Dutch Montagus Harrier Foundation

Scheemda, Netherlands

Dutch Montagus Harrier Foundation

Scheemda, Netherlands
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Tottrup A.P.,Copenhagen University | Pedersen L.,Copenhagen University | Onrubia A.,International Bird Migration Center | Klaassen R.H.G.,Dutch Montagus Harrier Foundation | And 2 more authors.
Journal of Avian Biology | Year: 2017

The current Northern Hemisphere migration systems are believed to have arisen since the last glaciation. In many cases, birds do not migrate strait from breeding to non-breeding areas but fly via a detour. All western European populations of red-backed shrikes Lanius collurio are assumed to reach their southern African wintering grounds detouring via southeast Europe. Based on theoretical considerations under an optimality framework this detour is apparently optimal. Here, we use individual geolocator data on red-backed shrikes breeding in Spain to show that these birds do indeed detour via southeast Europe en route to southern Africa where they join other European populations of red-backed shrikes and return via a similar route in spring. Disregarding potential wind assistance, the routes taken for the tracked birds in autumn were not optimal compared to crossing the barrier directly. For spring migration the situation was quite different with the detour apparently being optimal. However, when considering potential wind assistance estimated total air distances during autumn migration were overall similar and the barrier crossing shorter along the observed routes. We conclude that considering the potential benefit of wind assistance makes the route via southeast Europe likely to be less risky in autumn. However, it cannot be ruled out that other factors, such as following a historical colonisation route could still be important. © 2017 The Authors

Klaassen R.H.G.,Dutch Montagus Harrier Foundation | Klaassen R.H.G.,University of Groningen | Schlaich A.E.,Dutch Montagus Harrier Foundation | Schlaich A.E.,University of Groningen | And 3 more authors.
Journal of Avian Biology | Year: 2017

Time budgets are a powerful but hitherto seldom used way to study how migrants organise their bi-annual travels. We studied daily time budgets of travelling Montagu’s harriers Circus pygargus, based on GPS tracking data, in which we were particularly interested in how time budgets differ between regions and seasons, and are affected by wind. We found that Montagu’s harriers used a relatively broad daily time window for travelling by starting daily travels just after sunrise and ending daily travels just before sunset. Occasionally, flights were extended into the night. Montagu’s harriers frequently interrupted their daily flights for on average 1.5 h d–1. These interruptions occurred in all regions and seasons. The tracking data during interruptions suggested two different behaviours: in 41% of all interruptions the birds were moving (presumed foraging,) and in 32% they were stationary (presumed resting; the remaining interruptions could not be classified). The interruptions for foraging indicate that Montagu’s harriers have a fly-and-forage migration strategy (i.e. combine travelling and foraging on the same day), but the interruptions for resting illustrate that their travels comprise of more than fly-and-forage behaviour alone. The large number of interruptions for foraging in the Sahara Desert indicates that this region is less hostile for a migrating raptor than presumed previously. Importantly, harriers spent more time on interruptions for resting on days with stronger headwinds, suggesting that interruptions for resting serve a function of waiting for more favourable weather conditions. Daily variation in time budgets was largely explained by wind; harriers flew more hours per day, and interrupted their flights fewer hours per day, on days they experienced stronger tailwinds. In contrast, time budgets were similar between regions and seasons, suggesting that wind rather than landscape and season shape travel routines of Montagu’s harriers. © 2017 The Authors

Vardanis Y.,Lund University | Nilsson J.-T.,Lund University | Klaassen R.H.G.,Dutch Montagus Harrier Foundation | Klaassen R.H.G.,University of Groningen | And 3 more authors.
Animal Behaviour | Year: 2016

As the evolutionary responses to environmental change depend on selection acting on individual differences, disentangling within- and between-individual variation becomes imperative. In animal migration research, multiyear tracks are thus needed to estimate the individual consistency of phenotypic traits. Avian telemetry studies have recently provided the first evidence of individuality across space and time in animal migration. Here, we compare repeatability patterns of routes and timing between two migratory birds, the marsh harrier, Circus aeruginosus, and the osprey, Pandion haliaetus, as recorded by satellite tracking. We found interspecific contrasts with low repeatability in timing and duration and a high repeatability in routes for ospreys, but the reverse pattern for marsh harriers. This was mainly caused by (1) larger between-individual variation in routes for ospreys (broad-front migration) than for marsh harriers (corridor migration) and a higher degree of repeated use of the same stopover sites among ospreys, and (2) higher within-individual consistency of timing and duration among marsh harriers, while individual ospreys were more flexible. Our findings suggest that individuality in space and time is not a shared trait complex among migrants, but may show adaptive variation depending on the species' life history and ecology. © 2015 The Association for the Study of Animal Behaviour.

