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The mechanisms driving 3–5‐year population cycles of voles involve delayed density‐dependent feedback on vole populations. The key drivers of this feedback include prolonged periods of food depletion or predation mortality over more than one phase of the cycle. We review observational and experimental data gathered between the 1970s and 2010s on vole population fluctuations and the responses of their avian and mammalian predators in west‐central Finland, focusing on studies that have investigated these drivers. Least weasels and stoats were the main predators of voles, causing 77% of all kills, while 22% were killed by avian predators. The numbers of least weasels tracked vole densities with a 9–12‐month lag, which resulted in delayed density‐dependent kill rates of voles in winter. Experimental reduction of small mustelids and avian predators in unfenced areas (each 2.5–3 km2) prevented the cyclic decline of vole densities in the subsequent summer, whereas in areas with only least weasel reduction and in control areas, a decline in vole densities occurred. In another field experiment, the reduction of both mustelid and avian predator densities increased the autumn density of Microtus voles fourfold during the low phase of the cycle, accelerated the increase twofold, increased the autumn density of voles twofold in the peak phase, and delayed the initiation of decline. Our unique experimental results suggest that the collective impact of both mustelid and avian predators is a likely mechanistic explanation for high‐amplitude population cycles of voles in North Europe. In these highly seasonal environments with short summers, a shortage of high‐quality winter food may be the directly density‐dependent factor stopping the growth of vole populations. This allows predators to catch up with prey densities and impose population decline and prolong the low phase of the cycle in a delayed density‐dependent manner. On the basis of our unique series of large‐scale, replicated field experiments in both unfenced and fenced settings, where densities of vole predators were significantly reduced, we conclude that the collective impact of both mustelid and avian predators is a probable mechanistic explanation for high‐amplitude population cycles of voles in boreal regions of North Europe.

The authors would like to correct errors in the original publication of the article.

Phenotypic responses to climate affect individual fitness, but the extent to which this translates into effects on population dynamics remains poorly understood. We assemble 213 time series on phenotypes and population sizes of wild vertebrates globally and match them with local climate data. Our meta-analysis shows that morphological traits are mostly climate insensitive. However, phenology is earlier in warmer-than-average years, which contributes positively to population growth in most species. At lower latitudes, temperature has weaker effects on phenology but stronger direct negative effects on population growth, likely because these populations are less capable of tracking climate via plasticity. Variation in the phenology-mediated effect of temperature on population growth cannot be explained by latitude, generation time, migratory mode, or diet. This suggests that simple relationships between species characteristics and population responses to warming may not occur in nature. Instead, we may need to embrace ecological complexity by considering local-scale predictors that capture intra-specific variation. Climate change can alter when and how animals grow, breed, and migrate, but it is unclear whether this allows populations to persist. This global study shows that shifts in seasonal timing are key to helping vertebrate species maintain population growth under global warming.

The Academy of Finland is acknowledged for a grant to TE (project 8119367) and EK (project 250709). PLP was supported by a research grant (TE_291/2010) offered by the Romanian Ministry of Education and Science. T. Szép received funding from OTKA K69068 and JT from OTKA 75618. JMP was supported by a JAE grant from Consejo Superior de Investigaciones Científicas. SM-JM, FdL-AM, JF, JJS and FV were respectively supported by projects CGL2009-09439, CGL2012-36665, CGL2009- 11445, CGL2010-19233-C03-01 and CGL2008-00562 by the Spanish Ministry of Science and Innovation and FEDER and project EVITAR by the Spanish Ministry of Health. FV was also supported by the European Regional Development Fund. MACT was funded by a predoctoral FPU grant from the Spanish Ministry of Education (AP20043713). PM was supported by grant from the Polish Ministry of Science and Higher Education (project 2P04F07030), and the Foundation for Polish Science.

Well-known examples of high-amplitude, large-scale fluctuations of small-mammal populations include vole cycles in the boreal zone of Eurasia, lemming cycles in the high-arctic tundra of Eurasia and North America, snowshoe hare cycles in the boreal zone of North America, and outbreaks of house mice in southeastern Australia. We synthesize the recent knowledge of three key aspects of these animals' population cyles: (1) periodicity, amplitude, and spatiotemporal synchrony; (2) reproduction and survival; and (3) underlying mechanisms. Survival rather than reproductive rate appears to drive rates of population increase during these fluctuations. Food limitation may stop increases of cyclic vole, lemming, and hare populations, whereas the decline from peak numbers is caused by predation mortality. In house mice, without coevolved predators, outbreaks may be driven by rainfall, food supply, and disease.

