Showing papers in "Ardea in 2006"

Surfing on a green wave - how plant growth drives spring migration in the Barnacle Goose Branta leucopsis

Abstract: The nutritional quality of forage plants varies in space and time. This variation is presumed to drive the annual migration of herbivore species which follow peaks in the availability of high quality forage between sites. The green-wave hypothesis predicts that during spring migration to northern breeding sites, geese and other herbivorous waterfowl travel along a climatic gradient, taking advantage of the flush of spring growth of forage plants at each stopover site along the gradient. Here, we explore a basic assumption of the green wave hypothesis which states that there are successive waves of forage availability along the East-Atlantic Flyway from temperate to arctic sites, as spring advances. We use one of the migration routes of the Barnacle Goose Branta leucopsis as a model to compare data on food quality and quantity of forage plants with the timing of migration along its migratory corridor. We collected data on forage biomass and quality at three saltmarsh sites along the traditional migration route of the Barnacle Goose: a temperate staging site in the Wadden Sea, a Baltic stopover site and a Russian sub-arctic breeding site. In all areas forage biomass increased in spring, while the nutritional quality peaked early in the season and declined with increasing biomass. We combined data on forage biomass and nutritional quality in one measure, the nutrient biomass. For all sites, nutrient biomass showed a peak in early spring. We used observations on goose migration to examine whether the geese utilise these peaks in nutrient biomass, as is predicted by the green wave hypothesis. Our data show that the geese utilise the Wadden Sea staging site and the Baltic stopover site at the moments of peak nutrient biomass. At the Russian breeding site, geese arrive prior to the flush of spring growth of forage plants and profit from the peak in nutrient biomass when the goslings hatch and adult birds start moulting. We conclude that spring nutrient biomass is a key factor driving the timing of the annual northern migration of avian herbivores

The challenges of making eggs

Abstract: Egg formation is a demanding process both in terms of energy and nutrient requirements. Birds must not only collect specific nutrients for egg formation, but must do so over a brief period when food may not yet be plentiful. Supplementary feeding experiments show that timing of egg formation and the number and quality of eggs formed can depend on energetic and nutritional factors, although they may not all be affected in the same way. Resources required for egg formation may come both from body reserves accumulated before egg formation starts and resource intake during egg formation. Egg formation is not only costly in terms of resource requirement, but variation in egg formation effort also has consequences on the bird's fitness. Increased egg formation effort can lead to poorer body condition at the end of laying, poorer egg quality, reduced parental chick rearing ability and lower future reproductive success.

The timing of birds' breeding seasons : the Perrins hypothesis revisited especially for migrants

Abstract: Perrins (1970) galvanized thinking on the timing of birds' breeding seasons by pointing out that most individuals laid too late for the offspring to profit fully from the seasonal peak of food abundance, and suggested that the proximate cause was a shortage of food for the female when forming the eggs. This idea (the food constraint hypothesis) stimulated field experiments with supplementary food, and also catalyzed analysis of the seasonal trends of fitness for both parents and offspring. Most experiments resulted in minor advances in laying date hinting that other factors are also important, and the fitness comparisons underlined the view that laying date must be viewed as a trade-off between opposing seasonal trends affecting parents (later is better) and offspring (the earlier the better). Experimental advances of laying have revealed fitness costs (lowered survival) for the parent(s) counteracting the higher output of young. Laying date is thus best considered as an individually based compromise (individual optimisation hypothesis), with exact timing subject to local environmental control. Recent analyses of climate change (warming trend in spring) confirm responses in many but not all bird species, and where detailed data are available the advance documented in laying date seems often to fall short of the shift in the food peak. Migrants in particular may be unable to speed up their spring travels, in some species on account of time conflicts with moult. The larger bodied migrants breeding in the Arctic face severe time constraints as they must lay relatively early on the snowy tundra. Postulated to rely on endogenous stores to lay eggs and incubate them, finer resolution of their travel schedules by means of satellite telemetry combined with investigation of the isotopic signature of body tissues, eggs, and food sources show a mixed strategy to prevail: transport what you can ('capital') and supplement this on the breeding grounds ('income'). Stores acquired at stopover sites are of crucial importance for both survival and breeding and any'mismatch' caused by uncoupling of rates of climate change along the migratory pathway may have profound effects on the population level.

