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Predatie door haviken wordt verondersteld een belangrijke limitatie te zijn voor de overleving van adulte korhoenders op de Sallandse Heuvelrug. Om meer inzicht te krijgen in de ruimtelijke predatierisico’s voor korhoenders zijn twaalf haviken op de Sallandse Heuvelrug in 2019 en 2020 gevolgd met behulp van gsm-zenders: tien adulte broedvogels (vijf vrouwen, vijf mannen) van zeven paren en twee tweede-kalenderjaar vogels (niet-broedvogels of zwervers). We beschrijven hier predatie van korhoen door de gezenderde haviken en het terreingebruik van de haviken in relatie tot de broedcyclus en gebieden waar korhoenders zich concentreren. Er is op basis van deze studie geen aanwijzing voor een ‘specialisatie’ van een individuele havik op korhoen, noch kan door de beperkte korhoenpredatie door gezenderde haviken iets geconcludeerd worden over predatierisico in relatie tot vegetatiestructuur.

Each year about 100 European hamsters are released in the southern part of the province of Limburg. They are part of a breeding programme with genetic material from the last five remaining populations in northwest Europe. To investigate their survival and distribution, the movements of the hamsters are tracked with transmitters and their burrows recorded. In 2019 144 burrows were found in 19 kilometre quadrants. After two months almost 45% of the hamsters were still alive. Hamsters can only live in arable fields under an adapted management regime, and are unable to survive in conventional arable fields. To conserve the European hamster, at least 25% of arable land must provide suitable conditions for their survival. At the moment this percentage has not been achieved, with the exception of several very small areas. Jaarlijks worden ongeveer 100 hamsters uitgezet in Zuid-Limburg uit een fokprogramma waarin genetisch materiaal uit de laatste vijf Noordwest-Europese restpopulaties bewaard is gebleven. Om na te gaan hoe ze overleven en zich verspreiden, worden ze met zenders gevolgd en worden hun burchten in kaart gebracht. In 2019 zijn 144 burchten gevonden in 19 kilometervakken. De overleving van de uitgezette hamsters was na twee maanden bijna 45%. Hamsters kunnen alleen leven in akkers met aangepast beheer. Op reguliere akkers is dat niet meer mogelijk. Om de hamster te kunnen behouden, zal minstens 25 procent van de akkers overlevingsmogelijkheden moeten bieden. Momenteel wordt dat percentage nog niet gehaald, met uitzondering van enkele heel kleine deelgebieden.

Long-distance migratory birds rely on the acquisition of body stores to fuel their migration and reproduction. Breeding success depends on the amount of body stores acquired prior to migration, which is thought to increase with access to food at the fueling site. Here, we studied how food abundance during fueling affected time budgets and reproductive success. In a regime of plenty, we expected that 1) limitations on food harvesting would become lifted, allowing birds to frequently idle, and 2) birds would reach sufficient fuel loads, such that departure weight would no longer affect reproductive success. Our study system comprised brent geese (Branta b. bernicla) staging on high-quality agricultural pastures. Fueling conditions were assessed by a combination of high-resolution GPS tracking, acceleration-based behavioral classification, thermoregulation modeling, and measurements of food digestibility and excretion rates. Mark-resighting analysis was used to test for correlations between departure weight and offspring recruitment. Our results confirm that birds loafed extensively, actively postponed fueling in early spring, and took frequent digestion pauses, suggesting that traditional time constraints on harvest and fueling rates are absent on modern-day fertilized grasslands. Nonetheless, departure weight remained correlated with recruitment success. The persistence of this correlation after a prolonged stopover with access to abundant high-quality food, suggests that between-individual differences in departure condition are not so much enforced by food quality and availability during stopover, but reflect individual quality and longer-lived life-history traits, such as health status and digestive capacity, which may be developed before the fueling period.

