12 October 2010

Franklin's Passage Through Iowa

Every fall, thousands of Franklin's Gulls descend on the Des Moines River Valley corridor in central
Iowa. Numbers increase in earnest as soon as the fall season begins, peaking in late September and through the first couple of weeks of October. The most notable massings are found at Saylorville Lake (the famed Midwestern lake that hosted the 2007 Black-tailed Gull) and Lake Red Rock (Iowa's largest lake).

Both resevoirs were built by the Army Corps of Engineers to control water levels along the Des Moines River Valley
Olsen and Larsson note a maximum record of 37,480 Franklin's Gulls at Saylorville Lake in October of 1998.  Average counts range from 9,000-12,000 at Saylorville and 12,000-15,000 at Red Rock (Dinsmore per comm.). Both resevoirs are situated about 50 miles apart and they're used by the gulls primarily as an evening roost.

As a denizen of the Chicago area, I had never observed more than 3 Franklin's at once and so I planned a trip out to these lakes in order to better familiarize myself with the "Prairie Dove". An obvious observation that I soon made was that the Franklin's are not very interested in the fish that the lake holds, but rather, this species hawks the area skies for insects. Also, hundreds of individuals can be found working the recently plowed agriculture fields. The birds begin to disperse soon after sunrsie only to return as the sun begins to set. Any description I offer to describe this spectacle would be deficient at best. Here's a photo that depicts this magic!
Saylorville Lake, by Amar Ayyash, 10 October 2010
I arrived at Saylorville before sunrise and watched the sun gradually peek over the treeline. I gave the lake a once-over from the dam and spotted a sizable group of Franklin's on the beach at Cherry Glen. I drove around the lake and found my way to this flock in under 30 minutes. The gulls were engaging in what seemed like their morning ritual of preening and stretching their wings. Needless to say, there was no shortage of calling Franklin's as I approached the beach. I categorized their sounds as noticably higher pitched than Laughing Gull with a yelping quality that reminded me of Short-eared Owl.

With the sun to my back, I began counting the number of individuals with a pink suffusion on the underparts. I was a little disappointed with what seemed like a low ratio of 14:378. Franklin's consistenlty show this pink coloration much more than other gulls (Ross's Gull is a close 2nd). What I soon discovered after returning home is that this pink blemish is most common in breeding-condition adults; This is coupled with reddish legs and the reddish bill found on breeding birds.
Compared with the two Ring-billeds in the bottom right, Franklin's is a small, short-legged gull with a relatively darker mantle


As they began to take wing I noted what seemed like proportionaly befitting wing lengths for this diminutive gull.



The wings are broad with relatively rounded wingtips that could be somewhat likened to those of Little Gull, especially when they're held down.


The body is plump and barrel-like. The tail is short and the head is sunken with a short-neck appearance.


The thick eye-crescents, straighter bill and extensive white to the wingtip pattern should readily separate this species from Laughing Gull. The two are superficially alike and after close observation, one should not have any difficulty telling them apart; Franklin's should always have a fuller hood appearance in all basic plumages.

In my opinion, the most difficult ID issue with Franklin's and Laughing would be a fleeing juvenile in flight:

Top photo: Juvenile Laughing Gull, Salton Sea, CA; 9 AUG 2010
Bottom photo: Juvenile Franklin's Gull, Saylorville Lake, IA; 10 OCT 2010

Note how the Laughing Gull's underwing linings are duskier with marked flanks and a brownish collar around the neck. Franklin's shows white on the outer undertail feathers unlike any juvenile Laughing Gull. I do think these plumage features are less important than size and structurePlumages vary - proportions, more often do not. Take for example this juvenile trailing immediately behind the Ring-billed on the left:

This heavily marked juvenal is a result of a delayed partial preformative molt. The dusky underwing, flanks and collar are not commonly encountered this late in migration. The size of this individual easily eliminates Laughing.

I estimate that over 3/4 of the Franklin's Gulls at Saylorville and Red Rock are adults that have completed (or very close to completing) their prebasic molt. I ended my day by observing hundreds and hundreds of gulls pour in over the dam to roost on Red Rock. My count totals, based on select sample blocks, were 6,800 at Saylorville and 9,500 at Red Rock. 


As I headed home and drove east on Interestate 80, I came to the realization that Franklin's Gull will probably never be found in numbers east of the sites I had just explored. The smattering of sightings that are reported east and west of the Great Plains is really insignificant when one considers the hundreds of thousands that funnel down through parts of Kansas, Oklahoma and Texas. A recent correspondence with Kansas birder Chuck Otte revealed this, "Amar, here at Milford Lake (near Junction City, Kansas) I see all of the things you mentioned. They spend the night on the lake and I honestly feel that the overnight numbers at this time of year have to be approaching 200,000 to a quarter million". Tom Shane who lives in Garden City, Kansas wrote this, "We live in western Kansas and are excited to get just one Franklin's Gull".  This truly speaks to how narrow the migration corridor is for this species!

1 comment:

  1. Really enjoyed your description of the places, the gulls, their behavior, and their range. Very informative. Great educational photos too!
    Carolyn Fields

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