Klaassen R.H.G.,Lund University | Klaassen R.H.G.,Dutch Montagus Harrier Foundation | Klaassen R.H.G.,University of Groningen | Hake M.,Lund University | And 7 more authors.
Journal of Animal Ecology | Year: 2014

Information about when and where animals die is important to understand population regulation. In migratory animals, mortality might occur not only during the stationary periods (e.g. breeding and wintering) but also during the migration seasons. However, the relative importance of population limiting factors during different periods of the year remains poorly understood, and previous studies mainly relied on indirect evidence. Here, we provide direct evidence about when and where migrants die by identifying cases of confirmed and probable deaths in three species of long-distance migratory raptors tracked by satellite telemetry. We show that mortality rate was about six times higher during migration seasons than during stationary periods. However, total mortality was surprisingly similar between periods, which can be explained by the fact that risky migration periods are shorter than safer stationary periods. Nevertheless, more than half of the annual mortality occurred during migration. We also found spatiotemporal patterns in mortality: spring mortality occurred mainly in Africa in association with the crossing of the Sahara desert, while most mortality during autumn took place in Europe. Our results strongly suggest that events during the migration seasons have an important impact on the population dynamics of long-distance migrants. We speculate that mortality during spring migration may account for short-term annual variation in survival and population sizes, while mortality during autumn migration may be more important for long-term population regulation (through density-dependent effects). © 2013 The Authors. Journal of Animal Ecology © 2013 British Ecological Society.

Trierweiler C.,Dutch Montagus Harrier Foundation | Trierweiler C.,University of Groningen | Trierweiler C.,Institute of Avian Research Vogelwarte Helgoland | Klaassen R.H.G.,Dutch Montagus Harrier Foundation | And 6 more authors.
Proceedings of the Royal Society B: Biological Sciences | Year: 2014

Knowledge about migratory connectivity, the degree to which individuals from the same breeding site migrate to the same wintering site, is essential to understand processes affecting populations of migrants throughout the annual cycle. Here, we study the migration system of a long-distance migratory bird, the Montagu's harrier Circus pygargus, by tracking individuals from different breeding populations throughout northern Europe. We identified three main migration routes towards wintering areas in sub- Saharan Africa. Wintering areas and migration routes of different breeding populations overlapped, a pattern best described by 'weak (diffuse) connectivity'. Migratory performance, i.e. timing, duration, distance and speed of migration, was surprisingly similar for the three routes despite differences in habitat characteristics. This study provides, to our knowledge, a first comprehensive overview of the migration system of a Palaearctic-African long-distance migrant. We emphasize the importance of spatial scale (e.g. distances between breeding populations) in defining patterns of connectivity and suggest that knowledge about fundamental aspects determining distribution patterns, such as the among-individual variation in mean migration directions, is required to ultimately understand migratory connectivity. Furthermore, we stress that for conservation purposes it is pivotal to consider wintering areas as well as migration routes and in particular stopover sites. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Trierweiler C.,University of Groningen | Trierweiler C.,Institute of Avian Research Vogelwarte Helgoland | Trierweiler C.,Dutch Montagus Harrier Foundation | Mullie W.C.,Project Biological Management of Locusts and Grasshoppers | And 7 more authors.
Journal of Animal Ecology | Year: 2013

