20 July 2016

Manitowoc: Putative Great Lakes Gull & Summering Franklin's

Wes Serafin and I ventured up to the Wisconsin lakefront on Friday to look for summer gulls. Our most interesting bird for the day was this putative 4th cycle type Great Lakes Gull (Great Black-backed x Herring).

Manitowoc, Wisconsin. 15 July 2016.

The darker Herring type on the left is our presumed hybrid/backcross.
There's at least one other theory beside the hybrid possibility: A sub-adult Herring that has darker upperparts than a definitive adult.
  • 3rd/4th cycle types (and even presumed young adults?) do at times show darker gray upperparts to some extent, although I've never seen one that was this obviously dark (see open wing photos). Martin Reid made an astute comment suggesting frayed and worn feathers also appear darker, and this is likely due to a collection of shadows that are combined for a darker effect.

A 4th cycle "type" wingtip pattern not out of range for Herring.

Size and structure wasn't too helpful as the bird was also within range for Herring, although a bit bulgy (think Great Cormorant bulgy...). But then again, the presumed Great Lakes Gulls I've seen have ranged in size from Herring to typical Great Black-backed...

I think it may be best to leave this individual unidentified.

Summering Franklin's Gulls

It's unusual to have more than 1-2 Franklin's on Lake Michigan in the summer months, and so the 7-8 birds that have been in the Manitowoc impoundment since late May are quite special. All appear to be 1st summer individuals (~ 1 year olds), undergoing their 2nd presbasic molts.

This individual nicely shows an "average" molt pattern seen on this contingent of FRGUs.

P1-P5 fully grown, P6 half grown. P7 dropped. P8-P10 retained (1st alternate).
The thinking behind 1-year olds like this is that they migrated to South America last fall, molted their juvenile (1st basic) flight feathers via a complete prealternate molt (PA1). Soon after acquiring these 2nd generation primaries (1st alternate), the 2nd prebasic molt commences, and viola, a 3rd generation of primaries (P1-P6) and secondaries are grown. It's possible that PB2 begins on the winter grounds, during migration stopover sites or once the "breeding" grounds are reached. This is what makes Franklin's Gull a standout gull - the flight feathers (especially in adult birds) are replaced twice in roughly 12 months!

But then there are Franklin's - for reasons we don't know, and probably will never know - that don't molt any flight feathers in PA1 on the winter grounds, or may have incomplete/suspended PA1 molts when we see them in their 1st summer.

Here's an example (Illinois. 04 July 2010):

3 retained juvenile primaries. P1-P7 new via 1st prealternate molt. Whether this prealternate molt is incomplete, suspended or ongoing isn't clear. Only two new outer secondaries (S1-S2) and retained outer rectrices. 
It's suspected these absent/incomplete PA molts are tied to the amount of food (or lack thereof) on the winter grounds, but I digress. Back to the Manitowoc birds...this one decided it wanted to renew p8-p9 before growing p6, or dropping p7 altogether! 

P1-P5 new (B2). P6 dropped. P7 old (A1). P8-P9 new (B2). P10 old (A1).
I've labeled what I presume is happening here:

Note it may be P6 that's retained 1st alternate and P7 dropped. Nonetheless, it's interesting to see P8-P9 have been renewed "out of order".

My favorite Franklin's of the group, this individual showing 3 generations of primaries.

P1-P5 new (2nd basic). P6 dropped. P7-P9 1st alternate. P10 juvenile (=1st basic)! 
P-molt in this age group of Franklin's Gulls in the summer months is somewhat variable. It's too bad we don't have more detailed profiles of known-age, banded, birds from the colonies they're born in. This would be a great project for anyone interested in molt and gulls!!

01 July 2016

Monthly Notables June 2016

  • Little Gull (1st summer). Cayuga County, New York. 01 June 2016.
  • Western Gull (adult type). Costilla County, Colorado. 04 June 2016.
  • Lesser Black-backed Gull (1st summer). Portage, Manitoba. 07 June 2016.
  • Iceland Gull (1st summer). York County, Maine. 07 June 2016.
  • Glaucous Gull (1st summer). Pinelaas County, Florida. 10 June 2016.
  • Thayer's Gull (1st summer). Clallam County, Washington. 11 June 2016.
  • Franklin's Gull (1st summer type). Barnstable County, Massachusetts. 12 June 2016.
  • Western Gull (2nd summer type). Washington County, Colorado. 17 June 2016.
  • California Gull (2nd summer type). Kenai Peninsula County, Alaska. 17 June 2016.
  • Lesser Black-backed Gull (1st summer). Washington County, Colorado. 17 June 2016.
  • Franklin's Gull (2nd summer type). Barnstable County, Massachusetts. 23 June 2016.
  • Franklin's Gull (1st summer type). Leon County, Florida. 30 June 2016.

June 2016 Quiz


Both of our gulls appear to have mostly new upperparts, although notice some feathers have been dropped and others are actively growing (namely, lesser/greater coverts and lower tertials on the left bird). The tertial patterns appear to be 2nd generation on both individuals, but the outermost primaries that are visible have an old "brownish" aspect. These primaries are juvenile feathers (=1st basic). Therefore we can comfortably assume both birds are molting from 1st to 2nd cycle and are roughly a year old (2nd calendar year).


The disparity in size among these two individuals will most definitely be a deciding factor in assigning labels. The gull on the left has a genuinely hefty bill and legs with remarkable girth. The head is proportionally large and the body is reminiscent of a duck. All of these structural features, along with the ghost-white head and solid dark upperparts point directly to Great Black-backed Gull. The bird on the right looks like a mini version of the Great Black-backed but with a slimmer bill and more attenuated look to the rear - a classic Lesser Black-backed type. The heavy "grease" stain (or neck boa) on the lower hind-neck of the Lesser Black-backed is often present in this age group.

This photo was taken in Barnstable County, Massachusetts in mid-July.