Fluctuations in the abundance of main prey species might shape animal communities, by inducing numerical responses and dietary shifts in predators. Whether numerical responses and dietary shifts differ among individuals of different age and sex has so far gained little attention. These differences could affect how much predators consume main and alternative prey, thus causing variation in predation pressure on main and alternative prey species. We studied the effect of fluctuating main prey abundance (voles) in autumn on the age and sex composition of a food-hoarding population of Eurasian pygmy owls Glaucidium passerinum (327 individuals), and on the species composition of their food stores in western Finland during 2003–2017 (629 food stores). Numbers of yearlings (< 1-year old) of both sexes and adult (+ 1-year old) females increased with increasing vole abundance. During low vole abundance, adult owls stored more small birds and less small mammals than yearlings. Females stored more small mammals than males and showed a tendency to store less birds. The amount of consumed birds (the most important alternative prey), and in particular of crested, willow, great, and blue tits, increased with low vole densities. Our results show that numerical, functional, and total responses of pygmy owls, and probably also other vertebrate predators, to the availability of the main prey in winter are shaped by the age and sex composition of the predator population, which both show large spatio-temporal variation in boreal forests.

Recent wildlife population declines are usually attributed to multiple sources such as global climate change and habitat loss and degradation inducing decreased food supply. However, interactive effects of fluctuations in abundance of main foods and weather conditions on population densities and reproductive success have been studied rarely. We analysed long-term (1973–2018) data on Tengmalm’s owl ( Aegolius funereus ) and the influence of prey abundance and weather on breeding densities and reproductive success in western Finland. We found that fledgling production per breeding attempt declined and laying date of the owl population delayed during the period between 1973 and 2018. The breeding density of the owl population decreased with increasing temperature in winter (October–March), fledgling production increased with increasing temperature and precipitation in spring (April–June), whereas the initiation of egg-laying was delayed with increasing depth of snow cover in late winter (January–March). The decreasing trend of fledgling production, which was mainly due to starvation of offspring, was an important factor contributing to the long-term decline of the Tengmalm’s owl study population. Milder and more humid spring and early summer temperatures due to global warming were not able to compensate for lowered offspring production of owls. The main reason for low productivity is probably loss and degradation of mature and old-growth forests due to clear-felling which results in loss of coverage of prime habitat for main (bank voles) and alternative foods (small birds) of owls inducing lack of food, and refuges against predators of Tengmalm’s owls. This interpretation was also supported by the delayed start of egg-laying during the study period although ambient temperatures increased prior to and during the egg-laying period.

Physical condition is important for the ability to resist various parasites and diseases as well as in escaping predators thus contributing to reproductive success, over-winter survival and possible declines in wildlife populations. However, in-depth research on trends in body condition is rare because decades-long datasets are not available for a majority of species. We analysed the long-term dataset of offspring covering 34 years, male parents (40 years) and female parents (42 years) to find out whether the decline of Tengmalm’s owl population in western Finland is attributable to either decreased adult and/or juvenile body condition in interaction with changing weather conditions and density estimates of main foods. We found that body condition of parent owl males and females declined throughout the 40-year study period whereas the body condition of owlets at the fledging stage very slightly increased. The body condition of parent owls increased with augmenting depth of snow cover in late winter (January to March), and that of offspring improved with increasing precipitation in late spring (May to June). We conclude that the decreasing trend of body condition of parent owl males and females is important factor probably inducing reduced adult survival and reduced reproduction success thus contributing to the long-term decline of the Tengmalm’s owl study population. The very slightly increasing trend of body condition of offspring is obviously not able to compensate the overall decline of Tengmalm’s owl population, because the number of offspring in turn simultaneously decreased considerably in the long-term. The ongoing climate change appeared to work in opposite ways in this case because declining depth of snow cover will make the situation worse but increased precipitation will improve. We suggest that the main reasons for long-term decline of body condition of parent owls are interactive or additive effects of reduced food resources and increased overall predation risk due to habitat degradation (loss and fragmentation of mature and old-growth forests due to clear-felling) subsequently leading to decline of Tengmalm’s owl study population.

