Wolfgang Fiedler

Life-history variation predicts the effects of demographic stochasticity on avian population dynamics

Comparative analyses of avian population fluctuations have shown large interspecific differences in population variability that have been difficult to relate to variation in general ecological characteristics. Here we show that interspecific variation in demographic stochasticity, caused by random variation among individuals in their fitness contributions, can be predicted from a knowledge of the species’ position along a “slow‐fast” gradient of life‐history variation, ranging from high reproductive species with short life expectancy at one end to species that often produce a single offspring but survive well at the other end of the continuum. The demographic stochasticity decreased with adult survival rate, age at maturity, and generation time or the position of the species toward the slow end of the slow‐fast life‐history gradient. This relationship between life‐history characteristics and demographic stochasticity was related to interspecific differences in the variation among females in recruitment as well as to differences in the individual variation in survival. Because reproductive decisions in birds are often subject to strong natural selection, our results provide strong evidence for adaptive modifications of reproductive investment through life‐history evolution of the influence of stochastic variation on avian population dynamics.

Seed-dispersal distributions by trumpeter hornbills in fragmented landscapes

Frugivorous birds provide important ecosystem services by transporting seeds of fleshy fruited plants. It has been assumed that seed-dispersal kernels generated by these animals are generally leptokurtic, resulting in little dispersal among habitat fragments. However, little is known about the seed-dispersal distribution generated by large frugivorous birds in fragmented landscapes. We investigated movement and seed-dispersal patterns of trumpeter hornbills (Bycanistes bucinator) in a fragmented landscape in South Africa. Novel GPS loggers provide high-quality location data without bias against recording long-distance movements. We found a very weakly bimodal seed-dispersal distribution with potential dispersal distances up to 14.5 km. Within forest, the seed-dispersal distribution was unimodal with an expected dispersal distance of 86 m. In the fragmented agricultural landscape, the distribution was strongly bimodal with peaks at 18 and 512 m. Our results demonstrate that seed-dispersal distributions differed when birds moved in different habitat types. Seed-dispersal distances in fragmented landscapes show that transport among habitat patches is more frequent than previously assumed, allowing plants to disperse among habitat patches and to track the changing climatic conditions.

Epidemiological and ornithological aspects of outbreaks of highly pathogenic avian influenza virus H5N1 of Asian lineage in wild birds in Germany, 2006 and 2007.

In Germany, two distinct episodes of outbreaks of highly pathogenic avian influenza virus of subtype H5N1 (HPAIV H5N1) in wild birds occurred at the beginning of 2006, and in summer 2007. High local densities of wild bird populations apparently sparked clinically detectable outbreaks. However, these remained restricted in (i) number of birds, (ii) species found to be affected, (iii) time, and (iv) location despite the presence of several hundred thousands of susceptible wild birds and further stressors (food shortage, harsh weather conditions and moulting). Northern and southern subpopulations of several migratory anseriform species can be distinguished with respect to their preference for wintering grounds in Germany. This corroborates viral genetic data by Starick et al. (2008) demonstrating the introduction of two geographically restricted virus subpopulations of Qinghai-like lineage (cluster 2.2.A and 2.2.B) into northern and southern Germany, respectively, in 2006. The incursion of virus emerging in 2007, found to be distinct from the clusters detected in 2006 (Starick et al., 2008), may have been associated with moulting movements. Intensive past-outbreak investigations with negative results of live and dead wild birds and of terrestrial scavengers excluded continued circulation of virus on a larger scale. However, persistence of virus in small pockets of local wild bird populations could not be ruled out resiliently. 1.5% of investigated sera originating from cats sampled at the epicentres of the Ruegen 2006-outbreak contained H5-antibodies. Passive monitoring was found to be highly superior to live bird surveillance when aiming at the detection of HPAIV H5N1 in wild birds (P < 0.0001).

Climate variation and regional gradients in population dynamics of two hole-nesting passerines

Latitudinal gradients in population dynamics can arise through regional variation in the deterministic components of the population dynamics and the stochastic factors. Here, we demonstrate an increase with latitude in the contribution of a large-scale climate pattern, the North Atlantic Oscillation (NAO), to the fluctuations in size of populations of two European hole-nesting passerine species. However, this influence of climate induced different latitudinal gradients in the population dynamics of the two species. In the great tit the proportion of the variability in the population fluctuations explained by the NAO increased with latitude, showing a larger impact of climate on the population fluctuations of this species at higher latitudes. In contrast, no latitudinal gradient was found in the relative contribution of climate to the variability of the pied flycatcher populations because the total environmental stochasticity increased with latitude. This shows that the population ecological consequences of an expected climate change will depend on how climate affects the environmental stochasticity in the population process. In both species, the effects will be larger in those parts of Europe where large changes in climate are expected.

