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While life-history theory predicts a tradeoff between reproduction and survival, positive covariance, indicative of heterogeneity in individual quality, is often reported among individuals from natural populations. We review longitudinal studies of wild bird populations that test the relationship between annual reproductive success and lifespan and find the majority to report a positive correlation, while none reports a negative correlation. Heterogeneity in individual quality in resource acquisition, masking resource-based tradeoffs, therefore appears to be common in birds. Considering that there is little evidence for heritable variation in fitness, heterogeneity in individual quality among adults may be due to life-long effects of developmental conditions. In a 20-year case study on common terns Sterna hirundo, we test for life-long effects of cohort quality and within-cohort nest quality, but find no significant effects on long-term proxies of quality. Since other studies do find strong life-long effects of developmental conditions, we suggest that the brood reduction strategy adopted by common terns, causing the majority of offspring to die rapidly after hatching, efficiently reduces variation in offspring quality at independence. As such, a brood reduction strategy may contribute to reduced heterogeneity in adult survival in stochastic environments, both suggested to be more common and adaptive in long-lived species. Further study is required to assess heterogeneity in individual reproduction, especially in relation to environmental stochasticity and species' life-history strategies, in order to assess whether the relative strength of selection in early and late life may indeed affect the magnitude of heterogeneity in individual quality over life, and how this is mediated by parent-offspring conflict.

Although functional explanations for female engagement in extra-pair copulation have been studied extensively in birds, little is known about how extra-pair paternity is linked to other fundamental aspects of avian reproduction. However, recent studies indicate that the occurrence of extra-pair offspring may generally decline with laying order, possibly because stimulation by eggs induces incubation, which may suppress female motivation to acquire extra-pair paternity. Here we tested whether experimental inhibition of incubation during the laying phase, induced by the temporary removal of eggs, resulted in increased extra-pair paternity, in concert with a later cessation of laying, in blue tits (Cyanistes caeruleus). As expected, experimental females showed a more gradual increase in nocturnal incubation duration over the laying phase and produced larger clutches than controls. Moreover, incubation duration on the night after the first egg was laid predicted how extra-pair paternity declined with laying order, with less incubation being associated with more extra-pair offspring among the earliest eggs in the clutch. However, incubation duration on this first night was unrelated to our experimental treatment and independent of final clutch size. Consequently, the observed decline in extra-pair paternity with laying order was unaffected by our manipulation and larger clutches included proportionally fewer extra-pair offspring. We suggest that female physiological state prior to laying, associated with incubation at the onset of laying, determines motivation to acquire extra-pair paternity independent of final clutch size. This decline in proportion of extra-pair offspring with clutch size may be a general pattern within bird species.

The current development of tourism is environmentally unsustainable. Specifically, tourism's contribution to climate change is increasing while other sectors are reducing their greenhouse gas emissions. This paper has two goals: reveal the main structural cause for tourism's emission growth and show the consequences thereof for (mitigation) policies. It is reasoned that the main cause for tourism's strong emission growth is the time-space expansion of global tourism behavior. Contemporary tourism theory and geography fail to clearly describe this geographical development, making it difficult to understand this expansion and develop effective policies to mitigate environmental impacts. Therefore, this paper explores some elements of a 'new tourism geography' and shows how this may help to better understand the causes of the environmentally unsustainable development of tourism with respect to climate change and devise mitigation policies.

1. Climate change has caused a phenological mismatch between the timing of reproduction and the local food peak in many bird species. Late breeding birds therefore experience reduced food availability during chick rearing and are thus predicted to have an increased energy expenditure. Observational studies, however, show mixed results, perhaps because they compare energy expenditure across rather than within individuals at different levels of food availability.2. In a cross foster experiment, we measured daily energy expenditure (DEE) twice within individuals during chick feeding (when chicks were 6 and 14 days old) for 28 free-living female great tits (Parus major). To avoid confounding effects of chick age, these females reared on both occasions a standardized foster brood of eight 10-day-old chicks during the 24-h measuring period. For all birds, food availability declined between the two measurements.3. We show that DEE during chick feeding increased within females when food availability decreased. Variation in DEE within females is partly explained by brood visit rates, food availability and temperature.4. DEE during chick feeding could be affected by the investment in previous stages of the reproductive attempt. However, energy expenditure during chick feeding was not correlated to energy expenditure during egg laying, measured in these same females.5. Understanding of energetic costs during all phases of the reproductive cycle is important to forecast the consequences of climate warming on timing of reproduction.

Life-history theory suggests that the variation in the seasonal timing of reproduction within populations may be explained on the basis of individual optimization. Optimal breeding times would vary between individuals as a result of trade-offs between fitness components. The existence of such trade-offs has seldom been tested empirically. We experimentally investigated the consequences of altered timing of current reproduction for future reproductive output in the European coot (Fulica atra). First clutches of different laying date were cross-fostered between nests, and parents thereby experienced a delay or an advance in the hatching date. The probability and success of a second brood. adult survival until and reproduction in the next season were then compared to the natural variation among control pairs. Among control pairs the probability of a second brood declined with the progress of season. Delayed pairs were less likely and advanced pairs were more likely to produce a second brood. These changes were quantitatively as predicted from the natural seasonal decline. The number of eggs in the second clutch was positively related to egg number in the first clutch and negatively related to laying date. Compared to the natural variation, delayed females had more and advanced females had fewer eggs in their second clutch. The size of the second brood declined with the progress of season, but there was no significant effect of delay or advance. Local adult survival was higher following a delay and reduced following an advance. The effect of the experiment on adult survival was independent of sex. Laying date and clutch size of females breeding in the next year were not affected by treatment. The study demonstrates the existence of a trade-off between increased probability of a second brood and decreased parental survival for early breeding. Timing-dependent effects of current reproduction on future reproductive output may thus play an important role in the evolution of the seasonal timing of reproduction. [KEYWORDS: adult survival, Fulica atra, future reproduction, life-history evolution, multiple breeding, timing of reproduction]

