Hans-Günther Bauer

Changes in Behavioral Time Allocation of Waterbirds in Wing-Molt at Lake Constance

Abstract. The reduced mobility of flightless waterbirds during wing-feather molt should influence time allocation during the day, but time-budget studies are lacking in most species. Here, time budgets of flightless and fully-winged individuals at Lake Constance, Central Europe, were compared for five waterbird species with different feeding ecology and varying sensitivity to disturbances or predation pressure. Significant differences in diurnal activity budgets of flightless and fully-winged birds were observed in all five species. Different behaviors were responsible for the observed differences. Flightless Mute Swans Cygnus olor spent more time feeding while decreasing locomotory activity. Red-crested Pochard Netta rufina also increased feeding, but, in addition, had increased locomotory activity while resting less. In contrast, flightless individuals of both Gadwall Anas strepera and Tufted Ducks Aythya fuligula spent less time foraging, while there was no such change in Eurasian Coot Fulica atra. More consistent patterns were observed in vigilance behavior, which increased in three of the five species. Comfort activities, such as preening, increased in two species, and were unchanged in the remaining three. Social interactions, which constituted only a small part of the daily budget, only changed in Gadwall. The present data suggest that the five waterbird species meet the increased energy demands during molt by either one or a combination of behavioral adaptations, i.e. different strategies, such as higher nutrient intake (e.g. Mute Swan, Red-crested Pochard), lower energy consumption by reducing the locomotory component (e.g. Mute Swan, Tufted Duck) or a breakdown of energy reserves deposited prior to the molting period resulting in more time spent resting (e.g. Gadwall). Also, increased resting times during the day may indicate nocturnal feeding, which needs to be examined in more detail.

Cross-realm assessment of climate change impacts on species’ abundance trends

Climate change, land-use change, pollution and exploitation are among the main drivers of species’ population trends; however, their relative importance is much debated. We used a unique collection of over 1,000 local population time series in 22 communities across terrestrial, freshwater and marine realms within central Europe to compare the impacts of long-term temperature change and other environmental drivers from 1980 onwards. To disentangle different drivers, we related species’ population trends to species- and driver-specific attributes, such as temperature and habitat preference or pollution tolerance. We found a consistent impact of temperature change on the local abundances of terrestrial species. Populations of warm-dwelling species increased more than those of cold-dwelling species. In contrast, impacts of temperature change on aquatic species’ abundances were variable. Effects of temperature preference were more consistent in terrestrial communities than effects of habitat preference, suggesting that the impacts of temperature change have become widespread for recent changes in abundance within many terrestrial communities of central Europe.

Transmission dynamics of highly pathogenic avian influenza at lake constance (Europe) during the outbreak of winter 2005-2006

Highly pathogenic avian influenza virus (HPAI) H5N1 poses a serious threat to domestic animals. Despite the large number of studies on influenza A virus in waterbirds, little is still known about the transmission dynamics, including prevalence, behavior, and spread of these viruses in the wild waterbird population. From January to April 2006, the HPAI H5N1 virus was confirmed in 82 dead wild waterbirds at the shores of Lake Constance. In this study, we present simple mathematical models to examine this outbreak and to investigate the transmission dynamics of HPAI in wild waterbirds. The population dynamics model of wintering birds was best represented by a sinusoidal function. This model was considered the most adequate to represent the susceptible compartment of the SIR model. The three transmission models predict a basic reproduction ratio (R0) with value of approximately 1.6, indicating a small epidemic, which ended with the migration of susceptible wild waterbirds at the end of the winter. With this study, we quantify for the first time the transmission of HPAI H5N1 virus at Lake Constance during the outbreak of winter 2005–2006. It is a step toward the improvement of the knowledge of transmission of the virus among wild waterbirds.

