperiod induced increases in metabolic rate, nonshivering thermogenesis (NST), mitochondrial protein contents of brown adipose tissue, and cytochrome C oxidase activity of brown adipose tissue mitochondria in both species. Plateau pikas were more sensitive to cold (79% of the total NST response) than to short photoperiod (21%), while root voles were more sensitive to short photoperiod (60% of the total NST response) than to cold (40%), although cold clearly enhanced thermogenesis. Their thermogenic characteristics correlated with their preferred habitats: plateau pikas are found mainly in more exposed microhabitats in open sunny meadow, while root voles live in more sheltered microhabitats in relatively closed shrub. Our results also showed that temperature and photoperiod combined induce thermogenic adjustments in both species in seasonal acclimatization in their alpine meadow macrohabitat. Accepted: 10 November 1998     

Multiple captures provide evidence of small mammal social behavior

Social behavior of small mammals living under natural conditions often is inferred from live-trapping data, particularly from incidents in which two or more individuals are captured together in a trap. We examined whether multiple-capture data from a long-term study of prairie voles (Microtus ochrogaster) and meadow voles (Microtus pennsylvanicus) were consistent with well-known species differences in social behavior (whereas prairie voles are highly social and display monogamy, meadow voles are less social and promiscuous). When possible, we also examined multiple captures of two nontarget species, northern short-tailed shrews (Blarina brevicauda) and western harvest mice (Reithrodontomys megalotis). Percent of total captures that were multiple captures and percent of total adult captures that were male–female captures were highest for prairie voles and lowest for meadow voles; values for harvest mice and shrews were in between those of the vole species, but more similar to values for meadow voles. Repeat captures of the same male–female pair occurred most commonly in prairie voles, and multiple captures of this species typically involved individuals from the same social group. Multiple captures of adults and juveniles were more common in prairie voles than meadow voles, except for captures of at least one adult male and at least one juvenile, which did not differ between the two vole species. Multiple capture data for prairie voles and meadow voles were largely consistent with established species differences in social behavior, suggesting that such data can provide an accurate indication of social and mating systems of small mammals.     

Expression patterns of clock genes in the hypothalamus and eye of two Lasiopodomys species

ABSTRACT

To investigate the relationship between light sensing systems in the eye and circadian oscillators in the hypothalamus of subterranean rodents, we studied subterranean Mandarin voles (Lasiopodomys mandarinus) that spend their entire lives under dark conditions with degenerated eyes, and compared oscillatory expression patterns of clock genes in the hypothalamus and eye between Mandarin voles and their aboveground relatives, Brandt’s voles (L. brandtii). Individuals of both vole species were kept under a 12-h light/12-h dark condition or continuous dark condition for 4 weeks. In both species, the expressions of most genes showed significant cosine rhythmicity in the hypothalamus but relatively weak rhythmicity in the eye. The number of rhythmic genes in the eye of Mandarin voles increased under the dark condition, but the opposite trend was observed in the eye of Brandt’s voles. The expression levels of most clock genes in the hypothalamus of both vole species did not significantly differ between the two conditions, but unlike in Mandarin voles, these expression levels significantly decreased in the eye of Brandt’s voles kept under the dark condition. In both vole species, the peak phase of most clock genes exhibited advanced or invariant change in the hypothalamus under the dark condition, and the peak phase of most clock genes showed consistent changes between the eye and hypothalamus of Mandarin voles. However, most clock genes in the eye showed a delayed phase in Brandt’s voles kept under the dark condition. In conclusion, the hypothalamus plays an important role in both vole species irrespective of the light condition. However, the expression patterns of clock genes in the eye differed between the vole species, indicating that each species adapted differently to their environments.     

Predator-induced synchrony in population oscillations of coexisting small mammal species

Comprehensive analyses of long-term (1977-2003) small-mammal abundance data from western Finland showed that populations of Microtus voles (field voles M. agrestis and sibling voles M. rossiaemeridionalis) voles, bank (Clethrionomys glareolus) and common shrews (Sorex araneus) fluctuated synchronously in 3 year population cycles. Time-series analyses indicated that interspecific synchrony is influenced strongly by density-dependent processes. Synchrony among Microtus and bank voles appeared additionally to be influenced by density-independent processes. To test whether interspecific synchronization through density-dependent processes is caused by predation, we experimentally reduced the densities of the main predators of small mammals in four large agricultural areas, and compared small mammal abundances in these to those in four control areas (2.5-3 km(2)) through a 3 year small-mammal population cycle. Predator reduction increased densities of the main prey species, Microtus voles, in all phases of the population cycle, while bank voles, the most important alternative prey of predators, responded positively only in the low and the increase phase. Manipulation also increased the autumn densities of water voles (Arvicola terrestris) in the increase phase of the cycle. No treatment effects were detected for common shrews or mice. Our results are in accordance with the alternative prey hypothesis, by which predators successively reduce the densities of both main and alternative prey species after the peak phase of small-mammal population cycles, thus inducing a synchronous low phase.     