1. To elucidate the links between avian brood size, parental effort and parental investment, we measured daily energy expenditure (DEEfem), condition (residuals of mass on tarsus) and feeding rate in female great tits Parus major L. rearing broods in which the number of young was either reduced, unmanipulated or enlarged. 2. Female condition was negatively correlated with manipulation when measured at the nestling age of 8 days (measured during the day), which suggests a shift in allocation from self-feeding to chick-feeding. However, there was no detectable manipulation effect on condition measured at the nestling age of 12 days (measured during the night). Either female condition was only affected by manipulation in the early nestling phase or the females adjusted their diurnal mass trajectory in response to brood size manipulation. More detailed data are required to verify this point. There were no indications of a fitness cost associated with the condition during the day, but condition at night was positively related to winter survival. Since manipulation only affected condition during the day, there was no link between manipulation and winter survival. 3. The duration of the working day was not affected by manipulation and female feeding rate tended to flatten off with manipulated brood size. Similarly, brood reduction resulted in a lower DEEfem, whilst brood enlargement had no effect. This suggests that females worked at an energetic ceiling when rearing an unmanipulated brood. However, the level of this 'ceiling' in DEEfem was not fixed: it differed between years. This leads us to conclude that the observed ceiling was imposed by extrinsic factors (e.g. available foraging time) and not by an intrinsic factor such as maximum energy assimilation rate. We hypothesize that time limitation was the cause for the observed ceiling in energy expenditure and that the annual variation in the level of this ceiling was due to annual variation in ambient temperature. 4. A cost of reproduction was previously demonstrated in this population: brood enlargement caused a reduction in the incidence of second clutches. However, since DEEfem did not differ between control and enlarged broods, we judge it unlikely that daily energy expenditure is a general predictor for parental investment. [KEYWORDS: clutch size; condition; energy expenditure; cost of reproduction; parental effort; Parus major L. Starlings sturnus-vulgaris; kestrel falco-tinnunculus; parus-major; brood size; clutch size; blue tits; food availability; feeding frequency; field metabolism; trade-offs]

During egg-formation, energy and protein are deposited in the developing eggs but are, at the same time, needed by the laying female herself. This has been largely overlooked in the discussion on income and capital breeders (Drent & Daan 1980, Thomas 1988). We discuss data on exogenous versus endogenous energy and nutrients used during egg-formation for 12 well-studied species ranging from the Adelie Penguin Pygoscelis adelie (3400 g) to the Blue Tit Parus caeruleus (11 g) and calculate which part of the total energy and nutrient requirements (of clutch and laying female) originates from direct food intake and/or from body reserves. Because energy and nutrients are also needed by the laying female, some large species breeding in cold regions deposit sufficient reserve that they can fast completely during egg-formation (like the Adelie Penguin) and even throughout incubation (like the Elder Somateria mollissima). However, almost all smaller species must forage for most of their energy and nutrients during the egg-formation period. For the large species, energy and protein of the clutch represent 30% and 70%, respectively, of the total requirements of laying females, much more than in small species like passerines (4% and 40%). Therefore, the requirements for the clutch are much greater in larger than in smaller species, and egg-production is much more limited by protein than by energy. The effects of food supplementation on timing of laying (moderate advance), on number of eggs laid (not more, when corrected for date) and on egg size (not larger) of income and capital breeders/layers are discussed. It seems that neither the start of egg-laying nor the number or quality of eggs are directly related to the energetics of the laying female.

In experiments in which brood size is manipulated, it is impossible to disentangle the effects of changes in intensity and duration of parental care on parental fitness from those of changes in the parental energy budget. To determine whether a change in parental energy budget affects the costs of reproduction, we assessed the effects of increased levels of hopping activity, independent of parental care, on later reproductive decisions in zebra finches, Taeniopygia guttata. We imposed two levels of workload on individual, nonbreeding birds. After the workload periods, the birds were allowed to breed in ad libitum conditions. Each bird went through three alternating periods of working followed by breeding. The birds were more active, but weighed less and ate less, during the high workload than during the low workload periods. Clutch sizes and brood sizes did not vary with the previous work level. However, after a period on the high workload, reproduction, on average, was started 6 days later than after a low workload period. Females gained weight just before egg laying, but this might have been;a result of egg production. If so, the delay in reproduction did not simply reflect extra time needed to restore body mass after a period of increased activity. We conclude that the level of daily activity itself, or the resulting energy budget during the workload periods, delayed reproduction. We suggest that these observations on the effects of increased activity demonstrate a causal mechanism for reduced residual fitness of parents. (C) 1999 The Association for the Study of Animal Behaviour.

During egg-formation, energy and protein are deposited in the developing eggs but are, at the same time, needed by the laying female herself. This has been largely overlooked in the discussion on income and capital breeders (Drent & Daan 1980, Thomas 1988). We discuss data on exogenous versus endogenous energy and nutrients used during egg-formation for 12 well-studied species ranging from the Adelie Penguin Pygoscelis adelie (3400 g) to the Blue Tit Parus caeruleus (11 g) and calculate which part of the total energy and nutrient requirements (of clutch and laying female) originates from direct food intake and/or from body reserves. Because energy and nutrients are also needed by the laying female, some large species breeding in cold regions deposit sufficient reserve that they can fast completely during egg-formation (like the Adelie Penguin) and even throughout incubation (like the Elder Somateria mollissima). However, almost all smaller species must forage for most of their energy and nutrients during the egg-formation period. For the large species, energy and protein of the clutch represent 30% and 70%, respectively, of the total requirements of laying females, much more than in small species like passerines (4% and 40%). Therefore, the requirements for the clutch are much greater in larger than in smaller species, and egg-production is much more limited by protein than by energy. The effects of food supplementation on timing of laying (moderate advance), on number of eggs laid (not more, when corrected for date) and on egg size (not larger) of income and capital breeders/layers are discussed. It seems that neither the start of egg-laying nor the number or quality of eggs are directly related to the energetics of the laying female.