25-year study of the population development of central European songbirds: A general decline most evident in long-distance migrants

During the past century a decline hasbeen noted in European bird popula-tions, both in large species [1] andpossibly also in songbirds [2]. Todaythe “Red List” (of endangered spe-cies) includes about 50% of the avi-fauna in most Central Europeancountries; about 30% of species aredeclining to an extent that threatenstheir continued existence in CentralEurope. These include songbirds,mainly open-country species that areeasy to monitor. Trends in the num-bers of many unobtrusive songbirdspecies, however, have remainedlargely unclear [3]. To assess theirpopulation changes our institute be-gan a census program in 1972 with thehelp of hundreds of amateur ornitho-logists [4]. A trapping station in thisproject in southern Germany has pro-vided data on 35 species over 25 years– the first dataset based on strictlystandardized methods over such along period. During this entire periodthe number of trapped birds has fall-en slowly but continuously, by an av-erage of about 1% per year. The de-crease is greatest for long-distancemigrants, and it heralds profoundchanges in the Central European avi-fauna.Populations of large birds such as ea-gles and storks can be determined ac-curately, and most of the Europeanbreeding pairs are monitored. Forspecies that are more common or areharder to observe, such as crows andowls, only rough estimates are possi-ble [3]. Serious problems are encoun-tered in songbirds. Abundant, widelydistributed, and unobtrusive speciescannot be counted completely or di-rectly; regional estimates must bebased on indirect procedures such asrecording territorial song. Such esti-mates are often biased by varying,nonquantifiable “observer quality”[5]. Therefore only a few countrieshave established sufficiently reliableprograms for monitoring songbirdsduring the breeding period [6, 7].In 1968 we began testing standardizedtrapping procedures for monitoringsongbird populations in order to re-duce differences among observers bya more objective method. The resultswere positive [8], and in 1972 wetherefore initiated the “Mettnau-Reit-Illmitz” program (based onthree stations, Mettnau in southernGermany, Reit in northern Germany,and Illmitz in Austria. This programwas later extended, and temporarilygrew into an ESF network encom-passing Europe and Africa [9]). TheMettnau station has operated sincethe outset, and we report here on theresults of a full quarter of a century ofsongbird population monitoring.The samples are obtained by trappingpassage migrants during the autumnmigration while staging at rest sites.A suitable study area must (a) becharacterized by largely unchangingvegetation, (b) include different habi-tats so that birds with different eco-logical requirements can rest there,and (c) be a protected area of guaran-teed long-term existence. The Mett-nau peninsula, with a 50-year-old birdsanctuary, is ideal for the purpose[10]. The 35 songbird species selectedfor monitoring include regularly stag-ing long-, intermediate-, and short-distance migrants (Table 1).The birds are trapped in nylon netsnormally used to catch birds for ring-ing; 2 m high and 7 m long, they areset up between wooden bars on poles.A wall is formed by 52 nets extendingthrough 8 different habitats (from abrush zone through forested and wetregions). The annual trapping periodis June 30–November 6 and includesthe entire autumn migratory periodof songbirds in Central Europe. Thenets are checked hourly from dawnuntil soon after dusk; trapped birdsare ringed (to prevent double count-ing), subjected to biometric tests andthen released. The monitoring condi-tions (annual setting up of the nets,collecting the birds, data collection,etc.) are standardized as far as possi-ble [10]. Most of the investigatedbirds come from Central Europe, al-though some have traveled fromnorthern, eastern, and western Eu-rope, and a small proportion are localbreeding birds. These origins areknown from recoveries of ringed indi-viduals [11] and from biometric dataon population differentiation [10].Test studies have confirmed thatstandardized trapping procedures ef-fectively give reliable estimates ofsongbird populations. Safriel andLavee (1991) showed that the numberof palaearctic songbird migrants trap-ped in Sinai is correlated positivelywith estimates of their European pre-migratory population sizes [12]. Dunnet al. (1997) demonstrated that trendsin the annual capture indices of song-birds trapped during autumn migra-tion in Michigan are correlated posi-tively with trends in breeding birdsurvey data from their breedinggrounds and conclude that “intensivestandardized netting can be a usefulpopulation monitoring tool” [13]. Wehave consistently found that trends intrapping data reliably reflect thosefrom other sources such as single-spe-cies population studies and country-wide population estimates for RedLists, etc. [4]. Thus data from 147,661individuals that were caught at Mett-nau between 1972 and 1996 reflectthe population development of 35Central European songbird species,as follows.

