Bos D.,Altenburg and Wymenga ecological consultants |
Bos D.,University of Groningen |
Boersma S.,Fryske Feriening foar Fjildbiology FFF |
Engelmoer M.,Fryske Feriening foar Fjildbiology FFF Op Dijksman |
And 5 more authors.
Journal of Coastal Conservation | Year: 2014
In this study we evaluate the effect of coastal re-alignment on the utilisation of coastal grasslands by staging geese. We assessed vegetation change and utilisation by geese using repeated mapping and regular dropping counts in both the restored marsh and adjacent reference sites. All measurements were started well before the actual re-alignment. In addition, we studied the effects of livestock grazing on vegetation and geese, using exclosures. The vegetation transformed from fresh grassland into salt-marsh vegetation. A relatively large proportion of the de-embanked area became covered with secondary pioneer vegetation, and the overall cover of potential food plants for geese declined. Goose utilisation had initially dropped to low levels, both in autumn and in spring, but it recovered to a level comparable to the reference marsh after ten years. Exclosure experiments revealed that livestock grazing prevented the establishment of closed swards of grass in the poorly drained lower area of the restored marsh, and thereby negatively affected goose utilisation of these areas during spring staging. Goose grazing in the restored marsh during spring showed a positive numerical response to grass cover found during the preceding growing season. (1) The value of restored salt marsh as foraging habitat for geese initially decreased after managed re-alignment but recovered after ten years. (2) Our findings support the idea that the value of foraging habitats depends largely on the cover of forage plants and that this can be manipulated by adjusting both grazing and drainage. © 2014 Springer Science+Business Media Dordrecht.
Verkuil Y.I.,University of Groningen |
Verkuil Y.I.,Royal Ontario Museum |
Karlionova N.,National Academy of Sciences of Belarus |
Rakhimberdiev E.N.,Cornell University |
And 10 more authors.
Biological Conservation | Year: 2012
The fuelling performance of long-distance migrants at staging areas indicates local conditions and determines the viability of migration routes. Here we present a first case study where long-term fuelling performance was documented along two migration routes with differential population trends. Ruffs (. Philomachus pugnax) are shorebirds of inland freshwater wetlands that migrate from the sub-Saharan wintering grounds, via Europe, to the northern Eurasian breeding grounds. Assessments from 2001 to 2008 of fuelling during northward migration at the major western and eastern staging site revealed that daily mass gain rates steeply declined across years in the grasslands for dairy production in Friesland, The Netherlands, and remained constant in the Pripyat floodplains in Belarus, 1500. km further east. Migrants in Friesland decreased from 2001 to 2010 by 66%, amounting to a loss of 21,000 individuals when counts were adjusted for length of stay as determined by resightings. In the same period numbers in Pripyat increased by 12,000. Ruffs individually ringed in Friesland were resighted in subsequent springs at increasingly eastern sites including Pripyat. Our results corroborate published evidence for an eastward redistribution of Arctic breeding ruffs and suggest that the decreasing fuelling rates in the westernmost staging area contribute to this redistribution. The shift implies that responses occur within a single generation. The hypothesis that the choice of route during northward migration may be driven by food availability can now be tested by creating greater areas of wet grasslands in Friesland. When local staging conditions improve we predict that ruffs will make the reverse shift. © 2012 Elsevier Ltd.
Verkuil Y.I.,University of Groningen |
Verkuil Y.I.,Royal Ontario Museum |
Piersma T.,University of Groningen |
Piersma T.,Netherlands Institute for Sea Research |
And 5 more authors.