Advances in the study of irruptive migration

Abstract: This paper discusses the movement patterns of two groups of birds which are generally regarded as irruptive migrants, namely (a) boreal finches and others that depend on fluctuating tree-fruit crops, and (b) owls and others that depend on cyclically fluctuating rodent populations. Both groups specialise on food supplies which, in particular regions, fluctuate more than 100-fold from year to year. However, seed-crops in widely separated regions may fluctuate independently of one another, as may rodent populations, so that poor food supplies in one region may coincide with good supplies in another. If individuals are to have access to rich food supplies every year, they must often move hundreds or thousands of kilometres from one breeding area to another. In years of widespread food shortage (or high numbers relative to food supplies) extending many thousands or millions of square kilometres, large numbers of individuals migrate to lower latitudes, as an ‘irruptive migration’. For these reasons, the distribution of the population, in both summer and winter, varies greatly from year to year. In particular breeding areas, many species of irruptive migrants fluctuate in density according to food supplies at the time. The facts that the response to food change is rapid, and that increases in numbers from one year to the next are often greater than can be explained by high survival and reproduction from the previous year, imply that such year to year density changes are due mainly to movements. Ring recoveries and other data lend support to this view. In irruptive migrants, in contrast to regular migrants, site fidelity is poor, and few individuals return to the same breeding areas in successive years (apart from owls in the increase phase of a rodent cycle). Moreover, ring recoveries and radio-tracking confirm that the same individuals can breed in different years in areas separated by hundreds or thousands of kilometres. Extreme examples are provided by Common Crossbills Loxia curvirostra, in which individual adults were found in localities up to 3200 km apart in different breeding seasons, and Snowy Owls Nyctea scandiaca found in localities up to nearly 2000 km apart. The implication from irruptive migrations, that individuals can winter in widely separated localities in different years, is also supported by ring recoveries, at least in seed-eaters, in which individuals have been found in one winter hundreds or thousands of kilometres from where they were ringed in a previous winter. Most such shifts could be regarded as lying at different points on the same migration axis, but some were apparently on different axes, as the birds were recovered in winter far to the east or west of where they were ringed in a previous winter. Extreme examples include a Bohemian Waxwing Bombycilla garrulus (6000 km, Ukraine to Siberia), a Siskin Carduelis spinus (3000 km, Sweden to Iran), a Pine Siskin Carduelis pinus (3950 km, Quebec to California), and a Common Redpoll Carduelis flammea (8350 km, Belgium to China). Compared to regular (obligate) migrants, irruptive (facultative) migrants show much greater year to year variations in the proportions of individuals that migrate, and greater individual and year to year variations in the timing, directions and distances of movements. The control systems are flexible in irruptive migrants, enabling individuals to respond to feeding conditions at the time. However, regular and irruptive migrants are probably best regarded, not as distinct categories, but as representing opposite extremes of a continuum of migratory behaviour found among birds, from narrow and consistent at one end to broad and flexible at the other. Both systems are adaptive, the one to conditions in which resource levels are predictable in space and time, and the other to conditions in which resource levels are unpredictable. Depending on the predictability and stability of its food supply, the same species may behave as a resident or regular migrant in one part of its range, and as an irruptive migrant in another, as exemplified by particular species of both seed-eaters and rodent-eaters.

Factors affecting the site of investment, and the reliance on savings for arctic breeders : the capital–income dichotomy revisited

Abstract: The extent to which migratory birds that breed in the Arctic and winter in southern biomes rely on residual body stores for reproduction is unresolved. The short arctic summer and the limited availability of food early in the season constrain the time available for successful reproduction. Birds that are able to bring sufficient endogenous reserves to the breeding ground to meet, at least partially, the demands of egg-laying can initiate clutch production soon after arrival, thereby shortening the length of the breeding season and improving the chances of reproductive success. The amount of reserves available will be influenced by body size, the increased energetic and predation costs associated with carrying large stores, distances between staging sites and the location of the breeding grounds within the Arctic. Birds need not fly directly to the breeding grounds from the established temperate staging sites. Extensive feeding by migrants may occur in the Arctic, even within a few kilometres of the breeding sites as the birds track the retreating snowline. Irrespective of their size, birds are thus able to store some resources necessary for egg laying at local or regional scales. It is thus important to make a distinction between local capital and distant capital breeding. The extent to which a bird is characterized as a distant capital, local capital, or an income breeder not only varies between species, but also between individuals and seasons.

Year-round movements of Northern Common Eiders Somateria mollissima borealis breeding in Arctic Canada and West Greenland followed by satellite telemetry

Abstract: We implanted satellite transmitters to track Northern Common Eiders Somateria mollissima borealis from breeding grounds in West Greenland and eastern Arctic Canada, and from their wintering grounds in SW Greenland. We compared distances moved, timing, duration, and patterns of movement between migration flyways and between spring and autumn migration. Common Eiders used two wintering areas linked by three routes. Eiders tracked from a NW Greenland breeding colony (n = 10) migrated south along the coast to winter exclusively in west and southwest Greenland. Breeders from Arctic Canada wintered in two distinct areas with a tendency to segregate by sex. Some eastern Canadian Arctic Eiders from a colony near Southampton Island, migrated through Hudson Strait along the Labrador and Newfoundland coasts, to winter in Atlantic Canada. However, 60% (n = 25) originating from this colony crossed the Davis Strait to winter in SW Greenland, returning in spring to breed in Canada, linking the two north-south flyways. Seven of 8 Eiders implanted in SW Greenland in winter crossed the Davis Strait into Arctic Canada in spring to breed. Apparently more females than males from the Canadian colony (14/18 females and 1/6 males) followed the shorter east-west flyway in fall. Spring migration was initiated later in the Canadian Arctic. Tracked movements ranged from sedentary birds that nested within 45 km of their wintering area in SW Greenland, to migration routes that exceeded 2000 km. Spring migration speeds averaged c. 60 km d -1 , less than half that during moult migration (142 km d -1 ) and autumn migration (190 km d -1 ). This suggests that Eiders must stop to feed whilst travelling to breed, are constrained by sea ice conditions, or both. Climatic and sea ice conditions differ between the eastern Arctic Canada and west Greenland which influence wintering sites, timing and routes of spring migration.

