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Preservation of Boutaris stellaris and wet land area.
In Great Britain the Botaurus stellaris (English name is “bittern”) is a red listed bird specie. A hazardous past has led to an increasing interest for the protection and thereby the necessary factors needed for this breed to increase in size and get back to a healthy population.
During 1997-2001 searchers has collected information and systematically put it together trying to get an understanding of the bitterns behaviour and requirements. One of the most important issues have been to localise factors included in a successful nesting, which will lead to a better knowledge for the coming years conservation strategies.
Some facts about the bittern
Bittern is a shy bird that is more often heard than seen. It has a voice similar to the deep sound created when you blow some air over the top of an empty bottle. (http://cyberbirding.uib.no/nof/galleri/lyder.php) .
It is has a black little cap on the head, feathers are spotted and striped in black and light brown along the body. Feats are particularly well developed in size, and this is an advantage in the nest building. The size of the body is about 76 cm.
It is living in reed grass rich wetlands and marshes. Wetlands have the last 150 years all over Europe been reduced in favour for agriculture, and building areas. It has been treated as an area recourse that could be filled up with soil or stones and used for shortening roads (eg. in a bay), industrial building ground , or just a nice beach instead of a muddy bank. Lately the pollution from industry and agriculture has also led to a faster succession (increasing nutrient value), and the wet lands are growing into grass and shrub lands with inhibited flow of water. It is easy to understand that it is of high interest to transform a muddy and often bad smelling bay into a nice looking beach where tourists can spend their money on hotels and explorations. Therefore it has been easy to donate these areas without further thoughts about their role in the local bio system. Today we have the situation of bird species being threatened by extinction because of their dependence on these areas. Especially long travelling birds are completely depending on this rich wet land areas to recover or take a brake to build up new fat reservoir before continuing the journey.
A muddy bank is often located in an area of the coast where the wind is shy, and the water-streams are minimal. A river delta with fresh water brings small particles (colloidal solutions) and lots of nutrients from the land the water has passed through. In the meeting between fresh river water and salt sea water the small particles (colloids) will be salted out from the fresh water and precipitate on the sea bottom. This is why such a delta often is very muddy and the water-level is low. The vegetation typical for this environment is salt and nutrient loving plants, and there is a gradually succession from the water up to the trees which is nicely adjusted to the tide, salt concentration and light accessibility. This induces a highly special environment for specialised plants and animals. The nutrient rich river water is filtrated through the vegetation before it is realised and mixed with the sea water. One of the species living here is Phragmites australis (reed grass), a key plant in the nest building of bitterns.
What have been done to preserve bittern from distinction ?
To be able to conserve the bittern population in Great Brittan, female bitterns and their nesting habits have been investigated. It is generally more difficulties associated with observations of female birds because of the lack of singing since they do not behave territorial. The observations were done at the beginning and end of nesting periods to avoid scaring of the nesting birds, and by that death of chicks.
The results showed that a nesting bittern has special preference when it comes to where she is nesting.:
1-Vegetation has to be continuous, and dominated by Phragmites species.
2-The most narrow place should on average not undergo 100 m in width.
3-The area should be undisturbed ( average 2.8 ha in size).
4-It is observed that the female bittern prefer to nest where the stems of Phragmites australis is thick (3-10 years old).
There is uncertainties concerned to this observation. A thick stem on the reed grass insinuates that there is a continuous water level, even at the driest time of year (September) It is not clear if it is the water presence or the thickness of reed grass stems that is the factor preferred, or maybe both. Benefits of bout factors can easily be imagined :
-Thick stem on reed grass:
- It makes a better material for building nests.
-Continuous water around the nest:
-The bittern is eating fish, and thereby will have an easy way too food.
- It is observed thou that the bittern female can easily travel 2 km to find food for her young’s, so this might not be a good reason.
-The water makes a barrier for possible predators of the chickens.
The material mainly preferred for nest building (in more than 90% of the nests) is as follows :
- Cladium 51, 7%
- -Phragmatis australis 36, 7 %
- Junicus 5%
From the information obtained it is possible to enlarge the nesting areas for the Botaurus stellaris, and better conserve the areas already existing. There has to be a clear policy to avoid any building in these areas, and consequent make nature reserve out of popular nesting areas, and the nearby land to ensure peace in nesting period. It is clear that pollution has to be reduced to inhibit the succession in going unnaturally fast and turn reed grass area into sumps and grasslands. We can see that the size of undisturbed area rich in reed grass is an absolute necessary factor for nesting and therefore survival of the species. In the case of species that are crossing land boundaries it is of major importance that there is a cooperation between countries housing the species.
The following article: Nesting habitat selection by bitterns Botaurus stellaris in Britain
and the implications for wetland management
Gillian Gilbert a,*, Glen A. Tyler b, Christopher J. Dunn c, Ken W. Smith c
http://cyberbirding.uib.no/nof/galleri/lyder.php (pictures of bittern)
http://site.www.umb.edu/conne/leslie/lesliepage.htm (pictures of Phragmites australis)
|Notes (if any) by Peter Kabai:|