Abstract Social polygyny usually benefits males by increasing the number of offspring, whereas it is detrimental for females as they must share the resources provided by their mate. An intersexual conflict may exist in animals with obligatory bi-parental care, such as birds of prey, in which females incubate and brood, whereas males provision food for their families. Long-term ringing data from Eurasian kestrels (Falco tinnunculus) breeding in nest-boxes and data on density indices of main prey animals (voles) were collected during 1985–2013 in western Finland to study polygynous behaviour. Of 1294 males, 54 (4.2%) were encountered at two (53) or three (1) nests during the same breeding season. Polygyny occurred more frequently during years of high vole abundance. The distances between nests of corresponding primary and secondary females were greater (median 1010 m) than the distances from nests of primary females to the nearest vacant nest-box (median 455 m). Twenty-eight (53%) of 53 secondary females had nearest available monogamous male within 2 km from their nest-boxes, indicating that mating options were available. Secondary females produced 30% less fledged offspring than simultaneously laying monogamously paired females. The abundance of prey animals is apparently alleviating the effort of males mating with multiple females. Spacing out the nests of primary and secondary females implies deceptive behaviour in the nest-site selection of polygynous males. Contradicting the polygyny threshold model, reproductive success of secondary females was significantly reduced in comparison to monogamous females laying simultaneously. These results show that secondary kestrel females apparently made a maladaptive choice, likely because they were deceived to accept polygynous mating status during the courtship feeding period.Significance statementAs dedicated parental effort of both the male and the female is vital to ensure the offspring survival amongst animals with obligatory bi-parental care, polygyny should be inherently a maladaptive mating strategy for females. However, regular social polygyny has been documented in at least 10% of bird species from ten orders. Previous studies on breeding success of polygynous birds of prey indicate reduced offspring production of secondary female partners with no apparent cause for females to choose polygynous males over other mating options. We showed that polygyny in Eurasian kestrels is frequent when food is abundant facilitating males to provision their two or more females during courtship feeding. Polygynous males space out their two nests thus attempting to hide their mating status from their secondary partners which suffer from their mate choice in form of poor reproductive success. Therefore, amongst the “cost of polygyny to females” hypotheses, the deceptive behaviour of males during courtship feeding appeared to be an apparent explanation for maladaptive mate choice of secondary females.

Climate change increases the occurrence of extreme weather conditions, affecting ecosystems worldwide but possible impacts of these extremes on biological systems have been insufficiently studied. Among others, migratory raptors are particularly susceptible to adverse weather conditions. We analysed capture‐recapture data of Eurasian Kestrels (Falco tinnunculus) breeding in western Finland during 1985–2018 to study how environmental conditions in their boreal breeding areas and Mediterranean wintering areas affect adult survival rate. As predictors of apparent survival, we used density data of their primary prey (voles) from their breeding grounds, alongside seasonal minimum temperatures and rainy‐day frequencies of Finnish summer and Mediterranean winter. We also tested whether adverse weather in winter can result in carry‐over delays in the initiation of next breeding season (i.e., egg‐laying). We found that both frequent and infrequent rain in winter predicted low apparent survival rate, while summer weather conditions had no effect on survival. Vole abundance in breeding areas negatively correlated with apparent survival. Finally, frequent precipitation in Mediterranean wintering grounds resulted in delayed laying in the following spring during years of low vole abundance in the breeding grounds. We conclude that weather extremes in wintering areas are more acutely affecting annual adult survival in long‐distance migratory kestrels than weather conditions in breeding grounds, thus providing the first evidence of impacts of climate extremes on survival rate of migratory species in North Europe. Furthermore, our results suggest that effects of such disadvantageous weather conditions carry over from winter to spring. If climate change amplifies the frequency and magnitude of weather extremes in the Mediterranean, its long‐distance migrant inhabitants may encounter setbacks in population growth and stability. We analysed capture‐recapture data of breeding Eurasian kestrels (Falco tinnunculus) in western Finland during 1985–2018 to study how environmental conditions in their boreal breeding areas and Mediterranean wintering areas affect adult survival rate and timing of laying. We found that both frequent and infrequent precipitation in winter predicted reduced apparent survival rate and that frequent precipitation in wintering grounds resulted in delayed laying during years of poor prey availability.