Dispersal and climate change: a case study of the Arctic tern Sterna paradisaea

Dispersal is an important evolutionary process that can affect admixture of populations and cause rapid responses to changing climatic conditions due to gene flow from populations at different altitudes or latitudes already experiencing these conditions. We investigated long-term patterns of natal and breeding dispersal in a coastal seabird, the Arctic tern Sterna paradisaea , that experiences specific climatic conditions in the northern temperate and Arctic climate zones during breeding and different climatic conditions in the Antarctic during winter. Long natal and breeding dispersal distances were costly as shown by their effects on delayed breeding. Dispersal distances varied significantly among years, with natal dispersal showing a strong temporal increase during the last 70 years. Annual differences in dispersal distance could be accounted for by climate conditions in the breeding grounds and the winter quarters. Natal dispersal was related to climate conditions in both the year of hatching and the year of breeding, whereas breeding dispersal was only related to climate conditions in the second year of the dispersal event. Only the north Atlantic oscillation (NAO) index for winter showed a consistent temporal trend, suggesting that the temporal trend in natal dispersal distance must be caused by changes in the NAO (or associated phenomena). These findings indicate that dispersal can change rapidly in response to changing climate conditions.     

Long-term trends in the timing of breeding and brood size in the Red-Backed Shrike Lanius collurio in the Czech Republic, 1964–2004

Climate change has affected breeding dates and clutch sizes in many bird species. To date, most of the studies aimed at assessing the effects of climate change on these phenological events in birds have been on hole-nesting species and the changes linked either to local climate variation or to some large-scale composite variables, such as the North Atlantic Oscillation (NAO). Relatively less is known about the climate responses of open-nesting birds and on the relative roles of climate variables at different scales. Using bird ringing records covering a time span of 41 years, we documented shifts in the timing of breeding and brood size in a long-distance migrant, the Red-Backed Shrike (Lanius collurio) from a central European population. We found a 3- to 4-day shift towards earlier breeding and an increase in brood size by approximately 0.3 nestlings since 1964. The Red-Backed Shrikes start to breed in May and rear the first nestlings in June. During the period 1964–2004, temperatures in May significantly increased, while the increase in June temperatures was not significant. Simultaneous tests on the influence of local climate variables and the NAO index revealed a better performance of local climate. The increasing temperature in May was positively associated with the advancement of breeding. Similarly, at a local scale, higher May temperatures were followed by larger brood sizes, while a high amount of rainfall had a strong negative effect.     

Regime shifts in the breeding of an Atlantic puffin population

Timing of breeding is a key factor determining the reproductive success in bird populations and known to be affected by climate fluctuations. We investigated the long‐term (1978–2002) relationship between climate and hatching date within a population of Atlantic puffin Fratercula arctica at Røst in the Norwegian Sea. The timing of puffin breeding was found to be influenced by the North Atlantic Oscillation winter index (NAO). We isolated two temporal regimes, one where NAO had a significant effect on hatching date (1978–1986 and 1995–2002) and one where these variables were independent (1987–1994). Hatching date could be modelled using, in addition to NAO, hatching date and food abundance in the preceding breeding season (possibly proxies of parental effort). The models remained significant for regime 1 but not for regime 2. NAO differed between the two regimes suggesting that the shifts were induced by climate change, possibly via its effect on the availability of prey in the preceding year. The novelty of our study is the identification of temporal regimes in the effects of climate within one population.     

Adjustment of the annual cycle to climatic change in a long-lived migratory bird species

Climate change has advanced the phenology of many organisms. Migratory animals face particular problems because climate change in the breeding and the wintering range may be asynchronous, preventing rapid response to changing conditions. Advancement in timing of spring migration may have carry-over effects to other parts of the annual cycle, simply because advancement of one event in the annual cycle also advances subsequent events, gradually causing a general shift in the timing of the entire annual cycle. Such a phenotypic shift could generate accumulating effects over the years for individuals, but also across generations. Here we test this novel hypothesis of phenotypic response to climate change by using long-term data on the Arctic tern Sterna paradisaea. Mean breeding date advanced by almost three weeks during the last 70 years. Annual arrival date at the breeding grounds during a period of 47 years was predicted by environmental conditions in the winter quarters in the Southern Ocean near the Antarctic and by mean breeding date the previous year. Annual mean breeding date was only marginally determined by timing of arrival the current year, but to a larger extent by arrival date and breeding date the previous year. Learning affected arrival date as shown by a positive correlation between arrival date in year (i+1) relative to breeding date in year (i) and the selective advantage of early breeding in year (i). This provides a mechanism for changes in arrival date being adjusted to changing environmental conditions. This study suggests that adaptation to changing climatic conditions can be achieved through learning from year to year[Current Zoology 55(2):92-101,2009].     

