Late Summer Temperatures Research Articles

Marine climate in the Irish Sea: analysis of a 489-year marine master chronology derived from growth increments in the shell of the clam Arctica islandica

We demonstrate here that the growth increment variability in the shell of the long-lived bivalve mollusc Arctica islandica can be interpreted as an indicator of marine environmental change in the climatically important North Atlantic shelf seas. Multi-centennial (up to 489-year) chronologies were constructed using five detrending techniques and their characteristics compared. The strength of the common environmental signal expressed in the chronologies was found to be fully comparable with equivalent statistics for tree-ring chronologies. The negative exponential function using truncated increment-width series from which the first thirty years have been removed was chosen as the optimal detrending technique. Chronology indices were compared with the Central England Temperature record and with seawater temperature records from stations close to the study site in the Irish Sea. Statistically significant correlations were found between the chronology indices and (a) mean air temperature for the 14-month period beginning in the January preceding the year of growth, (b) mean seawater temperatures for February–October in the year preceding the year of growth (c) late summer and autumn air temperatures and sea surface temperatures for the year of growth and (d) the timing of the autumn decline in SST. Changes through time in the correlations with air and seawater temperatures and changes towards a deeper water origin for the shells in the chronology were interpreted as an indication that shell growth may respond to stratification dynamics.

Temperature reconstruction from tree‐ring maximum density of Balfour spruce in eastern Tibet, China

AbstractWood from Balfour spruce [Picea likiangensis var. balfouriana (Rehd. et Wils.)] was collected at three sites in eastern Tibet. Maximum latewood densities (MXD) were measured by X‐ray densitometry; individual series were first cross dated and then combined to form a standard chronology. This chronology was significantly correlated with late summer temperatures on the eastern Tibetan Plateau. It was used to reconstruct the August–September mean temperature for the period 1695–2000 A.D., and it explained the 63.5% of the total temperature variance. Wavelet analysis of the reconstructed temperature series suggested the existence of a 20‐year climatic cycle during the period 1800–1860 and a ∼50‐year cycle at the beginning of the twentieth century. Copyright © 2009 Royal Meteorological Society

Bayesian analysis of temperature sensitivity of plant phenology in Germany

The temperature sensitivity of 43 phenological phases was analysed in Germany within the period 1951–2006 with the help of a Bayesian approach. First a Bayesian model comparison of monthly temperatures and phenological phases throughout the year was conducted. We analysed the data as constant (mean onset date), as linear (constant trend over time) and as change point model (time varying change). The change point model involves the selection of two linear segments which match at a particular time. The matching point is estimated by an examination of all possible breaks weighted by their respective change point probability. Secondly a Bayesian coherence analysis was applied to investigate the relationship between phenological onset dates and an effective temperature generated as a weighted average of monthly means. Temperature weight coefficients were obtained from an optimization of a coherence factor by simulated annealing. Results reveal that late spring, summer and early autumn temperature months exhibit a clear preference for the change point model (>50%) indicating nonlinear change. The temperature development of April and August shows exceptionally high nonlinearities compared to the other months with change point model probabilities of 78% and 81% over the last five decades. For all phenophases a strong dependence of phenology on temperature is determined. We can classify two main temperature response patterns of the studied phenological phases: on the one hand spring phenophases are particularly sensitive to temperatures in April, exhibiting a prompt response. On the other hand summer phenophases are less influenced by temperature during or right before the month of the onset. They reveal a delayed response to nonlinear temperature changes mainly of April. Especially abrupt changes during the temperature sensitive stage of species cause a pronounced change in plant phenology regardless of the time of onset.