All across Africa: highly individual migration routes of Eleonora's falcon.

Eleonoras falcon (Falco eleonorae) is a rare raptor species that delays its breeding period until late summer to feed its young with passerines at the peak of autumn migration. Since the 1950s, this slender winged falcon has been believed to migrate along a historical route via the Red Sea to its main wintering area in Madagascar. In our study, we used satellite telemetry to investigate the real migration route of Eleonoras falcons and found that the species displayed a highly individual migration pattern. Furthermore, juvenile falcons migrated via West Africa to Madagascar and two juveniles could be tracked during spring migration and to their summering areas in East and West Africa. As juveniles migrated independently of adults, we discuss inherited navigation strategies forming part of a complex navigation system. We propose the idea of an orientation mechanism that naive falcons could apply during their long-distance migration towards their faraway wintering area located in the open ocean.

Recent changes in migratory behaviour of birds: A compilation of field observations and ringing data

Although large parts of bird migration behaviour, such as timing, duration and direction of migration, are controlled on a genetic basis, countless recent observations give evidence for a high degree of flexibility in migratory behaviour (Berthold 2000). This chapter aims to survey the patterns of various recent developments and their possible causes.

The Epidemiology of H5N1 Avian Influenza in Wild Birds: Why We Need Better Ecological Data

ABSTRACT In 2005 and 2006, highly pathogenic avian influenza H5N1 infected wild birds or poultry in at least 55 countries in Asia, Europe, and Africa. Scientists still have limited understanding of how these wild birds were infected and of how the virus behaves in a field setting. Better ecological and ornithological data are essential to resolve these uncertainties. At present, information on species identity, location and habitat, and sampling and capture methodology, as well as details of the affected bird populations, are inadequate or lacking for most incidents of H5N1 in wild birds. Greater involvement by ornithologists and ecologists, who have extensive experience in conducting field research on wild animals, is vital to improve our ability to predict outbreaks and reduce the environmental and socioeconomic impacts of H5N1 avian influenza.

Global warming and Bergmann’s rule: do central European passerines adjust their body size to rising temperatures?

Recent climate change has caused diverse ecological responses in plants and animals. However, relatively little is known about homeothermic animals’ ability to adapt to changing temperature regimes through changes in body size, in accordance with Bergmann’s rule. We used fluctuations in mean annual temperatures in south-west Germany since 1972 in order to look for direct links between temperature and two aspects of body size: body mass and flight feather length. Data from regionally born juveniles of 12 passerine bird species were analysed. Body mass and feather length varied significantly among years in eight and nine species, respectively. Typically the inter-annual changes in morphology were complexly non-linear, as was inter-annual variation in temperature. For six (body mass) and seven species (feather length), these inter-annual fluctuations were significantly correlated with temperature fluctuations. However, negative correlations consistent with Bergmann’s rule were only found for five species, either for body mass or feather length. In several of the species for which body mass and feather length was significantly associated with temperature, morphological responses were better predicted by temperature data that were smoothed across multiple years than by the actual mean breeding season temperatures of the year of birth. This was found in five species for body mass and three species for feather length. These results suggest that changes in body size may not merely be the result of phenotypic plasticity but may hint at genetically based microevolutionary adaptations.

Using Large-Scale Data from Ringed Birds for the Investigation of Effects of Climate Change on Migrating Birds: Pitfalls and Prospects

Publisher Summary Ringing recovery datasets at ringing centres cover large areas and long time-spans, and, therefore, they are interesting for investigating long-term changes in bird migration. This chapter analyses selected data from three German ringing centres “Helgoland,” “Hiddensee,” and “Radolfzell” to explore the value of German recovery data for investigating temporal changes in bird migration behavior. Although heterogeneity of the data in terms of ringing activity, recapture, re-sighting effort, recovery probabilities, or reporting probabilities of recoveries on a temporal, and spatial scale are major problems for these types of long-term analyses, the data offer promising possibilities. The possibilities of ringing and recovery databases at ringing centres cover larger areas and longer time-spans than most single studies; in contrast to pure observations and bird counts, individuals with deviant behavior (like wintering at northern latitudes by migrants) can be assigned to distinct populations; and the datasets are rapidly available in standardized, electronic format. German datasets are used to investigate prospects and pitfalls in using data from bird ringing databases for analyzing the effects of climate change on migrating birds.