Lukas Jenni

Bio: Lukas Jenni is an academic researcher from Swiss Ornithological Institute. The author has contributed to research in topics: Population & Corticosterone. The author has an hindex of 44, co-authored 86 publications receiving 5740 citations.

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

Abstract: 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.

Plasma Metabolite Levels Predict Individual Body-Mass Changes in a Small Long-Distance Migrant, the Garden Warbler

Abstract: -Change in body mass is an important measurement in many studies addressing changes in energy stores or condition. Usually, change in body mass is measured in birds caught twice, but this has a number of drawbacks (e.g. low number of retraps, retraps not representative of all first captures, adverse effects of first capture on body-mass development). Therefore, we investigated whether plasma metabolites correlate with body-mass change, and which metabolites could be used to predict body-mass change in birds caught once. In an experiment, 20 Garden Warblers (Sylvia borin) were given different amounts of food to induce stable, increasing, and decreasing body masses. Most of the eight plasma metabolites we examined were significantly correlated with the change in body mass between early morning and midday, the time of blood sampling, but not with body mass or various measures of activity. Metabolites that are known to characterize resorption were elevated in birds gaining body mass and metabolites characteristic of fasting were elevated in birds losing body mass. Triglycerides and ,B-hydroxy-butyrate together explained 61% of the variation in body-mass change (triglycerides alone 44% and ,3-hydroxy-butyrate alone 51%). These metabolites may be used to predict body-mass change in birds caught once, provided that the reliability and sensitivity of this method are checked in field tests. Received 27 September 1993, accepted 30 January 1994. BIRDS MAY FACE DEFICITS in their energy balance during the nonactive period of the day, during periods of several days, or even over a series of weeks. They usually build up energy stores in anticipation of such periods and as an adaptive compromise to different selective pressures (e.g. Lima 1986, Lehikoinen 1987, Moreno 1989, Ekman and Hake 1990, Rogers and Smith 1993). This results in fluctuating energy stores between foraging and nonforaging periods (usually day and night) superimposed on longer periods of net energy storage and net energy expenditure (King 1972). For instance, cold and short winter days, bad weather, incubation, feeding young, and migration may all be associated with decreasing energy stores and preceded by energy storage. Body mass is a crude but widely used estimate of energy stores because it is easy and harmless to measure. If corrected for size, body mass may be used as an indication of condition (e.g. Blem 1990). Changes in body mass may give a fairly accurate picture of the fluctuations in energy stores (e.g. Rogers and Rogers 1990). The measurement of changes in body mass of free-living birds is important in a variety of contexts. For instance, it may allow the assessment of the effects of food availability on energy storage in different habitats, under different weather conditions, and under different degrees of competition or predation (e.g. Bibby et al. 1976, Bibby and Green 1983, Buchanan et al. 1985, Lima 1985, Lindstrom 1990, Moore and Yong 1991). Body-mass changes may indicate periods of constraints and periods of adaptive mass variations during the annual cycle (Moreno 1989). Evaluation of body-mass changes may allow study of the pattern and environmental influences of energy storage during stopovers by migrants (e.g. Bibby et al. 1976, Mehlum 1983a, b, Biebach 1985, Biebach et al. 1986, Alerstam and Lindstrom 1990). In free-living birds, changes in body mass generally are measured in birds caught at least twice, usually at the same place. This, however, has a number of drawbacks: (1) changes in body mass are measured only in the subsample of retraps and this may reduce the sample size drastically, especially when trap shyness is a factor; (2) a certain group of birds may not be recaught and, thus, the sample of retraps may not be representative (e.g. Bibby et al. 1976, Biebach et al. 1986, Veiga 1986, Winker et al. 1992); and (3) first capture may have an adverse

Ski tourism affects habitat use and evokes a physiological stress response in capercaillie Tetrao urogallus: a new methodological approach

Abstract: 1. Human outdoor recreational activities are increasing and have a significant impact on wildlife. There are few methods suitable for investigating the response of rare and endangered species to human recreational activities, although the impact can be assessed at various scales by measuring both physiological and behavioural responses to disturbance. 2. Capercaillie Tetrao urogallus are suffering strong population declines throughout central Europe. We examined the effects of ski tourism on capercaillie habitat use and adrenocortical activity, measured non-invasively in droppings. 3. During three winters, 2003–06, we radio-tracked 13 capercaillie. In the southern Black Forest in Germany, we sampled 396 droppings of these and additional individuals before and after the start of the ski season. We tested whether the intensity of human winter recreational activities affected home range location and habitat use, and we identified those factors influencing the concentration of corticosterone metabolites (CM) in droppings. 4. Capercaillie used habitats subject to ski tourism. Although the latter did not affect home range location, capercaillie preferred undisturbed forests within their home ranges and avoided areas with high recreation intensity in the ski season. Faecal CM levels of individuals in areas with low recreation intensity were significantly lower than those in areas with moderate or high recreation intensity during the entire study period. 5. We conclude that ski tourism affects both habitat use and endocrine status in capercaillie, with potential negative consequences on body condition and overall fitness. 6. Synthesis and applications. This study demonstrates the relevance of studying wildlife responses at various temporal and spatial scales, and the value of using multiple methods applied to the same individuals to monitor the impact of human recreational activities on a free-ranging species. In order to protect capercaillie populations, we recommend that managers keep forests inhabited by capercaillie free from tourism infrastructure and retain undisturbed forest patches within skiing areas.