Mid-winter movements of up to several hundreds of kilometres are typical for many migratory bird species wintering in Africa. Unpredictable temporary food concentrations are thought to result in random movements of such birds, whereas resightings and recoveries of marked birds suggest some degree of site fidelity. Only detailed (e.g. satellite) tracking of individual migrants can reveal the relative importance and the causes of site choice flexibility and fidelity. The present study investigates how mid-winter movements of a Palaearctic-African migratory raptor, Montagu's harrier Circus pygargus, in the Sahel of West Africa are related to the availability of food resources. Thirty harriers breeding or hatched in northern Europe were satellite tracked (2005-2009). On average, four home ranges, each separated by c. 200 km, were visited during one overwinter stay in the Sahel. Wintering home ranges were similar in size to breeding season home ranges (average over wintering and breeding home range size c. 200 km2), and harriers showed high site fidelity between years. Most preferred habitat types in the Sahel were mosaics of grass- and cropland, indicating similar habitat preferences in both the breeding- and wintering seasons. The main prey of Montagu's harriers in the Sahel were grasshoppers Acrididae. Highest grasshopper numbers in the field occurred at relatively low vegetation greenness [normalized difference vegetation index (NDVI) values 0·17-0·27]. We used NDVI as a proxy of food availability for harriers. During their overwinter stay, Montagu's harriers moved in a South-South-western direction between consecutive home ranges. The birds selected areas within the range of NDVI values associated with high grasshopper numbers, thus tracking a 'green belt' of predictable changes in highest grasshopper availability. Contrary to earlier hypotheses of random movements in the Sahelian-wintering quarters, the present study shows that Montagu's harriers visited distinct home ranges, they were site-faithful and tracked seasonal changes in food availability related to previous rainfall patterns, caused by the shifting Intertropical Convergence Zone. Itinerancy may be the rule rather than an exception among insectivorous birds wintering in African savannahs. © 2012 The Authors. Journal of Animal Ecology © 2012 British Ecological Society.

Vansteelant W.M.G.,University of Amsterdam | Bouten W.,University of Amsterdam | Klaassen R.H.G.,Dutch Montagus Harrier Foundation | Klaassen R.H.G.,University of Groningen | And 6 more authors.
Journal of Avian Biology | Year: 2015

Given that soaring birds travel faster with supportive winds or in good thermal soaring conditions, we expect weather conditions en route of migration to explain commonly observed regional and seasonal patterns in the performance of soaring migrants. We used GPS-loggers to track 13 honey buzzards and four Montagu's harriers for two to six migrations each. We determined how tailwinds, crosswinds, boundary layer height (a proxy for thermal convection) and precipitation affected hourly speeds, daily distances and daily mean speeds with linear regression models. Honey buzzards mostly travel by soaring while Montagu's harriers supplement soaring with flapping. Therefore, we expect that performance of harriers will be less affected by weather than for buzzards. Weather conditions explained between 30 and 50% of variation in migration performance of both species. Tailwind had the largest effect on hourly speeds, daily mean speeds and daily travel distances. Honey buzzards travelled significantly faster and farther, and Montagu's harriers non-significantly faster, under better convective conditions. Honey buzzards travelled at slower speeds and shorter distances in crosswinds, whereas harriers maintained high speeds in crosswinds. Weather conditions varied between regions and seasons, and this variation accounted for nearly all regional and seasonal variation in flight performance. Hourly performance was higher than predicted at times when we suspect birds had switched to intermittent or continuous flapping flight, for example during sea-crossings. The daily travel distance of Montagu's harriers was determined to a significant extent by their daily travel time, which differed between regions, possibly also due to weather conditions. We conclude with the implications of our work for studies on migration phenology and we suggest an important role for high-resolution telemetry in understanding migratory behavior across entire migratory journeys. © 2014 The Authors. Journal of Avian Biology published by Nordic Society Oikos.