West Nile virus (WNV) and Usutu virus (USUV) are arboviruses that are maintained in enzootic transmission cycles between mosquitoes and birds and are occasionally transmitted to mammals. As arboviruses are currently expanding their geographic range and emerging in often unpredictable locations, surveillance is considered an important element of preparedness. To determine whether sera collected from resident and migratory birds in the Netherlands as part of avian influenza surveillance would also represent an effective source for proactive arbovirus surveillance, a random selection of such sera was screened for WNV antibodies using a commercial ELISA. In addition, sera of jackdaws and carrion crows captured for previous experimental infection studies were added to the selection. Of the 265 screened serum samples, 27 were found to be WNV-antibody-positive, and subsequent cross-neutralization experiments using WNV and USUV confirmed that five serum samples were positive for only WNV-neutralizing antibodies and seven for only USUV. The positive birds consisted of four Eurasian coots (Fulica atra) and one carrion crow (Corvus corone) for WNV, of which the latter may suggest local presence of the virus, and only Eurasian coots for USUV. As a result, the screening of a small selection of serum samples originally collected for avian influenza surveillance demonstrated a seroprevalence of 1.6% for WNV and 2.8% for USUV, suggesting that this sustained infrastructure could serve as a useful source for future surveillance of arboviruses such as WNV and USUV in the Netherlands.

The Ministry of Agriculture, Nature and Food Quality requires that the Dutch population of European hamster is surveyed each year. This consists of a census of inhabited burrows in the various known habitats patches. The European hamster is present only in the southern part of the province of Limburg and has a preference for arable farmland where cereals or alfalfa are grown. In 2002 the hamster was reintroduced into areas with a specially adapted cropland management regime. In recent years attempts have been made to find new forms of hamster friendly land management practices which can be easily integrated into the farm management and are cheaper to carry out. The area of hamster friendly arable land with suitable habitat is currently more than 700 hectares. Monitoring of the hamster population by means of burrow counts and tagged animals shows that in practice hamsters struggle to survive long enough to produce sufficient litters to enable the population to grow. The latest censuses indicate that there are fewer than 200 inhabited burrows spread over approx. 20 kilometre grids. The hamster population is therefore still critically endangered and restocking remains necessary. Jaarlijks wordt in opdracht van het ministerie van Landbouw, Natuur en Voedselkwaliteit de Nederlandse hamsterpopulatie gemonitord. Dit bestaat uit een telling van bewoonde burchten in de verschillende leefgebieden. De hamster komt alleen voor in het zuiden van Limburg en heeft een voorkeur voor (winter)- graanakkers of akkers met luzerne. De hamster is in 2002 geherintroduceerd in gebieden met een aangepast agrarisch akkerbeheer. De laatste jaren is met het zogenaamde HOEB-project (Hamster op Eigen Benen, 2015-2018) getracht nieuwe vormen van hamstervriendelijk beheer te vinden die enerzijds goed inpasbaar zijn in de agrarische bedrijfsvoering en anderzijds minder kosten qua beheer. Dankzij het HOEB-project is het totaal areaal hamstervriendelijk beheerde akkers met geschikt habitat uitgebreid met ruim 200 ha tot ruim 700 ha. Het is nog afwachten wanneer deze uitbreiding ook een effect gaat laten zien op de hamsterpopulatie. Ondanks alle inspanningen is het tot op heden nog niet gelukt een robuuste populatie te creëren die zelfstandig kan overleven. De monitoring van hamsters, aan de hand van burchttellingen en door middel van gezenderde dieren, laat zien dat het in de praktijk nog steeds erg lastig is voor hamsters om voldoende lang te overleven en voldoende worpen te krijgen om de populatie te laten groeien. De laatste tellingen wijzen op een aantal van minder dan 200 bewoonde burchten, verdeeld over ca. 20 kilometerhokken. Daarmee is de hamster nog steeds ernstig bedreigd en bijplaatsingen blijven vooralsnog noodzakelijk om de populatie te ondersteunen.

In the past decades, large-scale conservation programs have been implemented to halt the decline of farmland species. The mechanisms explaining the effectiveness of these programs remain poorly understood. Here we test the recent hypothesis that the effects of conservation management are determined by the ecological contrasts in limiting resources they create relative to the baseline situation. We examine responses of wintering seed-eating farmland birds to the experimental establishment of winter food plots in areas with contrasting food availability. We found that farmland bird abundance and species richness were strongly positively related to seed availability, regardless of compositional differences between agricultural landscapes. In line with the ecological contrast hypothesis, the responses of wintering farmland birds increased with increasing conservation induced contrast in a key limiting resource. Both contrasts and relative responses were negatively related to baseline food availability, but the absolute bird density in food plots was unrelated to baseline food availability. This indicates that both relative and absolute effects of conservation management need to be considered to properly evaluate the effectiveness of conservation management.

