Migratory connectivity and population-specific migration routes in a long-distance migratory bird

Knowledge about migratory connectivity, the degree to which individuals from the same breeding site migrate to the same wintering site, is essential to understand processes affecting populations of migrants throughout the annual cycle. Here, we study the migration system of a long-distance migratory bird, the Montagu''s harrier Circus pygargus, by tracking individuals from different breeding populations throughout northern Europe. We identified three main migration routes towards wintering areas in sub-Saharan Africa. Wintering areas and migration routes of different breeding populations overlapped, a pattern best described by ‘weak (diffuse) connectivity’. Migratory performance, i.e. timing, duration, distance and speed of migration, was surprisingly similar for the three routes despite differences in habitat characteristics. This study provides, to our knowledge, a first comprehensive overview of the migration system of a Palaearctic-African long-distance migrant. We emphasize the importance of spatial scale (e.g. distances between breeding populations) in defining patterns of connectivity and suggest that knowledge about fundamental aspects determining distribution patterns, such as the among-individual variation in mean migration directions, is required to ultimately understand migratory connectivity. Furthermore, we stress that for conservation purposes it is pivotal to consider wintering areas as well as migration routes and in particular stopover sites.     

Timing of autumn bird migration under climate change: advances in long-distance migrants,delays in short-distance migrants

As a response to increasing spring temperature in temperate regions in recent years, populations of many plant and animal species, including migratory birds, have advanced the seasonal start of their reproduction or growth. However, the effects of climate changes on subsequent events of the annual cycle remain poorly understood. We investigated long-term changes in the timing of autumn migration in birds, a key event in the annual cycle limiting the reproductive period. Using data spanning a 42-year period, we analysed long-term changes in the passage of 65 species of migratory birds through Western Europe. The autumn passage of migrants wintering south of the Sahara has advanced in recent years, presumably as a result of selection pressure to cross the Sahel before its seasonal dry period. In contrast, migrants wintering north of the Sahara have delayed autumn passage. In addition, species with a variable rather than a fixed number of broods per year have delayed passage, possibly because they are free to attempt more broods. Recent climate changes seem to have a simple unidirectional effect on the seasonal onset of reproduction, but complex and opposing effects on the timing of subsequent events in the annual cycle, depending on the ecology and life history of a species. This complicates predictions of overall effects of global warming on avian communities.     

Detours in bird migration

Bird migration routes often follow detours where passages across ecological barriers are reduced in extent. This occurs in spite of the fact that long barrier crossings are within the birds' potential flight range capacity. Long-distance flights are associated with extra energy costs for transport of the heavy fuel loads required. This paper explores how important the fuel transport costs, estimated on the basis of flight mechanics, may be to explain detours for birds migrating by flapping flight. Maximum detours in relation to expanse of the barrier are predicted for cases where birds travel along the detour by numerous short flights and small fuel reserves, divide the detour into a limited number of flight steps, and where a reduced barrier passage is included in the detour. The principles for determining the optimum route, often involving a shortcut across part of the barrier, are derived. Furthermore, the effects of differences in fuel deposition rates and in transport costs for the profitability of detours are briefly considered. An evaluation of a number of observed and potential detours in relation to the general predictions of maximum detours, indicates that reduction of fuel transport costs may well be a factor of widespread importance for the evolution of detours in bird migration at wide ecological barriers.     

It is time to move: linking flight and foraging behaviour in a diving bird

Although the adaptive value of flight may seem obvious, it is the most difficult behaviour of birds to monitor. Here, we describe a technique to quantify the frequency and the duration of flights over several months by implanting a data logger that records heart rate (fH), hydrostatic pressure (diving depth) and the body angle of a large sea duck species, the common eider (Somateria mollissima). According to the mean fH recorded during flight and the parameters recorded to identify the fH flight signature, we were able to identify all flights performed by 13 individuals during eight months. We cumulated local flight time (outside migrations) and found that activity occurs primarily during dawn and morning and that flying activities are strongly related to diving activities (Pearson's r=0.88, permutation test p<0.001). This relationship was interpreted as a consequence of living in a dynamic environment where sea currents move the ducks away from the food patches. We believe that the technique described here will open new avenues of investigation in the adaptive value of flight.     

Biphasal long-distance migration in green turtles

Sea turtles have recently been shown to have the sensory ability to use magnetic information for guidance in the open ocean, although the importance of different potential navigational cues remains unknown. Between May and August 2001, we satellite-tracked green turtles, Cheloniamydas, during their >2000-km postnesting migration from Ascension Island to Brazil, following five individuals both during their transoceanic crossing and while on the Brazilian coast. None of the turtles travelled directly to its final destination but, instead, there were extended (up to 792 km) movements along the coast after the oceanic crossings. The extent of movement along the coast was unrelated to the oceanic crossing route. For example, individuals whose final destination was in the north of Brazil did not follow a more northerly oceanic crossing than those with a more southerly final destination. These observations show that green turtles returning from Ascension Island do not swim directly to their final destination, but instead conduct migration in two distinct phases: a fairly direct open ocean crossing, following which they turn north or south along the coast to reach their final destination. This long-distance migration may therefore be conducted without turtles needing to resort to sophisticated navigational skills. These previously unidentified long coastal movements may heighten the risk of turtles being captured by fishermen. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