To study zebra finch allocation of energy to day and night at two different workloads, we assessed the daily energy turnover from: (1) metabolizable energy of the food, and (2) doubly-labeled water. In both experiments we imposed two levels of activity on captive zebra finches (Taeniopygia guttata), by applying different computer-controlled workload schedules. A low workload required 20 hops, and a high workload 40 hops to obtain 10 s access to food. In experiment 1, we further measured nocturnal energy expenditure by overnight oxygen consumption. From experiment 2 we derived an estimate of the costs of hopping activity, from inter-individual association of daily amount of hopping and daily energy expenditure. Surprisingly, the daily energy budget was, on average, reduced slightly when birds were subjected to a high workload. Since hopping activity was 50% higher during the high workload than during the low workload, the birds apparently compensated, even over-compensated, for the increased energetic demands of activity. Nocturnal energy expenditure was indeed reduced for the high workload, which was largely due to a reduction in resting metabolic rate. Economizing on energy was more than could have been accomplished by a reduction in mass alone, and we discuss the occurrence and potential mechanisms of physiological compensation. The amount of energy saved during the night did account for part of the total amount of energy saved. We surmise that the strategy of energetic compensation observed during the night was extended into the inactive hours of the day.

We present data on the natural variation in daily energy expenditure (DEE, measured by the doubly labelled water technique) of individual female Great Tits Parus major tending their brood near the northern border of the species' distribution. We expected that longer foraging days would result in a higher energy expenditure. Female DEE, visitation rate and the duration of the active period were measured at the nestling age of 12 days. There was a positive relationship between the duration of activity period and brood size. Female DEF was positively associated with the duration of the activity period and the number of young in the nest. Energy expenditure was not related to temperature or feeding rates. Despite the longer foraging day and lower ambient temperatures, female DEE did not differ from the values obtained in central Europe. This result suggests that there are differences in foraging cost and/or mode with latitude.

1. Little is known about long-term effects of brood size on fitness components of offspring. This is unfortunate because such information is needed to predict optimal brood size. Furthermore, ontogenetic circumstances are potentially important in explaining the large individual differences in lifetime reproductive success documented in many species.2. In a laboratory study the long-term effect of brood size manipulation on mortality and morphological development of offspring was investigated. Young zebra finches Taeniopygia guttata were reared in small or large broods. Young were exchanged in such a way that natural siblings from different rearing conditions could be compared.3. Manipulated brood size affected offspring morphology permanently (measurements were taken up to the age of 12 months). Individuals reared in small broods were heavier, had longer tarsi and wings, higher beaks, were in better condition, and males had redder beaks. The experiment did not affect beak length or female beak redness. Individuals from large broods had caught up on wing length and males from large broods on beak redness by 6 months of age, which may reflect priority of investment in traits important to fitness.4. Mortality of offspring raised in large broods was higher both before and after independence. After independence the effect of manipulated brood size on mortality was sex specific; females were most likely to die. This suggests that the optimal sex ratio of offspring may depend on brood size.5. The effect of brood size on mortality after independence was probably partly mediated by size and condition during the nestling phase and possibly by peer aggression among adult offspring. Sex-linked mortality could not be explained by a sex difference in morphological development. Why females are more vulnerable remains to be discovered.

We experimentally reduced clutch size of Great Tits Parus major to investigate the effects on parental care (including Daily Energy Expenditure, DEE, measured with doubly labelled water), and the relationship between DEE and the residual reproductive Value. The length of a working day was not affected, but the nestling phase was 0.7 days (4%) shorter in experimental clutches. Males fed reduced broods at a lower rate, but DEE and mass (loss) were not significantly affected by the experiment. However, male DEE was positively correlated with feeding frequency, and this relationship did not differ between control and experimental males. This suggests that the experiment resulted in a slight reduction in male DEE, and lack of statistical significance can be attributed to the power of the test applied. Females fed reduced broods at a lower rate, but female DEE and mass (loss) were not affected by the clutch size manipulation. Female DEE was not correlated with feeding frequency, the original number of eggs in the nest or the actual number of young. The division of labour (feeding rate, DEE) was not affected by the clutch size manipulation. Female DEE was significantly higher than male DEE, and this could be caused by the fact that only the female roosts with the young. There was no consistent relationship between DEE and parental survival or future reproductive success. Since the experimental reduction in clutch size led to an increase in residual reproductive Value (more second clutches), but not to a decrease in DEE, this costs of reproduction is apparently not contingent on increased rate of energy turnover. It is suggested that birds with equal DEE may differ in their residual reproductive value as a consequence of variation in energy allocation between reproductive effort and e.g. aspects of physiological maintenance and repair.

We studied temporal variation in reproductive performance of Marsh Harriers Circus aeruginosus in two land reclamations in The Netherlands, i.e. South Flevoland and the Lauwersmeerpolder, embanked in 1968 and 1969 respectively. The number of breeding pairs in Flevoland rapidly increased to a maximum of 350 pairs (± 1 pair km-2) in 1977, followed by a sharp decline in the 1980s due to large-scale cultivation. The same trend was observed in the Lauwersmeer, although colonization was retarded and peak densities were reached later. In both study areas mean clutch size as well as the number of fledglings per nest decreased in the course of the twenty years of study. Two factors were responsible for this decline in reproductive output: (1) decrease of food abundance in the course of the years, and (2) an increase of nest predation, mainly by the Red Fox Vulpes vulpes. Superimposed on these long-term changes, annual fluctuations in density of the Common Vole Microtus arvalis had a considerable effect on the number of breeding pairs, as well as the fledgling production. Mean annual clutch size was associated positively, and laying date negatively, with the average annual temperature during the pre-laying phase. Our results indicate that the early stages of succession, during the first decade after reclamation, are characterized by high prey abundance (i.e. vole 'plagues') and low densities of ground predators, and offer favorable breeding conditions for Marsh Harriers. The simultaneous negative effects in recent years of less breeding habitat, decreased prey abundance and increased predation on reproductive output, exert pressure on these populations. The intense nest predation (50% of all nests), as recorded in the Lauwersmeer since 1990, may eventually cause local extinction in the absence of, relatively safe, inundated breeding habitat.

