Wing Tagging Marsh Harriers  Circus Aeruginosus in Norfolk

The Sex of nestling Marsh Harriers

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 had been pioneering work on developing the toe span method to sex Marsh Harrier nestlings using the Dutch protocol prior to the wing tagging project 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.

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