The molecular and metabolic essentials for long-distance flight in insects

Summary The mechanism of long-distance flight in insects was investigated by comparing lipid mobilization and transport in gregarious- and solitary-phase locusts and in the American cockroach. Unlike the gregarious-phase locust, both the American cockroach and the solitary locust were unable to form low-density lipophorin (loaded with increased amount of diacylglycerol) even when injected with adipokinetic hormone (AKH). The cockroach fat body responded to AKH. However, not only does the American cockroach lack apolipophorin-III (apoLp-III) in the haemolymph, but the fat body contains only an extremely small amount of diacylglycerol and a relatively large triacylglycerol pool. By contrast, the solitary-phase locust had apoLp-III in the haemolymph, but the fat body was only one-seventh or less in weight of the fat body of the gregarious locust. Furthermore, the fat body of the solitary locust contains a very small amount of triacylglycerol (1/20 or less of that of the gregarious locust) with only a trace of diacylglycerol. It was concluded that in the American cockroach and the solitary locust, the stores of fuel in the fat body are insufficient to maintain prolonged flight.Abbreviations AKII adipokinetic hormone - apoLp-III apolipophorin III - HDLp high-density lipophorin - LDLp low-density lipophorin - LTP lipid transfer particle - MW molecular weight - SDS-PAGE sodium dodecyl sulphate-polyacrylamide gel electrophoresis     

Metabolic profile of long-distance migratory flight and stopover in a shorebird

Migrating birds often complete long non-stop flights during which body energy stores exclusively support energetic demands. The metabolic correlates of such long-distance travel in free-living migrants are as yet poorly studied. Bar-tailed godwits, Limosa lapponica taymyrensis, undertake a 4500 km flight to their single spring stopover site and thus provide an excellent model in which to determine the energy fuels associated with endurance travel. To this end, we evaluated plasma concentrations of six key metabolites in arriving godwits caught immediately upon landing near their stopover site. Initial metabolite levels were compared with levels after 5 h of inactive rest to determine how flight per se affects energy metabolism. Birds refuelling on the stopover site were also examined. Arriving godwits displayed elevated plasma free fatty acids, glycerol and butyrate, confirming the importance of lipid fuel in the support of extended migratory activity. Further-more, elevated plasma triglycerides in these birds suggest that fatty acid provisioning is facilitated through hepatic synthesis and release of neutral lipids, as previously hypothesized for small migrants with high mass-specific metabolic rates. Finally, elevations in plasma uric acid suggest that protein breakdown contributes to the support of long-distance movement, to possibly maintain citric acid cycle intermediates, gluconeogenesis and/or water balance.     

The geometry of the Pareto front in biological phenotype space

When organisms perform a single task, selection leads to phenotypes that maximize performance at that task. When organisms need to perform multiple tasks, a trade‐off arises because no phenotype can optimize all tasks. Recent work addressed this question, and assumed that the performance at each task decays with distance in trait space from the best phenotype at that task. Under this assumption, the best‐fitness solutions (termed the Pareto front) lie on simple low‐dimensional shapes in trait space: line segments, triangles and other polygons. The vertices of these polygons are specialists at a single task. Here, we generalize this finding, by considering performance functions of general form, not necessarily functions that decay monotonically with distance from their peak. We find that, except for performance functions with highly eccentric contours, simple shapes in phenotype space are still found, but with mildly curving edges instead of straight ones. In a wide range of systems, complex data on multiple quantitative traits, which might be expected to fill a high‐dimensional phenotype space, is predicted instead to collapse onto low‐dimensional shapes; phenotypes near the vertices of these shapes are predicted to be specialists, and can thus suggest which tasks may be at play.     

Power and metabolic scope of bird flight: a phylogenetic analysis of biomechanical predictions

For flying animals aerodynamic theory predicts that mechanical power required to fly scales as P proportional, variant m (7/6) in a series of isometric birds, and that the flight metabolic scope (P/BMR; BMR is basal metabolic rate) scales as P (scope) proportional, variant m (5/12). I tested these predictions by using phylogenetic independent contrasts from a set of 20 bird species, where flight metabolic rate was measured during laboratory conditions (mainly in wind tunnels). The body mass scaling exponent for P was 0.90, significantly lower than the predicted 7/6. This is partially due to the fact that real birds show an allometric scaling of wing span, which reduces flight cost. P (scope) was estimated using direct measurements of BMR in combination with allometric equations. The body mass scaling of P (scope) ranged between 0.31 and 0.51 for three data sets, respectively, and none differed significantly from the prediction of 5/12. Body mass scaling exponents of P (scope) differed significantly from 0 in all cases, and so P (scope) showed a positive body mass scaling in birds in accordance with the prediction.     

