Consider this presumed first summer bird. The gray upperwing coverts and tertials are a result of the first prealternate molt. New primaries are also coming in:
|Franklin's Gull. LaSalle County, IL. 04 July 2010.|
|First alternate primaries (P1-P7). Notice the three outer primaries (P8-P10) are juvenile. Most of the secondaries are also juvenile feathers.|
Now to the puzzle bird that this post's title is referring to:
|Franklin's Gull. Chicago, IL. 25 March 2011.|
After giving the puzzle-bird some thought, I guessed that it may not have molted any primaries in PA1. This is not unheard of especially with birds that winter farther north.
|Franklin's Gull with puzzling outer primaries.. Chicago, IL. 25 March 2011.|
It may have acquired second generation primaries more or less around the time of the second prebasic molt (1st summer). The older, outer four primaries, would therefore be retained from 2nd basic. The newer primaries, P1-P6 may be 2nd alternate (2nd winter), which presumably were acquired via an incomplete prealternate molt (on the wintering grounds?). Whether or not PA2 is incomplete or suspended is beyond the scope of this post, but it's obvious P1-P6 are newer than P7-P10. It may just be that primary molt will resume with the outer primaries once this bird settles down for the breeding season (just as in the LaSalle County bird above).
The only confusing consequence of my explanation is whether a first cycle Franklin's can migrate to South America and back to North American with its first basic primaries (i.e., its juvenile primaries). One has to wonder whether this bird ever migrated as far south as the majority of Franklin's do during their first winter. Or perhaps it roamed the interior during its first journey back north, never making it to the breeding grounds in the northern Great Plains or the Prairie Provinces.