Influence of environmental factors and female size on reproductive output in an invasive temperate marine gastropod Rapana venosa (Muricidae)

Life history and reproductive strategies influence population dynamics at the inter- and intra-specific level. Environmental conditions suitable for gonad development and spawning, the reproductive range, may be a smaller portion of the broader species distribution. The only known breeding population of veined rapa whelks (Rapana venosa) in North America is in Chesapeake Bay, USA. There is considerable interest in the potential reproductive range of this non-indigenous species given the rapa whelk’s negative impacts on commercial shellfish species in both its native and introduced ranges. Weight-specific reproductive output is described for wild caught Chesapeake Bay rapa whelks maintained in flow-through mesocosms for 2 years. Measured reproductive output within and between egg capsule deposition seasons (years) in relation to water temperature, salinity, daylength, and female size is used to describe the rapa whelk’s reproductive range. Egg capsule production is influenced by seasonal and absolute water temperatures as well as seasonal daylength cycles. Egg capsule deposition by Chesapeake Bay rapa whelks begins at water temperatures of approximately 18°C and continues for 11–15 weeks. Forty to 70% of female whelks deposited egg capsules in most weeks during this season, producing 150–200 egg capsules female−1 week−1. Water temperatures >28°C caused reduced egg capsule production relative to temperatures of 20–25°C. Egg capsule production was positively related to seasonal changes in daylength, and two peaks of egg capsule deposition were observed in the 2001 and 2002 deposition seasons. The combination of declining daylength and higher water temperatures in late summer was associated with the cessation of egg capsule deposition. A lower average weight specific reproductive output in 130–145 mm SL rapa whelks (average 12 ± 1%) than in 90–106 mm SL rapa whelks (average 22 ± 1% of body weight) may reflect a life history that balances the physiological costs of maintaining a large body mass with the production of many planktonic larvae from multiple clutches of egg capsules per breeding season over a 10–15-year lifespan. Estimates of the cumulative day-degree requirements corresponding to the annual initiation of egg capsule deposition were 238 and 236 for 2001 and 2002, respectively. Reproductive output and day-degree requirements for Chesapeake Bay rapa whelks were similar to values calculated from previous studies of native muricids (Eupleura caudata and Urosalpinx cinerea). A latitudinal range of 30–41° (N and S) is predicted as the realized reproductive range for rapa whelk populations on the basis of the day-degree requirements for native whelks and reproductively active invasive rapa whelk populations.

Asymmetrical thermal constraints on the parapatric species boundaries of two widespread generalist butterflies

Abstract 1. The sibling species Papilio glaucus and Papilio canadensis meet in a narrow hybrid zone believed to be maintained by temperature thresholds acting independently on both species. The present study tests if this assertion is true for the cold‐adapted species, P. canadensis, which is presumed to be limited by the effect of high temperatures in late summer and/or autumn on pupal survival.2. Three experiments were conducted examining the effects of: (i) short periods of high temperature stress in autumn, (ii) prolonged warm temperatures in autumn, and (iii) temperatures simulating warmer winters/longer springs upon the survival of P. canadensis and P. glaucus.3. Results indicated that short periods of high temperatures did not induce the high mortality rates required to be the key factor limiting the range of P. canadensis. However, P. canadensis did exhibit a considerably lower tolerance to high temperature extremes, prolonged warm temperatures in autumn, and conditions simulating shorter/warmer winters than P. glaucus.4. Differences in temperature tolerance throughout the pupal stage are likely to be a significant factor in maintaining the southern range limit of P. canadensis. Further warming as may occur during climate change, particularly in winter and spring, will likely affect the dynamics of southerly populations of P. canadensis.

Rapid warming of the ocean around South Georgia, Southern Ocean, during the 20th century: Forcings, characteristics and implications for lower trophic levels

