Heiner Flinks

Brutzeitliche Beutewahl beim SeggenrohrsängerAcrocephalus paludicola

Aquatic Warblers inhabitCarex Marshes (Magnocaricia) exceptionally rich in arthropods. Contrasting with the otherAcrocephalus species their mating system is some form of polygyny resp. promiscuity and the female alone feeds her nestlings. At 17 nests females fed large prey items compared with the arthropod fauna of the vegetation. Food was collected close to the nest and feeding rate proved to be high. Therefore richness of arthropods in the vegetation seems to form a prerequisite to this mating system untypical amongAcrocephalus warblers.

Offspring pay sooner, parents pay later: experimental manipulation of body mass reveals trade-offs between immune function, reproduction and survival

IntroductionLife-history theory predicts that organisms trade off survival against reproduction. However, the time scales on which various consequences become evident and the physiology mediating the cost of reproduction remain poorly understood. Yet, explaining not only which mechanisms mediate this trade-off, but also how fast or slow the mechanisms act, is crucial for an improved understanding of life-history evolution. We investigated three time scales on which an experimental increase in body mass could affect this trade-off: within broods, within season and between years. We handicapped adult skylarks (Alauda arvensis) by attaching extra weight during first broods to both adults of a pair. We measured body mass, immune function and return rates in these birds. We also measured nest success, feeding rates, diet composition, nestling size, nestling immune function and recruitment rates.ResultsWhen nestlings of first broods fledged, parent body condition had not changed, but experimental birds experienced higher nest failure. Depending on the year, immune parameters of nestlings from experimental parents were either higher or lower than of control nestlings. Later, when parents were feeding their second brood, the balance between self-maintenance and nest success had shifted. Control and experimental adults differed in immune function, while mass and immune function of their nestlings did not differ. Although weights were removed after breeding, immune measurements during the second brood had the capacity to predict return rates to the next breeding season. Among birds that returned the next year, body condition and reproductive performance a year after the experiment did not differ between treatment groups.ConclusionsWe conclude that the balance between current reproduction and survival shifts from affecting nestlings to affecting parents as the reproductive season progresses. Furthermore, immune function is apparently one physiological mechanism involved in this trade-off. By unravelling a physiological mechanism underlying the trade-offs between current and future reproduction and by demonstrating the different time scales on which it acts, our study represents an important step in understanding a central theory of life-history evolution.

Nestling food of the congeneric and sympatric Rusty-margined and Social flycatchers

Abstract We studied the food of nestling Rusty-margined (Myozetetes cayanensis) and Social flycatchers (M. similis) in 1998 and 1999 at Barro Colorado Island, Panama. Food samples were taken from nestlings by fecal analysis and the neck-collar method. In both species most food items were beetles, winged ants, dragonflies, spiders, and seeds of Miconia spp. Water animals (mainly backswimmers, freshwater snails, and dragonfly larvae) constituted 7.8%–13.5% of animal prey. The nestlings of the Social Flycatcher received significantly more flying insects, while the proportion of fruits and seeds was significantly higher in the diet of Rusty-margined Flycatcher nestlings. Length of animal prey varied from 4–25 mm in the Rusty-margined Flycatcher and 2–50 mm in the Social Flycatcher, and the length of fruits and seeds were 4–11 mm and 2–19 mm, respectively. The average length of animal food was larger in the Rusty-margined Flycatcher despite its slightly smaller size. The number of broods with nestlings or fledglings present in the study area was positively correlated with the abundance of fruits in the Social Flycatcher.

Nestling and Adult Diet of the Willie Wagtail Rhipidura leucophrys Near Madang, Papua New Guinea

The Willie Wagtail Rhipidura leucophrys is a common species in most man-made habitats in New Guinea (Coates 1990) but its food preferences have not been studied in detail (Clapp 1982). Cameron (1985) studied habitat preferences, foraging ecology and food of adult Willie Wagtails in Australia. Our analysis of their diet is part of a more extensive study of a Willie Wagtail population in optimal (high breeding density) but highly changed habitat at the northern limit of its geographical range (Dyrcz 1994).

