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Borken, Germany

Salewski V.,Michael Otto Institute im NABU | Hochachka W.M.,Cornell University | Flinks H.,Am Kuhm 19
Journal of Ornithology | Year: 2014

Declining body size has been suggested to be a response of animals to global warming, but analyses of time series have led to contradictory results. One problem is that each trait related to body size may vary in response to factors other than temperature and independently of size. We analyse trends of three morphological traits of a passerine bird species: the Stonechat Saxicola torquata. Wing lengths were increasing and tail length mostly decreasing between 1989 and 2012. Variation in tarsus length showed no consistent trend. Wing length increased with increasing temperature. Concomitant decreasing tail length suggests, however, that increasing wing length cannot be explained by increasing temperatures during the study period. As tarsus length is a surrogate for overall size, we argue that there was no detectable trend in body size. Wing and tail length are related to flight performance, and increasing wing and decreasing tail length could be indicative of selection for more effective flight, related to either longer migration distances or increased predation pressure. The first scenario is unlikely given the strong suggestions of reduced migratory activity in birds as a response to climate change. The density of the Sparrowhawk Accipiter nisus recently increased almost tenfold in the study area, but the hypothesis of changing morphology as a response to increasing predation pressure remains to be tested. Our study suggests, however, that linking fluctuating lengths in single morphological traits to body size change as a response to global warming may be premature when alternative hypotheses are not considered. © 2014 Dt. Ornithologen-Gesellschaft e.V. Source


Hegemann A.,University of Groningen | Matson K.D.,University of Groningen | Flinks H.,Am Kuhm 19 | Tieleman B.I.,University of Groningen
Frontiers in Zoology | Year: 2013

Introduction: Life-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.Results: When 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.Conclusions: We 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. © 2013 Hegemann et al.; licensee BioMed Central Ltd. Source


Geiger F.,Wageningen University | Hegemann A.,University of Groningen | Gleichman M.,Wageningen University | Flinks H.,Am Kuhm 19 | And 5 more authors.
Journal of Ornithology | Year: 2014

In recent decades, Skylark (Alauda arvensis) populations in Europe have declined sharply due to agricultural intensification. Insufficient reproduction rates are one reason. Increased winter mortality may also be important, but studies outside the breeding season are scarce and mostly limited to the UK. We studied habitat selection of wintering Skylarks in an agricultural area in the Netherlands. We monitored Skylarks between November 2008 and March 2009 on 10 survey plots including 77 different arable fields and permanent grasslands and covering in total 480 ha. We simultaneously measured food availability, vegetation structure and field boundary characteristics. We also analysed 158 faecal pellets collected on potato and cereal stubble fields to relate Skylark diet to seasonal changes in food availability and foraging habitat. We show that cereal stubble fields larger than 4.3 ha, surrounded by no or low boundary vegetation and a density of dietary seeds of more than 860 seeds m-2, were most suitable for wintering Skylarks. Skylark group densities were low on permanent grasslands and on maize stubble fields. Densities of dietary seeds were highest in soils of potato stubble fields followed by cereal stubble fields, grasslands and maize stubble fields. Skylarks showed a strong preference for cereal grains, but their proportion in the diet fell sharply at the end of November, indicating that cereal grains were depleted and birds had to switch to less profitable food sources, such as weed seeds and leaves. We conclude that Skylarks wintering in agricultural landscapes possibly suffer from a lack of energy-rich food sources and only a few fields provide sufficient food. Conservation measures should strive to improve the wintering situation by creating food-rich habitats such as over-winter stubble with a rich layer of weeds on large fields and localised in open areas. © 2013 Dt. Ornithologen-Gesellschaft e.V. Source


Ottens H.J.,Dutch Montagus Harrier Foundation | Kuiper M.W.,Wageningen University | Flinks H.,Am Kuhm 19 | Van Ruijven J.,Wageningen University | And 5 more authors.
Ardea | Year: 2014

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. Source


Flinks H.,Am Kuhm 19 | Salewski V.,University of Osnabruck
Journal of Ornithology | Year: 2012

Wing and tail length measurements are important tools in ornithology. Amongst linear measurements, wing length has been considered to be the best indicator for body size for taxonomy and ecomorphology, as well as for studies about the impact of climate change on morphology. As feathers are dead tissue, abrasion will lead to a reduction in wing and tail length within a moult cycle. The aim of our study was to analyse the effect of feather abrasion on wing and tail length in the Stonechat Saxicola torquata. Generalized additive models revealed that wing lengths and tail lengths decrease significantly between the termination of feather growth and the next moult. The decrease in wing length was faster with increasing feather age. The decrease in tail length was nearly linear through time. Multiple measurements of recaptured individuals revealed a similar decrease in wing length to that observed in analyses based on single measurements of multiple individuals. An analysis of the length of the third outermost primary revealed the same pattern. Hence, the decrease in wing and tail length over time was caused by within-bird changes and not by mortality, emigration or immigration associated with wing and tail length. We found that feather abrasion was more pronounced in females compared to males at least during the breeding season, but there were no strong indications that feather abrasion was more pronounced in birds before their first complete moult compared to older individuals. A review of previous studies showed that a reduction in wing length of about 0. 2-0. 5 %/month is a common phenomenon. Our study shows that feather abrasion must be taken into account when analysing time-series of wing and tail length measurements to avoid spurious conclusions. © 2012 Dt. Ornithologen-Gesellschaft e.V. Source

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