The Southern Ocean is known to have warmed considerably during the second half of the 20th century but there are few locations with data before the 1950s. In addition, assessments of change in this region are hampered by the strong seasonal bias in sampling, with the vast majority of data collected during the austral summer. However, oceanographic measurements near South Georgia span most of the last century, and we here consider almost year-round data from this location over an 81-year period (1925–2006). We observe significant warming between the early and late 20th century, with differential warming between summer and winter months and an indication that late 20th century summer temperatures peaked ∼6 days earlier. To quantify the long-term warming trend in this highly variable data, a mixed model utilising a Residual Maximum Likelihood (REML) method was used. Over the 81-year period, a mean increase of ∼0.9 °C in January and ∼2.3 °C in August was evident in the top 100 m of the water column. Warming diminished below 100 m and approached 0 at 200 m. Thus the long-term warming around South Georgia is substantial—more so than documented previously for the circumpolar warming of the Southern Ocean. We examine potential causal effects of this trend, including local atmospheric and cryospheric change, the influence of upstream waters and the role of coupled modes of climate variability such as El Niño/Southern Oscillation and the Southern Annular Mode (SAM). It is likely that all of these play a part in the observed temperature increase. However, the role of the SAM is strongly indicated, via its likely role in the circumpolar warming trend in the Southern Ocean, and also by the atypical response of the South Georgia region to changes in heat fluxes associated with the SAM. Furthermore, the combination of a regional decline in ice extent and strong upstream warming likely explains a significant part of the strong seasonal variation apparent in the warming trend. In addition, we consider the implications that long-term warming has for South Georgia's lower trophic levels. For Euphausia superba, at their northern limit, we find a significant negative relationship between summer South Georgia water temperatures and mean summer density of E. superba across the southwest Atlantic sector of the Southern Ocean. Simple abundance and growth rate relationships with our long-term temperature data appear to show declining habitat suitability for E. superba. In contrast, the warming trend is likely to favour other macro- and mesozooplankton species that occupy the more northerly parts of the Antarctic Circumpolar Current, and it is likely to promote phytoplankton growth.

Changing climate sensitivity of black spruce ( Picea mariana Mill.) in a peatland–forest landscape in Interior Alaska

Dendroclimatological research is often based on the assumption that the relationship between tree growth and climate is not variable over time. Here we test this assumption by exploring if climate sensitivity of Picea mariana (Mill.) trees growing in open-stand lowland forest and on top of a neighboring peatland in Interior Alaska is stable or changing over time. Climate–growth correlations at the study sites are strongly dependent on microtopography and vary substantially over time. Trees growing in the open forest site generally display stronger climate–growth correlations, especially significantly negative correlations with late summer temperatures (July, August) starting in the period 1920–1970. Trees growing on the peatland site are less climate sensitive, but display positive correlations between annual growth and temperature of October and December in the early 20th century, while in the late 20th century, significant negative correlations exist with January and February temperatures. This study, thus, demonstrates a transient climate–growth response for P. mariana (Mill.) on two sites typical for lowland Interior Alaska. However, due to multiple possible explanations (e.g. changing climate, coupled with aging trees and a growing peatland surface) it is not possible at this time to pinpoint the exact cause for these changes in the climate–growth relationships.

Fish Community Responses to Half‐Log Additions in Warmwater Streams

AbstractHalf‐log habitat enhancement structures are commonly used for stream restoration projects to increase fish abundance and biomass. Half logs (N = 108) were added to nine headwater streams of the upper Wabash River basin, Indiana, in July 2003. Study sites (25 m in length) were sampled with backpack electrofishing once each month during July–October 2003 and April–September 2004 to document the colonization and use of half logs by fish under agriculture, forest, and fallow‐field land uses. Index of biotic integrity (IBI) scores did not change significantly after half‐log additions. The effects of half‐log habitat enhancement structures were variable by month, stream, and in some cases, individual fish species. Species richness and biomass significantly increased in two study streams during spring and fall due to the presence of bluntnose minnow Pimephales notatus and longear sunfish Lepomis megalotis. Absolute abundance within most sites increased during periods of low flow and high temperature in late summer and early fall, when fish are most vulnerable to predation and require habitat refugia. Fish use of half logs was also dictated by the amount of instream habitat, especially where percentages of aquatic vegetation (mean = 0.0%) and large woody debris (mean = 0.67%) were low and the percentage of pool habitat was moderate (mean = 10.53%). In this study, we found that with the exception of IBI scores, significant manipulation response was variable by stream and species and was influenced by instream habitat and time of year.

