De Levende Natuur nummer 5 van 2007 (English summary)


DLN 2007-5

Do threatened breeding bird species benefit from the new Biesbosch?

Meijer, R. & B.A.M. Weel

Since the end of 1970 the habitats in the freshwater tidal area Biesbosch have changed dramatically due to the closing of the sluices in the Haringvliet. The tides which shaped the area disappeared to a large extent and the production of reed and withies almost came to a halt. The reed beds dried out and changed into fields with nettles and other rough herbs. Later on willows and elder began to dominate part of the vegetation. Most holms changed into willow woods. Especially the last decade new marshes were constructed by removing part of the top soil of some polders and inundating them. All these changes had an enormous impact on breeding bird populations. In this paper the trends in numbers in the Biesbosch of species listed on the Dutch Red List are compared with those in The Netherlands. This comparison is made for the species groups which are typical for the area. It is shown that the overall picture is the same in the Biesbosch as on the national level: most species show marked declines in both areas. Of 29 regular breeding bird species 10 show a worse trend in the Biesbosch, 7 a similar and 12 a better trend. Of these 12 species 5 are new for the area and/or showing a marked increase: Common tern (Sterna hirundo), Purple heron (Ardea purpurea), Teal (Anas crecca), Green woodpecker (Picis viridis) and Nightingale (Luscinia megarhynchos). It is shown that the new marshes had a very positive effect on several species of pioneer habitats and birds of water and marshes. The future of the breeding bird populations depends on the outcome of the plans to develop new nature and the protection of these areas especially against recreation.

Conservation of Corncrakes (Crex crex) in grassland in The Netherlands

Koffijberg, K.

In the past century successful breeding of Corncrakes in grassland has become increasingly difficult, and low reproduction rates have caused major population declines in a large part of the species' breeding range, as is the case in The Netherlands. The species has become increasingly dependent from agricultural grassland that is mown annually. In The Netherlands, many Corncrakes are attracted by meadows that have a late mowing regime because of protection of meadow birds like Black-tailed Godwit (Limosa limosa). However, for Corncrakes these meadows often act as an 'ecological trap' and when mowing proceeds from 15 June onwards, many broods and singing males are disturbed. A national conservation scheme, including delayed mowing until 1 August and mowing from the inside out was implemented in 2001. Without these protection measures, 70% of all Corncrake settlements would be disturbed annually. Additionally, experiments have started with mosaic-like habitat management, providing Corncrakes with vegetation cover from May to September. Smaller numbers of Corncrakes also breed in renaturated areas in floodplain meadows, often in the first years after reconstruction. After 5-6 years numbers seem to level off of decline again. It is hypothesized that lack of large-scale vegetation dynamics obstruct Corncrakes in their movements, making this habitat less suitable for breeding over longer periods. More habitat dynamics, caused by specific management-measures and/or reconstruction of new areas might provide the necessary floodplain dynamics to keep enough suitable habitat available. Together with conservation measures in agricultural grassland, these measures provide Corncrakes good opportunities to keep their status as a typical breeding bird in Dutch floodplain meadows.

An ecological and population genetic framework for reintroduction

Groot Bruinderink, G.W.T.A., M.J.M. Smulders & H.P. Koelewijn

In 1987 IUCN guidelines for reintroduction of species were launched. They offer a tool to enhance carefulness and chance of success of reintroduction projects. In the past many reintroduction cases have failed. Therefore, and because IUCN guidelines in practice leave room for ad hoc interpretation, a framework is suggested in which pros and cons of reintroductions can be balanced on ecological and population genetic arguments. In this paper such a framework is suggested. It is based on the principle: ‘no reintroduction, unless…’ (fig. 1). The framework was inspired by the current practice of reintroductions in The Netherlands. If ultimately the balance is in favour of reintroduction, IUCN guidelines and national legislation on the reintroduction of species should be followed

Long-term effects of environmental education on knowledge, attitude and behaviour towards nature and environment

Bulten, M.C. & P. Jansen

Numerous activities are carried out for the purpose of environmental education of children in The Netherlands. On the base of educators’ experiences as well as scientific research it is highly plausible that environmental education can make contributions on knowledge, positive attitude and more friendly behaviour towards nature and environment.

To investigate long term impacts of environmental education on a quantitative statistical base, Veldwerk Nederland, in cooperation with the universities of Utrecht and Wageningen, has carried out this research. The central research question is: Do pupils of primary schools, which participate in relatively many environmental education activities, have a significantly different knowledge, attitude or behaviour towards nature and environment on a long term, compared to pupils who did not or less participated in environmental education activities?

In 5 areas distributed over The Netherlands 25 primary schools were sampled. Pupils who had left these schools 1 year, 7 years and 15 years ago were interviewed about their knowledge, attitude and behaviour towards nature and environment.

The results of the research give evidence that pupils who participated in more environmental education in primary school, have significantly more knowledge about nature and environment, and a significantly more positive attitude and behaviour towards them over a period of several years. The advice from the research group towards the Dutch government is to train teachers in these activities, to stimulate primary schools in environmental education and create sustainable funding and possibilities for carrying out these activities.

Bewick’s swans foraging close to roosting places migrate the fastest

Gils, J.A. van & W. Tijsen

This study was triggered by the apparent heterogeneity in the use of agricultural fields in the Wieringermeerpolder by migratory Bewick’s swans. We wondered why some fields with leftovers of sugar beets remaining after the farmers’ harvest were used more intensively than others, while all fields seem to offer similar amounts of food. So foraging costs could probably explain the observed spatial heterogeneity. We used the time spent feeding on a field by a flock of swans as a surrogate of an individual’s energy intake rate. This way we showed that an individual’s intake rate when abandoning a field was lower when further from roads and higher when further from its nighttime roost. When taking these costs into account, we calculated that the net benefits at which each field was left corresponded with the net benefits obtained in the long run. A foraging model accurately and correctly predicted the true number of birds that made use of the stopover. This model can thus serve as a valuable tool to manage and protect the relatively small and declining population of Bewick’s swans.