Maximum daily energy intake: It takes time to lift the metabolic ceiling

Conventionally, maximum capacities for energy assimilation are presented as daily averages. However, maximum daily energy intake is determined by the maximum metabolizable energy intake rate and the time available for assimilation of food energy Thrush nightingales (Luscinia luscinia) in migratory disposition were given limited food rations for 3 d to reduce their energy stores. Subsequently, groups of birds were fed ad lib. during fixed time periods varying between 7 and 23 h per day. Metabolizable energy intake rate, averaged over the available feeding time, was 1.9 W and showed no difference between groups on the first day of refueling. Total daily metabolizable energy intake increased linearly with available feeding time, and for the 23-h group, it was well above suggested maximum levels for animals. We conclude that both intake rate and available feeding time must be taken into account when interpreting potential constraints acting on animals' energy budgets. In the 7-h group, energy intake rates increased from 1.9 W on the first day to 3.1 W on the seventh day. This supports the idea that small birds can adaptively increase their energy intake rates on a short timescale

Migrating shorebirds as integrative sentinels of global environmental change

Many shorebirds travel over large sections of the globe during the course of their annual cycle and use habitats in many different biomes and climate zones. Increasing knowledge of the factors driving variations in shorebird numbers, phenotype and behaviour may allow shorebirds to serve as 'integrative sentinels' of global environmental change. On the basis of numbers, timing of migration, plumage status and body mass, shorebirds could indicate whether ecological and climate systems are generally intact and stable at hemispheric scales, or whether parts of these systems might be changing. To develop this concept, we briefly review the worldwide shorebird migration systems before examining how local weather and global climatic features affect several performance measures of long-distance migrants. What do variations in numbers, phenotype and behaviour tell us about the dependence of shorebirds on weather and climate? How does data on migrating shorebirds integrate global environmental information? Documenting the dependencies between the population processes of shorebirds and global environmental features may be an important step towards assessing the likely effects of projected climate change. In the meantime we can develop the use of aspects of shorebird life histories on large spatial and temporal scales to assay global environmental change

Southward migration and fuel deposition of Red Knots Calidris canutus

We compared the differences between spring and autumn in migration speed, fuelling rates and fuel loads of migrating Red Knots Calidris canutus. As a basis we used ringing data from Ottenby Bird Observatory, southeastern Sweden, collected 1948–2003, with morphometrical data from 1990–2003. Numbers ringed varied between 0 and 301 per year (average 56). Morphometrics, recoveries and recaptures of ringed birds indicated that most birds belonged to the Afro-Siberian subspecies C. c. canutus, possibly mixed with some Nearctic Red Knots C. c. islandica. Median trapping dates were 5 August (adults) and 31 August (juveniles). Mean body masses were low and almost equal for adults (111.8 g) and juveniles (111.4 g). The mean estimated fuel loads were 13–14% of lean body mass (LBM). In juveniles fuel loads increased with date. Among the few birds stopping over for longer than one day (2% of adults, 14% of juveniles), adult birds stayed on average 2.5 days and juveniles 3.4 days, with an overall average fuel deposition rate of 2.8% of LBM d–1. The autumn migration speed was estimated from ringing recoveries at 86 km d–1, which equals the speed of spring migration calculated from published information. The observed fuelling rate was as high as that of Red Knots at major spring stopover sites. We conclude that migration in autumn is as fast as in spring, although the generally small fuel loads indicate that migration is carried out in much smaller steps

Mate Guarding by Curlew Sandpipers (Calidris Ferruginea) during Spring Migration in North Siberia

It is poorly known whether arctic-breeding shorebirds form pairs before or after arrival at the breeding site. We describe the display and mate-guarding of curlew sandpipers Calidris ferruginea at at stopover site in high arctic Siberia, suggesting that in this species pairs may be formed before the birds reach their final nesting localities.Key words: shorebirds, mate guarding, migration, curlew sandpiper, Calidris ferrugineu, SiberiaOn ne sait pas très bien si les oiseaux de rivage qui nichent dans l'Arctique forment des couples avant où après leur arrivée sur l'aire de reproduction. On décrit le comportement de cour et de garde du partenaire chez le bécasseau cocorli (Calidris ferruginea) à un site de passage en Sibérie boréale, en suggérant que chez cette espèce, les couples se constituent avant que les oiseaux n'atteignent leur aire de ponte finale.Mots clés : oiseaux de rivage, garde du partenaire, migration, bécasseau cocorli, Culidris fermginea, Sibéri

Timing of spring migration in birds: long-term trends, North Atlantic Oscillation and the significance of different migration routes

We studied long-term trends and the yearly variation in mean spring passage time in 36 passerine bird species trapped at Ottenby Bird Observatory in south-eastern Sweden. Between the years 1952-2002, data were available for 22-45 years depending on species. Most long-distance migrant species passed progressively earlier over the study period (range: 2.5 days earlier to 0.7 days later per 10 years, with an average of 0.9 days earlier per 10 years). The annual variation in timing of migration in most species, regardless of migration distance, correlated negatively with the winter index of the North Atlantic Oscillation (NAO), a large-scale climate phenomenon influencing the climate in the North Atlantic region. Birds passed earlier after mild and humid winters., corresponding to the high phase of the NAO. This corroborates the pattern round at a nearby migration site with a comparable dataset (Helgoland, 600 km WSW of Ottenby). However, short/medium-distance migrant species at Otterby, in contrast to the situation at Helgoland, have shown no general trend of earlier passage in recent years. This was probably a consequence of the shorter study period at Ottenby, which included only the last 22-32 years (41 years at Helgoland), when the NAO showed no significant trend. At the species-specific level, the long-term trends in passage time were similar at the two sites, and there was some congruence to the extent that a given species was affected by NAO. Long-distance migrants wintering south and south-east of the breeding grounds showed some of the strongest changes in long-term trends (passing progressively earlier) at Ottenby, and for some of these species passage time varied negatively with NAO. Obviously, and contrary to previous suggestions, variations in NAO also influence birds migrating through eastern Europe, although the direct or indirect mechanisms through which this is achieved are unknown