Keeping up with early springs: rapid range expansion in an avian herbivore incurs a mismatch between reproductive timing and food supply

Within three decades, the barnacle goose population wintering on the European mainland has dramatically increased in numbers and extended its breeding range. The expansion has occurred both within the Arctic as well as by the colonization of temperate areas. Studies of performance of individuals in expanding populations provide information on how well species can adapt to novel environments and global warming. We, therefore, studied the availability of high quality food as well as timing of reproduction, wing moult, fledgling production and postfledging survival of individually marked geese in three recently established populations: one Arctic (Barents Sea) and two temperate (Baltic, North Sea). In the Barents Sea population, timing of hatching was synchronized with the peak in food availability and there was strong stabilizing selection. Although birds in the Baltic and North Sea populations bred 6–7 weeks earlier than Arctic birds, timing of hatching was late in relation to the peak in food availability, and there was moderate to strong directional selection for early breeding. In the Baltic, absolute timing of egg laying advanced considerably over the 20‐year study period, but advanced little relative to spring phenology, and directional selection on lay date increased over time. Wing moult of adults started only 2–4 weeks earlier in the temperate populations than in the Arctic. Synchronization between fledging of young and end of wing moult decreased in the temperate populations. Arctic‐breeding geese may gradually accumulate body stores from the food they encounter during spring migration, which allows them to breed relatively early and their young to use the peak of the Arctic food resources. By contrast, temperate‐breeding birds are not able to acquire adequate body stores from local resources early enough, that is before the quality of food for their young starts to decrease. When global temperatures continue to rise, Arctic‐breeding barnacle geese might encounter similar problems.     

Decline of a montane Mediterranean pied flycatcher Ficedula hypoleuca population in relation to climate

Certain populations of long‐distance migratory birds are suffering declines, which may be attributed to effects of climate change. In this article, we have analysed a long‐term (1991–2015) data set on a pied flycatcher Ficedula hypoleuca population breeding in nest‐boxes in a Mediterranean montane oak forest, exploring the trends in population size due to changes in nestling recruitment, female survival and female immigration. We have related these changes in population parameters to local climate, winter NAO index and to breeding density. During the last 25 yr the population has declined by half, mainly in association with a decrease in nestling mass and structural size which had repercussions on the probability of nestling recruitment to the population. Lower local nestling recruitment in certain years was linked to lower female immigration rate in the same years. On the other hand, the local survival of females remained stable throughout the study period. Laying date and breeding success were negatively affected by local temperatures while breeding, recruitment rate likewise by minimum temperature prior to breeding in April. As minimum April temperatures have increased across the study period, this may have affected recruitment and immigration rates negatively. On the other hand, tarsus length and body mass of nestlings were positively associated with winter NAO index, pointing to more global climatic links. Moreover, there was also a negative temporal trend in body mass of adults, implying increasingly difficult conditions for breeding. Declining recruit production in the study area could be attributed to a mismatch between the timing of arrival and breeding in the population, and the peak of food availability in this area.     

Lagged effects of North Atlantic Oscillation on spittlebug Philaenus spumarius (Homoptera) abundance and survival

The North Atlantic Oscillation (NAO) is a large‐scale pattern of climate variability that has been shown to have important ecological effects on a wide spectrum of taxa. Studies on terrestrial invertebrates are, however, lacking. We studied climate‐connected causes of changes in population sizes in island populations of the spittlebug Philaenus spumarius (L.) (Homoptera). Three populations living in meadows on small Baltic Sea islands were investigated during the years 1970–2005 in Tvärminne archipelago, southern Finland. A separate analysis was done on the effects of NAO and local climate variables on spittlebug survival in 1969–1978, for which survival data existed for two islands. We studied survival at two stages of the life cycle: growth rate from females to next year's instars (probably mostly related to overwintering egg survival), and survival from third instar stage to adult. The latter is connected to mortality caused by desiccation of plants and spittle masses. Higher winter NAO values were consistently associated with smaller population sizes on all three islands. Local climate variables entering the most parsimonious autoregressive models of population abundance were April and May mean temperature, May precipitation, an index of May humidity, and mean temperature of the coldest month of the previous winter. High winter NAO values had a clear negative effect on late instar survival in 1969–1978. Even May–June humidity and mean temperature of the coldest month were associated with late instar survival. The climate variables studied (including NAO) had no effect on the growth rate from females to next year's instars. NAO probably affected the populations primarily in late spring. Cold and snowy winters contribute to later snow melt and greater spring humidity in the meadows. We show that winter NAO has a considerable lagged effect on April and May temperature; even this second lagged effect contributes to differences in humidity. The lagged effect of the winter NAO to spring temperatures covers a large area in northern Europe and has been relatively stationary for 100 years at least in the Baltic area.     