Influences of climate on the radial growth of lodgepole pine in Alberta

We examined a network of 17 lodgepole pine ( Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) sites in Alberta in the cordilleran forests along the eastern slopes of the Rocky Mountains and in western Cypress Hills, using a dendrochronological approach to identify the principal climatic factors that have influenced the historical, regional-scale pattern of radial growth of lodgepole pine. Correlation and regression analysis of the regional growth–climate relationships showed that radial growth was negatively associated with late-summer temperatures, and positively related to the late-summer precipitation totals from the previous growth season. Radial growth also responded positively to winter and spring temperatures, and was negatively related to late winter–early spring precipitation. The results suggested that the lag in response to heat and moisture stress, cold and snowy winters, and the length of the current growing season are important determinants of the radial growth of lodgepole pine in Alberta.

Ticks biting humans in the urban area of Istanbul

A passive surveillance for tick bites in humans was undertaken in the city of Istanbul (Turkey) in the summer and autumn of 2006. From 1,054 reported tick bites, most were females of Ixodes ricinus (27%) and nymphs of Hyalomma aegyptium (50%). A few adults of Hyalomma m. marginatum, Rhipicephalus sanguineus and Dermacentor marginatus were also recorded. We investigated potential risk factors for I. ricinus and H. aegyptium with spatial statistics. Climate features at 1-km resolution (monthly minimum temperatures in late summer and autumn and rainfall) and vegetation features at high resolution (density and heterogeneity of forest-type vegetation as well as distance of reporting site to these vegetation features) are useful variables explaining high reporting clusters for both Ixodes and Hyalomma. While Ixodes is highly reported in dense highly heterogeneous vegetation patches, Hyalomma is commonly found in areas far from forest-type features and in the small, relatively dry vegetation patches within the urban fabric.

Predicting range expansion of the map butterfly in Northern Europe using bioclimatic models

The two main goals of this study are: (i) to examine the range shifts of a currently northwards expanding species, the map butterfly (Araschnia levana), in relation to annual variation in weather, and (ii) to test the capability of a bioclimatic envelope model, based on broad-scale European distribution data, to predict recent distributional changes (2000–2004) of the species in Finland. A significant relationship between annual maximum dispersal distance of the species and late summer temperature was detected. This suggests that the map butterfly has dispersed more actively in warmer rather than cooler summers, the most notable dispersal events being promoted by periods of exceptionally warm weather and southerly winds. The accuracy of the broad-scale bioclimatic model built for the species with European data using Generalized Additive Models (GAM) was good based on split-sample evaluation for a single period. However, the model’s performance was poor when applied to predict range shifts in Finland. Among the many potential explanations for the poor success of the transferred bioclimatic model, is the fact that bioclimatic envelope models do not generally account for species dispersal. This and other uncertainties support the view that bioclimatic models should be applied with caution when they are used to project future range shifts of species.

Pattern and determinants of hospitalization during heat waves: an ecologic study

BackgroundNumerous studies have investigated mortality during a heatwave, while few have quantified heat associated morbidity. Our aim was to investigate the relationship between hospital admissions and intensity, duration and timing of heatwave across the summer months.MethodsThe study area (Veneto Region, Italy) holds 4577408 inhabitants (on January 1st, 2003), and is subdivided in seven provinces with 60 hospitals and about 20000 beds for acute care. Five consecutive heatwaves (three or more consecutive days with Humidex above 40°C) occurred during summer 2002 and 2003 in the region. From the regional computerized archive of hospital discharge records, we extracted the daily count of hospital admissions for people aged ≥75, from June 1 through August 31 in 2002 and 2003. Among people aged over 74 years, daily hospital admissions for disorders of fluid and electrolyte balance, acute renal failure, and heat stroke (grouped in a single nosologic entity, heat diseases, HD), respiratory diseases (RD), circulatory diseases (CD), and a reference category chosen a priori (fractures of the femur, FF) were independently analyzed by Generalized Estimating Equations.ResultsHeatwave duration, not intensity, increased the risk of hospital admissions for HD and RD by, respectively, 16% (p < .0001) and 5% (p < .0001) with each additional day of heatwave duration. At least four consecutive hot humid days were required to observe a major increase in hospital admissions, the excesses being more than twofold for HD (p < .0001) and about 50% for RD (p < .0001). Hospital admissions for HD peaked equally at the first heatwave (early June) and last heatwave (August) in 2004 as did RD. No correlation was found for FF or CD admissions.ConclusionThe first four days of an heatwave had only minor effects, thus supporting heat health systems where alerts are based on duration of hot humid days. Although the finding is based on a single late summer heatwave, adaptations to extreme temperature in late summer seem to be unlikely.