The effect of territory quality on the time and energy allocation of Oystercatchers was investigated on the island of Schiernonnikoog in the Dutch part of the Wadden Sea. Low quality leapfrog territories required a higher level of parental effort for successful reproduction than high quality resident territories. The time budgets of residents and leapfrogs differed slightly, the main difference occurring during the chick-rearing stage when leapfrogs spent on average 8.2% of the time available during low water in flight in order to transport food to the chicks, compared to only 2.9% in residents. In both residents and leapfrogs, inactivity (including preening) constituted a considerable part of the time budget, comprising almost 50% of the low water period during the pre-laying stage and decreasing to 23% during the incubation stage when each bird spent almost hat: the time on the clutch. Analysis of individual time budgets during the incubation stage revealed that time spent inactive must be considered 'surplus time' since this can be reallocated to foraging when the proportion of time devoted to incubation increased. Obligatory inactivity required less than 10% of the rime available during low water. The persistence of 'surplus' time during the chick-rearing stage suggests that parental effort is not constrained by a shortage of time. Energy expenditure, estimated from time-budgets, agreed well with energy consumption, calculated from observed food intake, and with measurements using doubly labelled water. It varied from 2.1 x BMR during the incubation stage to 2.7 x BMR during the chick-rearing stage. These values are much lower than the maximum energy expenditure reported for many other bird species during the reproductive cycle. During the chick-rearing stage, daily energy expenditure of leapfrogs was 6-7% higher than that of residents due to the additional costs involved in the transportation of food. Despite the fact that the reduced reproductive success of leapfrogs, as compared to that of residents, is mainly caused by the failure of the parents to provision their chicks with a sufficient amount of food, leapfrogs did not increase their parental effort to a considerable extent. This would fit the interpretation that long-living species like the Oystercatchers are reluctant to work very hard during one reproductive cycle.

Knots Calidris canutus live highly seasonal lives, breeding solitarily on high arctic tundra and spending the non-breeding season in large social flocks in temperate to tropical estuaries. Their reproductive activities and physiological preparations for long flights are reflected in pronounced plumage and body mass changes, even in long-term captives of the islandica subspecies (breeding in north Greenland and northeast Canada and wintering in western Europe) studied in outdoor aviaries. The three to four fattening episodes in April-July in connection with the flights to and from the high arctic breeding grounds by free-living birds, are represented by a single period of high body mass, peaking between late May and early July in a sample of ten captive islandica knots studied over four years. There are consistent and synchronized annual variations in basal metabolic rate and thermal conductance in three istandica knots. Basal metabolic rate was highest during the summer body mass peak. Within the examined individuals, basal metabolic rate scales on body mass with an exponent of about 1.4, probably reflecting a general hypertrophy of metabolically expensive muscles and organs. Any potential effect of moult on basal metabolic rate was obscured by the large seasonal mass-associated variations. In breeding plumage, insulation (the inverse of thermal conductance) was a factor of 1.35 lower than in winter plumage. This was paralleled by the dry mass of contour feathers being a factor of 1.17 lower. In this subspecies the breeding season is indeed the period during which the costs of thermoregulation are lowest. In captive knots seasonal changes in basal metabolic rate and thermal conductance likely reflect an anticipatory programme adaptive to the variable demands made by the environment at different times of the year.

Knots Calidris canutus live highly seasonal lives, breeding solitarily on high arctic tundra and spending the non-breeding season in large social flocks in temperate to tropical estuaries. Their reproductive activities and physiological preparations for long flights are reflected in pronounced plumage and body mass changes, even in long-term captives of the islandica subspecies (breeding in north Greenland and northeast Canada and wintering in western Europe) studied in outdoor aviaries. The three to four fattening episodes in April-July in connection with the flights to and from the high arctic breeding grounds by free-living birds, are represented by a single period of high body mass, peaking between late May and early July in a sample of ten captive islandica knots studied over four years. There are consistent and synchronized annual variations in basal metabolic rate and thermal conductance in three istandica knots. Basal metabolic rate was highest during the summer body mass peak. Within the examined individuals, basal metabolic rate scales on body mass with an exponent of about 1.4, probably reflecting a general hypertrophy of metabolically expensive muscles and organs. Any potential effect of moult on basal metabolic rate was obscured by the large seasonal mass-associated variations. In breeding plumage, insulation (the inverse of thermal conductance) was a factor of 1.35 lower than in winter plumage. This was paralleled by the dry mass of contour feathers being a factor of 1.17 lower. In this subspecies the breeding season is indeed the period during which the costs of thermoregulation are lowest. In captive knots seasonal changes in basal metabolic rate and thermal conductance likely reflect an anticipatory programme adaptive to the variable demands made by the environment at different times of the year.

Two alternative particle image velocimetry (PIV) methods have been developed, applying laser light sheet illumination of particle-seeded flows around marine organisms, Successive video images, recorded perpendicular to a light sheet parallel to the main stream, were digitized and processed to map the how velocity in two-dimensional planes, In particle tracking velocimetry (PTV), displacements of single particles in two subsequent images were determined semi-automatically, resulting in flow diagrams consisting of non-uniformly distributed velocity vectors, Application of grid-cell averaging resulted in pow field diagrams with uniform vector distribution, In sub-image correlation PIV (SCPIV), repetitive convolution filtering of small sub-areas of two subsequent images resulted in automatic determination of cross-correlation peaks, yielding flow field diagrams with regularly spaced velocity vectors, In both PTV and SCPIV, missing values, caused by incomplete particle displacement information in some areas of the images or due to rejection of some erroneous vectors by the vector validation procedure, were interpolated using a two-dimensional spline interpolation technique.The resultant vector how fields were used to study the spatial distribution of velocity, spatial acceleration, vorticity, strain and shear, These flow fields could also be used to test for flow in the third dimension by studying the divergence, and to detect the presence and location of vortices, The results offer detailed quantitative descriptions of the flow morphology and can be used to assess dissipated energy, The versatile character of the technique makes it applicable to a wide range of fluid mechanical subjects within biological research, So far it has been successfully applied to map the flow around swimming copepods, fish larvae and juvenile fish and the ventilation current of a tube-living shrimp.