Birth timing and population changes in greater horseshoe bat colonies (Rhinolophus ferrumequinum) are synchronized by climatic temperature

We counted the births of greater horseshoe bats born at three small breeding colonies in southwest Wales and south-west England at the extreme edge of the species distribution over nine summers (1984–1993). Overall birth timing was almost identical at the three sites (mean of mean birth dates = 13–14 July), but varied widely from year to year. Mean birth timing was synchronized at the three sites in a given year. Early births followed warm springs; a significant negative regression of mean birth date on mean April plus May temperature was evident. A rise of 2^oC accelerated mean birth date by about 18 days. Population levels fell at all three sites following the very late mean birth date of 28 July recorded in 1986, after an extremely cold spring and summer. Recovery of populations in all sites followed a series of warm springs and early mean birth dates, but was hampered by birth sex ratios favouring males for several years. These findings confirm climate, through its effect upon birth timing, and possibly also on sex ratios, as a major factor controlling bat populations, and hence the distribution of bat species.     

Agriculture, fertilizers and life history of a coastal seabird

1. Leakage of fertilizers from farmland has affected levels of nitrogen and phosphorus in many coastal areas, reducing limitation of primary productivity with consequences for timing and magnitude of the annual peak in phytoplankton and zooplankton. Such changes in nutrient availability may have affected temporal patterns of abundance of marine invertebrates and vertebrates that are the main prey of seabirds. 2. We investigated the extent to which changes in the use of fertilizers by farmers affected timing of breeding, clutch size, recruitment and longevity of a coastal seabird, the Arctic tern Sterna paradisaea Pont., in Denmark. 3. Timing of breeding advanced with the increase in use of fertilizers, with an effect as a consequence of a phenotypic response of individuals exposed to different levels of fertilizers. 4. Annual mean clutch size increased with the amount of fertilizer. While individual Arctic terns increased their clutch size with fertilizer level, there was no evidence of individual Arctic terns in different years changing their clutch size in response to changes in fertilizer use. 5. Annual recruitment rate, estimated as the proportion of young that were subsequently recovered as adults, was related to fertilizer use. 6. Mean longevity, estimated as the maximum age of adult individuals, decreased in response to fertilizer use. 7. These findings provide evidence of fertilizer use in agriculture having significant indirect effects on timing of reproduction, clutch size, recruitment and longevity of a seabird.     