The predation risks of interspecific eavesdropping: weasel–vole interactions

Competing species benefit from eavesdropping on each other's signals by learning about shared resources or predators. But conspicuous signals are also open to exploitation by eavesdropping predators and should also pose a threat to other sympatric prey species. In western Finland, sibling voles Microtus rossiameridionalis and field voles M. agrestis compete for food and space, and both species rely upon scent marks for intraspecific communication. Both vole species are prey to a range of terrestrial scent hunting predators such as least weasels, however, the competitively superior sibling voles are taken preferentially. We tested in large out‐door enclosures whether field voles eavesdrop on the signals of its competitor, and whether they behave as though this eavesdropping carries a risk of predation. We presented field voles with scent marks from unknown conspecifics and sibling voles and measured their visitation, activity and scent marking behaviours at these scents under high (weasel present) and low (weasel absent) predation risk. Field voles readily visited both field and sibling vole scents under both high and low predation risk; however their activity at sibling vole scent marks declined significantly under increased predation risk. In contrast, predation risk did not affect field voles’ activity at conspecific scents. Thus, field voles were compelled to maintain eavesdropping on heterospecific scents under an increased risk of predation, however they compensated for this additional risk by reducing their activity at these risky scents. Scent marking rates declined significantly under high predation risk. Our results therefore reveal a hidden complexity in the use of social signals within multi‐species assemblages that is clearly sensitive to the potential for increased predation risk. The predation risks of interspecific eavesdropping demonstrated here represents a significant generalisation of the concept of associational susceptibility.     

Possible atypical course of tularemia (persistence) in the common vole Microtus arvalis Pall

The possibility of the atypical course of tularemia with the prolonged persistence of Francisella tularensis in common voles (M. arvalis), the twin species of East European voles (M. rossiaemeridionalis), was studied. Experiments were made on 33 animals grown in the laboratory. F. tularensis strain 165 was used. The animals were infected by feeding them according to the previously developed scheme. 7 out of 33 voles showed the atypical course of tularemia: in 3 voles the disease took a prolonged course with bacteriuria and death on days 25-34; 3 other voles with bacteriuria registered before days 33, 66 and 172 (the term of observation) survived. The surviving animals were killed on day 183, and the presence of bacteria in their organs and seroconversion were established. One vole excreted no bacteria with urine and had no bacteria in its organs (the animal was examined on day 156), but in its blood specific antibodies were detected. To determine bacteriuria, the immunofluorescence test was used together with biological assays. Thus, M. arvalis, like M. rossiaemeridionalis studied earlier, can harbor F. tularensis at the period between epizootics. When voles of the former species penetrate stacks of straw and hayricks, conditions appear for the transfer of the infection to the latter species, M. rossiaemeridionalis. Therefore, in the foci of the meadow-field type each of these two species of voles may be not only of epizootic, but also of epidemic importance.     

Vole diet on experimentally managed reforestation areas in northern Sweden

In northern Sweden two field experiments with the reforestation techniques soil scarification, ploughing, burning and grass herbicidal treatment were performed. Small rodents were trapped regularly on the managed plots and their stomachs were examined microscopically for diet composition. Both bank voles Clethrionomys glareolus and field voles Microtus agrestis were common on the reforestation areas while only a small number of grey-sided voles Clethrionomys rufocanus were taken. All three species underwent a population cycle during the studies. The management techniques generally resulted in small and irregular effects on the food selection. The most pronounced changes were lower intake of grasses by M. agrestis after herbicidal treatment and of filamentous tree lichens by C. glareolus after most treatments.
Both bank voles and field voles ate predominantly forbs in the summer half of the year, whereas the field voles took also a considerable amount of grass. As a complement to green vegetable-matter bank voles ate berries and fungi in summer-autumn and tree lichens at other times of the year, but seeds and animals food only in very small amounts. Ail three species consumed large quantities of dwarf-shrubs in autumn and especially in winter. Considerable amounts of bark were eaten by field voles and a smaller proportion by bank voles in autumn-winter.
Both for bank and field voles there were indications of worsening food conditions as the population cycle went on, There were, for example, an increase in grass and bark intake in field voles and a decrease in seeds and berries for the hank vole.     