Home range size, habitat use, activity patterns and hunting behaviour of urban-breeding Northern Goshawks Accipiter gentilis

Abstract: The Northern Goshawk Accipiter gentilis typically prefers woodland habitat for nesting and hunting. In recent decades, however, the species has started colonising urban environments across Europe. Here I present the first study on the ranging behaviour of urban-breeding Goshawks. Each year from 1997 to 1999, I tracked a different adult male during the breeding season in the city of Hamburg, Germany (858 hours of total tracking time; n = 5364 radio-fixes). All corresponding pairs raised young in the year of data collection (3, 3 and 4 juveniles). Average home range size was 863 ha (100% Minimum Convex Polygons). Males spent 88% of daylight hours in patches of urban green space (mainly parks) and made short but regular hunting excursions into the matrix of built-up habitat. Built-up habitat was used less frequently than expected from its percentage availability. However, 42% of all recorded kills (n = 143) were made in this habitat type, indicating that it offered good foraging opportunities. Hawks spent 9.7% of daylight hours in active flight (1.8% inter-perch flights, 7.9% soaring). Daily activity patterns were bimodal, with peaks in the early morning and in the evening. I observed one hawk hunting regularly after sunset under artificial light conditions. Goshawks hunted by perched hunting (49%), soaring (33%), and fast contour-hugging flights (11%; n = 220 hunts). Average hunting success was 16% (n = 176 directly observed attacks), or one kill every 35 min of active flight. Home range size was smaller, time spent flying was shorter, and hunting success was higher for the monitored urban hawks than for non-urban individuals from earlier studies. Taken together, my data suggest that living conditions for Goshawks are more favourable in the city of Hamburg than in many non-urban environments.

Daily stopovers as optimal migration strategy in a long-distance migrating passerine : the Northern Wheatear Oenanthe oenanthe

Abstract: Selection for early arrival is expected to shape optimal stopover decisions in migrating birds to minimise time spent on migration. Optimality models predict that fuel loads at departure from stopover sites and stopover duration should depend strongly on search and settling costs as well as on individual fuel deposition rates. In previous years little attention was paid to natural search and settling costs. In the Northern Wheatear Oenanthe oenanthe, a nocturnal long distance migrant, we found evidence for low search and settling costs suggesting that these birds have the capacity to gain body mass from the first day of stopover. Positive correlation between fuel deposition rates and departure fuel loads in males met model predictions for time minimising strategies with an expected global variation in fuel deposition rates and search and settling costs of less than one day. Assuming such low search and settling costs, a time minimising migrant experiencing a stopover site with average fuel deposition rates of 4% of lean body mass is expected to depart with fuel loads less than 17% of its lean body mass. Data on fuel loads from different stopover sites in Europe show that Northern Wheatears generally fulfil these model predictions. Such low fuel loads are expected to force the birds to rest and refuel daily.

Using stable isotopes to quantitatively track endogenous and exogenous nutrient allocations to eggs of birds that travel to breed

Abstract: Conventional approaches to measuring endogenous nutrient allocations to reproduction in birds have relied on the sampling of several individuals within populations in order to contrast mass gains of the clutch with mass loss of the laying female's tissues. The reasoning has been that mass loss of female endogenous tissues during laying can be attributed to 'capital' investment into reproduction. Apart from the destructive nature of this work, problems associated with this approach involve uncertain conversion efficiencies between endogenous reserves and eggs and the general loss of information on individual strategies. As a result, the role of endogenous reserves have likely been overestimated in most cases. Stable isotope measurements of endogenous reserves and egg components can help to trace quantitatively the relative allocation of endogenous vs. exogenous reserves to eggs in cases where local (breeding season) diets differ isotopically from endogenous reserves typically acquired on the wintering or staging grounds prior to arrival to breed. Fortunately several avian species change 'isoscapes' when travelling to breed and so are amenable to isotopic tracking of their body nutrients to eggs. For example, birds wintering in coastal marine biomes and travelling to terrestrial or freshwater biomes experience a general depletion in the isotopes of several elements (C, N, H, O and S) in their local foodwebs. Previous captive studies have allowed us to estimate the isotopic (δ 13 C and δ 15 N) fractionation factors between diet and several egg components (lipid-free yolk, albumen, yolk lipid, shell carbonate) for herbivorous and carnivorous 'income' breeders. Currently, we are using the carnivore model to also estimate fractionation expected between endogenous reserves and eggs. The net result of this work has been an isotopic multi-source mixing model to predict the relative allocation of endogenous vs. exogenous protein and lipid capital to eggs. While refinement is needed for this model, it provides a firm basis for future avian isotopic tracking studies involving nutrient allocations.

Breeding dispersal of great tits Parus major in a homogeneous habitat : effects of sex, age, and mating status

Abstract: We studied patterns of breeding dispersal of adult Great Tits Parus major in a homogeneous habitat (extensive orange plantations) in eastern Spain. Data included 482 movements of known individuals gathered during 11 years. Most birds (67%) did not change territory between seasons. Dispersal propensity was independent of sex, and decreased with age at least up to the sixth year of life. Of birds that changed territory, 92% moved less than 200 m. Young females dispersed significantly farther than adult males, while values for young males and adult females were intermediate. About two thirds of the birds kept the same mate in consecutive years. Both males and females that changed mate dispersed more often than faithful individuals, and females, but not males, dispersed also farther after mate change. Most individuals changed mate because of the death of their partner. The probability of dispersal was similar for widows and divorcees of either sex. However, distances moved by widowed females were longer than those of widowed males or divorced males or females. We discuss these results within the context of breeding dispersal in passerines. Results generally agree with the ideas that (1) females disperse more than males; (2) dispersal tendency decreases with age; and (3) dispersal is more frequent after mate change. However, the interactions among sex, age and mating status, as well as characteristics of the habitat, modulate these general trends, so that dispersal patterns could vary both within and between populations of the same species.