A RINGING STUDY OF MIGRATORY BARN SWALLOWS IN WEST MALAYSIA

The Barn Swallow is a non-breeding winter visitor to West Malaysia (Malaya), abundant in season, by day feeding aerially over a wide range of habitats and by night normally roosting gregariously in trees, reed-beds or on service wires in towns. Records of ringed birds have demonstrated that those reaching Malaya breed in the Palaearctic region from 108°E eastwards between 37° and 51°N. Recoveries south of the breeding range suggested that migrating birds may follow either a continental route or a more easterly track through the Philippines and Borneo. Counts at roost sites in a reed-bed and in towns demonstrated a seasonal increase in numbers from late July to a peak in November, followed by a decline of about 20% to a level maintained until mid-February when departure commenced. Most birds had left by early May, but a few lingered and possibly overlapped with the first returning migrants in June. There was no evidence that any individuals remained in Malaya through the nuptial period. Repeats during winter at three regularly sampled urban roosts indicated that many birds on passage were present until November and again in late March–early April; from December to February the winter population was relatively stable and comparatively sedentary. Although the distances between towns were small in relation to the demonstrated foraging range of Barn Swallows, only 17% of 1,955 repeats of ringed birds represented a shift in roost site. Most shifts were towards the centrally situated and most populous roost of the three; interchanges between the outer pair of towns were few. A complete moult occurred on the wintering grounds, during which young of the year acquired adult plumage. Replacement of the primaries extended virtually throughout the moulting period, at an average rate of 2.4 feathers per month in the proximal part of the tract and 1.3 feathers per month in the distal part. Adults on average moulted slightly earlier than juveniles, but there was a wide scatter in timing between individuals of both age groups. There was no evidence that the initiation of moult was related to the dates of post-nuptial migration. The date of departure on prenuptial migration, however, was normally delayed until primary moult was complete. Large weight gains in March and April occurred only in swallows which had completed the moult. At this period the mean weight of birds in fresh plumage was about 30% above the lowest winter mean, and was significantly higher than that of contemporary samples of birds in which moult was continuing. In final samples in late April and early May mean weights showed a decline, indicating that late birds departed with reduced deposits of metabolic reserves. The gonads of adults of both sexes among passage and arriving birds in July and August had largely completed post-nuptial regeneration, and subsequently remained quiescent. Preliminary stages of recrudescence were observed in females from February onwards, and in males from March. Recrudescence was most advance in specimens which had completed the moult, but did not approach breeding condition in any bird before departure. Returning birds tended to be conservative in their choice of winter roost. Among 1,276 records, 82% were recaptured in the town of original ringing. Again shifts towards the centrally situated roost were more numerous than between the peripheral pair. The frequency of returns varied significantly with the month of ringing, being higher for December-March, lower for July-November and April-May. Survival rates, calculated from returns after one and two breeding seasons, indicated an annual mortality of 60–72%, higher among juveniles than adults. Comparison of results of successive years suggested that unfavourable conditions in 1967 resulted in lower survival of juveniles in particular than in 1966. There was no evidence of mortality at the roost sites, and it is argued that heavy losses probably occur during the migratory journeys.     

Breeding performance of kestrels at Eskdalemuir, south Scotland

The performance of 144 pairs of European kestrels breeding in upland young conifer plantations was studied from 1976 to 1979. Laying started between 15 April and 1 June, and was 14 days later, on average, in the poor vole year of 1977 than in the other years. Some 38% of pairs failed to fledge young, mainly because they deserted clutches during incubation. The proportion of pairs that failed was positively correlated with total rainfall in May, but apparently not with estimated spring vole numbers. There was a marked seasonal decline in both clutch size and the probability of breeding successfully, so that early laying pairs fledged 2.7 times as many young per attempt as did late pairs. Within years, there was considerable variation in the laying date between pairs. On the available data, environmental factors, such as the habitat or vole numbers around the nest, appeared to have less influence on this variation than did the age of the pair members, their pairing date or their previous breeding experience.     

Selection on laying date is connected to breeding density in the pied flycatcher

Timing of reproduction and clutch size are important determinants of breeding success, especially in seasonal environments. Several recent bird population studies have shown changes in breeding time and in natural selection on it. These changes have often been linked with climate change, but few studies have investigated how the traits or natural selection are actually connected with climatic factors. Furthermore, the effect of population density on selection has been rarely considered, despite the potential importance of density in demographic processes. We studied variation in natural selection on laying date and on clutch size in relation to measures of spring phenology and population density in a long-term study of pied flycatchers in SW Finland. The phenological stage of the environment at mean egg-laying did not affect the direction of selection on either laying date or on clutch size. There was, however, stronger selection for earlier laying date when the breeding density of the population was high, suggesting that early breeding is not necessarily beneficial as such, but that its importance is emphasized when high population density increases competition. In addition, early breeding was favoured when the pre-breeding period was cool, which may indicate an increased advantage for the fittest individuals in harsher conditions. In the middle of the twentieth century, there was selection for large clutch size, which subsequently ceased, along with an overall decrease in recruit production. Our results indicate that attention should be paid to demographic factors such as breeding density when studying natural selection and temporal changes in it.     

Divergent patterns of impact of environmental conditions on life history traits in two populations of a long-distance migratory bird

Some areas have experienced recent dramatic warming due to climate change, while others have shown no change at all, or even recent cooling. We predicted that patterns of selection on life history would differ between southern and northern European populations of a long-distance migratory bird, the barn swallow Hirundo rustica, because global patterns of weather as reflected by large-scale weather phenomena such as the North Atlantic Oscillation (NAO) and the El Niño-Southern Oscillation (ENSO) have different effects on environmental conditions in different parts of the world frequented during the annual cycle. We investigated relationships between mean arrival date, dispersal rate and yearling survival rate among years, using two long-term population studies in Spain and Denmark. We found evidence of a difference in the effects of normalized difference vegetation index in North and West Africa on mean arrival date of male barn swallows, with the effect differing significantly between populations. Second, there was a significant interaction between ENSO and population on dispersal rate, showing that conditions in Africa during winter differentially affected dispersal in the two populations. Finally, the NAO index in winter had an effect on yearling survival that differed between populations. These findings highlight the divergent patterns of response to climate change among populations, and they suggest that climate change can differentially affect important life history traits with potential implications for maintenance of viable populations and gene flow among populations.     