Do delayed effects of overgrazing explain population cycles in voles?

Theoretical models predict that delayed density-dependent processes with a time-lag of approximately nine months are sufficient to generate regular 3–5 year fluctuations in densities of northern small rodents. To examine whether this time-lag could be generated by plant-herbivore interactions, we studied delayed effects of overgrazed food plants on voles. We introduced field voles ( Microtus agrestis ) in four large predator-proof enclosures that had suffered heavy grazing during the preceding autumn and winter, and compared them with voles introduced to previously ungrazed control areas. We found no detrimental effects of previous grazing on population growth, reproduction or body condition of voles. Chemical analyses did not show consistent effects of grazing on nutritional components of common food plants (grasses). These results suggest that short-term population cycles of Microtus voles in grassland habitats are not primarily driven by delayed effects of plant-herbivore interactions.     

Bank Voles in Southern Eurasia: Vicariance and Adaptation

Phylogeographic lineages are interpreted as the product of repeated isolation in glacial refugia, leading to vicariant differentiation. Being restricted to a given geographic area could also promote adaptive divergence in response to local conditions. The role of phylogeny and climate in the evolution of the bank vole (Myodes glareolus) was investigated here, focusing on molar tooth shape, a morphological feature related to the exploitation of food resources. A balanced role of phylogeny and climate was demonstrated. Response to environmental factors led to morphological convergence of bank voles from different lineages living in similar environments, and to within-lineage divergence in extreme environments. An important interaction of climate and phylogeny was found, suggesting that each lineage is living in a particular environment. This lineage-specific adaptation to a range of environmental conditions may have conditioned the potential of post-glacial recolonization of each lineage. Morphological covariation with environmental conditions further highlights the potential of adaptation of this species.     

Spatio‐temporal covariation in abundance between the cyclic common vole Microtus arvalis and other small mammal prey species

Populations of the common vole Microtus arvalis in mid‐western France show cyclic dynamics with a three‐year period. Studies of cyclic vole populations in Fennoscandia have often found inter‐specific synchrony between the voles and other small mammals which share the voles' predators. Although predators are central to the favoured mechanism to explain Fennoscandian vole cycles and the spatial variation of small mammal populations, their role in vole cycles elsewhere, including France, is less clear. Establishing whether alternative prey species in France cycle in parallel with voles as they do in Fennoscandia is thus an important step towards understanding the generality of predators' influence on cyclic vole populations. We applied spatial and temporal autocorrelation and cross‐correlation methods to French populations of M. arvalis and two sympatric non‐cyclic small mammal species, Apodemus sylvaticus and Crocidura russula. Patterns of time‐lagged cross‐correlation between the abundance of M. arvalis and the other two species suggested synchrony in their dynamics beyond that expected of stochastic environmental variation, and indicated a weak three‐year cycle in A. sylvaticus and C. russula that was in phase with that of M. arvalis. We interpret the synchrony between these species as the effect of shared predators and environmental stochasticity. Abundance within species showed weak spatial autocorrelation in June at scales consistent with dispersal being the mechanism responsible, but a more general lack of spatial structure within and between species was consistent with the strong spatial synchrony at regional scales often found in fluctuations of small mammal abundance.     

Microhabitat use, giving-up densities and temporal activity as short- and long-term anti-predator behaviors in common voles

We used depletable food patches to determine the effect of microhabitat (mowed versus unmowed adjacent grasslands) and time (day versus night) on the foraging behavior of common voles (Microtus arvalis). The food remaining after 12‐h periods (giving‐up density, GUD) measured the vole's habitat selection under predation risk. In accord with several other rodent species and the effects of avian predators, voles had significantly lower GUDs in the unmowed than mowed portion of the grassland. GUDs in patches along the border between adjacent habitats were more similar to the risky mowed grassland than the safe unmowed grass. Time interacted strongly with microhabitat. In the mowed grass, voles had significantly higher GUDs at night than day. Whereas in the unmowed grass, GUDs were significantly higher during the day than night. Vole GUDs did not vary with time along the boundary. This suggests that predators are more abundant or effective in the mowed grass at night (owls?), and in the unmowed grass during the day (weasels?). In terms of predation risk, the voles perceived the mowed grass at night as the riskiest and the unmowed grass at night as the safest. Voles may have difficulties assessing resources under high predation risk: GUDs among patches were well equalized in the unmowed microhabitat whereas in the mowed grass only day GUDs did not vary significantly among patches. We linked these results to the vole's day‐night‐activity and life span. For the 533 voles live‐trapped at the study area, the ratio of day versus night captures for each individual served as an activity index and the span between first and last capture measured minimum life span. In accord with higher GUDs at night, very few individuals behaved selectively towards the night, but individual life expectancy increased with temporal opportunism. Microhabitat differences in GUDs reflect short‐term strategies of predator avoidance and the trapping data reflect long‐term patterns of anti‐predator behavior.     