Migrating birds stop over longer than usually thought: an improved capture–recapture analysis

Abstract: Migrating animals often divide their journey into alternating phases of migration bouts and stopping over. For investigating many questions of migration ecology it is crucial (1) to estimate the duration of stopover phases, and (2) to test whether animals of different groups differ in their stopover behavior. Using recent advances in capture–recapture statistics, we show how total stopover duration can be estimated from capture–recapture data. The probabilities of immigration are estimated and modeled by recruitment analysis and are converted into the time the animals spent at the stopover place before capture; the probabilities of emigration are estimated and modeled by survival analysis and are converted into the time the animals spent at the stopover place after capture. The sum of the two parts is the total stopover duration. Tests for differences between groups can be addressed by an appropriate model selection procedure. Two examples of migrating passerine birds at a stopover site in Switzerland illustrate this method. Mean total stopover duration was 12.3 d for Reed Warblers and 7.1 d for Reed Buntings. This was considerably higher than values obtained by the minimum stopover duration estimation (6.0 and 4.4 d, respectively). Because of the fundamental weaknesses of the minimum stopover duration estimation, which has been widely used in migration ecology, many findings obtained by this method need to be reconsidered.

Fuel deposition of three passerine bird species along the migration route.

Abstract: The rate at which migrant birds replenish their energy stores at intermittent stopovers largely determines overall migration speed, the manner in which migration proceeds and success of migration. In this study, data on the fuel deposition rate (FDR) of three long-distance migrants from 17 ringing sites along their autumn migration route were used to examine: (1) effects of endogenous factors on FDR, and (2) how relationships between exogenous factors and FDR affect the organisation of migration. We developed a model to estimate FDR from retrapped birds which takes into account time of day and various other factors which might influence FDR. The two endogenous factors, moult and current energy stores, generally reduced FDR. This may result in lower departure energy loads and more stopovers than expected from optimal migration theory. Differences between species with respect to seasonal, year-to-year and geographical patterns of FDR could be related to differences in availability and predictability of food resources, and help to explain differences in the organisation of migration. A low FDR in northern and central Europe could be related to low, but predictable, food resources and an early departure during moult of the reed warbler (Acrocephalus scirpaceus); FDRs varying between years were related to large spatial and year-to-year variation in the density of the main prey of the sedge warbler (Acrocephalus schoenobaenus); and a high FDR in the garden warbler (Sylvia borin) was related to abundant food resources, due to a switch from a purely invertebrate diet to a mixed diet including fruits which are abundant over large areas of Europe and north Africa. This study demonstrated that the organisation of migration is the outcome of a complex interplay of the seasonal timing of moult, food availability and predictability and a seasonal switch in diet, and can be modified by individual birds in response to a limited amount of time in which to migrate.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Abstract: The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Citizen Science as an Ecological Research Tool: Challenges and Benefits

Abstract: Citizen science, the involvement of volunteers in research, has increased the scale of ecological field studies with continent-wide, centralized monitoring efforts and, more rarely, tapping of volunteers to conduct large, coordinated, field experiments. The unique benefit for the field of ecology lies in understanding processes occurring at broad geographic scales and on private lands, which are impossible to sample extensively with traditional field research models. Citizen science produces large, longitudinal data sets, whose potential for error and bias is poorly understood. Because it does not usually aim to uncover mechanisms underlying ecological patterns, citizen science is best viewed as complementary to more localized, hypothesis-driven research. In the process of addressing the impacts of current, global “experiments” altering habitat and climate, large-scale citizen science has led to new, quantitative approaches to emerging questions about the distribution and abundance of organisms across spa...

Shifts in phenology due to global climate change: the need for a yardstick

Abstract: Climate change has led to shifts in phenology in many species distributed widely across taxonomic groups. It is, however, unclear how we should interpret these shifts without some sort of a yardstick: a measure that will reflect how much a species should be shifting to match the change in its environment caused by climate change. Here, we assume that the shift in the phenology of a species’ food abundance is, by a first approximation, an appropriate yardstick. We review the few examples that are available, ranging from birds to marine plankton. In almost all of these examples, the phenology of the focal species shifts either too little (five out of 11) or too much (three out of 11) compared to the yardstick. Thus, many species are becoming mistimed due to climate change. We urge researchers with long-term datasets on phenology to link their data with those that may serve as a yardstick, because documentation of the incidence of climate changeinduced mistiming is crucial in assessing the impact of global climate change on the natural world.

Long-distance migration: evolution and determinants

Abstract: Long distance migration has evolved in many organisms moving through different media and using various modes of locomotion and transport. Migration continues to evolve or become suppressed as shown by ongoing dynamic and rapid changes of migration patterns. This great evolutionary flexibility may seem surprising for such a complex attribute as migration. Even if migration in most cases has evolved basically as a strategy to maximise fitness in a seasonal environment, its occurrence and extent depend on a multitude of factors. We give a brief overview of different factors (e.g. physical, geographical, historical, ecological) likely to facilitate and/or constrain the evolution of long distance migration and discuss how they are likely to affect migration. The basic driving forces for migration are ecological and biogeographic factors like seasonality, spatiotemporal distributions of resources, habitats, predation and competition. The benefit of increased resource availability will be balanced by costs associated with the migratory process in terms of time (incl. losses of prior occupancy advantages), energy and mortality (incl. increased exposure to parasites). Furthermore, migration requires genetic instructions (allowing substantial room for learning in some of the traits) about timing, duration and distance of migration as well as about behavioural and physiological adaptations (fuelling, organ flexibility, locomotion, use of environmental transport etc) and control of orientation and navigation. To what degree these costs and requirements put constraints on migration often depends on body size according to different scaling relationships. From this expos it is clear that research on migration warrants a multitude of techniques and approaches for a complete as possible understanding of a very complex evolutionary syndrome. In addition, we also present examples of migratory distances in a variety of taxons. In recent years new techniques, especially satellite radio telemetry, provide new information of unprecedented accuracy about journeys of individual animals, allowing re-evaluation of migration, locomotion and navigation theories. (Less)