Great Blue Heron Fan-like Feather Display

When I first studied the photos and video clips depicting this feather display and bird behavior, I asked myself “What is going on here?”

Although I have watched lots of great blue herons over the years, this is the first time that I’ve seen a great blue heron fan its breast feathers like this.  The arrangement of these breast feathers when fully spread made me think of the fanned feather displays of wild turkeys, sage grouse, prairie chickens, and sharp-tailed grouse during their various dance / breeding displays on their leks.

In an attempt to solve the problem, I will treat it as I were trying to determine the definition of a “new” word encountered while reading.

The first clue will be the context of the activity, just as the context of how a word is used in a written passage typically provides some insights as to what the word means.  As with reading, the result is a “best first guess”.

However, to be sure of a “new” word’s definition (and its various nuances) one really needs to consult a dictionary for the accepted definition.

In this context, I have formulated the following working hypotheses to contemplate until such time as I am able to consult the “dictionary”, which in this case will be one or more appropriate life history study reports for the great blue heron.

My first hypothesis is that the fanned feather display is a breeding behavior.

My second hypothesis is that the fanned feather display is an aggressive / displeasure behavior directed at my intrusion on the scene.

My third hypothesis is that the fanned feather display is an aggressive / territorial / personal space threat posture behavior directed at a nearby great egret.

These hypotheses are based on the following narrative of the situation.

When I first drove up in my vehicle, a great blue heron flushed from the nearby boat ramp.  The great blue heron flew across the narrow inlet and in turn flushed a great egret from its perch.  As the great egret flew off, the great blue heron landed and occupied the great egret’s former perch.

As I sat in my vehicle with my camera pointed at the great blue heron, the great egret returned to the perch tree, landed and occupied a new perch position 5 to 8 feet above and to the side of the great blue heron.  The great egret looked around, walked 3 to 4 feet closer along its new limb perch, and started to preen its feathers.

The great blue heron alternately looked in my direction, looked up toward the great egret, and tucked its head in its breast feathers in an apparent sleep / dozing posture.  At the same time, the great blue heron fanned its breast feathers – sometimes in an exaggerated fashion, sometimes in a near-normal posture.

At the moment, my analyses of the various working hypotheses leads me to believe that the great blue heron was irritated primarily by the presence of the great egret and possibly secondarily somewhat irritated by my intrusion (i.e., the initial flush and my continued presence).

I did not see or detect the presence of a second great blue heron in the area, although my view was limited by a tree line on my side of the inlet.  Also, late-December seems to be early for any serious great blue heron breeding activities.

My guess is that the great blue heron’s fanned breast feather display was a non-vocal, persistent, non-contact signal to the great egret that the great blue heron was alert, irritated, and that the great egret had best mind its manners.

Although this is the first time that I have personally seen this behavior, and I have not yet read about this posture, I would be surprised if this posture and its associated behavior have not been studied before.

I’ll know for sure when I encounter the appropriate “dictionary” (i.e., an applicable life history / behavioral study for the great blue heron).