Density-dependent immigration promotes population stability in a long-distance migratory bird

The spatial structure of populations determines the relative importance of reproduction, survival and movement on population dynamics. However, the mechanisms by which local individuals and immigrants interact and the subsequent effects of immigrants on productivity are poorly known. We developed an integrated population model (IPM) to study the extent and consequences of immigration on the dynamics of a neotropical migrant (American redstart, Setophaga ruticilla) over an 11-year period in Ontario, Canada. New immigrants represented the majority of the study population each year with higher immigration rates for males than females and for first-year breeders than breeders in their second year or older. Immigration was negatively density dependent, with immigrants replacing previously established breeders in a compensatory manner following their death or emigration. Because of the tradeoff between immigration and apparent survival, neither had a strong influence on population growth and reproductive output was most strongly correlated with a change in abundance between years. However, if immigration ceased, the study population would become locally extinct within 7 years and thus immigrants were essential for local population persistence. We found no evidence for reduced breeding success when immigrants represented a higher proportion of the study population. Our research highlights the importance of movement in the stability of open populations and the strong correlation between the fates of local breeders and the number of immigrants entering the population. We recommend the use of IPMs to address the spatial scale over which immigration occurs and how different scales influence its contribution to population dynamics.     

The economics of bird migration

Piersma, T. 2000. The economics of bird migration. Ostrich 71(1): 362.

Through their migrations birds spin a worldwide web of migratory routes. Even at the level of individuals and populations, the migrations can cover a large part of the globe. Many factors are involved in the evolution and maintenance of all these migration systems: the contingencies of earth history, the sensory and metabolic evolutionary potential of flying organisms, the distribution of predators and parasites, and energetic considerations. In this presentation I aim to briefly outline the use of energetics in studies on the maintenance of today's flyways. My overview will focus on the shorebird species seasonally migrating between wintering grounds in coastal African and the breeding grounds in the Canadian, Greenlandic, European and Siberian Arctic.

Every individual animal has to balance its energy budget but depending on size, it can balance the discrepancies between energy expenditure and energy intake through the use or storage of nutrients at various time scales. Energy thus provides a common currency to relate ecological phenomena that are separated in space and time. I will describe methods to estimate energy expenditure, energy intake and the use of energy stores, and how these estimates can be translated as an annual energy budget of a coastal shorebird species. This will then be used to evaluate the repercussions of wintering at tropical latitudes and at temperate latitudes, and how such knowledge might help us to understand the evolution of a migration system. Population-specific energy budgets provide only one of the possible uses of energetics approach. Studies at the individual level, at which it is rarely possible to quantify such budgets completely, nevertheless benefit from energetic considerations when the functional significance of variations in migratory timing and seasonal body mass and plumage changes are the focus of attention.     

Bird flight and optimal migration

The development of the mechanical and aerodynamical theory of bird flight has greatly stimulated research at widely different levels in the field of bird movement. Recent work has shown that the drag of bird bodies is less than was previously assumed. Furthermore, the structure and circulation of wingtip vortices in the wake of flying birds have been revealed, with implications for estimating flight performance on the basis of vortex theory. Predictions about optimal speed and flight behaviour have been successfully tested by field studies using optical and radar registration. Flight theory also allows predictions about optimal fuel deposition rules for migrating birds. Research about bird flight, with the dynamic interplay between theoretical development and empirical work in biophysics, physiology and ecology, represents a fine example of a highly successful use of the optimality approach in biology.     

利用HYSPLIT模型分析麦蚜远距离迁飞前向轨迹

为了监测麦蚜远距离迁飞,本文利用HYSPLIT-4气流动力模型模拟空中不同高度麦蚜24h内的迁飞轨迹,分析其扩散方向和距离。结果表明:氦气球携带的10-100m各高度设置的粘板均捕捉到了麦蚜,各高度迁飞轨迹几乎一致,迁飞距离没有显著差异。100m高空起始迁飞的麦蚜,24h内最远模拟迁飞至达山西省太原市,最大直线迁飞距离494.43km。4月21-28日,豫西洛宁捕获点的麦蚜其中有6d由南向北迁飞。     

Individuality in bird migration: routes and timing

The exploration of animal migration has entered a new era with individual-based tracking during multiple years. Here, we investigated repeated migratory journeys of a long-distance migrating bird, the marsh harrier Circus aeruginosus, in order to analyse the variation within and between individuals with respect to routes and timing. We found that there was a stronger individual repeatability in time than in space. Thus, the annual timing of migration varied much less between repeated journeys of the same individual than between different individuals, while there was considerable variation in the routes of the same individual on repeated journeys. The overall contrast in repeatability between time and space was unexpected and may be owing to strong endogenous control of timing, while short-term variation in environmental conditions (weather and habitat) might promote route flexibility. The individual variation in migration routes indicates that the birds navigate mainly by other means than detailed route recapitulation based on landmark recognition.