1. Climate change has caused a phenological mismatch between the timing of reproduction and the local food peak in many bird species. Late breeding birds therefore experience reduced food availability during chick rearing and are thus predicted to have an increased energy expenditure. Observational studies, however, show mixed results, perhaps because they compare energy expenditure across rather than within individuals at different levels of food availability. 2. In a cross foster experiment, we measured daily energy expenditure (DEE) twice within individuals during chick feeding (when chicks were 6 and 14 days old) for 28 free-living female great tits (Parus major). To avoid confounding effects of chick age, these females reared on both occasions a standardized foster brood of eight 10-day-old chicks during the 24-h measuring period. For all birds, food availability declined between the two measurements. 3. We show that DEE during chick feeding increased within females when food availability decreased. Variation in DEE within females is partly explained by brood visit rates, food availability and temperature. 4. DEE during chick feeding could be affected by the investment in previous stages of the reproductive attempt. However, energy expenditure during chick feeding was not correlated to energy expenditure during egg laying, measured in these same females. 5. Understanding of energetic costs during all phases of the reproductive cycle is important to forecast the consequences of climate warming on timing of reproduction.

SYNOPSIS. The flexible phenotypes of birds and mammals often appear to represent adjustments to alleviate some energetic bottleneck or another. By increasing the size of the organs involved in digestion and assimilation of nutrients (gut and liver), an individual bird can increase its ability to process nutrients, for example to quickly store fuel for onward flight. Similarly, an increase in the exercise organs (pectoral muscles and heart) enables a bird to increase its metabolic power for sustained flight or for thermoregulation. Reflecting the stationary cost of organ maintenance, changes in the size of any part of the ‘‘metabolic machinery’’ will be reflected in Basal Metabolic Rate (BMR) unless changes in metabolic intensity also occur. Energetic bottlenecks appear to be set by the marginal value of organ size increases relative to particular peak requirements (including safety factors). These points are elaborated using the studies on long-distance migrating shorebirds, especially red knots Calidris canutus. Red knots encounter energy expenditure levels similar to experimentally determined ceiling levels of ca. 5 times BMR in other birds and mammals, both during the breeding season on High Arctic tundra (probably mainly a function of costs of thermoregulation) and during winter in temperate coastal wetlands (a function of the high costs of processing mollusks, prey poor in nutrients but rich in shell material and salt water). During migration, red knots phenotypically alternate between a ‘‘fueling [life-cycle] stage’’ and a ‘‘flight stage.’’ Fueling red knots in tropical areas may encounter heat load problems whilst still on the ground, but high flight altitudes during migratory flights seem to take care of overheating and unacceptably high rates of evaporative water loss. The allocation principles for the flexible phenotypes of red knots and other birds, the costs of their organ flexibility and the ways in which they ‘‘organize’’ all the fast phenotypic changes, are yet to be discovered.

Summary Animals usually are not willing to perform at levels, or for lengths of time, of which they should be maximally capable. In stating this, exercise performance and inferred capacity are gauged with respect to body size and the duration of particular levels of energy expenditure. In such relative terms, the long-term metabolic ceiling of ca. 7 times basal metabolic rate in challenged but energy-balanced individuals may be real and general, because greater performance over long periods requires larger metabolic machinery that is ever more expensive to maintain. Avian marathon migrants relying on stored fuel (and therefore not in energy balance) that work for 9 consecutive days at levels of 9–10 times basal metabolic rate are exceptional performers in terms of the ‘relative expenditure’ on ‘duration of a particular activity’ curve nevertheless. Here I argue that metabolic ceilings in all situations (energy balanced or not) have their origin in the fitness costs of high performance levels due to subsequently reduced survival, which then precludes the possibility of future reproduction. The limits to performance should therefore be studied relative to ecological context (which includes aspects such as pathogen pressure and risk of overheating), which determines the severity of the survival punishment of over-exertion. I conclude that many dimensions of ecology have determined at which performance levels (accounting for time) individual animals, including human athletes, begin to show physiological restraint. Using modern molecular techniques to assay wear and tear, in combination with manipulated work levels in different ecological contexts, might enable experimental verification of these ideas.

The concentrations of persistent organic pollutants, such as DDT and its metabolites (DDTs), hexachlorocyclohexane isomers (HCHs), cyclodienes (Cycls), and polychlorinated biphenyls (PCBs), were measured in livers and subcutaneous fat tissues of six Accipitridae and four Falconidae bird species from different areas in Greece. This is the first report of persistent organochlorine (OC) pollutants in birds of prey tissues presented for Greece and the Eastern Mediterranean region. Accumulation patterns of OCs found in birds suggested that the predominant contaminants were p,p'-dichlorodiphenyldichloro-1,1-ethylene (DDE) and PCBs, whereas Cycls and HCHs occurred at low concentrations only. Concentration values of p,p'-DDE ranged from nondetected to 19,518.72 ng/g wet wt in livers and from nondetected to 2679.19 ng/g wet wt in fat. Total PCB levels ranged from 1.01 to 7419.43 ng/g and from 3.25 to 490.10 ng/g wet weight for liver and fat samples, respectively. Higher-chlorinated PCBs such as 118, 138, 153, and 180 predominated in both the liver and subcutaneous fat samples, a pattern comparable to that observed in birds from other European countries. No significant differences in mean concentrations of OCs are detected between species. Hepatic concentrations were in general higher than the fat concentrations showing depleted fat stores in most birds. Concentration ranges were also found in lower or similar levels to those reported for birds in other regions. Variation of OCs levels in bird tissues could be due to different causes of death, with a subsequent effect on body lipid levels, and different feeding and migration habits. The liver PCB levels reported in this study are below the concentrations currently believed to exert mortality or ecotoxicological effects. On the contrary, in some cases p,p'-DDE concentrations were higher than the reported effect values for birds of the same families and could be associated with sublethal effects. Arch Environ Contam Toxicol

The variation in time and energy allocation of female great tits, Parus major, was studied in five different European populations across a latitudinal gradient. Daily energy expenditure (DEE) was measured in females tending 12-day-old broods. The number of daylight hours used by the parents to collect food for the brood increased with latitude, while DEE and feeding rate per brood tended to level off with latitude. Individual variation in DEE could be explained by variation in ambient temperature (–), the duration of activity period (+) and area, but not by brood size, female body mass, brood mass or feeding rate. When the effect of ambient temperature and the duration of the activity period on the day of energy expenditure measurements were controlled for, female DEE still tended to level off with latitude. Temperature and activity alone can thus not explain the observed pattern. The present study suggests that parents at southern latitudes may be under a time constraint and do not increase energy expenditure because they have no more daylight hours available for foraging, while birds at northern latitudes may be under an energy constraint because they do not make full use of the long daylight period available.