Low pathogenic avian influenza virus can mutate to a highly pathogenic strain that causes severe clinical signs in birds and humans. Migratory waterfowl, especially ducks, are considered the main hosts of low pathogenic avian influenza virus, but the role of geese in dispersing the virus over long-distances is still unclear. We collected throat and cloaca samples from three goose species, Bean goose (Anser fabalis), Barnacle goose (Branta leucopsis) and Greater white-fronted goose (Anser albifrons), from their breeding grounds, spring stopover sites, and wintering grounds. We tested if the geese were infected with low pathogenic avian influenza virus outside of their wintering grounds, and analysed the spatial and temporal patterns of infection prevalence on their wintering grounds. Our results show that geese were not infected before their arrival on wintering grounds. Barnacle geese and Greater white-fronted geese had low prevalence of infection just after their arrival on wintering grounds in the Netherlands, but the prevalence increased in successive months, and peaked after December. This suggests that migratory geese are exposed to the virus after their arrival on wintering grounds, indicating that migratory geese might not disperse low pathogenic avian influenza virus during autumn migration.

Breeding success of many Arctic‐breeding bird populations varies with lemming cycles due to prey switching behavior of generalist predators. Several bird species breed on islands to escape from generalist predators like Arctic fox Vulpes lagopus, but little is known about how these species interact. We studied brent geese Branta bernicla bernicla that share islands with gulls (Larus spec.) in Taimyr, Siberia (Russia). On one hand, gulls are egg predators, which occasionally steal an egg when incubating geese leave the nest for foraging bouts. On the other hand, gulls import marine resources to the islands, enriching the soil with their guano. We considered three hypotheses regarding clutch size of brent geese after partial nest predation. According to the “predator proximity hypothesis”, clutch size is expected to be smallest close to gulls, because of enhanced predator exposure. Conversely, clutch size is expected to be largest close to gulls, because of the supposedly better feeding conditions close to gulls, which might reduce nest recess times of geese and hence egg predation risk (“guano hypothesis”). Furthermore, gulls may defend their nesting territory, and thus nearby goose nests might benefit from this protection against other gulls (“nest association hypothesis”). We mapped goose and gull nests toward the end of the goose incubation period. In accordance with the latter two hypotheses, goose clutch size decreased with distance to the nearest gull nest in all but the lemming peak year. In the lemming peak year, clutch size was consistently high, indicating that partial nest predation was nearly absent. By mapping food quantity and quality, we found that nitrogen availability was indeed higher closer to gull nests, reflecting guanofication. Unlike predicted by the nest association hypothesis, a predation pressure experiment revealed that egg predation rate decreased with distance to the focal gull nests. We therefore propose that higher food availability close to gulls enables female geese to reduce nest recess time, limiting egg predation by gulls.

A key issue in conservation is where and how much management should be implemented to obtain optimal biodiversity benefits. Cost-effective conservation requires knowledge on whether biodiversity benefits are higher when management is concentrated in a few core areas or scattered across the landscape, and how these effects vary between species. To address these questions, we examined species-specific behavioural responses of over-wintering farmland birds to enhanced seed availability. In a two-year experiment we first examined the relationship between landscape-scale seed availability and farmland bird density. Then we investigated the relative resource delivery (difference in bird densities between landscapes with and without additional management) and the efficiency (number of individuals supported per unit management) of conservation actions, both at the landscape-scale (ca 100 ha) and at the scale of the conservation measures (3.6 ha). The conservation actions were targeted towards ten seed-eating farmland bird species, but we also considered the responses of seven non-targeted and more generalist seed-eating species, seven species that are less dependent on seeds and three species of birds of prey. We found a positive relationship between bird density and landscape-scale seed availability for eleven species and, for four of these species, the slope of this relationship changed before and after a threshold seed density. For two seed-eating specialists, the number of individuals using conservation patches declined with landscape-scale seed availability. In addition, we found that the relative resource delivery declined with landscape scale seed availability for three seed-eating specialists and was independent of landscape-scale seed availability in four other species. Our results suggest that farmland specialists may benefit most from winter food additions if conservation actions result in high landscape-scale seed availability. This may be achieved by concentrating conservation measures or by establishing measures in areas with high baseline seed availability. By contrast, species that can utilize a wider range of habitats and resources may benefit more from scattering measures across larger areas. Therefore, optimal management for the full range of farmland birds in wintertime may require a combination of core areas with concentrated management and more widely distributed smaller patches of conservation measures.