Einfluß des Nestlingsalters auf die Nahrungszusammensetzung nestjunger Schwarzkehlchen (Saxicola torquata)

1984–1986 wurden 654 Kotproben mit 3754 Beutetieren bei 1–14tägigen Nestlingen des Schwarzkehlchens gewonnen. Im Laufe der Nestlingszeit stieg die Anzahl der Beutetiere von 2,06 auf maximal 9,61 Individuen pro Kotballen an. Die Nahrung war altersabhängig verschieden zusammengesetzt. Der Spinnenanteil von ca. 50 % in den ersten Nestlingstagen sank gegen Ende der Nestlingszeit unter 10 %; der Anteil der Käfter stieg dagegen von 0 % bis über 50 % an. Eine Abschätzung der Biomasse unterstreicht die große Bedeutung der Raupen als Nahrung für alle Altersstufen. Ihr durchschnittlicher relativer Anteil von 23 % stieg auf 75 % an. Mit fortschreitendem Nestlingsalter stieg der Anteil hart chitinisierter Beutetiere, während der Anteil weich chitinisierter Beutetiere sank. Somit spielten gegenüber der leichten Verdaulichkeit die Abundanz und Erreichbarkeit der Beutetiere für die jagenden Altvögel eine immer größere Rolle. 654 droppings of 1 to 14 days old nestlings were sampled during the breeding seasons 1984 through 1986 in a lowland valley in North-Rhine-Westfalia. The number of 3754 prey items could be verified. The number of prey item per dropping increased from 2,06 to the maximum of 9,61 during the nestling period. Diet composition changed significantly as a function of nestling age. The proportion of spiders of 50 % in the first days after hatching decreased to a proportion of 10 %, while coleoptera increased from 0 % to more than 50 %. The biomass was estimated for the main taxonomic prey categories. The result underlined the special importance of caterpillars as nestling diet over the whole nestling period. The average proportion of 23 % rose to 75 % with respect of the biomass. It could be demonstrated that the proportion of hard chitinised food increased with nestling age while the proportion of soft chitinised food decreased. As the nestlings grew older the abundance and availability of prey got more important for the hunting adult Stonechats than the easy digestibility of food.

Diet Analysis of Wetland Passerine Nestlings Using Neck Collars or Faecal Sampling Produces Similar Results

Two methods are commonly used to study the diet of nestling passerines: the neck collar method and faecal sampling. Most studies apply either method, however, few methodological studies comparing both methods exist and are mainly limited to farmland birds. Furthermore, existing methodological studies only include high-level taxonomic diet categories. Here, we compared both methods using two wetland species, the Reed Bunting Emberiza schoeniclus and the Sedge Warbler Acrocephalus schoenobaenus, and included family level as a lower taxonomic prey level. We found no differences between the two methods in the dietary composition of high-level taxonomic categories (mainly orders) and only small differences in some orders at the family level. Hence, we recommend using the less invasive and easily accessible faecal sampling method rather than the use of neck collars in diet composition studies.

Do Field Margins Enrich the Diet of the Eurasian Skylark Alauda arvensis on Intensive Farmland

To help restore food availability for birds, arable field margins (extensively managed strips of land sown with grasses and forbs) have been established on European farmland. In this study we describe the effect of field margins on the diet of Eurasian Skylark nestlings and adults living on intensively managed Dutch farmland. We tested the hypotheses that field margins offer a higher diversity of invertebrate prey than intensively managed crops, and that the diet of nestlings receiving food from field margins will therefore be more diverse than that of other nestlings. Field margins had a greater variety of invertebrate prey groups to offer than the intensively managed crops. Coleoptera were the most frequently and most abundantly eaten prey group by both adults and nestlings. Together, Coleoptera, Diptera, Lepidoptera, Hymenoptera and Araneae accounted for 91% of the nestling diet. Nestlings ate larger prey items and a larger proportion of larvae than adults. Almost 75% of both adults and nestlings consumed plant material, perhaps indicating a scarcity of invertebrate resources. When provided with food from field margins, the mean number of invertebrate orders in the nestling diet increased significantly from 4.7 to 5.5 and the number of families from 4.2 to 5.8 per sample. Thus, birds that used field margins for foraging could indeed provide their young with more invertebrate prey groups than birds only foraging in crops and grassland.