Biological Journal of the Linnean Society | Year: 2012
Long-distance migrant waders breeding in the Arctic often have globally structured populations, largely because they were isolated in glacial or interstadial refugia or were restricted to fragmented coastal wetlands in winter. Conversely, inland species using continentally distributed wetlands appear to be less structured (more often panmictic), presumably because they are less likely to have been isolated by multiple refugia or by current events. We analyzed genetic variation in a widely distributed inland species, the ruff (Philomachus pugnax), sampled from seven Eurasian breeding localities, and from migration routes and wintering areas in Europe and Africa. One mitochondrial marker (N=118) and eight nuclear microsatellites (N=170) showed: (1) high genetic variation; (2) large genetic distances among mitochondrial (private) haplotypes within breeding populations; (3) the absence of a signature of isolation-by-distance; and (4) a distribution of private microsatellite alleles indicating dispersal between Scandinavia and Siberia but not between western and eastern Siberia. These results were consistent with a large refugial population during the Last Glacial Maximum, and postglacial long range expansions spreading ancestral polymorphisms, and not with a stepping-stone model of gene flow. The divergence between breeding populations in Europe and Siberia was dated to approximately 12000 years ago. Although genetic population structure is presently statistically non-existent, support for evolving population structure came from analyses of geographical variation in two relevant phenotypic traits: wing length and the timing of migration. Analysis of 6077 individuals sampled on migration in 2002-08 revealed that, in each year, shorter-winged birds migrated through significantly later than longer-winged birds. The late-passing birds were associated with more westerly breeding localities. In conclusion, the lack of genetic structuring in ruffs (and other inland species we examined) contrasts with strong structuring in many coastal species. This suggests that the ability to use more widely available inland habitat influences the evolution of genetic structure and the maintenance of genetic variation in waders. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society.
Hooijmeijer J.C.E.W.,University of Groningen |
Gill Jr. R.E.,U.S. Geological Survey |
Mulcahy D.M.,U.S. Geological Survey |
Tibbitts T.L.,U.S. Geological Survey |
And 7 more authors.
Journal of Ornithology | Year: 2014
Satellite telemetry has become a common technique to investigate avian life-histories, but whether such tagging will affect fitness is a critical unknown. In this study, we evaluate multi-year effects of implanted transmitters on migratory timing and reproductive performance in shorebirds. Shorebirds increasingly are recognized as good models in ecology and evolution. That many of them are of conservation concern adds to the research responsibilities. In May 2009, we captured 56 female Black-tailed Godwits Limosa limosa limosa during late incubation in The Netherlands. Of these, 15 birds were equipped with 26-g satellite transmitters with a percutaneous antenna (7.8 % ± 0.2 SD of body mass), surgically implanted in the coelom. We compared immediate nest survival, timing of migration, subsequent nest site fidelity and reproductive behaviour including egg laying with those of the remaining birds, a comparison group of 41 females. We found no effects on immediate nest survival. Fledging success and subsequent southward and northward migration patterns of the implanted birds conformed to the expectations, and arrival time on the breeding grounds in 2010-2012 did not differ from the comparison group. Compared with the comparison group, in the year after implantation, implanted birds were equally faithful to the nest site and showed equal territorial behaviour, but a paucity of behaviours indicating nests or clutches. In the 3 years after implantation, the yearly apparent survival of implanted birds was 16 % points lower. Despite intense searching, we found only three eggs of two implanted birds; all were deformed. A similarly deformed egg was reported in a similarly implanted Whimbrel Numenius phaeopus returning to breed in central Alaska. The presence in the body cavity of an object slightly smaller than a normal egg may thus lead to egg malformation and, likely, reduced egg viability. That the use of implanted satellite transmitters in these large shorebirds reduced nesting propensity and might also lead to fertility losses argues against the use of implanted transmitters for studies on breeding biology, and for a careful evaluation of the methodology in studies of migration. © 2013 Dt. Ornithologen-Gesellschaft e.V.
Zwarts L.,Altenburg and Wymenga Ecological Consultants |
Bijlsma R.G.,Groningen Institute for Evolutionary Life science
Ardea | Year: 2015
For a study of long-distance migrants in sub-Saharan Africa, a census method was developed that combined precision and accuracy regarding bird numbers and tree choice. The number of birds present in trees and shrubs can be counted accurately, although it is time-consuming. We describe how much time is needed to detect all birds present in trees, using data collected in over 2000 plots across West Africa during the dry season (October-March in 2007-2015). The observation time per tree depended on tree size, number of birds present and the opacity of the crown. The giving-up time of the observers increased with canopy volume, but was independent of the number of birds in a tree. Detection probabilities of bird species differed relative to microhabitat choice and feeding techniques. Species-specific detectabilities hardly varied during the day or the season. All foraging birds and immobile birds (save a few percent in dense canopies) were detected using the individual-tree-approach. Bird density is expressed as number per canopy volume, but little information is lost when density is given as number per canopy surface. The variation in bird density was large and differed per tree species. Within tree species, bird density was related to the opacity of the crown, the abundance of insects and whether there were berries or flowers. These findings suggest that, to collect biologically relevant information, the density of tree-dwelling birds should be measured at the level of the individual tree, and not per surface area, habitat type or tree species (as is typical in published studies).
