08 March 2011

GBBGs and Glaucous Gulls - Calumet Park

An interesting observation that I've made for several years now is the tendency for Great Black-backed Gulls and Glaucous Gulls to be found together along the southern lakeshore in Illinois. Locally, GBBGs are best found at Calumet Park and other adjacent lakefront spots in Indiana such as Hammond Marina and Whiting. Coincidentally, the state's premier gull-watching hotspot, "North Point Marina", harbors a greater amount of Thayer's and Kumlien's Gulls, whereas the southern lakeshore is best for the bigger species -GBBG and Glaucous. I've inquired about this phenomenon of GBBGs favoring the southern lakeshore and the best explanation I've received is that it must be "food-related". Perhaps the aquatic makeup along the northern lakeshore differs from that along the southern lakeshore. Perhaps water-temperature variation plays a role in the selection of wintering sites. After all, the distance from one site to the other is about a 60 mile stretch. One thought that I'll personally offer is that the smaller species, Kumlien's and Thayer's, deliberately choose not to winter alongside the larger species for obvious reasons such as having to forfeit some of their catches. It's my opinion that the larger species have acquired "prime" wintering quarters along the lakefront, as the warm water discharges at State Line Power and the BP Refinery in Whiting afford them a constant supply of fish. Could it be that the Glaucous Gull is the only white-winger that can regularly stand side-by-side with the sometimes ravenous GBBG?! More evidence will be needed to verify these thoughts.

Adult Glaucous Gull larger in body size than the two GBBGs on right. Calumet Park, IL; 6 MAR 2011.
It's not often that these larger species (GBBG and Glaucous Gull) allow close approach on Lake Michigan. I've often wondered about the summering locations of our GBBGs. Why is it that wintering GBBGs in Cape May allow close approach but those that winter on Lake Michigan flee as soon as humans step on the beach? Perhaps our birds summer in locations where humans are perceived as a threat. Perhaps our wintering population has had negative encounters with banders in their breeding colonies.

An adult GBBG fleeing as I approach the beach - a typical behavior on Lake Michigan. Calumet Park 6 MAR 2011
I was quite pleased with how close I was able to get to several GBBGs on this date. Some - usually 1st cycles - allow me to get within 30 ft if I spend 5-10 minutes slowly inching up while chumming the more common Ring-billeds. The larger species sometimes feel more at ease once I get friendly with the Ring-billeds, although I've yet to have an adult GBBG come in for chum:

2nd cycle GBBG. Calumet Park, IL; 6 MAR 2011.

My first 3rd cycle to have ever come in for chum. Whihala Beach, IN; 6 MAR 2011.
 The Glaucous Gulls on this day were very cooperative at Calumet Park, allowing me to get within 20 ft of them. There was a nice-sized algae mat forming on the beach and many Herrings Gulls with American Coots, Mallards, American Black Ducks and even an American Wigeon were out feeding on the shore. The Glaucous Gulls were aware of my presence, but the evident food supply presented along the shore and my slow approach and chumming of the Ring-billeds seemed to put them at ease:

A great day for Glaucous Gull! I got the impression some of the birds had just arrived from other wintering locations.

Adult Glaucous Gull with adult Ring-billed Gull. Calumet Park, IL; 6 MAR 2011.

2nd cycle GLGU. 6 MAR 2011

 1st cycle GLGU. 6 MAR 2011.
The highlight bird on this day was this putative Laughing X Ring-billed hybrid that just appeared on the beach right before my eyes:

It's believed that this is a reoccurring individual that has bee seen in this area for the last 7 years. Here is a more detailed write-up:  http://anythinglarus.blogspot.com/2010/03/laughing-ring-billed-gull.html