Changes in biological production in the mixed water region (MWR) of the northwestern North Pacific during the last 27 kyr

Piston core PC6 (40°N, 143°E) provides the first record of biological production and alkenone sea surface temperature (SST) in the mixed water region (MWR) off Sanriku, Japan, in the northwestern North Pacific over the last 27 kyr. Biogenic opal content was low until the early Holocene, and rapidly increased at 6 calendar kiloyears before present (cal kyr BP). Low biological production in the MWR resulted from the reduced duration of the phytoplankton bloom during the glacial period (27–18 cal kyr BP), and from nutrient depletion, especially silica, during the deglaciation (15–9.5 cal kyr BP). In spite of the decreased amount of nutrients in the Oyashio water, biological production increased in the late Holocene (6 cal kyr BP–present). The data revealed that nutrients supplied from deeper levels by eddies played an important role in biological production in the MWR, contrary to the conventional concept that the Oyashio current has controlled productivity in this region. Alkenone-SST during the glacial period was on average 13.6 °C, which is close to the modern SST (14.6 °C) in June, but this timing is not consistent with the CLIMAP results (13.4–14.3 °C in August). This result indicates that alkenone-SST recorded not late spring but summer temperatures, owing to a bloom shift caused by surface water cooling during the last glacial period. Alkenone-SST was even lower during the deglaciation than during the LGM and reached a minimum (9.4 °C) at 14.0 cal kyr BP. δ 15N was very high during the deglaciation, implying that nutrients in the euphotic zone were depleted around the core site. Nutrient stress probably had a physiological impact on coccolithophorids and resulted in the apparent minimum alkenone-SST. These findings indicate that the reconstruction of SST by alkenones can sometimes be very complex and possibly misleading.

Response of Pinus uncinata Recruitment to Climate Warming and Changes in Grazing Pressure in an Isolated Population of the Iberian System (NE Spain)

ABSTRACTTo infer future changes in the distribution of tree species in response to climatic variability, we need an understanding of the recruitment dynamics and their climatic controls at the species’ distribution limit. We studied the recruitment processes in an isolated population of Pinus uncinata Ram. located at the southwestern limit of the species’ distribution in Europe (Iberian System, NE Spain). We assessed (1) the temporal patterns of pine recruitment, and (2) how climate influenced recruitment. To reconstruct the recent recruitment episodes and to assess the climatic influence on recruitment and radial growth we employed dendrochronological methods. We mapped, measured the size, and estimated the age of all P. uncinata individuals located within a 50 m × 40 m plot. Additional age data were obtained from individuals located in four nearby 20 m × 20 m plots. The main episodes of tree establishment (early 1960s, late 1980s) coincided with low radial growth during a period with reduced grazing pressure. Grazing pressure and tree recruitment were not related at the spatiotemporal scale of this study. High May, August, and September minimum temperatures and high April precipitation were positively associated with recruitment, whereas high maximum April and June temperatures were negatively associated with recruitment. The studied population was in equilibrium with climate until the late 1990s, one of the warmest decades in the 20th century, when recruitment decreased despite the availability of suitable sites for establishment and the presence of reproductive individuals. We suggest that late-summer temperatures might have a non-linear negative threshold effect on recruitment rather than a linear effect. Despite increasing evidence of climate-induced recruitment episodes in isolated cold mountain forests, threshold effects of temperature on recruitment may imply limited range shifts of these populations in response to climate warming.

