By Chris Heward, Wetlands Research Assistant
Every now and again we make a mistake. It’s not too common thankfully, but in the past whilst attempting to satellite-tag migrant woodcock, we’ve mistakenly tagged British residents. Four of the sixty-four woodcock we’ve tagged since 2012 have turned out to be non-migratory Brits. Although this can generate some interesting data, it is doesn’t tell us very much about woodcock migration, which is the real aim of our Woodcock Watch project.
Mistaking a resident bird for a migrant is easily done as the two populations are physically identical in terms of their appearance, but we can use weight as a guide. A migrant ought to prepare for its 2,000 km + journey by increasing its body fat and muscle mass. Residents, on the other hand should slim down a little, no longer needing to carry the fat stores that have helped them survive the winter.
When I tagged Nellie III s/he weighed 360g, a weight that put him/her squarely in the category of ‘migrant’. But by the 4th April, I was beginning to question this assumption. Whilst all our other tagged birds were in Eastern Europe and Russia, Nellie III was still happily loitering in Norfolk. It looked like s/he was planning on staying after all.
On 6th April, however, we received a series of transmissions showing Nellie III in the process of crossing the North Sea. What a huge relief! Not only was I pleased to see Nellie III finally on the move, s/he transmitted regularly during the crossing; something that we have only rarely observed before.
It does, of course, leave us with some unanswered questions, foremost amongst them; why did s/he leave so late? This may become clearer when we see Nellie III’s final summer location. It could be that, if the journey is short, there was no need to depart as early as our other birds; all of which appear to be heading for Russia.
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