1. Little is known about long-term effects of brood size on fitness components of offspring. This is unfortunate because such information is needed to predict optimal brood size. Furthermore, ontogenetic circumstances are potentially important in explaining the large individual differences in lifetime reproductive success documented in many species. 2. In a laboratory study the long-term effect of brood size manipulation on mortality and morphological development of offspring was investigated. Young zebra finches Taeniopygia guttata were reared in small or large broods. Young were exchanged in such a way that natural siblings from different rearing conditions could be compared. 3. Manipulated brood size affected offspring morphology permanently (measurements were taken up to the age of 12 months). Individuals reared in small broods were heavier, had longer tarsi and wings, higher beaks, were in better condition, and males had redder beaks. The experiment did not affect beak length or female beak redness. Individuals from large broods had caught up on wing length and males from large broods on beak redness by 6 months of age, which may reflect priority of investment in traits important to fitness. 4. Mortality of offspring raised in large broods was higher both before and after independence. After independence the effect of manipulated brood size on mortality was sex specific; females were most likely to die. This suggests that the optimal sex ratio of offspring may depend on brood size. 5. The effect of brood size on mortality after independence was probably partly mediated by size and condition during the nestling phase and possibly by peer aggression among adult offspring. Sex-linked mortality could not be explained by a sex difference in morphological development. Why females are more vulnerable remains to be discovered.

We studied temporal variation in reproductive performance of Marsh Harriers Circus aeruginosus in two land reclamations in The Netherlands, i.e. South Flevoland and the Lauwersmeerpolder, embanked in 1968 and 1969 respectively. The number of breeding pairs in Flevoland rapidly increased to a maximum of 350 pairs (± 1 pair km-2) in 1977, followed by a sharp decline in the 1980s due to large-scale cultivation. The same trend was observed in the Lauwersmeer, although colonization was retarded and peak densities were reached later. In both study areas mean clutch size as well as the number of fledglings per nest decreased in the course of the twenty years of study. Two factors were responsible for this decline in reproductive output: (1) decrease of food abundance in the course of the years, and (2) an increase of nest predation, mainly by the Red Fox Vulpes vulpes. Superimposed on these long-term changes, annual fluctuations in density of the Common Vole Microtus arvalis had a considerable effect on the number of breeding pairs, as well as the fledgling production. Mean annual clutch size was associated positively, and laying date negatively, with the average annual temperature during the pre-laying phase. Our results indicate that the early stages of succession, during the first decade after reclamation, are characterized by high prey abundance (i.e. vole 'plagues') and low densities of ground predators, and offer favorable breeding conditions for Marsh Harriers. The simultaneous negative effects in recent years of less breeding habitat, decreased prey abundance and increased predation on reproductive output, exert pressure on these populations. The intense nest predation (50% of all nests), as recorded in the Lauwersmeer since 1990, may eventually cause local extinction in the absence of, relatively safe, inundated breeding habitat.

Reproduction of the Seychelles warbler (Acrocephalus sechellensis), a single-island endemic species living close to the equator, is characterized by a pronounced annual rhythm. The bird usually raises only one or two clutches of one egg each per year. Observational data suggest that seasonal changes in feeding conditions are an important proximate factor controlling reproduction. This hypothesis could be tested by transferring breeding pairs from Cousin Island to islands previously unoccupied at the same latitude. These islands, Aride and Cousine, have a higher food supply but similar vegetation and climate. After translocation to Aride Island, with high food availability year-round, individual breeding pairs prolonged their reproductive season (some bred year-round), increased the annual number of broods, and improved the reproductive success per nest-building attempt. Annual production of yearlings per pair on Aride was on average 23 times higher than that of the same pair on Cousin before the transfer. After translocation to Cousine Island, where food availability varied seasonally and was intermediate between Cousin and Aride, individual pairs increased the annual number of broods, but reproductive success per nest-building attempt remained the same. Annual production of yearlings per pair on Cousine was on average 5 times higher than that of the same pair on Cousin before the transfer. Thus the experiments, controlled for group size, breeding partner, breeder age, and experience, showed that food supply can be an important proximate factor in the timing of reproduction in the tropics. The differences in reproductive timing and success by warblers on the three islands are due not to genetic differences but entirely to differences in environmental conditions.

We examined the relationship between daily energy expenditure (DEE) and basal metabolic rate (BMR) in birds and mammals. Two models of the relationship between DEE and BMR were distinguished: a ''shared pathways'' model in which DEE replaces BMR in the active organism and a ''partitioned pathways'' model in which DEE includes BMR-that is, BMR is separate from the metabolic pathways that result in activity metabolism (ACT), and DEE = ACT + BMR. The appropriate null hypotheses for the relationship between basal and active metabolism are r(DEE . BMR) = 0 and r(ACT . BMR) = 0, respectively. Correlations of the residuals (d and b) of the logarithms of DEE and BMR from their allometric regressions with the logarithm of body mass were tested against these null models. Using phylogenetically independent contrasts, we found no significant relationship between DEE and BMR in birds, but a strong relationship (r(db) = 0.86) among mammals. Thus, the hypothesis that sustained working capacity is related to basal metabolism is supported for mammals but not for birds. Residuals of metabolic variables from allometric regressions on body mass were greater for mammals than for birds and suggest that mammals are more diversified in their energetic physiology. The idea that sustainable energy expenditure may be pushed to physiological limits in mammals but not in birds is not supported, however, because the ratio of DEE to BMR has a somewhat lower mean and greater variance in mammals compared to birds. The nature of the relationship between DEE and BMR in mammals and the apparent absence of such a relationship in birds remain major puzzles in animal physiology.