Plasticity in parental provisioning and chick growth in Little Penguins Eudyptula minor in years of high and low breeding success

Abstract: We measured parental care (attendance patterns, foraging trip durations and meal sizes) and chick growth patterns in 45-54 pairs of Little Penguins Eudyptula minor at a breeding colony in southeast Australia during five breeding seasons. Chick survival and productivity were 'good' in two years, 'bad' in two years and intermediate in the fifth; these differences probably reflected changes in food availability. In 'bad' years, parents lengthened foraging trip durations from 1-2 days to 2-5 days, and shortened the length of the guard period by 25%. Meal sizes varied strongly with chick age, but were reduced only slightly in the 'bad' year and varied only slightly with the number of chicks in the brood and with the number of parents visiting the nest. Hence, food intake by chicks depended mainly on the frequency of feeds rather than on meal size. Chicks responded to reduced provisioning rates both by reducing mass growth ('imposed' response) and by delaying development ('induced' response). The chicks' responses were primarily 'imposed' during the period of rapid growth (days 13-35), but were mixed and more varied later in the period of development. The ability of Little Penguins to adjust their foraging behaviour to reduced food availability is probably constrained by their short foraging range (< 20 km) and their nocturnal behaviour at the breeding colony, which limits foraging trip durations to discrete numbers of days.

Strategies for the transition to breeding in time-selected migration

Abstract: In time-selected migration birds adapt their fuel deposition and flight behaviour to maximise sustained migration speed. What are the expectations for the final part of spring migration when the transition to breeding takes place and the criterion of a maximum total migration speed is no longer relevant? Two possible strategies representing different ends of the capital – income spectrum are evaluated. In the first strategy the birds gain an advancement in the breeding cycle by depositing breeding resources while still on migration, as long as the marginal resource deposition rate at the final stopover site, devaluated for the flight transport costs, exceeds that at the breeding destination. In the second strategy an early arrival at the breeding site, before competitors, is of overriding importance, and sprint migration is predicted. In this case migration towards the breeding grounds would to a large degree be a race between competitors, where the birds are expected to change from a maximum sustained speed during much of migration to a final sprint. In such sprint migration the birds exhaust their resources and expose themselves to increased risks in order to obtain the critical priority benefits associated with an arrival before competitors. If and to what degree these strategies exist among migratory birds is unknown. Predictions are given for testing if capital breeding is driven by differential resource gain rates at stopover versus breeding sites. For testing the strategy of sprint migration, investigations of the migrants’ flight behaviour on their final approach to the breeding destinations will be decisive. Inspection of satellite tracking data for two Ospreys Pandion haliaetus revealed an accelerated final approach to the breeding site including nocturnal flights in addition to the regular diurnal thermal soaring migration in one but not the other individual.

Movements of a nomadic waterfowl, Grey Teal Anas gracilis, across inland Australia: results from satellite telemetry spanning fifteen months

Abstract: We used lightweight satellite transmitters to follow the movements of 17 Grey Teal Anas gracilis between September 2003 and November 2004 in two contrasting landscapes, the agricultural districts of southern Australia and the desert landscapes of the interior. Tagged birds moved large distances (up to 343 km) between occupied sites in a short period (hours), remained in the vicinity of those sites for extended periods (months), ventured up to 453 km from their point of release and travelled more than 2000 km in one year. We describe patterns of movement in a nomadic waterfowl for 15 months from September 2003, a period of severe drought. Based on the current analysis there appears to be no remarkable difference in the observed patterns of movement of those released in the agricultural landscapes and those released in the desert. As in waterfowl elsewhere, movements appear to occur in response to changes in local food abundance that threaten survival or the imperative to move in order to breed successfully. In Grey Teal, the proximate cues for movement transcend the local landscape and some birds are responding to temporary cues hundreds of kilometres distant. This is in contrast to the universal seasonal cues associated with migration systems elsewhere.

An isotopic assessment of protein from diet and endogenous stores: Effects on egg production and incubation behaviour of geese

Abstract: Little empirical information exists to assess to what degree geese use a capital versus income breeding strategy for investing nutrients into eggs. We used stable isotope methods to directly estimate the sources of protein deposited into egg yolks of Brent Branta bernicla and Emperor Geese Anser canagicus on the Yukon-Kuskokwim Delta, Alaska, USA. Approximately 59 and 45% of protein in egg yolks of Brent and Emperor Geese, respectively, was derived from exogenous sources (i.e. food plants on the local breeding area). Within clutches of Brent Goose eggs, first-laid eggs exhibited slightly higher contributions from endogenous reserves than last-laid eggs. This pattern was less clear for Emperor Geese, which may have been a consequence of possibly analysing eggs that were laid by intraspecific nest parasites rather than by hosts. For both these species, individuals exhibited large variability in the percent contribution of exogenous versus endogenous stores to eggs, and future studies should identify ecological factors related to this variation. Those Emperor Geese in poor body condition incubated their nests less constantly, and based on δ 13 C values, they fed on terrestrial foods while off their nests. Although not a pure capital breeder, Emperor Geese used nutrients garnered on spring staging areas to fuel virtually all their own maintenance during incubation and to contribute half or more of the nutrients in eggs. These results highlight the ecological importance of these spring staging habitats to geese.

