15 May 2014

Recondsidering Tertial Replacement in 1st Cycle Ring-billeds

Post-juvenile molt in first cycle Ring-billeds typically commences in early August, beginning with 2nd generation scapulars. This feather replacement is sometimes extensive and appears to take place quickly as the fall season approaches. By fall, many individuals have almost entirely renewed their scapulars:

1st cycle Ring-billed with a considerable amount of juvenile scapulars replaced. A few median and lesser upperwing coverts have also been replaced. Benton Harbor, Michigan. 01 September 2012.
Usually, there's not much upperwing covert replacement until the 2nd calendar year via the first prealternate molt. Many individuals may go until mid-spring with no upperwing coverts replaced at all:

1st cycle Ring-billed. Upperwing coverts in relatively good condition considering the date.
30 April 2014. Tinley Park, Illinois.
But what about tertial replacement? As my post title suggests, perhaps we need to revisit this feather group: Do 1st cycle Ring-billeds replace their tertials in the first plumage cycle? If so, through what molt? Traditionally, the literature has held that 1st cycle Ring-billeds rarely, if ever, replace tertials. About two years ago, I began to suspect differently as I was finding more and more individuals with juvenile primaries that showed one or two, and sometimes all of their tertials renewed.

1st cycle Ring-billed with advanced post-juvenile molt. Note almost 100% 2nd generation scapulars, moderate upperwing covert replacement, and most interesting, a couple of new tertials (with black centers).
Chicago, Illinois. 27 September 2012.

Now here's an August bird showing one replaced lower tertial.

1st cycle Ring-billed. Extensive scapular molt with moderate upperwing covert replacement. Note the new tertial tucked in the lowest row. Chicago, Illinois. 25 August 2012.
Admittedly, I've never found a 1st calendar year (HY) Ring-billed with all tertials renewed, suggesting that perhaps the individuals I had found were anomalies. And so I paid particular attention to this feather group this spring and have found at least a dozen first cycles with all of their tertials renewed:

Note the white fringes on the newer tertials and upperwing coverts. Does this suggest these feathers were very recently replaced? Tinley Park, Illinois.  06 May 2014.
1st cycle Ring-billed. Same individual above. Note 1st basic (juvenile) primaries with renewed tertials.
Tinley Park, Illinois. 06 May 2014.
 A few more examples:

Tinley Park, Illinois. 06 May 2014.
Tinley Park, Illinois. 06 May 2014.
Tinley Park, Illinois. 15 May 2014.
Tinley Park, Illinois. 15 May 2014.
The evidence I've presented suggests that some individuals, and perhaps many more than we're aware of, do indeed molt their tertials - entirely! But through what molt? This is where it gets tricky...

I was wondering if this can be the result of an early 2nd prebasic molt. Peter Pyle weighed in on this question and suggested it would have to be via the first plumage cycle (i.e., PA1 or PF?):

"The May birds have replaced the tertials during the inserted first-cycle
molt(s). Although tertials are among the earliest feathers replaced during
prebasic molts, at earliest the single middle tertial should have been
growing or replaced by the time p1 drops. That 3-4 replaced tertials are
fully grown before p1 has dropped (in at least the one bird with open
wings) indicates that they had been replaced previously during the winter.

In gulls and shorebirds, the extent of inserted first-cycle molts
correlates well with how far south an individual bird goes for winter, and
a possibility is that these May birds had wintered near the southern end
of the winter range in Mexico or the Caribbean, farther south than occurs
in most other North American gulls. Most birds wintering in the U.S.
appear not to replace tertials. This might explain why first-cycle tertial
replacement had not been detected before or documented in the literature.
Good discovery!"

As Pyle suggests, these tertials are likely first alternate feathers, but what seems perplexing to me is that tertials are technically flight feathers (the innermost secondaries), and for flight feathers to be among the last feathers replaced in a prealternate molt, seems unconventional to me - at least with the large white-headed gulls. I do wonder if they're 2nd basic feathers, making them the first feathers replaced in the 2nd prebasic molt, almost matching the timing of P1 being dropped.

Consider this individual that I found today, 15 May 2014:

It indeed has begun the 2nd prebasic molt, identified by the loss of the innermost primaries:

1st cycle Ring-billed with entirely renewed tertials. Note P1-P2 have dropped, an indication that PB2 has begun.
Tinley Park, Illinois.
What adds to the confusion is not knowing exactly which molt produced the renewed scapulars and/or upperwing coverts. Are these feathers replaced via a prealternate or preformative molt? If prealternate, then it appears this plumage molts in two parts: beginning in late summer with the scapulars (see the first 2 images in this post), suspended for most of the winter, and then resuming in spring with the upperwing coverts (and presumbably the tertials with some birds - see the last 6 images). Of course other body feathers, being less obvious to pinpoint, are replaced during this time as well.

Peter and I are currently discussing the possibility of there being two inserted molts in the first cycle. This to me makes much more sense, paralleling what we see with Bonaparte's Gull, for instance, which exhibits the Complex Alternate Strategy. It may just be that the 2nd generation scaps we see in late summer birds (HY) are preformative feathers, while the new, fresh, upperwing coverts (and tertials in some individuals) acquired in early spring (SY) are first alternate.

Those individuals that show moderate upperwing covert replacement in late summer through early fall (see photos 3 & 4), might be said to undergo extensive PF molts. Those with no upperwing coverts replaced, and less scapular renewal may have limited PF molts. This remains to be seen.

For now more research will be needed to verify 2 inserted molts in the first cycle, and whether or not tertial replacement is via a late PA1 molt, or an early PB2 molt. I feel that we're closer to better understanding molt in first cycle Ring-billed Gulls. Banded birds, museum specimens and more field hours should eventually clarify these questions. This ultimately comes down to knowing how many times a feather tract has molted in a plumage cycle!