Exorcising the `segment length curse': summer temperature reconstruction since AD 1640 using non-detrended stable carbon isotope ratios from pine trees in northern Finland

Stable carbon isotope ratios from the latewood cellulose of 12 trees from two sites in northern Finland are used to construct an isotope chronology covering AD 1640 to 2002. By measuring isotopic ratios of every sample independently it is possible to identify and remove the juvenile portion of each δ 13C series, correct the individual series for anthropogenic changes in atmospheric carbon dioxide isotopic ratios and concentrations, and to quantify changes in signal strength through time. Most importantly, it is possible to demonstrate that there are no long-term trends in the carbon isotope series that are related to tree age. This means that it is not necessary to detrend the series and so they have the potential to retain climate information at all temporal frequencies. The correlation between the non-detrended carbon isotope series and July/August mean temperature is high ( r=0.72) and comparison with meteorological records suggests that the dominant control over tree ring δ13C at these high latitude, moist sites is photosynthetic rate rather than stomatal conductance. Summer temperature reconstructions based on three different calibrations are presented, with verification based on a mixture of jacknife and split period designs, providing robust and near identical results. Reconstructed late summer temperatures in the early 1900s are very low but the years centred around AD 1660 and 1760 appear to have experienced warmer summers than the late twentieth century, thus our late summer reconstruction does not show a recent warming trend. Our results are in agreement with other palaeoclimate reconstructions for northern Fennoscandia, which show late twentieth-century warming occurring predominantly in the winter. Our results suggest that, where replication and common signal strength are sufficiently high, stable carbon isotope dendroclimatology may provide high resolution proxy time series that also record climate information at lower temporal frequencies, thus avoiding the `segment length curse' that can apply to palaeoclimate reconstructions based on other tree ring parameters such as ring widths and density.

Temperature climatology and trend estimates in the UTLS region as observed over a southern subtropical site, Durban, South Africa

Abstract. Temperature trends in the UTLS region are under-reported, particularly in the Southern Hemisphere, and yet temperature is one of the most important indicators of changes in dynamical and radiative processes in the atmosphere. Here radiosonde data from Durban, South Africa (30.0° S, 30.9° E) over the period 1980 to 2001 (22 years) between 250 and 20 hPa are used to derive a mean temperature climatology and to determine trends. The seasonal cycle at the 250-hPa level is anti-correlated with the seasonal cycles at the 150-hPa and 100-hPa heights. The 100-hPa level (local tropopause) exhibits a minimum temperature in late summer and a maximum in winter, and closely corresponds to previous results for tropical regions. Based on a Fourier analysis, both the annual cycle (AO) and the semi-annual cycle (SAO) are dominant, although the former is about 4 times stronger. The AO is strongest at the 100-hPa height. A trend analysis reveals a cooling trend at almost all heights in the UTLS region, with a maximum cooling rate of 1.09±0.41 K per decade, at 70-hPa. Cooling rates are in good agreement with other studies and are slightly higher in summer than in winter.

Long-term changes in summer phytoplankton communities of the open northern Baltic Sea

Changes in the biomass and species composition of phytoplankton may reflect major shifts in environmental conditions. We investigated relationships between the late summer biomass of different phytoplankton taxa and environmental factors, and their long-term (1979–2003) trends in two areas of the Baltic Sea, the northern Baltic proper (NBP) and the Gulf of Finland (GF), with statistical analyses. An increasing trend was found in late summer temperature and chlorophyll a of the surface water layer (0–10 m) in both areas. There was also a significant decrease in summer salinity and an increase in winter dissolved inorganic nitrogen to phosphorus (DIN:DIP) ratio in the NBP, as well as increases in winter DIN concentrations and DIN:SiO 4 ratio in the GF. Simultaneously, the biomass of chrysophytes and chlorophytes increased in both areas. In the NBP, also the biomass of dinophytes increased and that of euglenophytes decreased, whereas in the GF, cyanobacteria increased and cryptophytes decreased. Redundancy analysis (RDA) indicated that summer temperature and winter DIN concentration were the most important factors with respect to changes in the phytoplankton community structure. Thus, the phytoplankton communities seem to reflect both hydrographic changes and the ongoing eutrophication process in the northern Baltic Sea.