Changes in timing of autumn migration in North European songbird populations

Abstract: Although studies of changes in the timing of passerine spring migration are numerous, less is known about timing of their autumn departure. We present phenological data on 22 species based on mist-netted birds caught on the Baltic island of Christianso during autumn migration between 1976 and 1997. We used least square and quantile regression to test for changes in departure time of the last individuals and the date at which 5%, 50% and 95% of the season total remaining to be trapped (corrected for catch effort). For the entire group of 22 migrants there was no overall change in median departure (-0.0426 days year -1 , P = 0.40). Testing the 12 species for which the entire migration period was included (thus excluding many long-distance migrants), we found an overall earlier departure (-0.18 days year -1 , P = 0.007). Short-distance migrants tended to show earlier departure, while long-distance migrants only showed advanced departure amongst the last individuals to leave. The magnitude of change in departure time was correlated with migration distance, longer distance migrants showing the least change. Overall, timing of autumn migration was more variable between species than the unidirectional change reported in studies of spring arrival.

Pied Flycatchers Ficedula hypoleuca travelling from Africa to breed in Europe: Differential effects of winter and migration conditions on breeding date

Abstract: In most bird species there is only a short time window available for optimalbreeding due to variation in ecological conditions in a seasonalenvironment. Long-distance migrants must travel before th ...

Techniques to link individual migration patterns of seabirds with diet specialization, condition and breeding performance

Abstract: Relationships between seabird breeding and food supply have been subject to much study, but we know little about the influence of food supply in winter on survival and subsequent breeding performance of seabirds, or about the extent to which migrations and winter home ranges of seabirds are influenced by food abundance. The Great Skua Stercorarius skua is a colonially breeding seabird that displays a wide range of feeding techniques during and outside the breeding season. We deployed satellite PTTs and data loggers to determine migration routes and winter quarters of breeding adult Great Skuas. We also studied dietary preferences by direct observations and by use of fatty acid and stable isotope signatures, and measured body condition and breeding performance of individually colour marked birds. Our objective was to develop methods to investigate whether winter foraging conditions may influence subsequent breeding performance, and to collect data to assess whether migrations and winter ranges differed between individuals in ways that may relate to fitness. We found large differences in the winter home ranges of individual Great Skuas, with some wintering off Iberia and others off west Africa. The latter behaviour was unexpected and may represent a new habit to exploit waste from fisheries that have recently developed on the west African continental shelf. Fatty acid signatures provide a clear signal of the presence of demersal fish from fishery discards in skua diet and can be used to assess the feeding preference of individuals. Stable isotopes of C and N in primary feathers show changes in diet of individuals through the period of moult, which is thought to be from September to December. These approaches show that combining the use of data loggers and sampling of forensic markers of colour ringed adults permits the winter diet of individuals to be related to their geographic location in winter and to their subsequent breeding performance.

Reconstructing palaeoflyways of the late Pleistocene and early holocene Red Knot Calidris canutus

Abstract: Bird migration systems must have changed dramatically during the glacial-interglacial cycles of the Pleistocene and as novel habitats became available since the last glacial maximum. This study combines molecular dating of population divergence times with a review of polar-centred palaeovegetation and intertidal habitats world-wide to present a hypothesis for the evolution of Red Knot Calidris canutus flyways. Divergence dates from coalescent analysis of mitochondrial control region sequences indicate that C. c. canutus diverged from the most recent common ancestor (MRCA) of Red Knots about 20 000 (95% Cl 60 000-4000) years ago. About 12 000 (95% Cl 45 000-3500) years ago this MRCA diverged into two lineages, now represented by the North American breeding C. c. roselaari, C. c. rufa and C. c. islandica and the Siberian breeding C c. piersmai and C. c. rogersi, respectively Divergence times of these two Siberian breeding subspecies are about 6500 (95% Cl 25 000-1000) years ago, and populations of the North American breeding subspecies are estimated to have diverged within about the last 1000 years. These divergence times suggest that all ancestral populations of knots emerged within the last glacial period of the Pleistocene via an eastward expansion into North America. This scenario implies that, contrary to contemporary opinions, C. c. islandica was not recently derived from C. c. canutus despite the fact that they are morphologically similar and that their contemporary migration routes overlap in the Wadden Sea. Instead, C. c. islandica is most closely related to the other North American breeding subspecies C. c. roselaari and C. c. rufa. Thus, C. c. islandica only recently pioneered its current migration route to Europe, following the amelioration of winter conditions in the Wadden Sea and the formation of staging habitat in Iceland. This implies that, in Red Knots at least, the Greenland/Iceland migratory route was established very recently from breeding grounds in the Americas to wintering grounds in Europe and not vice versa as previously believed.

