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Boxing Day: ageing Black-necked Grebe

25 December. Boxing Day! Rinse and I don't need much time to think when were asked to ring a few birds in bird hospital De Wulp. The star of the day is a Black-necked Grebe.

The poor bird has been bitten in the neck by something, probably a dog. It's recovering fast, but it still needs some time before it can be released. But leave that to the ladies!

Ageing is based on two features. The pale orange iris indicates a young bird; I'd expect a more reddish iris in an adult (see here).

More importantly are the juvenile scapulars, that are obviously still brown instead of black. So yes, this is a young bird (1 cy). Apparently this is only the 14th Black-necked Grebe ever to be ringed in the Netherlands.

It reminded me of the Slavonian Grebe we ringed here back in 2013. Ageing works the same way as in Black-necked. This bird had a red iris, but this was in February - nearly three months later.

There wasn't much contrast in the wing of today's Black-necked:

But brown, juvenile feathers (e.g. the greater coverts) were found in the wing of the Slavonian at the time:

So this too was a 1st winter. I remember it was in great shape: it only got disorientated by lights during the night and therefore ended up at the wrong place (it flew into a building and couldn't get out). It was released straight after the health check: there was no need to keep it inside any longer.

After we ringed the brebe, it became clear only star birds were available, with Guillemot, Razorbill and Kingfisher also ringed. And a lovely Red-throated Loon that frequently uttered a wailing alarm call. Rinse knew this call from the nesting sites in the arctic, but at least it did manage to impress me:

#BlackneckedGrebe #RedthroatedLoon

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Little Bunting
The most interesting thing about this chapter is the sexing of birds. This could be done on the basis of lateral crown stripe: a new feature for me. Because of overlap between adult females and young males, birds should first be aged. The authors emphasize that this is their vision, and not necessarily the final answer to this matter. I found one in the field in October (Figure 4-5) of which I took reasonable pictures. The very rounded tail feathers look adult, as do the tertials and large coverts. The lateral crown stripe appears to be jet black and is separated from other feathers, such as the greyer back of the head. The orange-red crown stripe really stands out. Conclusion: according to this book this must be an adult male! The deep brown-red cheek - a variable feature according to this book - also fits that. So it works then? Well… how useful this really is, remains the question: based on this book I would label two "females" in Shirihai & Svensson (p546 both top right and bottom right) as males! The caption of one of these even mentions "safely identified as a female" because it has a relatively dull plumage for an adult bird. But is also has a jet black, strongly separated lateral crown stripe! The bird at the bottom right even has a pretty deeply coloured cheek, which I would be happy to call a male. Is this due to different insights, and if so, who should I believe? Or am I not interpreting this correctly? In any case, it is fascinating!

© 2018 by Vincent van der Spek