Climate Variables and Their Role in Site Discrimination of Invasive Insect Species Distributions

This study investigated the influence of climate variables on insect establishment patterns by using discriminant analysis to classify the climatic preferences of two groups of polyphagous insect species that are intercepted at New Zealand’s border. One group of species is established in New Zealand, and the other group is comprised of species that are not established. The discriminant analysis classified the presence and absence of most species significantly better than chance. Late spring and early summer temperatures correctly classified a high proportion of sites containing the presence of both established and nonestablished species. Soil moisture and winter rainfall were less effective discriminating the presence of most of the species studied here. Cold winter air temperature was also a good classifier for the insect species that are not established in New Zealand. This study showed that multivariate statistical techniques such as discriminant analysis can help distinguish the climatic limits of insect distributions over large geographical scales.

Climate change may account for the decline in British ring ouzels Turdus torquatus

1. Climate change is already affecting biodiversity, but the number of species for which reliable models relate weather and climate to demographic parameters is low. 2. We modelled the effect of temperature and rainfall on the breeding success and territory occupancy of ring ouzels Turdus torquatus (L.) in northern Britain, using data from a range of study areas, including one where there was a long-term decline in ring ouzel abundance. 3. Timing of breeding was significantly related to meteorological variables affecting birds in the early spring, though there was no evidence that laying dates had advanced. Breeding success was not significantly related to weather variables; instead, over 90% of annual variation in this parameter could be explained by density dependence. 4. Annual change in territory occupancy was linked to rainfall and temperature the preceding summer, after the main breeding season and to rainfall in the wintering grounds 24 months previously, coincident with the period of juniper Juniperus sp. (L.) flowering. High temperature in late summer, intermediate levels of late summer rainfall, and high spring rainfall in Morocco 24 months previously all had negative impacts on territory occupancy the following year. 5. All three weather variables have changed over recent decades, with a significant increase in summer temperature, a significant decrease in summer rainfall, and a nonsignificant decline in Moroccan spring rainfall. A model based on these trends alone predicted an annual decline in occupancy of 3.6% (compared with an observed decline of 1.2%), and suggested that increased summer temperatures may underlie declines in the British ring ouzel population. 6. Changes in summer temperature after the main breeding period could affect the survival rates of adult and/or juvenile birds. An improved understanding of the post-breeding ecology of ring ouzels is required to elucidate the mechanisms and causes of this relationship. Such knowledge might allow management aimed at buffering the impacts of climate change on ring ouzels.

Estimating the timing of growth rings in Atlantic cod otoliths using stable oxygen isotopes

A technique involving micro‐scale sampling of otolith carbonate and analyses of stable oxygen isotope composition was used to relate the zone appearance of the otolith to the seasonal temperature cycle. Otolith opacity could then be related to the timing of zone formation. Otoliths from two groups of Atlantic cod Gadus morhua held under known temperature conditions over a period of 4 and 6 years were examined. The otolith translucency followed the same pattern as the estimated temperature (from otolith δ18O values) in the yearly increments three and four, meaning that the translucent zones were deposited at the seasonal highest temperature in late summer and early autumn. The relative light intensities of otolith yearly increments five and six of older fish (deposited in the same years), however, were not significantly correlated to the estimated temperatures since increased otolith translucency also occurred at low temperatures. This might have been caused by stress in connection with gonad development or starvation during the spawning period. The results showed that this method of coupling otolith opacity and stable oxygen isotope composition can be used to estimate the timing of zone formations in otoliths.