Spring stopover routines in Russian Barnacle Geese Branta leucopsis tracked by resightings and geolocation

Abstract: tBy attaching 9-g loggers (recording dusk and dawn times to a memory chip) to the coded leg rings of Barnacle Geese Branta leucopsis caught in a breeding colony at Tobseda (68 degrees 35'N, 52 degrees 20'E) on the arctic coast of the Russian Federation in 2003 and by their recapture and retrieval in the 2004 season, we reconstructed the year-round movements of 19 females. We analysed spring migration movements of logged birds until they entered the zone of continuous daylight (c. 20 May), supplemented by ring reading in the colony. The technique also enabled description of incubation rhythm in these arctic breeders, allowing inferences about attempt and timing of breeding without the necessity of direct observation. Although the birds did not necessarily travel together, most travelled on 14-15 (9 individuals) and 17-18 May (10 birds) when favourable conditions for long-distance flights prevailed. The majority of birds remained in the Wadden Sea well into May, and only 6 staged more than a week anywhere in the Baltic (median staging period 4 days). The majority reached the White Sea by 18 May (latest 25 May) after which near-continuous light precluded further locations. Most tracked individuals spotted in the colony arrived during 6-11 June (mean 8), on average 4 days before first egg date. The median laying date for 17 'logger' birds (from direct observation or backdating from start of incubation) was 13 June (range 5-19), the same as for the colony as a whole in 2004 (n = 385). We conclude that most Tobseda birds tend to overfly the Baltic, and eastern White Sea staging areas are used for on average three weeks before arrival at the breeding colony Judging from the timing in 2004, rapid follicular development must commence at pre-colony staging sites, and from observations in 2002 we suspect these to be on the Kanin Peninsula 360 km W of the nesting area. The Barnacle Geese from the newly established Tobseda colony have apparently pioneered a modified spring migratory routine, possibly partly under the influence of their shorter travel distance. The extended stay in the Wadden Sea fits with the trends in May census data over the past 15 years and may indicate that spring feeding conditions are better than formerly, that the Baltic staging sites are filled to capacity, or some combination of these factors.

Diet and habitat use of Svalbard Pink-footed Geese Anser brachyrhynchus during arrival and pre-breeding periods in Adventdalen

Abstract: The feeding behaviour of Pink-footed Geese Anser brachyrhynchus was studied in Adventdalen, Svalbard, during 15-28 May 2004 to determine habitat use of newly arrived birds based on their distribution in relation to the major vegetation types present. Goose numbers increased from initial arrival on 15 May to 380-440 during 23-28 May, with a brief arrival peak of 990 on 20 May. Geese fed initially on grass-rich communities associated with gravel out-wash fans, but shifted to wet meadow habitats as the thaw progressed, and increasingly used moss tundra and heath habitats after 22 May. Less than 20% of observed geese fed by grubbing the substrate prior to 21 May, but more than 85% did so from 24 May onwards as rising air temperatures exceeded freezing point and the substrate progressively thawed, permitting excavation of subterranean plant storage organs. This pattern was reflected in the diet based on examination of epidermal fragments in the droppings, which showed geese initially fed on above ground dead material from the previous growing season (most abundant in the productive out-wash fans). However, as the substrate thawed, from 22 May geese fed increasingly on the more nutritious Equisetum spp. and finally on below-ground storage organs of Bistorta viviparum as these became available with substrate thaw. The implications of these changes are discussed in the context of the energetic implications for arriving birds and their subsequent reproductive output.

Arctic geese, migratory connectivity and agricultural change : calling the sorcerer's apprentice to order

Abstract: The current favourable numerical status of most arctic-breeding goose populations conceals an increasing dependence on man-modified habitats for much of the year. Almost all populations are now heavily dependent on agricultural crops when the birds are away from the arctic breeding grounds. We examine the current understanding of the ecology of migration, highlighting the role of hot spots that provide fuelling stations which bridge the gap between the wintering and breeding grounds. Isotopic signatures of eggs indicate nutrients are being flown into the breeding grounds from afar. The susceptibility of geese to disturbance at these stopover sites, many of which are agricultural lands, may lead to reproductive failures. The near-complete loss of natural habitat, even in northern sites, makes the birds captive of agricultural policy. Barnacle Geese Branta leucopsis staging on managed grassland on their spring stopover accumulate more fat but less protein compared to traditional sites, and there is evidence of lower breeding success for individuals feeding on cultivated grass. This population, breeding on Spitsbergen, has been closely followed during a phase of population increase over the past thirty years. We show that although locally on the breeding grounds density-dependent effects have been confirmed (lower reproductive output, enhanced emigration) new colonies are still arising, and there has been no slowing of overall growth of the population. Worldwide, the most spectacular response to agricultural change is that of the Lesser Snow Goose Anser caerulescens cuerulescens. The populations have become so numerous that their spring grubbing activities are having a deleterious impact on arctic wetlands where they breed. It would be erroneous to generalise this example to conclude all long-distance migrating geese should be reduced. Current management polices are insufficiently grounded in basic research on the interaction of geese and their food resources which must include experiments in view of impending climate change. We advocate a vigorous intensification of individual-based research programmes.

Resource-dependent weather effect in the reproduction of the White Stork Ciconia ciconia

Abstract: Weather affects the breeding success of White Stork Ciconia ciconia, but the effect has not been studied in the context of different food resources or habitat quality. The aim of this study was to determine whether the impact of weather conditions on breeding success was dependent on habitat quality The effect of weather on reproduction was analysed in two populations that differed significantly in the availability of suitable feeding habitats. Multiple regression analyses revealed that of the weather variables analysed (average temperature and rainfall in April, May and June), rainfall in May and temperature in June explained a significant part of the variation in numbers of fledged chicks per pair, but only in the population with poorer food resources. The lack of weather influence in the population with richer food resources was tentatively explained by the larger brood sizes. More effective heat conservation in larger broods, and thus lower chick mortality during cold weather, could be the underlying mechanism for the different response to weather in the two populations.