The influence of climate on the timing and rate of spring bird migration

Ecological processes are changing in response to climatic warming. Birds, in particular, have been documented to arrive and breed earlier in spring and this has been attributed to elevated spring temperatures. It is not clear, however, how long-distance migratory birds that overwinter thousands of kilometers to the south in the tropics cue into changes in temperature or plant phenology on northern breeding areas. We explored the relationships between the timing and rate of spring migration of long-distance migratory birds, and variables such as temperature, the North Atlantic Oscillation (NAO) and plant phenology, using mist net capture data from three ringing stations in North America over a 40-year period. Mean April/May temperatures in eastern North America varied over a 5°C range, but with no significant trend during this period. Similarly, we found few significant trends toward earlier median capture dates of birds. Median capture dates were not related to the NAO, but were inversely correlated to spring temperatures for almost all species. For every 1°C increase in spring temperature, median capture dates of migratory birds averaged, across species, one day earlier. Lilac (Syringa vulgaris) budburst, however, averaged 3 days earlier for every 1°C increase in spring temperature, suggesting that the impact of temperature on plant phenology is three times greater than on bird phenology. To address whether migratory birds adjust their rate of northward migration to changes in temperature, we compared median capture dates for 15 species between a ringing station on the Gulf Coast of Louisiana in the southern USA with two stations approximately 2,500 km to the north. The interval between median capture dates in Louisiana and at the other two ringing stations was inversely correlated with temperature, with an average interval of 22 days, that decreased by 0.8 days per 1°C increase in temperature. Our results suggest that, although the onset of migration may be determined endogenously, the timing of migration is flexible and can be adjusted in response to variation in weather and/or phenology along migration routes.     

Inter‐annual variability and long‐term trends in breeding success in a declining population of migratory swans

Population declines among migratory Arctic‐breeding birds are a growing concern for conservationists. To inform the conservation of these declining populations, we need to understand how demographic rates such as breeding success are influenced by combinations of extrinsic and intrinsic factors. In this study we examined inter‐annual variation and long‐term trends in two aspects of the breeding success of a migratory herbivore, the Bewick's swan Cygnus columbianus bewickii, which is currently undergoing a population decline: 1) the percentage of young within the wintering population and 2) mean brood size. We used an information‐theoretic approach to test how these two measures of productivity were influenced over a 26 yr period by 12 potential explanatory variables, encompassing both environmental (e.g. temperature) and intrinsic (e.g. pair‐bond duration) factors. Swan productivity exhibited sensitivity to both types of explanatory variable. Fewer young were observed on the wintering grounds in years in which the breeding period (May to September) was colder and predator (Arctic fox) abundance was higher. The percentage of young within the wintering population also showed negative density‐dependence. Inter‐annual variance in mean swan brood size was best explained by a model comprised of the negative degree days during the swan breeding period, mean pair‐bond duration of all paired swans (i.e. mean pair duration), and an interaction between these two variables. In particular, mean pair duration had a strong positive effect on mean brood size. However, we found no long‐term directional trend in either measure of breeding success, despite the recent decline in the NW European population. Our results highlight that inter‐annual variability in breeding success is sensitive to the combined effects of both intrinsic and extrinsic factors.     

A population model for the black tern Chlidonias niger in West-Europe

Based on empiric data of breeding success and accurate number trends in The Netherlands, a population model for the black tern was constructed. This model is based on Leslie matrices. Reproductive parameters from the four most important landscape types (river landscape, agricultural grasslands, peat marsh and heath land/moors) are used as model input. Highly accurate national population trend data were used to obtain the best (least square) estimate of overall adult and subadult survival (resp. 0.849 and 0.595). Estimating survival parameters in this way might be useful for threatened (bird) species, especially if catching and ringing is difficult or less desired from a conservation perspective. The model shows the actual importance of the river landscape as the main source for reproductive output of the Dutch black tern population. The prediction model was subsequently used to test different conservation strategies for the Dutch black tern population. Conservation strategies ranged from a null scenario (no change in conservation effort) to in- or decreasing the number of rafts in the most productive landscape (river landscape) to a scenario where breeding success is improved recently in agricultural grasslands via minimizing disturbance. For all scenarios, the model predicts a slow to rapid population increase in the Dutch black tern population after 10–20 years. Improving breeding success in agricultural grasslands habitat has the highest added value.     