PubMed | University of Amsterdam, CNRS Chizé Center for Biological Studies, University of Groningen and Dutch Montagus Harrier Foundation
Type: Journal Article | Journal: The Journal of animal ecology | Year: 2016

Hundreds of millions of Afro-Palaearctic migrants winter in the Sahel, a semi-arid belt south of the Sahara desert, where they experience deteriorating ecological conditions during their overwintering stay and have to prepare for spring migration when conditions are worst. This well-known phenomenon was first described by R.E. Moreau and is known ever since as Moreaus Paradox. However, empirical evidence of the deteriorating seasonal ecological conditions is limited and little is known on how birds respond. Montagus Harriers Circus pygargus spend 6months of the year in their wintering areas in the Sahel. Within the wintering season, birds move gradually to the south, visiting several distinct sites to which they are site-faithful in consecutive years. At the last wintering site, birds find themselves at the southern edge of the Sahelian zone and have no other options than facing deteriorating conditions. We tracked 36 Montagus Harriers with GPS trackers to study their habitat use and behaviour during winter and collected data on the abundance of their main prey, grasshoppers, in Senegal. Since grasshopper abundance was positively related to vegetation greenness (measured as normalized difference vegetation index, NDVI), we used NDVI values as a proxy for prey abundance in areas where no field data were collected. Prey abundance (grasshopper counts and vegetation greenness) at wintering sites of Montagus Harriers decreased during the wintering period. Montagus Harriers responded to decreasing food availability by increasing their flight time during the second half of the winter. Individuals increased flight time more in areas with stronger declines in NDVI values, suggesting that lower food abundance required more intense foraging to achieve energy requirements. The apparent consequence was that Montagus Harriers departed later in spring when their final wintering site had lower NDVI values and presumably lower food abundance and consequently arrived later at their breeding site. Our results confirmed the suggestions Moreau made 40years ago: the late wintering period might be a bottleneck during the annual cycle with possible carry-over effects to the breeding season. Ongoing climate change with less rainfall in the Sahel region paired with increased human pressure on natural and agricultural habitats resulting in degradation and desertification is likely to make this period more demanding, which may negatively impact populations of migratory birds using the Sahel.

Jukema J.,Haerdawei 62 | Wiersma P.,Dutch Montagus Harrier Foundation
Ardea | Year: 2014

We measured primary moult scores of 1051 Eurasian Golden Plovers Pluvialis apricaria staging in pastures in The Netherlands from 1978 to 2011. We hypothesized that moult may have advanced due to earlier breeding resulting from global climate change. At the same time, intensification of agricultural practices has changed the environment on which the Golden Plovers depend during migration and staging, which may have affected their condition and moult schedule. Primary moult has advanced by 8 days from 1990 to 2011, without visible changes preceding 1990. This suggests that long-term changes in weather might have caused the change in moult timing. In the absence of the variable year, the North Atlantic Oscillating (NAO) index, averaged over September-October, significantly correlated with timing of moult. However, this was a weaker relationship than that of year and timing of moult. Apparently, year correlates better with relevant weather parameters than NAO. Because moult speed at the staging areas has not changed from 1978 to 2011, the birds must have started moult earlier. Advanced breeding has been shown to have occurred in several bird species breeding in northern temperate latitudes. Golden Plovers start to moult during breeding, and therefore we think that the advancement of moult has been the result of an earlier start of breeding and not of changes in agricultural practice in The Netherlands.

Kuiper M.W.,Wageningen University | Ottens H.J.,Dutch Montagus Harrier Foundation | Ottens H.J.,Leiden University | Cenin L.,Dutch Montagus Harrier Foundation | And 5 more authors.
Agriculture, Ecosystems and Environment | Year: 2013

Agri-environment schemes have been established in many European countries to counteract the ongoing decline of farmland birds. In this study, the selection of foraging habitat by breeding skylarks was examined in relation to agri-environmental management on Dutch farmland. Field margin use was quantified and, based on the observed flight distances, the appropriateness of the current spatial arrangement of field margins in the study landscape was evaluated. Skylarks preferred field margins for foraging over all other habitat types relative to their surface area within the territories. The visiting rate of field margins decreased with increasing distance to the nest, and especially dropped markedly when the distance between the nest and a field margin exceeded 100. m. Analysis of the current spatial arrangement of field margins in the landscape suggested that the area of skylark breeding habitat within 100. m of a field margin could be increased by 46%. This was due to the placement of field margins alongside unsuitable breeding habitat and to the positioning of field margins at short distances from each other. The efficiency of agri-environmental management for skylarks can likely be improved by a more careful spatial arrangement of field margins in the landscape. © 2013 Elsevier B.V.

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