American Black Tern -v- Eurasian Black Tern (1 Viewer)

Hi all.

I was wondering if anyone could help me out with the differnces in these two species of black tern as i will be going to see a first summer american black tern tomorrow and would like to know what i am looking at otherwise i reckon it would be a complete waste. I suppose what i am really looking for is a link to a comparative website with pictures of the two. The best i could come up with is here:
http://www.martinreid.com/Main website/blte.html

Unforntunately this only covers the juveniles.

Any help would be much appreciated asap as i will be leaving at three in the morning.

Seán.

I've read somewhere about the head pattern an analogy that American has more of 'headphone' shaped black cap maring behind the eye because of the more restricted black. This seems to be true from the photo on surfbirds.

Simon

Check these adult surinamensis, and notice the White-winged Black Tern jet black underparts where the black on head reaches to upper mantle.

http://www.wildbirdgallery.com/images/birds/chlidonias_niger/surinamensis.htm

http://www.pbase.com/image/61795469 (notice the obvious contrast between white leading edge of the wing against black underparts)

niger:

http://www.wildbirdgallery.com/images/birds/chlidonias_niger/niger.htm

Notice on surinamensis juvenile the head pattern (mentioned by Simon, but also the much larger dark breast patch, and the darker flanks:

http://www.pbase.com/image/49993126

http://www.pbase.com/image/46699919

and darker rump of surinamensis:

http://www.pbase.com/carolmhorner/image/47680827

http://www.pbase.com/carolmhorner/image/47680827

But chek head pattern on this niger:

http://www.pbase.com/image/50354642

JanJ