De Levende Natuur nummer 2 van 2017 (English summary)

Effects of habitat loss on Black-tailed Godwit and other farmland birds

D. Bos, R. Kentie, G. Hoekstra, Y. van der Heide, E. Wymenga, F. Hoekema, J.C.E.W. Hooijmeijer & T. Piersma

The loss of breeding habitat is one of several factors that are likely to contribute to the ongoing decline of the bird populations of dairy farmland. A large-scale economic development around the city of Leeuwarden in the province of Friesland (The Netherlands) allowed us to examine the downstream effects of loss of meadow on the local population of farmland birds in general and Black-tailed Godwits (Limosa limosa) in particular. Here, the construction of a new motorway and the development of urban area south west of Leeuwarden, led to a total net loss of 161 ha of meadows during the years 2010-2014. Associated with these developments there was an enhanced disturbance and changes in details of the land management over ca. 785 ha, while 917 ha of farmland became isolated. Together, these changes can be considered as a ‘natural experiment’. We documented the number of territories of common species of farmland bird before and after the main change had taken place. We examined to what extent individually marked Godwits were able to successfully acquire a new nest location in subsequent years between 2007 and 2015. We distinguished between birds that were potentially affected by the developments, given their nest location in the year of first capture, and a control group of birds that were not. The latter mainly consisted of birds in south west Friesland that were subject to a long term study on population dynamics. Using the software Mark we calculated resighting rates for Godwits in the ‘control’ and contrasted these to the ‘experimental’ group. Similarly, we calculated differences in nest site fidelity, from the distances between the original nest location and the location of newly acquired territory.
The number of territories for different species of farmland birds, including Godwit, strongly declined in the study area, and faster than in the remainder of the province. In response to disturbance, 26 out of 68 disturbed individually marked Black-tailed Godwits moved to a different zone. Fourteen individuals did not, or moved just a little bit within the zone. For 28 disturbed birds there is no information of nests after the main disturbance. The resighting rates for individually marked Godwits that had been classified as ‘experimental birds’ were not lower in comparison to the control group. The apparent nest success was markedly lower for nests in disturbed areas in the years of the disturbance than that of reference nests. New nest locations were spatially oriented in the south and west of the study area and appeared to be selected in areas that were characterised by the presence of other Godwits. New nest locations were also associated with herb rich meadows. The distances over which nest were found in subsequent years were within 2 km, but there was one pair that resettled 15 km away. As deduced from observations of alarming behaviour, multiple experimental birds with new territories produced hatchlings. We assume that the chances of Godwits successfully acquiring a new nest location can indeed be positively enhanced by providing nearby good quality breeding habitat, areas which are attractive based on the presence of other Godwits. However, preventing the loss of habitat is the preferred option.

A century vegetation in ‘de Zumpe’ (1915-2015)

Th.G. Giesen

In the last century the nature reserve ‘de Zumpe’ (east of Doetinchem, The Netherlands) has been strongly affected by increased drainage of the surrounding agricultural area.
Using historical data it was possible to determine the changes in species composition from 1915 (when the nature reserve was established) until now. In the period till 1960 vegetation diversity was high, and nowadays rare species characteristic of wet seepage areas were abundant. After 1960 most of these species disappeared because of increased drainage in the surrounding leading to lower groundwater levels and a decrease in seepage fluxes. Only more common seepage species remained.
Around the millennium, most of these drainage systems have been removed. As a result the water level rose and more alkaline groundwater reached the rhizosphere and surface. In combination with internal restoration measures this resulted in a strong increase in species diversity. Many species that had disappeared because of hydrological degradation returned, and new species that have never been observed before were found.

Effects of air traffic on white-fronted geese and wigeon?

R. Lensink, H. Steendam & K.L. Krijgsveld

In winter 2006/2007 during 10 days observations have been made on the disturbance of feeding geese as a result of air traffic near Groningen Airport Eelde. Four types of air traffic were distinguished: small planes (1-4 persons), medium sized planes (20-40 persons), large planes (>100 persons) and helicopters. Four types of reaction were identified: no reaction, flight and return, flight to nearby location within the range of vision and further flights beyond our scope. Flock size of disturbed and non-disturbed flocks was equal. Flight height of passing aircraft did not affect the rate of disturbance of geese flocks. Small planes had a limited effect both on flocks and individual birds followed by medium sized en large planes. Helicopters caused most disturbance. Disturbance by other sources (humans, cars, agricultural activities) was less frequently observed, but if apparent, led to more often and longer lasting disturbance.

Restoration and monitoring of fish migration in the River Roer at the ECI hydropower plant

R. Gubbels

The ECI hydropower plant in the city of Roermond is situated in the lower course of the river Roer. During decades the hydropower plant (and therebefore an old watermill) obstructed the migration of fish. To solve this problem, a fish pass and fish guidance system was built in 2007.

Between 2009 and 2014 an extensive monitoring of the up- and downstream migration of fish was conducted by a team of volunteers. During the monitoring 130.000 fish (47 species) were caught. A lot of species specific knowledge about migration characteristics and migration patterns was collected. These data resulted in new insights in the migration of fish.

• Downstream spawning migration of adult fish as well as the downstream migration of juvenile and subadult fish turns out to be much more common than reported in literature.
• Downstream migration of silvereel (Anguilla Anguilla), usually starting in autumn, ends in most years already before October/November.
• Migration of most fish species is especially triggered by fluctuations in water temperature. Fluctuations in water discharge appear to have no effect.
• As expected, downstream migrating smolts of salmon (Salmo salar) and seatrout (Salmo trutta trutta) nearly always choose the shallow positioned bypass and eels the deep positioned bypass. However, also fish species as perch (Perca fluviatilis), pikeperch (Stizostedion lucioperca) and ruffe (Gymnocephalus cernuus) especially choose the deep positioned bypass.

A negative outcome of the construction of a fish pass at the ECI hydropower plant is the colonization of the river Roer by invasive exotic fish species like round goby (Neogobius melanostomus). This species probably has an negative effect on certain native fish species.
The water authority Limburg is going to implement the collected migration knowledge in the planning, construction and monitoring of future fish passes and fish guidance systems.