Die Entwicklung der Brutvogelbestände am Bodensee: Vergleich halbquantitativer Rasterkartierungen 1980/81 und 1990/91@@@The development in the breeding birds of Lake Constance: comparison of grid mapping in 1980/81 and 1990/91

Die halb-quantitative Rasterkartierung Bodensee wurde 1990/91 auf 88.3 % der zehn Jahre zuvor kartierten Fläche wiederholt. Nur 25 % der Rasterfelder wurden von denselben Beobachtern kartiert wie vor zehn Jahren. Daher wurden Veränderungen nur dann als gesichert betrachtet, wenn sie mindestens auf dem 2 %-Niveau signifikant waren. Dies war bei 62 Arten der Fall, wovon 29 Arten zu- und 33 abnahmen. 145 Vogelarten wurden registriert (vorher 143), die Artenzahl pro Rasterfläche ist jedoch ebenso rückläufig wie der Gesamtbestand aller Vogelarten. Neben Zunahmen bei einigen Vogelarten der menschlichen Siedlungsflächen und des Waldes ragen solche von Feuchtgebiets- und Wasservögeln hervor, die am Bodensee effizient geschützt sind. Bemerkenswert sind der erhebliche Bestandsrückgang beim Haussperling und die insgesamt stark negative Entwicklung bei den Langstreckenziehern, unter denen keine Singvogelart mehr eine gesicherte Zunahme verzeichnen konnte. Drastische Bestandseinbrüche fast aller Bodenbrüter des offenen Kulturlandes wurden festgestellt. The distribution and number of breeding birds at Lake Constance was mapped on 278 grids of 4 km2 in 1990/91, covering 88.3 % of the area of 1980/81. As only 25 % of the grids were censused by the same observers as in 1980/81, changes were only considered real if significant on the 2 % level at least. This was the case in 62 species, 29 of which were increasing, 33 decreasing. A total of 145 breeding species was found (143 before), however, the number of species per grid and the total number of territories registered were lower than ten years ago. Apart from increases of species of urban settlements (e.g. Feral Pigeon, Collared dove, Black Redstart, Serin) and forests (e.g. Sparrowhawk, Goshawk, Great Spotted Woodpecker, Mistle thrush), the favourable development in species living in reedbeds and in waterbirds was notable. The latter is due to effective conservation measures at Lake Constance. Remarkable was the considerable loss in breeding numbers of the House Sparrow and the generally negative development of long-distance migrants, especially passerine species. A drastic population decline was found for almost the complete guild of ground-nesting birds in open habitats.

Depth-specific and spatiotemporal variation of δ13C and δ15N in Charophytes of Lake Constance: implications for food web studies.

Macrophytes are at the base of many lake food webs providing essential food resources for animals at higher trophic level, such as invertebrates, fish and waterbirds. However, data regarding the spatiotemporal variation in isotopic composition of macrophytes are generally missing. We measured the carbon and nitrogen stable isotope ratios of Charophytes at Lake Constance, where they constitute a major food source for waterbirds. Our data reveal seasonal and site-specific differences as well as depth-specific variations in isotopic carbon values within the littoral zone. Charophytes were enriched in (13)C at sites of higher productivity: the δ(13)C values were high in summer, at shallow and at relatively nutrient-rich sites, and comparatively low in winter, and in deeper and nutrient-poorer sites. In contrast, no temporal or spatial trend was found to explain the variability in the isotopic nitrogen values. These results imply that the seasonal timing of food intake (relative to turnover rates of consumers tissue) and the potential depth of foraging need to be taken into account when calculating the relative contribution of energy sources to diets of consumers such as waterbirds.

Depth-specific and spatiotemporal variation of δ13C and δ15N in Charophytes of Lake Constance: implications for food web studies: Variation in δ13C and δ15N in Charophytes of Lake Constance

Macrophytes are at the base of many lake food webs providing essential food resources for animals at higher trophic level, such as invertebrates, fish and waterbirds. However, data regarding the spatiotemporal variation in isotopic composition of macrophytes are generally missing. We measured the carbon and nitrogen stable isotope ratios of Charophytes at Lake Constance, where they constitute a major food source for waterbirds. Our data reveal seasonal and site-specific differences as well as depth-specific variations in isotopic carbon values within the littoral zone. Charophytes were enriched in (13)C at sites of higher productivity: the δ(13)C values were high in summer, at shallow and at relatively nutrient-rich sites, and comparatively low in winter, and in deeper and nutrient-poorer sites. In contrast, no temporal or spatial trend was found to explain the variability in the isotopic nitrogen values. These results imply that the seasonal timing of food intake (relative to turnover rates of consumers tissue) and the potential depth of foraging need to be taken into account when calculating the relative contribution of energy sources to diets of consumers such as waterbirds.