Publications

# The impact of tourism upon some breeding wader species on the isle of Vlieland in the Netherlands' Wadden Sea

Roos, G.T. de

## Summary

Birds and man are of importance to eachother, directly and indirectly, positively or negatively.

Populations of wild birds may decrease or even become extinct due to human activities because they are threatened directly or because theire characteristic habitats are destroyed. On the other hand, human effects might consist of protection or the creation of new habitats, e.g. by constructing dikes of drift sand or basalt piers on Vlieland.

Direct protection by establishing bird sanctuaries is often necessary to prevent local extinction of certain species. On the other hand protection of species like Herring Gull ( *Larus argentatus* ) may have negative effects upon other species.

In order to convince people that certain nature management measures should be taken, solid knowledge should be available of the effects and interactions of various factors affecting bird populations.

Though the original motivation was to study the effects of tourism upon numbers of nest sites or territories, effects of the factors landscape/vegetation and altitude (above Amsterdam ordnance datum (+NAP))/hydrology were investigated in the same way. The literature concerning the effects of the three above-mentioned factors has been reviewed.

The isle of Vlieland. in the Dutch Wadden Sea was chosen as the research area because it attracts many of tourists and contains many different habitats attracting large numbers of birds, in particular waders. Attention was restricted to the (European) Oystercatcher *(Haematopus ostralegus),* the Curlew *(Numenius arquata* ) *,* the Redshank ( *Tringa totanus* ) and the Kentish Plover ( *Charadrius alexandrinus* ).

In order to study the effects of and interactions between the factors (1) landscape/vegetation, (2) altitude/hydrology and (3) tourism upon numbers of nest sites or territories, data were collected and mapped as outlined in chapter 2. The vegetation maps reveal how an area is subdivided into smaller areas of different vegetation types, the altitude maps indicate the different altitude classes. Three tourism zones were defined for the interpretation of aerial photographs. Yearly breeding bird maps give the precise location of nest sites or approximate territory centres. Various tables were obtained by combining breeding bird maps with those for the three above-mentioned factors.

For the 'non-experimental' study plots 3,..., 6 chapter 3 outlines the statistical evaluation of the effects of separate factors upon the (expected) nest density, while chapters 4, 5 and 6 outline the interaction between the three factors.

Two 'experimental' plots were considered in order to investigate more carefully in chapter7tourism effects. During the years 1974, 1975,plot 1 was open to the public whereas plot 2 was closed by means of no-trespassing signs. During the years 1976, 1977the situation was reversed.The relations between the results, mentioned in sections 3.1, ..., 7. 1, are as follows:*Conclusionsf or the Oystercatcher.*

(1) Results for the non-experimental study-plots. All three factors (vegetation, altitude and tourism) have an effect if they are considered separately for the nonexperimental study-plots (section 3. 1), which means that Oystercatchers prefer to nest in certain vegetation types, altitude classes and tourism zones (section 3. 1).

No sufficient proof for effects of the vegetation was obtained if the altitude is taken into account, while the evidence for altitude effects was sufficient if the vegetation is taken into account, which means that the null-hypothesis that no altitude effects exist if the vegetation is taken into account could be rejected (section 4. 1).

Even if the vegetation is taken into account, tourism zone 1 is more attractive than zone 3. However taking tourism into account, vegetation effects could be established for plot 4, but not for plot 3 (section 5. 1).

If the altitude is taken into account, when tourism effects could be proved for plot 3, but not for 4, though indications also exist here. For the reverse problem sufficient evidence is available for the existence of altitude effects, if tourism is taken into account (section 6. 1).

Summarizing the Oystercatcher results for the non-experimental study-plots we obtain the opinion that tourism is an important factor though altitude effects are not negligible.

(2) Results for the experimental study-plots. The experimental study-plots suggest that some time is needed before the effects of no-trespassing signs become noticeable: the data for 1974/1976 does not lead to sufficient evidence for such effects which clearly exist for 1975/1977. The confidence interval [ 1. 2, 4. 11 for the parameter v, which describes the effect of the no trespassing signs, means that if an area like plot 1 or plot 2 is closed by means of such signs, then two years later one may expect 1.2-4.1 times as many Oystercatcher nests (the actual numbers to be obtained may fall beyound these bounds because of chance fluctuations) (section 7.1). In 1978 both plots were open to the public and this remained so afterwards. The data for 1978, 1979 and 1980 are in line with the abovementioned conclusions: the figures for plot 2 are not markedly different from those in 1976/1977 when plot 2 was also open to the public, the figures for plot 1 show a decrease when compared with those in 1976 and 1977, obviously because plot 1 was closed to the public then.*Conclusions for the Curlew.* Landscape and tourism but no altitude effects could be established if the factors were considered separately (section 3. 1).

If landscape/altitude relations are investigated then possible effects of each factor can be explained as caused by the other. The interpretation of the difference between this result and the above-mentioned significance of landscape effects will be that some kind of dependence exists between landscape and altitude (section 4. 1).

No sufficient proof was obtained for tourism effects if the landscape is taken into account, though the data still suggests that such effects exist. No landscape effects seem to exist if tourism is taken into account (section 5. 1).

Sufficient evidence was obtained for tourism effects if the altitude is taken into account. No altitude effects seem to exist if tourism is taken into account (section 6.1).

Summarizing the results for the Curlew, tourism seems an important factor.*Conclusions for the Redshank.* Landscape effects, altitude effects and tourism effects could be established if these factors were considered separately (section 3.1).

Sufficient evidence for landscape effects was obtained for plots 5 and 6 if the altitude is taken into account. On the other hand, altitude effects exist for plot 5 if the landscape is taken into account, while the results for plot 6 were not significant (section 4. 1).

Sufficient evidence was obtained for tourism effects if the landscape is taken into account, while the evidence for landscape effects was also sufficient if tourism is taken into account (section 5. 1).

Tourism has effect if the altitude is taken into account. On the other hand altitude effects, if tourism is taken into account, were significant for plot 6 but not for 5 (section 6. 1).

Summarizing the results for the Redshank it is clear that both tourism effects and landscape effects exist.*Conclusions for the Kentish Plover.* The number of Kentish Plover nests in the open area shows a significant decrease if the most separate years 1964 and 1980 are compared. For the closed (military) area the decrease was not significant.

Sufficient evidence was obtained for tourism effects if the 1980 data were used and the distance to high tide level is taken into account. This was not the case if the 1964 data were used.

No effects of the distance to high tide level seem to exist if tourism is taken into account.

In our opinion, the decline of the number of nests in the open area is the result of an increase in the number of visitors.