Chestnut-sided Warbler

Today, I had two Chestnut-sided Warblers side by side in the net. That in itself is not so remarkable, given how common they are here in Tortuguero, Costa Rica, as migrants and winter visitors. I see these birds practically every day, usually a little higher in the canopy. I don't catch them very often.

In fact, since I've been here, I've only caught two individuals before these two. One was on the 21st of October, my first day of banding here. The other was on the 29th of October. That second bird got out of the net on its own, before I could extract it.

What is remarkable about today's capture, however, is that one of the birds was already banded - and it wasn't the October 21 bird! Unfortunately, I don't have access to the banding database of this site, so I cannot yet be 100% sure of this, but I think this may be a recapture from somewhere else!

As you can see when you click on the photo, the band ends in a 6. The full band code was 211094346. I looked at the (paper) banding records going back to 16 October 2010, when Evan Adams started banding here, and I do not find any record of this band. In fact - and here's the kicker - I do not find any 0 or similar sized band records that start with 211!

This last bit of evidence tells me that the series from which this band came is not from here. I aged the bird as a HY (hatch year) bird, based on a molt limit visible in the primary coverts. So, unless I am very much mistaken, this bird was very likely banded somewhere else earlier this year!

If so, it would be a great capture, for this is really why we band birds in the first place. But again, just like the recent putative Bicknell's Thrush captures, we won't know for sure until later. I'll have to check with the site coordinator whether this is really a recapture from someplace else. If so, it will likely take a bit more time before we know where it was banded.

Postscript 24 November 2010:
This bird was banded right here in Tortuguero in October 2008! Not a hatch year bird then; I still need a lot more experience ageing warblers, which is more difficult than, say, thrushes. But the recapture, two years later, seems to imply either winter site fidelity or, at the very least, a preference for using the same migration route among years. A third capture outside migration season would clinch it. But what are the odds of that?