Pre-nesting site use of satellite transmitter tagged Svalbard Pink-footed Geese Anser brachyrhynchus

Abstract: We deployed satellite transmitters (PTTs) on Pink-footed Geese Anser brachyrhynchus to discover pre-nesting sites on Svalbard. 14 adult male were caught in Vest Stadil Fjord, Denmark and fitted with PTTs powered by batteries (n = 11; 30 g) or by solar power (n = 3; 45 g), March 2003 and 2004. All geese staged in the Trondheim Fjord area, mid Norway, for 2-3 weeks before onward migration to VesterÅlen, north Norway, where average arrival and departure dates were 10 and 17 May 2003 and 15 and 19 May 2004. Average staging period in VesterÅlen of satellite tagged geese was 4-6 days. No staging areas were identified between VesterÅlen and Svalbard. Average arrival dates in Svalbard were 22 May 2003 and 21 May 2004. On arrival to Svalbard geese staged in southwestern coastal areas of Spitsbergen (n = 5) and around Isfjord, central Spitsbergen (n = 6), areas which tend to thaw early in spring. Geese staged on average at two staging areas before 1 June during a total staging period of about 8 days. First egg dates in the two years in Sassendalen, central Spitsbergen, were mainly between 26 and 31 May, so tagged geese should have arrived at their breeding areas before 1 June. Therefore, rapid follicular development must be initiated in VesterÅlen, confirmed by observations of oocyte development in birds shot on arrival in Svalbard. A pre-nesting increase in male abdominal profile indices in Svalbard indicates income feeding as a supplement to the capital invested in follicular growth on migration. We here present the first and most comprehensive study on the distribution of pre-nesting sites on Svalbard and staging periods of the geese. Such habitats can have a substantial influence on the reproductive success.

Effects of distance to wintering area on arrival data and breeding performance in great cormorants Phalacrocorax carbo

Abstract: Great Cormorants Phalacrocorax carbo sinensis breeding in the same colony often vary markedly in where they winter and in their date of arrival. The main aim of this study was to explore whether date of arrival, fledgling production and lifetime reproductive success were related to the distance migrated in spring. Based on resightings and dead recoveries of colour-ringed birds we identified the approximate wintering area for 195 breeding males and 179 breeding females. Based on daily searches for colour-ringed individuals in the study colony we found timing of arrival to vary by up to 1.5 months for a given distance to the wintering area. Males and females wintering 300 km from the colony. For breeders wintering 601–2500 km from the colony, date of arrival was only weakly related to distance from the colony, probably because of an earlier onset of spring migration from the most southern wintering areas, allowing these individuals to catch up with birds wintering further north. Mean fledgling production per individual did not decrease with increasing distance to the wintering area. However, lifetime reproductive success of males wintering 301–900 km from the colony was lower than among males wintering closer to or further from the colony. These birds had fewer breeding seasons, suggesting that wintering at intermediate distances was a poor strategy for males. Females that arrived early and were presumed to winter locally had more breeding seasons and thus higher lifetime reproductive success than migrating females. We found that in this population long-distance migrants do not arrive later, do not breed with lower success or less frequently than those wintering at intermediate distances from the colony.

Scaling of migration and the annual cycle of birds

Abstract: In a seasonally fluctuating environment migratory birds face decisions relating to how to schedule their main life-history activities, i.e. breeding, moult and migration. The time required to complete any one of these depends on overall size. In this paper I derive scaling functions about how time required for breeding, moult and migration depends on body mass. The sum of these increases with increasing body mass with a critical mass where the duration of non-overlapping breeding, moult and migration is equal to one year. Beyond this mass one or more of the processes must be modified. Large species may refrain from annual breeding and skip years without breeding. The replacement of one set of feathers may also take more than one year, or in long-distance migrants the timing of moult is shifted from a post-breeding moult before autumn migration to a post-migration moult in the wintering area. Different adaptations for efficient migration are also discussed. Finally, I use a simple graphical model to derive a condition for when overloading fuel at the final stopover site is worthwhile, leading to arrival at the breeding site with surplus energy that may be used as capital for breeding.

Body transformations, condition, and survival in Red Knots Calidris canutus travelling to breed at Alert, Ellesmere Island, Canada

Abstract: This paper reviews the nutrient storage dynamics and body changes of Red Knots Calidris canutus islandica during migration through their final spring stopover area in Iceland and after arrival on the breeding grounds in the northeastern Canadian High Arctic at Alert. In Iceland, Red Knots not only accumulate large stores of fat and protein, but also undergo extensive morphological changes (increases in 'flight machinery' - flight muscles, heart, fat - and decreases in 'baggage' - stomach, intestines, leg muscles) that leave them well adapted for the flight to the breeding grounds. At Alert, early arrivals have substantial stores of fat and protein remaining. Subsequent body changes involve a rapid loss of these stores and a simultaneous rebuilding of various organs (e.g. restoration of digestive apparatus, development of gonads) which transforms them from a state adapted for flight to one that is suitable for breeding. Stable isotope studies show few of the stores, if any, are used for egg production. The stores could also be used as an energy source for early season survival during food shortage or poor weather. Their major purpose, however, may be to fuel the physical changes needed for breeding. The level of stores acquired at the final stopover during migration can affect survival in several ways. (1) Enhanced survival under difficult conditions: birds captured in Iceland and known to have survived a series of particularly severe summers had been in significantly better condition when caught than birds for which there were no subsequent records. (2) Longer average survival: for previously-banded birds captured in Iceland there was a positive relationship between numbers of summers survived and their condition in Iceland. (3) Reduced survival associated with inadequate stores; in North America, many rufa Red Knots passing through the final stopover area in Delaware Bay, USA, were unable to acquire adequate stores in the period 1997-2002 -this led to a dramatic decrease in annual survival rate, which was enough to account for a 50% decrease in the wintering population in Tierra del Fuego. Failure to maintain adequate habitat and food resources required by Red Knots and other shorebirds at their final spring stopover areas will almost surely lead to reduced reproductive success and survival, and consequent population decline.

