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Another two from last Summer - both with darker mantle than nearby argenteus, both with yellow(ish) legs, both with broken band on P5 on one wing only, but on opposite wings. My question is, does this P5 pattern rule out michahellis or not? Thanks.

Hi Tim,
Interesting bird this is. Yellow legs and a shade darker than argenteus sounds okay for michahellis, but the wingtip is odd. Of course there is individual variation between populations with eastern birds showing less black, but in your bird the distribution of black doesn't match western birds. Black on P5 has a thin pattern, but also see that deep tongue on innerweb of P8. Ideally you would like to have more than 50% black there with a diffuse gradient. Here it is a deep tongue with a clear-cut border. See e.g.: http://gull-research.org/ylg/ylg5cy/5cynov016.html