Ultradian rhythms and the nutritional importance of caecotrophy in captive Brandt’s voles (<Emphasis Type="Italic">Lasiopodomys brandtii</Emphasis>)

Ingestion of soft faeces derived from caecal contents, caecotrophy, in herbivorous small mammals is considered an adaptation to the metabolic disadvantage of small body size, especially when feeding on diets of low quality. We investigated daily activity patterns in captive Brandt’s voles (Lasiopodomys brandtii), including feeding, locomotion, caecotrophy, and defaecation, by continuous 24 h visual observation; and estimated the contribution of soft faeces ingestion (caecotrophy) to intake of protein and energy. Brandt’s voles ingested 68.8 ± 7.4 fecal pellets per day, averaging 17 ± 2% of total faeces produced. The amount of faeces ingested did not differ between female and male voles or between night and day time. All animals showed average 3 h ultradian cycles in behaviour during the course of the day and night. The contributions of caecotrophy to the dietary intake of crude protein and metabolizable energy were estimated respectively as 9 and 8% on a high-protein, easily digested commercial rabbit pellet diet. However, the importance of caecotrophy to the field voles is likely to be higher on a natural diet of lower nutrient density. The rhythm of caecotrophy in voles depended mainly on the rhythm of the colonic separation mechanism in the proximal colon and passage in the distal colon, and may be regulated by feeding and other activity rhythms. Ultradian rhythms in caecotrophy helped to minimise potential conflicts in utilizing the gut, especially in balancing the caecal fermentation and salvaging nutrients contained in caecal bacteria.     

光周期对布氏田鼠和长爪沙鼠体重和能量代谢的影响

本文测定了光周期对雄性布氏田鼠和长爪沙鼠的体重、基础代谢率和能量代谢的影响。动物从长光照(16L∶8D , LD) 转入短光照(8L∶16D , SD) 条件下驯化6 周(田鼠) 和7 周(沙鼠) 。结果显示: (1) 无论在LD还是SD 条件下, 两种动物的体重都趋于增加, 但反应程度不同也具有种间差异性。两种动物的体重对光周期的反应有时段性, 约14 d 前两种动物的体重增加迅速, 而后增加缓慢, 3 周左右趋于稳定。短光照条件下布氏田鼠和长爪沙鼠的体重分别增长了37 %和11 % , 均低于长光照组(分别为47 %和25 %) , 说明短光照条件下布氏田鼠和长爪沙鼠的体重增长较长光照缓慢; (2) 光照对两种动物的摄入能、消化能和可代谢能均没有显著影响,摄入能与体重的增长无关; (3) 光照对两种动物的基础代谢率无显著影响。这些结果表明: 布氏田鼠和长爪沙鼠在自然环境中, 可能以光周期作为一种信号, 当环境温度降低、食物质量变劣时, 采取降低体重以减少绝对能量需求的策略而适应环境。     

Timing of vole hunting in aerial predators: RAPTOR GROUP RUG/RIJP*

In a short but intense field investigation, surface activity of common voles in a cropped lucerne field was assayed by live-trapping while, simultaneously, hunting activity and yield of three species of raptors were recorded by continuous observation. Pronounced short-term rhythms in trappability of the vole population ran parallel with fluctuations in yield per hour of flight-hunt of hen harriers and kestrels. These raptors, as well as Rough-legged buzzards, hunted more at times of increased vole surface activity; hen harriers saved c. 15 hours of flight-hunt per day by such temporal adjustment, corresponding to about 12% of their daily energy intake. Voles suffered a predation rate of an estimated 0 2% per day; under such heavy predation and temporal concentration of raptor hunting at times of increased vole activity, surface feeding in synchrony with the vole majority was associated with increased risk of predation.