Speed of spring migration of Tundra Swans Cygnus columbianus in accordance with income or capital breeding strategy

Abstract: Large migratory birds may bring along stores in order to survive adverse conditions and produce a clutch upon arrival (‘capital breeders’) or they may acquire all the necessary resources on the breeding grounds (‘income breeders’). Whether birds are capital- or income-breeders may depend on the distance between the last stopover site and the breeding grounds and the length of the summer season. The degree of capital-breeding may therefore differ among flyway populations of the same species. I used migration speed as a proxy for the degree of capital-breeding, and compared the observed migration speeds of satellite-tracked Tundra Swans Cygnus columbianus from all four main flyway populations with those predicted by an allometric model for 6-kg waterfowl. Average overall spring migration speed of Tundra Swans was 52.2 km/d, close to that predicted under a capital-breeding strategy (i.e. carrying the stores for the whole clutch and allowing for 8 days of starvation). This migration speed was in accordance with the speed at which the ice retreats in spring. However, the energy stores for clutch formation and survival on the breeding grounds may be primarily put on at the last stopover. Tundra Swans (‘Whistling Swans’) in the Nearctic, and especially in the Western Nearctic, make use of the rapid advancement of spring on their last leg and accelerate their migration speed accordingly, and so probably rely on income-breeding. In the Western Palearctic, Tundra Swans (‘Bewick’s Swans’) are faced with a slow advancement of spring on their last track, and they may fare better by building up stores on the last stopover and bring these to the breeding grounds. This may not be an option for swans in the Eastern Palearctic, as they are confronted with a very long last leg. The variation in migration speeds on the last leg suggests a large variation in the degree of capital-breeding among flyway populations of Tundra Swans.

Movements of European stonechats Saxicola torquata according to ringing recoveries

Abstract: Ringing recoveries of European Stonechats Saxicola torquata increased more than tenfold to 1162 since the last in-depth analysis in 1965 This paper presents a new overview over all recoveries and detailed analyses of Stonechats ringed during the breeding season in Britain, Benelux countries, and Germany Stonechats showed stronger migratory tendencies than previously thought Birds of known origin from all parts of Europe were recorded in north African winter quarters Local overwintering was only observed in Britain, France, Spain, and Italy Benelux Stonechats were fully migratory, just as their German conspecifics British Stonechats were partially migrant; according to conservative estimates almost half (421%) of the British Stonechats migrated Instead of segregating into residents and migrants they travelled over a continuous range of distances Some reached north African winter ranges but median routes were shorter than those of Benelux and German Stonechats Surprisingly, natal dispersal and post-fledging movements were longer in British partial migrants than in continental obligate migrants These movements tended to be biased in migration directions Sexes and age classes showed identical migratory behaviour, an unusual observation among individually migrating birds Furthermore, migration of Stonechats did not change consistently over the last decades, counter to predictions In conclusion, European Stonechats are predominantly migratory but partial migration and summer movements seem to be surprisingly plastic

Relationships of songbird occupation with habitat configuration and bird abundance in patchy reed beds

Abstract: Correlations of richness and distribution of passerines were studied in a complex of 40 vegetation patches dominated by Common Reed Phragmites australis (0.05-28.66 ha) in south-eastern Spain. Fourteen morphological, hydrological and vegetative parameters of the reed beds, as well as characteristics of the avian species, were quantified to identify variables related to the occupation of the reed beds by passerines. Variables related to habitat patchiness and structural complexity of emergent vegetation were the best predictors of avian species richness, but their importance changed seasonally. Spatial configuration (size, perimeter and isolation) of the reed beds was the best predictor in winter, and the vegetative complexity was best during the breeding period. The capacity of passerines to occupy habitat patches in space and time was linked to species abundance. Differences in abundance among the various bird species appeared to favour the order of disappearance in the complex when the reed beds lost species richness ('nested' pattern). The results highlight the need for the conservation, restoration, or creation of large heterogeneous and non-isolated reed beds to maintain the greatest number of bird species that depend on these scarce and ecologically valuable habitats.

Modelling phenotypic flexibility : an optimality analysis of gizzard size in Red Knots Calidris canutus

Abstract: Reversible phenotypic changes, such as those observed in nutritional organs of long-distance migrants, increasingly receive the attention of ornithologists. In this paper we review the cost-benefit studies that have been performed on the flexible gizzard of Red Knots Calidris canutus. By varying the hardness of the diet on offer gizzard mass could experimentally be manipulated, which allowed quantification of the energetic costs and benefits as a function of gizzard size. These functions were used to construct an optimality model of gizzard mass for Red Knots on migration and during winter. Two possible currencies were assumed, one in which Knots aim to balance their energy budget on a daily basis (satisficers), and one in which Knots aim to maximise their daily energy budget (net rate maximisers). The model accurately predicted variation in gizzard mass that we observed (1) between years, (2) within years, and (3) between sites. Knots maintained satisficing gizzards during winter and rate-maximising gizzards when fuelling for migration. The model-exercise revealed the importance of digestive constraints and quality of prey in the life of Knots.