Variation in laying date in relation to spring temperature in three species of tits (Paridae) and pied flycatchers Ficedula hypoleuca in southernmost Sweden

This study documents the advancement of laying dates in three species of tits (Paridae) in southernmost Sweden during recent decades, and the absence of a similar response in the pied flycatcher Ficedula hypoleuca. It is based on several different nestbox studies; the oldest one starting in 1969. During 1969 to 2012, mean spring temperatures in the study area increased by between 0.06 and 0.08°C per year, depending on the period considered. Great tits Parus major, blue tits Cyanistes caeruleus and marsh tits Poecile palustris, which generally start egg laying between the last week of April and the first week of May, all advanced laying date at a similar rate during the study period (0.25 d yr^–1). This indicates that these species were similarly affected by increasing temperatures. When accounting for mean spring temperature variation, we still found an advancement of laying date over the study period, mostly due to such relationships among marsh and blue tits. This result could reflect ongoing microevolution favouring earlier laying, but could also be a result of other factors such as increased intra‐ or inter‐specific competition for early breeding. Pied flycatchers, which generally lay during the third week of May, did not significantly advance the date of egg laying despite that the long‐term trend in the increase in ambient temperature during the 30‐d period preceding the start of egg laying was similar for pied flycatchers compared to the tit species.     

桂西南石灰岩地区部分鸟类繁殖资料记述

2010～2012年每年的3～7月采用系统搜寻法和根据亲鸟的行为及活动路径确定巢址的方法,在广西弄岗国家级自然保护区弄岗保护站辖区及其周边林区和农田进行了寻巢及观察,超过40种鸟类的巢被发现.本文摘录了18种鸟类的繁殖资料进行报道,主要内容包括生活习性、繁殖时间、窝卵数、卵大小和巢大小等.本文为今后石灰岩地区的鸟类研究提供基础资料.     

Dramatic changes in the return date of Guillemots Uria aalge to colonies in Shetland, 1962–2005

Capsule Changes in return date coincided with marked changes in population size that probably resulted in fluctuating competition for nest-sites.

Aims To document the changes in return dates over a 44-year period and to identify the factors associated with these changes.

Methods We compared changes in return date at Shetland colonies with those for the Isle of May, southeast Scotland, and with the available information on population size, the abundance of some fish species eaten by Common Guillemots and large-scale changes in the oceanography and climate of the eastern Atlantic as reflected by the winter index of the North Atlantic Oscillation (NAO).

Results Common Guillemots normally return to colonies in Shetland in late winter. However, during the 1960s return dates became gradually earlier with birds present from early October. Autumn return remained the norm for about ten years after which return dates gradually reverted back to late winter. In contrast, Common Guillemots on the Isle of May, 400 km south of Shetland, showed no marked shift, returning in October each year. There was a strong negative correlation between date of return of Shetland birds and population size, whereas on the Isle of May birds came back earlier when there was a large positive winter NAO index. There was no convincing evidence that changes in wintering areas or fish abundance influenced when birds returned to the colonies, although the fish data may not have been collected on the correct spatial scale.

Conclusion Competition for high quality nest-sites is the most likely reason for Common Guillemots returning to the colonies during the autumn and winter.     

Large-scale climatic phenomena and timing of breeding in a local population of the Osprey Pandion haliaetus in southern Finland

The effects of large-scale climatic phenomena on the timing of breeding in the Osprey Pandion haliaetus were studied during 1981–2006 in a small local population of about 20 pairs near the southern coast of Finland. The timing of breeding was estimated on the basis of the wing length of the largest young within the brood. The wing lengths were plotted against the date of the measurement to get a linear regression model characterizing the average developmental stage of broods in relation to date. This model was used when converting the measurements to correspond to the median date of all the measurements. Large-scale climatic phenomena were characterized by the winter and monthly indices of the North Atlantic oscillation (NAO). A significant positive relationship between the winter NAO index and timing of breeding in the Osprey, as indicated by the wing length of the largest young in the brood, was found. The relationship was even stronger when only the monthly value of January was considered. These relationships seemed to be linked with consequent earlier ice melting after mild winters. The results indicate prominent effects of large-scale climatic phenomena and that they can be monitored with relatively modest effort.