Oosterveld E.B.,Altenburg and Wymenga ecological consultants |
Nijland F.,Weidevogelmeetnet Friesland |
Musters C.J.M.,Leiden University |
de Snoo G.R.,Wageningen University
Journal of Ornithology | Year: 2011
Since 2000, a new management technique has been introduced to stop the rapid decline of grassland breeding shorebirds in the Netherlands, called 'mosaic management'. The most important difference from earlier Agri-Environment Schemes is that the mosaic management is conducted at a landscape scale (150-650 ha) rather than an individual farm scale (50-60 ha) and that there is purposeful planning of the spatial distribution and layout of management measures within a local area. We tested the effectiveness of the mosaic management by analysing breeding population trends of Northern Lapwing (Vanellus vanellus), Black-tailed Godwit (Limosa limosa), Redshank (Tringa totanus) and Oystercatcher (Haematopus ostralegus) in comparison with three other management types: individual management, regular farmland and nature reserves. After the introduction of mosaic management, populations of Black-tailed Godwit and Redshank stabilised and Northern Lapwing populations increased. Oystercatcher decreased, but this was also due to reduced winter survival. Populations in the mosaic management areas showed a greater annual improvement of 0-18% compared to other management types. The mosaic areas did not appear to be 'sink' areas as productivity in the mosaic areas seemed to be sufficient to support the observed densities. However, with the exception of Northern Lapwing, the change of trend was not greater in the mosaic areas than in the other management types. So, for the species other than Northern Lapwing, the good performance cannot be attributed to the mosaic management. The mosaic areas were good breeding habitats beforehand and continue to be so. It is possible that the mosaic management is part of the success, but not exclusively so. Our results show that modern farming can still be combined with grassland breeding shorebird management. However, further study of success factors is urgently needed for the conservation of the remaining good habitats on farmland and restoration of lost ones. © 2010 The Author(s).
Zwarts L.,Altenburg and Wymenga Ecological Consultants |
Van Der Kamp J.,Altenburg and Wymenga Ecological Consultants |
Klop E.,Altenburg and Wymenga Ecological Consultants |
Sikkema M.,Altenburg and Wymenga Ecological Consultants |
Wymenga E.,Altenburg and Wymenga Ecological Consultants
Ardea | Year: 2014
Mangrove forests attract many insectivorous birds. Bird density in West African mangroves in January-March 2014 is higher in Avicennia (21 birds/ha canopy) than in Rhizophora (11 birds/ha). The Palearctic species are dominant in the most northern mangroves (14-16°N), but further south resident birds become as numerous as migrants (11-12°N). The European Reed Warbler Acrocephalus scirpaceus is the most common winter visitor in West African mangroves between 12 and 16°N, with an estimated total of 4-6 million birds, which may account for 30-50% of the European population. The mortality of European Reed Warblers while crossing the Sahara desert in spring is higher when their Sudan-Guinean wintering areas have been drought-stricken in the preceding winter. European Reed Warblers wintering in mangroves suffer the same fate, because mangroves in the Sahel region massively die off in drought years.
Wymenga E.,Altenburg and Wymenga Ecological Consultants |
Zwarts L.,Altenburg and Wymenga Ecological Consultants
Waterbirds | Year: 2010
Rice fields in West Africa comprise mangrove swamp rice and rain-fed rice cultivations along the coast, rice fields in floodplains and river valleys, and inland irrigated cultivations. All these rice systems constitute important habitats for African and migratory Palaearctic waterbirds. Density counts reveal the presence of about 16 wetland-related birds per ha during the northern winter if the habitat is still damp or covered by water; this declines to about four birds/ha if the fields are dry. The coastal rice fields (South Senegal-Guinea-Conakry) harbour 1.17 million wetland-related birds during the northern winter, and the inland rice fields of Office du Niger (Mali) contain 730,000. In former floodplain areas, the high bird numbers in rice fields offer, to some degree, an ecological compensation for the loss of floodplains. In the Inner Niger Delta, for example, the construction of the Selingue Dam and the Office du Niger irrigation scheme resulted on average in the loss of 12 % of the wintering waterbirds. However, the ecological loss is larger than these numbers suggest because most bird species in irrigated rice fields are common, while rare and endangered species are concentrated in the remaining West African floodplains that have not been converted to cultivated rice fields.