The effect of territory quality on the time and energy allocation of Oystercatchers was investigated on the island of Schiernonnikoog in the Dutch part of the Wadden Sea. Low quality leapfrog territories required a higher level of parental effort for successful reproduction than high quality resident territories. The time budgets of residents and leapfrogs differed slightly, the main difference occurring during the chick-rearing stage when leapfrogs spent on average 8.2% of the time available during low water in flight in order to transport food to the chicks, compared to only 2.9% in residents. In both residents and leapfrogs, inactivity (including preening) constituted a considerable part of the time budget, comprising almost 50% of the low water period during the pre-laying stage and decreasing to 23% during the incubation stage when each bird spent almost hat: the time on the clutch. Analysis of individual time budgets during the incubation stage revealed that time spent inactive must be considered 'surplus time' since this can be reallocated to foraging when the proportion of time devoted to incubation increased. Obligatory inactivity required less than 10% of the rime available during low water. The persistence of 'surplus' time during the chick-rearing stage suggests that parental effort is not constrained by a shortage of time. Energy expenditure, estimated from time-budgets, agreed well with energy consumption, calculated from observed food intake, and with measurements using doubly labelled water. It varied from 2.1 x BMR during the incubation stage to 2.7 x BMR during the chick-rearing stage. These values are much lower than the maximum energy expenditure reported for many other bird species during the reproductive cycle. During the chick-rearing stage, daily energy expenditure of leapfrogs was 6-7% higher than that of residents due to the additional costs involved in the transportation of food. Despite the fact that the reduced reproductive success of leapfrogs, as compared to that of residents, is mainly caused by the failure of the parents to provision their chicks with a sufficient amount of food, leapfrogs did not increase their parental effort to a considerable extent. This would fit the interpretation that long-living species like the Oystercatchers are reluctant to work very hard during one reproductive cycle.

Knots Calidris canutus live highly seasonal lives, breeding solitarily on high arctic tundra and spending the non-breeding season in large social flocks in temperate to tropical estuaries. Their reproductive activities and physiological preparations for long flights are reflected in pronounced plumage and body mass changes, even in long-term captives of the islandica subspecies (breeding in north Greenland and northeast Canada and wintering in western Europe) studied in outdoor aviaries. The three to four fattening episodes in April-July in connection with the flights to and from the high arctic breeding grounds by free-living birds, are represented by a single period of high body mass, peaking between late May and early July in a sample of ten captive islandica knots studied over four years. There are consistent and synchronized annual variations in basal metabolic rate and thermal conductance in three istandica knots. Basal metabolic rate was highest during the summer body mass peak. Within the examined individuals, basal metabolic rate scales on body mass with an exponent of about 1.4, probably reflecting a general hypertrophy of metabolically expensive muscles and organs. Any potential effect of moult on basal metabolic rate was obscured by the large seasonal mass-associated variations. In breeding plumage, insulation (the inverse of thermal conductance) was a factor of 1.35 lower than in winter plumage. This was paralleled by the dry mass of contour feathers being a factor of 1.17 lower. In this subspecies the breeding season is indeed the period during which the costs of thermoregulation are lowest. In captive knots seasonal changes in basal metabolic rate and thermal conductance likely reflect an anticipatory programme adaptive to the variable demands made by the environment at different times of the year.

Two alternative particle image velocimetry (PIV) methods have been developed, applying laser light sheet illumination of particle-seeded flows around marine organisms, Successive video images, recorded perpendicular to a light sheet parallel to the main stream, were digitized and processed to map the how velocity in two-dimensional planes, In particle tracking velocimetry (PTV), displacements of single particles in two subsequent images were determined semi-automatically, resulting in flow diagrams consisting of non-uniformly distributed velocity vectors, Application of grid-cell averaging resulted in pow field diagrams with uniform vector distribution, In sub-image correlation PIV (SCPIV), repetitive convolution filtering of small sub-areas of two subsequent images resulted in automatic determination of cross-correlation peaks, yielding flow field diagrams with regularly spaced velocity vectors, In both PTV and SCPIV, missing values, caused by incomplete particle displacement information in some areas of the images or due to rejection of some erroneous vectors by the vector validation procedure, were interpolated using a two-dimensional spline interpolation technique. The resultant vector how fields were used to study the spatial distribution of velocity, spatial acceleration, vorticity, strain and shear, These flow fields could also be used to test for flow in the third dimension by studying the divergence, and to detect the presence and location of vortices, The results offer detailed quantitative descriptions of the flow morphology and can be used to assess dissipated energy, The versatile character of the technique makes it applicable to a wide range of fluid mechanical subjects within biological research, So far it has been successfully applied to map the flow around swimming copepods, fish larvae and juvenile fish and the ventilation current of a tube-living shrimp.

Hatching asynchrony in birds produces an age and size hierarchy among siblings. Later-hatching chicks have a competitive disadvantage, and brood reduction may occur when food availability is insufficient to raise all chicks. When early-hatched chicks fail to survive or if the circumstances allow raising all chicks, mothers should reverse the disadvantage to later-hatched chicks. Increasing deposition of maternal androgens with the laying sequence has been suggested to compensate for detrimental effects of hatching asynchrony, allowing a more precise adjustment of the survival probabilities of each chick. Here, we show for blackheaded gulls that the increase in yolk testosterone with each successive egg is greater when the mother incubates longer before clutch completion, which is the major determinant of the degree of hatching asynchrony. This finding supports the idea that yolk testosterone has a compensatory function in the context of hatching asynchrony. Our data further show that if the time needed to complete a clutch is lengthened, the developmental differences due to incubation between the first- and the last-laid eggs increase. In addition, the onset of incubation before clutch completion occurs sooner as the breeding season progresses. Both long inter-egg intervals and the seasonal shift in incubation behavior enhance the necessity of compensation for later-hatching chicks. Indeed, yolk levels of testosterone increased more steeply over the laying order, if the duration of the egg-laying period was extended and in later-laid clutches. We suggest that prolactin plays a key role in the adjustment of testosterone allocation to the incubation pattern. Key words: hatching asynchrony, maternal effects, yolk androgens. [Behav Ecol 15:893–897 (2004)]

