De Levende Natuur nummer 1 van 2013 (English summary)


DLN 2013-1

Feral cats on Schiermonnikoog

T. op de Hoek, M.J.J. Schrama & C. Smit

Following the idea that the feral cat population at Schiermonnikoog implicates a potential threat to endangered bird species we estimated feral cat abundance, and determined their distribution over the island as well as their diet. In addition, we compared the population of feral cats with the population of housecats at Schiermonnikoog. We used camera trapping in combination with a capture-recapture data analysis, collection of droppings, diet analyses and a questionnaire. We estimated the population of feral cats at the Schiermonnikoog at about 50 individuals. In the 180 droppings that we analyzed we found 410 individual prey items; mainly voles (58.6%), hares or rabbits (14.8%) and birds (13.7%). Few feral cat sightings near the village in combination with high birth control of village cats (and no sightings in the field) suggest that the contribution of the village (cats) to the feral population is marginal. Based on the estimated population size and diet information, we were able to estimate the annual consumption rates by feral cats and thus their effects on prey species. Our results show that a self-sustaining feral cat population exists and that predation by cats is likely to affect at least some small bird species and hares and/or rabbits.

Does the Ring-necked Parakeet form a threat for the Noctules bat?

A.-J. Haarsma & C. van der Graaf

The forest estates along the coast of The Netherlands are an important habitat for several bat species. The Noctules bat (Nyctalus noctula) uses tree cavities made by woodpeckers as maternity and winter roosts. From October to April they hibernate in large numbers in cavities selected for their size, safety for potential predators and quality of wood. The same habitat and tree cavities are also used by the Ring-necked Parakeet (Psittacula krameri), an introduced species with a strong population increase since 1968. In contrast to most native bird species, the breeding season of the Ring-necked Parakeet starts already in early winter. Their nesting behaviour includes extensive adaptations to the exterior and interior of tree cavities made with their sharp beak. In this article we express our concerns about the possible negative effects of the competition for tree cavities between the two species, such as disturbance during hibernation and the loss of suitable winter roosts, and we ask for observations.

Development of the vegetation structure in the river foreland Blauwe Kamer

E.M. Langbroek, C. Bakker & C. Smit

Large scale restoration of riverine habitats, followed by management by large herbivores has been undertaken in the Blauwe Kamer area along the river Rhine. The aims of this and many similar projects along the Dutch rivers were to reduce flooding risks and enhance biodiversity. For these outcomes the development of the vegetation structure is crucial. Based on literature, three possible developments would have been plausible: (1) stabilization of the vegetation pattern shortly after the restoration, (2)  an ongoing succession towards shrubs and forest, or (3) cyclical succession. An analysis based on aerial photographs was done to evaluate the development of vegetation patterns in the Blauwe Kamer. We found that in the first sixteen years after restoration of the floodplain large scale changes in the vegetation pattern still took place, ruling out the stabilization hypothesis. On tens of hectares the vegetation kept switching between short, grassy vegetation and tall swards, supporting the cyclical succession hypothesis. On other parts a slow but steady increase of shrubs and trees was visible, confirming the ongoing succession hypothesis. These results implicate a refinement of the 2nd and 3rd hypotheses. Vegetation development may be reversible on the short term (from swards to grassy) or unidirectional (development to woody vegetation).  An analysis over a larger time scale is needed to see whether cyclic succession in woody vegetation will occur. These results may aid site managers to decide in which circumstances additional management may be needed to achieve goals in terms of flooding safety or biodiversity.

Ambitions of Natuurmonumenten for nature and landscape in 2040

B.F. van Tooren & J.J. de Graeff

Natuurmonumenten presents its ambition for the next decades. In the past Natuurmonumenten focused strongly on achieving more nature reserves. However, that is not enough to preserve bodiversity in The Netherlands. Outside the reserves loss of biodiversity is still going on. The new perspective is based on three  principles. The first is that The Netherlands is characterized by many different landcapes. Just this varity causes a high biodiversity and should be maintained. To do this, only the combined efforts off al inhabitants can help, within but even more outside the reserves. In the future Natuurmonumenten will give more attention to improving  the varity of nature and landscapse outside the reserves, and will seek partners in doing so. Second, climate change and in general the need to sustainability ask for drastic measures. In our opinion, solutions are needed that use ‘building with nature’ principles instead of technocratical solutions. Third, and perhaps even the most important factor, we have to regain the connection of people, especially children, with nature.