Now that I’ve rediscovered the login details for the BF site, here’s another bird from Shetland, a Grasshopper Warbler trapped last weekend (11th May) in my garden in the south mainland.
I was chuffed with my first locustella in the garden – looking forward to the next species (and hoping it won’t be too long). The next day I caught it while I had the nets open for migrants in general. When I got it back to the ringing bench I was surprised to find that it was surprisingly short-winged. Plumage-wise it didn’t look like anything other than a fairly standard spring gropper but I rebagged it and went to check the critical biometrics in the BB paper on Eastern Grasshopper Warbler by Paul Harvey and Brian Small – read it here.
I measured the key features: wing 60.5, tail 55, tail/wing thus 0.91, tail graduation 20.0. P2 fell level with P4, and P4 was slightly emarginated. All of which means that it looks better for straminea, if not conclusively so (proportionately, it’s very long-tailed for a small naevia; and both the tail/wing ratio and the tail graduation measurement are close to or beyond the limit for naevia in the various sources given in the BB paper). Paul Harvey nipped down the road and checked my measuring.
Following the bird on Fair Isle last autumn, which was confirmed as straminea by DNA analysis, some lab work on the one flank feather I found in the bird bag afterwards is going to be the acid test for this bird too.
If it proves to be just a nominate gropper, it does raise the question of how useful the biometrics are, and suggests that all you can reasonably do without a DNA sample is identify the extremes – i.e. that a large majority of straminea might go unproven, even in the hand. All of which reinforces the cautious approach that the authors of the BB paper took I guess.