Under a Creative Commons license.-- et al., Biomonitoring using raptors as sentinels can provide early warning of the potential impacts of contaminants on humans and the environment and also a means of tracking the success of associated mitigation measures. Examples include detection of heavy metal-induced immune system impairment, PCB-induced altered reproductive impacts, and toxicity associated with lead in shot game. Authorisation of such releases and implementation of mitigation is now increasingly delivered through EU-wide directives but there is little established pan-European monitoring to quantify outcomes. We investigated the potential for EU-wide coordinated contaminant monitoring using raptors as sentinels. We did this using a questionnaire to ascertain the current scale of national activity across 44 European countries. According to this survey, there have been 52 different contaminant monitoring schemes with raptors over the last 50. years. There were active schemes in 15 (predominantly western European) countries and 23 schemes have been running for >. 20. years; most monitoring was conducted for >. 5. years. Legacy persistent organic compounds (specifically organochlorine insecticides and PCBs), and metals/metalloids were monitored in most of the 15 countries. Fungicides, flame retardants and anticoagulant rodenticides were also relatively frequently monitored (each in at least 6 countries). Common buzzard (Buteo buteo), common kestrel (Falco tinnunculus), golden eagle (Aquila chrysaetos), white-tailed sea eagle (Haliaeetus albicilla), peregrine falcon (Falco peregrinus), tawny owl (Strix aluco) and barn owl (Tyto alba) were most commonly monitored (each in 6-10 countries). Feathers and eggs were most widely analysed although many schemes also analysed body tissues. Our study reveals an existing capability across multiple European countries for contaminant monitoring using raptors. However, coordination between existing schemes and expansion of monitoring into Eastern Europe is needed. This would enable assessment of the appropriateness of the EU-regulation of substances that are hazardous to humans and the environment, the effectiveness of EU level mitigation policies, and identify pan-European spatial and temporal trends in current and emerging contaminants of concern., This paper arises from work carried out by the EURAPMON Research Networking Programme which is funded by the European Science Foundation. Thanks to MINECO for the financial support of the project CGL2011-16063-E.

We experimentally reduced clutch size of Great Tits Parus major to investigate the effects on parental care (including Daily Energy Expenditure, DEE, measured with doubly labelled water), and the relationship between DEE and the residual reproductive Value. The length of a working day was not affected, but the nestling phase was 0.7 days (4%) shorter in experimental clutches. Males fed reduced broods at a lower rate, but DEE and mass (loss) were not significantly affected by the experiment. However, male DEE was positively correlated with feeding frequency, and this relationship did not differ between control and experimental males. This suggests that the experiment resulted in a slight reduction in male DEE, and lack of statistical significance can be attributed to the power of the test applied. Females fed reduced broods at a lower rate, but female DEE and mass (loss) were not affected by the clutch size manipulation. Female DEE was not correlated with feeding frequency, the original number of eggs in the nest or the actual number of young. The division of labour (feeding rate, DEE) was not affected by the clutch size manipulation. Female DEE was significantly higher than male DEE, and this could be caused by the fact that only the female roosts with the young. There was no consistent relationship between DEE and parental survival or future reproductive success. Since the experimental reduction in clutch size led to an increase in residual reproductive Value (more second clutches), but not to a decrease in DEE, this costs of reproduction is apparently not contingent on increased rate of energy turnover. It is suggested that birds with equal DEE may differ in their residual reproductive value as a consequence of variation in energy allocation between reproductive effort and e.g. aspects of physiological maintenance and repair. [KEYWORDS: Parus major; clutch size; parental effort; daily energy expenditure Doubly labeled water; flycatcher ficedula-albicollis; measuring energy-metabolism; starlings sturnus-vulgaris; kestrel falco-tinnunculus; brood size; breeding birds; reproductive effort;savannah sparrows; expenditure]

We present data on the natural variation in daily energy expenditure (DEE, measured by the doubly labelled water technique) of individual female Great Tits Parus major tending their brood near the northern border of the species' distribution. We expected that longer foraging days would result in a higher energy expenditure. Female DEE, visitation rate and the duration of the active period were measured at the nestling age of 12 days. There was a positive relationship between the duration of activity period and brood size. Female DEF was positively associated with the duration of the activity period and the number of young in the nest. Energy expenditure was not related to temperature or feeding rates. Despite the longer foraging day and lower ambient temperatures, female DEE did not differ from the values obtained in central Europe. This result suggests that there are differences in foraging cost and/or mode with latitude.

Introduction: Life-history theory predicts that organisms trade off survival against reproduction. However, the time scales on which various consequences become evident and the physiology mediating the cost of reproduction remain poorly understood. Yet, explaining not only which mechanisms mediate this trade-off, but also how fast or slow the mechanisms act, is crucial for an improved understanding of life-history evolution. We investigated three time scales on which an experimental increase in body mass could affect this trade-off: within broods, within season and between years. We handicapped adult skylarks (Alauda arvensis) by attaching extra weight during first broods to both adults of a pair. We measured body mass, immune function and return rates in these birds. We also measured nest success, feeding rates, diet composition, nestling size, nestling immune function and recruitment rates.Results: When nestlings of first broods fledged, parent body condition had not changed, but experimental birds experienced higher nest failure. Depending on the year, immune parameters of nestlings from experimental parents were either higher or lower than of control nestlings. Later, when parents were feeding their second brood, the balance between self-maintenance and nest success had shifted. Control and experimental adults differed in immune function, while mass and immune function of their nestlings did not differ. Although weights were removed after breeding, immune measurements during the second brood had the capacity to predict return rates to the next breeding season. Among birds that returned the next year, body condition and reproductive performance a year after the experiment did not differ between treatment groups.Conclusions: We conclude that the balance between current reproduction and survival shifts from affecting nestlings to affecting parents as the reproductive season progresses. Furthermore, immune function is apparently one physiological mechanism involved in this trade-off. By unravelling a physiological mechanism underlying the trade-offs between current and future reproduction and by demonstrating the different time scales on which it acts, our study represents an important step in understanding a central theory of life-history evolution.