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Wing Tagging Marsh Harriers Circus Aeruginosus in Norfolk |
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The Sex of nestling Marsh Harriers and ring size. |
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Traditionally all Marsh Harriers in Britain were ringed with F rings
internal diameter 9.0 mm, however some ringers had noticed that when
some pulli had transitioned from the white and fluffy stage to greater
feather devolpment or were almost ready to fledge that F rings were
tight on the tarsus and had to be shaped so that the ring could slide up
and down but could not be rotated. Enquiries to many European ringing
schemes provided the information that either these schemes were using a
ring size for males which was 9.0mm internal diameter or 11.0mm internal
diameter for females or were using 11.00mm for both males and females.
In order for correct ring sizes to be used pulli must first be sexed. Although for many years continental ringers had been using the toe span method developed by the Dutch to sex Marsh Harrier nestlings in the nest it was not used in Britain. North West Norfolk RG began work on developing the toe span method to sex Marsh Harrier nestlings using the Dutch protocol and was able to present enough evidence to the British Trust for Ornithology(BTO) for them to adopt it. This means that it is now a mandatory prerequisite that nestlings must be sexed before ringing with the correct size ring as males and females take different size rings. Males must be fitted with size F internal diameter 9.0mm and females size G internal diameter 11.0mm. The Project provided an ideal opportunity to develop the toe span method further with increased access to nests coming from participants in the project. Back to Marsh Harrier homepage
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